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1

OVERVIEW OF THE ATACAMA COSMOLOGY TELESCOPE: RECEIVER, INSTRUMENTATION, AND TELESCOPE SYSTEMS  

SciTech Connect

The Atacama Cosmology Telescope was designed to measure small-scale anisotropies in the cosmic microwave background and detect galaxy clusters through the Sunyaev-Zel'dovich effect. The instrument is located on Cerro Toco in the Atacama Desert, at an altitude of 5190 m. A 6 m off-axis Gregorian telescope feeds a new type of cryogenic receiver, the Millimeter Bolometer Array Camera. The receiver features three 1000-element arrays of transition-edge sensor bolometers for observations at 148 GHz, 218 GHz, and 277 GHz. Each detector array is fed by free space millimeter-wave optics. Each frequency band has a field of view of approximately 22' x 26'. The telescope was commissioned in 2007 and has completed its third year of operations. We discuss the major components of the telescope, camera, and related systems, and summarize the instrument performance.

Swetz, D. S.; Devlin, M. J.; Dicker, S. R. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Ade, P. A. R. [School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, Wales CF24 3AA (United Kingdom); Amiri, M.; Battistelli, E. S.; Burger, B.; Halpern, M.; Hasselfield, M. [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z4 (Canada); Appel, J. W.; Essinger-Hileman, T.; Fisher, R. P.; Fowler, J. W.; Hincks, A. D.; Jarosik, N. [Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States); Chervenak, J. [Code 553/665, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Doriese, W. B.; Hilton, G. C.; Irwin, K. D. [NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO 80305 (United States); Duenner, R. [Departamento de Astronomia y Astrofisica, Facultad de Fisica, PontificIa Universidad Catolica, Casilla 306, Santiago 22 (Chile)

2011-06-01T23:59:59.000Z

2

THE ATACAMA COSMOLOGY TELESCOPE: A MEASUREMENT OF THE PRIMORDIAL POWER SPECTRUM  

SciTech Connect

We present constraints on the primordial power spectrum of adiabatic fluctuations using data from the 2008 Southern Survey of the Atacama Cosmology Telescope (ACT) in combination with measurements from the Wilkinson Microwave Anisotropy Probe and a prior on the Hubble constant. The angular resolution of ACT provides sensitivity to scales beyond l = 1000 for resolution of multiple peaks in the primordial temperature power spectrum, which enables us to probe the primordial power spectrum of adiabatic scalar perturbations with wavenumbers up to k {approx_equal} 0.2 Mpc{sup -1}. We find no evidence for deviation from power-law fluctuations over two decades in scale. Matter fluctuations inferred from the primordial temperature power spectrum evolve over cosmic time and can be used to predict the matter power spectrum at late times; we illustrate the overlap of the matter power inferred from cosmic microwave background measurements (which probe the power spectrum in the linear regime) with existing probes of galaxy clustering, cluster abundances, and weak-lensing constraints on the primordial power. This highlights the range of scales probed by current measurements of the matter power spectrum.

Hlozek, Renee; Dunkley, Joanna; Addison, Graeme [Department of Astrophysics, Oxford University, Oxford OX1 3RH (United Kingdom); Appel, John William; Das, Sudeep; Essinger-Hileman, Thomas; Fowler, Joseph W.; Hajian, Amir; Hincks, Adam D. [Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States); Bond, J. Richard [Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8 (Canada); Carvalho, C. Sofia [IPFN, IST, Av. RoviscoPais, 1049-001Lisboa, Portugal and RCAAM, Academy of Athens, Soranou Efessiou 4, 11-527 Athens (Greece); Devlin, Mark J.; Klein, Jeff [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Duenner, Rolando; Gallardo, Patricio [Departamento de Astronomia y Astrofisica, Facultad de Fisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Halpern, Mark; Hasselfield, Matthew [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z4 (Canada); Hilton, Matt [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Hughes, John P. [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8019 (United States); Irwin, Kent D. [NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO 80305 (United States); and others

2012-04-10T23:59:59.000Z

3

THE ATACAMA COSMOLOGY TELESCOPE: HIGH-RESOLUTION SUNYAEV-ZEL'DOVICH ARRAY OBSERVATIONS OF ACT SZE-SELECTED CLUSTERS FROM THE EQUATORIAL STRIP  

SciTech Connect

We present follow-up observations with the Sunyaev-Zel'dovich Array (SZA) of optically confirmed galaxy clusters found in the equatorial survey region of the Atacama Cosmology Telescope (ACT): ACT-CL J0022-0036, ACT-CL J2051+0057, and ACT-CL J2337+0016. ACT-CL J0022-0036 is a newly discovered, massive ({approx_equal} 10{sup 15} M{sub Sun }), high-redshift (z = 0.81) cluster revealed by ACT through the Sunyaev-Zel'dovich effect (SZE). Deep, targeted observations with the SZA allow us to probe a broader range of cluster spatial scales, better disentangle cluster decrements from radio point-source emission, and derive more robust integrated SZE flux and mass estimates than we can with ACT data alone. For the two clusters we detect with the SZA we compute integrated SZE signal and derive masses from the SZA data only. ACT-CL J2337+0016, also known as A2631, has archival Chandra data that allow an additional X-ray-based mass estimate. Optical richness is also used to estimate cluster masses and shows good agreement with the SZE and X-ray-based estimates. Based on the point sources detected by the SZA in these three cluster fields and an extrapolation to ACT's frequency, we estimate that point sources could be contaminating the SZE decrement at the {approx}< 20% level for some fraction of clusters.

Reese, Erik D.; Mroczkowski, Tony; Devlin, Mark J.; Dicker, Simon R. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); Menanteau, Felipe; Baker, Andrew J. [Department of Physics and Astronomy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854-8019 (United States); Hilton, Matt [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Sievers, Jonathan; Bond, J. Richard; Hajian, Amir [Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8 (Canada); Aguirre, Paula; Duenner, Rolando [Departamento de Astronomia y Astrofisica, Facultad de Fisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Appel, John William; Das, Sudeep; Essinger-Hileman, Thomas; Hincks, Adam D. [Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States); Fowler, Joseph W.; Hill, J. Colin [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States); Halpern, Mark; Hasselfield, Matthew [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z4 (Canada); and others

2012-05-20T23:59:59.000Z

4

Cornell Caltech Atacama Telescope (CCAT): a 25 m aperture telescope above 5000 m altitude  

E-Print Network (OSTI)

Cornell, California Institute of Technology (Caltech), and Jet Propulsion Lab (JPL) have joined together to study development of a 25 meter sub-millimeter telescope (CCAT) on a high peak in the Atacama region of northern Chile, where the atmosphere is so dry as to permit observation at wavelengths as short as 200 micron. The telescope is designed to deliver high efficiency images at that wavelength with a total 1/2 wavefront error of about 10 microns. With a 20 arc min field of view, CCAT will be able to accommodate large format bolometer arrays and will excel at carrying out surveys as well as resolving structures to the 2 arc sec. resolution level. The telescope will be an ideal complement to ALMA. Initial instrumentation will include both a wide field bolometer camera and a medium resolution spectrograph. Studies of the major telescope subsystems have been performed as part of an initial Feasibility Concept Study. Novel aspects of the telescope design include kinematic mounting and active positioning of primary mirror segments, high bandwidth secondary mirror segment motion control for chopping, a Calotte style dome of 50 meter diameter, a mount capable of efficient scanning modes of operation, and some new approaches to panel manufacture. Analysis of telescope performance and of key subsystems will be presented to illustrate the technical feasibility and pragmatic cost of CCAT. Project plans include an Engineering Concept Design phase followed by detailed design and development. First Light is planned for early 2012.

Thomas A. Sebring; Riccardo Giovanelli; Simon Radford; Jonas Zmuidzinas

2006-10-17T23:59:59.000Z

5

APECS - The Atacama Pathfinder Experiment Control System  

E-Print Network (OSTI)

APECS is the distributed control system of the new Atacama Pathfinder EXperiment (APEX) telescope located on the Llano de Chajnantor at an altitude of 5107 m in the Atacama desert in northern Chile. APECS is based on Atacama Large Millimeter Array (ALMA) software and employs a modern, object-oriented design using the Common Object Request Broker Architecture (CORBA) as the middleware. New generic device interfaces simplify adding instruments to the control system. The Python based observer command scripting language allows using many existing software libraries and facilitates creating more complex observing modes. A new self-descriptive raw data format (Multi-Beam FITS or MBFITS) has been defined to store the multi-beam, multi-frequency data. APECS provides an online pipeline for initial calibration, observer feedback and a quick-look display. APECS is being used for regular science observations in local and remote mode since August 2005.

D. Muders; H. Hafok; F. Wyrowski; E. Polehampton; A. Belloche; C. Koenig; R. Schaaf; F. Schuller; J. Hatchell; F. v. d. Tak

2006-05-04T23:59:59.000Z

6

NIST Technologies Contribute to Top Science Stories of 2011  

Science Conference Proceedings (OSTI)

... Science News and Physics Today highlighted experiments at the Atacama Cosmology Telescope in Chile that measured "gravitational lensing" of ...

2012-01-10T23:59:59.000Z

7

Supernova Cosmology Project  

NLE Websites -- All DOE Office Websites (Extended Search)

The Hubble Space Telescope Cluster Supernova Survey: The Hubble Space Telescope Cluster Supernova Survey: An Intensive HST Survey for z>1 Type Ia Supernovae by Targeting Galaxy Clusters Survey Paper: Dawson et al. (The Supernova Cosmology Project) 2009, AJ, 138, 1271 [ADS] [arXiv] We present a new survey strategy to discover and study high redshift Type Ia supernovae (SNe Ia) using the Hubble Space Telescope (HST). By targeting massive galaxy clusters at 0.9 0.95, nine of which were in galaxy clusters. This strategy provides a SN sample that can be used to decouple the effects of host galaxy extinction and intrinsic color in high redshift SNe, thereby reducing one of the largest systematic uncertainties in SN cosmology.

8

NIST Contributes to Top Science Stories of 2012  

Science Conference Proceedings (OSTI)

... Both discoveries were based on microwave data taken with the Atacama Cosmology Telescope in Chile, which has a camera made of ...

2013-01-08T23:59:59.000Z

9

Quantum Cosmology  

E-Print Network (OSTI)

We give an introduction into quantum cosmology with emphasis on its conceptual parts. After a general motivation we review the formalism of canonical quantum gravity on which discussions of quantum cosmology are usually based. We then present the minisuperspace Wheeler--DeWitt equation and elaborate on the problem of time, the imposition of boundary conditions, the semiclassical approximation, the origin of irreversibility, and singularity avoidance. Restriction is made to quantum geometrodynamics; loop quantum gravity and string theory are discussed in other contributions to this volume.

Claus Kiefer; Barbara Sandhoefer

2008-04-04T23:59:59.000Z

10

String Gas Cosmology  

E-Print Network (OSTI)

String gas cosmology is a string theory-based approach to early universe cosmology which is based on making use of robust features of string theory such as the existence of new states and new symmetries. A first goal of string gas cosmology is to understand how string theory can effect the earliest moments of cosmology before the effective field theory approach which underlies standard and inflationary cosmology becomes valid. String gas cosmology may also provide an alternative to the current standard paradigm of cosmology, the inflationary universe scenario. Here, the current status of string gas cosmology is reviewed.

Brandenberger, Robert H

2009-01-01T23:59:59.000Z

11

Scientific Potential of Einstein Telescope  

E-Print Network (OSTI)

Einstein gravitational-wave Telescope (ET) is a design study funded by the European Commission to explore the technological challenges of and scientific benefits from building a third generation gravitational wave detector. The three-year study, which concluded earlier this year, has formulated the conceptual design of an observatory that can support the implementation of new technology for the next two to three decades. The goal of this talk is to introduce the audience to the overall aims and objectives of the project and to enumerate ET's potential to influence our understanding of fundamental physics, astrophysics and cosmology.

B. Sathyaprakash; M. Abernathy; F. Acernese; P. Amaro-Seoane; N. Andersson; K. Arun; F. Barone; B. Barr; M. Barsuglia; M. Beker; N. Beveridge; S. Birindelli; S. Bose; L. Bosi; S. Braccini; C. Bradaschia; T. Bulik; E. Calloni; G. Cella; E. Chassande-Mottin; S. Chelkowski; A. Chincarini; J. Clark; E. Coccia; C. Colacino; J. Colas; A. Cumming; L. Cunningham; E. Cuoco; S. Danilishin; K. Danzmann; R. De. Salvo; T. Dent; R. De. Rosa; L. Di. Fiore; A. Di. Virgilio; M. Doets; V. Fafone; P. Falferi; R. Flaminio; J. Franc; F. Frasconi; A. Freise; D. Friedrich; P. Fulda; J. Gair; G. Gemme; E. Genin; A. Gennai; A. Giazotto; K. Glampedakis; C. Gräf; M. Granata; H. Grote; G. Guidi; A. Gurkovsky; G. Hammond; M. Hannam; J. Harms; D. Heinert; M. Hendry; I. Heng; E. Hennes; S. Hild; J. Hough; S. Husa; S. Huttner; G. Jones; F. Khalili; K. Kokeyama; K. Kokkotas; B. Krishnan; T. G. F. Li; M. Lorenzini; H. Lück; E. Majorana; I. Mandel; V. Mandic; M. Mantovani; I. Martin; C. Michel; Y. Minenkov; N. Morgado; S. Mosca; B. Mours; H. Müller-Ebhardt; P. Murray; R. Nawrodt; J. Nelson; R. Oshaughnessy; C. D. Ott; C. Palomba; A. Paoli; G. Parguez; A. Pasqualetti; R. Passaquieti; D. Passuello; L. Pinard; W. Plastino; R. Poggiani; P. Popolizio; M. Prato; M. Punturo; P. Puppo; D. Rabeling; I. Racz; P. Rapagnani; J. Read; T. Regimbau; H. Rehbein; S. Reid; L. Rezzolla; F. Ricci; F. Richard; A. Rocchi; S. Rowan; A. Rüdiger; L. Santamaria; B. Sassolas; R. Schnabel; C. Schwarz; P. Seidel; A. Sintes; K. Somiya; F. Speirits; K. Strain; S. Strigin; P. Sutton; S. Tarabrin; A. Thüring; J. van den Brand; M van Veggel; C. Van Den Broeck; A. Vecchio; J. Veitch; F. Vetrano; A. Vicere; S. Vyatchanin; B. Willke; G. Woan; K. Yamamoto

2011-08-05T23:59:59.000Z

12

Inflationary Cosmology  

E-Print Network (OSTI)

The big bang model and the history of the early universe according to the grand unified theories are introduced. The shortcomings of big bang are discussed together with their resolution by inflationary cosmology. Inflation, the subsequent oscillation and decay of the inflaton, and the resulting "reheating" of the universe are studied. The density perturbations produced by inflation and the temperature fluctuations of the cosmic background radiation are discussed. The hybrid inflationary model is described. Two "natural" extensions of this model which avoid the disaster encountered in its standard realization from the overproduction of monopoles are presented. Successful "reheating" satisfying the gravitino constraint takes place after the end of inflation in all three versions of hybrid inflation. Adequate baryogenesis via a primordial leptogenesis occurs consistently with the solar and atmospheric neutrino oscillation data. The primordial lepton asymmetry is turned partly into baryon asymmetry via the sphalerons which are summarized.

G. Lazarides

2001-11-26T23:59:59.000Z

13

Second experiments in the robotic investigation of life in the Atacama Desert of Chile  

E-Print Network (OSTI)

The Atacama Desert of northern Chile may be the most lifeless place on Earth, yet microorganisms do survive in some areas. The distribution and diversity of life in the Atacama remains unexplored and is the focus of the Life in the Atacama project. To conduct this investigation, survey traverses across the desert with biologic and geologic instruments will allow us to create biogeographic maps. We accomplish these surveys with an autonomous astrobiology rover. In this paper we motivate the Life in the Atacama project and report on the second of three field seasons of scientific investigation and technical experiments in Chile. We describe the rover, instruments, algorithms and assess intermediate results. These results provide insight into the design of an effective robotic astrobiologist for future planetary investigations and into the best methods to conduct astrobiologic surveys. 1

David Wettergreen; Nathalie Cabrol; Vijayakumar Baskaran; Francisco Calderón; Paul Tompkins; Daniel Villa; Chris Williams; Michael Wagner

2005-01-01T23:59:59.000Z

14

Hubble space telescope; A new window opens on the universe  

Science Conference Proceedings (OSTI)

This paper reports on the Hubble space telescope. The telescope is expected to help answer key questions in astronomy, astrophysics, and cosmology, such as how stars and galaxies form and evolve; the size and age of the universe; the nature of quasars, black holes, and other exotic objects; the characteristics of planets in our solar system; and evidence for existence of planets orbiting other stars.

Seltzer, R.J. (C and EN, Washington, DC (US))

1990-04-09T23:59:59.000Z

15

Strong down-valley low-level jets over the Atacama Desert: observational characterization  

Science Conference Proceedings (OSTI)

The near-surface wind and temperature regime at three points in the Atacama Desert of northern Chile is described using two-year multi-level measurements from 80-m towers located in an altitude range between 2100 and 2700 m ASL. The data reveal ...

Ricardo C. Muñoz; Mark J. Falvey; Marcelo Araya; Martin Jacques-Coper

16

Constraints on cosmological parameters  

E-Print Network (OSTI)

A cosmological model with total density close to critical (and flat geometry), dominated by dark matter and dark energy of unknown nature, and consistent with the basic predictions of the inflationary scenario is a very good fit to a variety of cosmological probes: the anisotropy of the CMB, the large scale distribution of matter, the luminosity distance of high-redshift type Ia supernovae and so on. These high-quality data have established a new standard of precision in the determination of cosmological parameters. CMB and Physics of the Early universe

Amedeo Balbi; Amedeo Balbi

2006-01-01T23:59:59.000Z

17

Dark gravity and cosmology  

E-Print Network (OSTI)

The previous version of this article was a first attempt to confront the Dark Gravity theory to cosmological data. However, more recent developments lead to the conclusion that the cosmological principle is probably not valid in Dark Gravity so that this kind of analysis is at best very premature. A more recent and living review of the Dark Gravity theory can be found in gr-qc/0610079

F. Henry-Couannier; A. Tilquin; C. Tao; A. Ealet

2005-09-05T23:59:59.000Z

18

Supernova Cosmology Project  

NLE Websites -- All DOE Office Websites (Extended Search)

& Additional Info The Hubble Space Telescope Cluster Supernova Survey: V. Improving the Dark Energy Constraints Above z>1 and Building an Early-Type-Hosted Supernova Sample N....

19

The First VERITAS Telescope  

E-Print Network (OSTI)

The first atmospheric Cherenkov telescope of VERITAS (the Very Energetic Radiation Imaging Telescope Array System) has been in operation since February 2005. We present here a technical description of the instrument and a summary of its performance. The calibration methods are described, along with the results of Monte Carlo simulations of the telescope and comparisons between real and simulated data. The analysis of TeV $\\gamma$-ray observations of the Crab Nebula, including the reconstructed energy spectrum, is shown to give results consistent with earlier measurements. The telescope is operating as expected and has met or exceeded all design specifications.

J. Holder; R. W. Atkins; H. M. Badran; G. Blaylock; S. M. Bradbury; J. H. Buckley; K. L. Byrum; D. A. Carter-Lewis; O. Celik; Y. C. K. Chow; P. Cogan; W. Cui; M. K. Daniel; I. de la Calle Perez; C. Dowdall; P. Dowkontt; C. Duke; A. D. Falcone; S. J. Fegan; J. P. Finley; P. Fortin; L. F. Fortson; K. Gibbs; G. Gillanders; O. J. Glidewell; J. Grube; K. J. Gutierrez; G. Gyuk; J. Hall; D. Hanna; E. Hays; D. Horan; S. B. Hughes; T. B. Humensky; A. Imran; I. Jung; P. Kaaret; G. E. Kenny; D. Kieda; J. Kildea; J. Knapp; H. Krawczynski; F. Krennrich; M. J. Lang; S. LeBohec; E. Linton; E. K. Little; G. Maier; H. Manseri; A. Milovanovic; P. Moriarty; R. Mukherjee; P. A. Ogden; R. A. Ong; J. S. Perkins; F. Pizlo; M. Pohl; J. Quinn; K. Ragan; P. T. Reynolds; E. T. Roache; H. J. Rose; M. Schroedter; G. H. Sembroski; G. Sleege; D. Steele; S. P. Swordy; A. Syson; J. A. Toner; L. Valcarcel; V. V. Vassiliev; S. P. Wakely; T. C. Weekes; R. J. White; D. A. Williams; R. Wagner

2006-04-06T23:59:59.000Z

20

High resolution telescope  

DOE Patents (OSTI)

A large effective-aperture, low-cost optical telescope with diffraction-limited resolution enables ground-based observation of near-earth space objects. The telescope has a non-redundant, thinned-aperture array in a center-mount, single-structure space frame. It employs speckle interferometric imaging to achieve diffraction-limited resolution. The signal-to-noise ratio problem is mitigated by moving the wavelength of operation to the near-IR, and the image is sensed by a Silicon CCD. The steerable, single-structure array presents a constant pupil. The center-mount, radar-like mount enables low-earth orbit space objects to be tracked as well as increases stiffness of the space frame. In the preferred embodiment, the array has elemental telescopes with subaperture of 2.1m in a circle-of-nine configuration. The telescope array has an effective aperture of 12m which provides a diffraction-limited resolution of 0.02 arc seconds. Pathlength matching of the telescope array is maintained by an electro-optical system employing laser metrology. Speckle imaging relaxes pathlength matching tolerance by one order of magnitude as compared to phased arrays. Many features of the telescope contribute to substantial reduction in costs. These include eliminating the conventional protective dome and reducing on-site construction activities. The cost of the telescope scales with the first power of the aperture rather than its third power as in conventional telescopes. 9 figs., 1 tab.

Massie, N.A.; Oster, Y.

1990-01-01T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


21

High resolution telescope  

DOE Patents (OSTI)

A large effective-aperture, low-cost optical telescope with diffraction-limited resolution enables ground-based observation of near-earth space objects. The telescope has a non-redundant, thinned-aperture array in a center-mount, single-structure space frame. It employs speckle interferometric imaging to achieve diffraction-limited resolution. The signal-to-noise ratio problem is mitigated by moving the wavelength of operation to the near-IR, and the image is sensed by a Silicon CCD. The steerable, single-structure array presents a constant pupil. The center-mount, radar-like mount enables low-earth orbit space objects to be tracked as well as increases stiffness of the space frame. In the preferred embodiment, the array has elemental telescopes with subaperture of 2.1 m in a circle-of-nine configuration. The telescope array has an effective aperture of 12 m which provides a diffraction-limited resolution of 0.02 arc seconds. Pathlength matching of the telescope array is maintained by an electro-optical system employing laser metrology. Speckle imaging relaxes pathlength matching tolerance by one order of magnitude as compared to phased arrays. Many features of the telescope contribute to substantial reduction in costs. These include eliminating the conventional protective dome and reducing on-site construction activites. The cost of the telescope scales with the first power of the aperture rather than its third power as in conventional telescopes.

Massie, Norbert A. (San Ramon, CA); Oster, Yale (Danville, CA)

1992-01-01T23:59:59.000Z

22

High resolution telescope  

DOE Patents (OSTI)

A large effective-aperture, low-cost optical telescope with diffraction-limited resolution enables ground-based observation of near-earth space objects. The telescope has a non-redundant, thinned-aperture array in a center-mount, single-structure space frame. It employs speckle interferometric imaging to achieve diffraction-limited resolution. The signal-to-noise ratio problem is mitigated by moving the wavelength of operation to the near-IR, and the image is sensed by a Silicon CCD. The steerable, single-structure array presents a constant pupil. The center-mount, radar-like mount enables low-earth orbit space objects to be tracked as well as increases stiffness of the space frame. In the preferred embodiment, the array has elemental telescopes with subaperture of 2.1m in a circle-of-nine configuration. The telescope array has an effective aperture of 12m which provides a diffraction-limited resolution of 0.02 arc seconds. Pathlength matching of the telescope array is maintained by an electro-optical system employing laser metrology. Speckle imaging relaxes pathlength matching tolerance by one order of magnitude as compared to phased arrays. Many features of the telescope contribute to substantial reduction in costs. These include eliminating the conventional protective dome and reducing on-site construction activities. The cost of the telescope scales with the first power of the aperture rather than its third power as in conventional telescopes. 9 figs., 1 tab.

Massie, N.A.; Oster, Y.

1990-12-31T23:59:59.000Z

23

Moving mesh cosmology: tracing cosmological gas accretion  

E-Print Network (OSTI)

We investigate the nature of gas accretion onto haloes and galaxies at z=2 using cosmological hydrodynamic simulations run with the moving mesh code AREPO. Implementing a Monte Carlo tracer particle scheme to determine the origin and thermodynamic history of accreting gas, we make quantitative comparisons to an otherwise identical simulation run with the smoothed particle hydrodynamics (SPH) code GADGET-3. Contrasting these two numerical approaches, we find significant physical differences in the thermodynamic history of accreted gas in haloes above 10^10.5 solar masses. In agreement with previous work, GADGET simulations show a cold fraction near unity for galaxies forming in massive haloes, implying that only a small percentage of accreted gas heats to an appreciable fraction of the virial temperature during accretion. The same galaxies in AREPO show a much lower cold fraction, gas accretion rate which, at this same halo mass, is an order o...

Nelson, Dylan; Genel, Shy; Sijacki, Debora; Keres, Dusan; Springel, Volker; Hernquist, Lars

2013-01-01T23:59:59.000Z

24

Unified phantom cosmologies  

E-Print Network (OSTI)

We present a general algorithm based on the concept of form-invariance which can be used for generating phantom cosmologies. It involves linear transformations between the kinetic energy and the potential of the scalar field, and transforms solutions of the Einstein-Klein-Gordon equations which preserve the weak energy condition into others which violate it, while keeping the energy density of the field positive. All known solutions representing phantom cosmologies are unified by this procedure. Using the general algorithm we obtain those solutions and show the relations between them. In addition, the scale factors of the product and seed solutions are related by a generalization of the well-known $a\\to a^{-1}$ duality.

Luis P. Chimento; Ruth Lazkoz

2004-05-26T23:59:59.000Z

25

Measuring Cosmology with Supernovae  

E-Print Network (OSTI)

Over the past decade, supernovae have emerged as some of the most powerful tools for measuring extragalactic distances. A well developed physical understanding of type II supernovae allow them to be used to measure distances independent of the extragalactic distance scale. Type Ia supernovae are empirical tools whose precision and intrinsic brightness make them sensitive probes of the cosmological expansion. Both types of supernovae are consistent with a Hubble Constant within ~10% of H_0 = 70 km/s/Mpc. Two teams have used type Ia supernovae to trace the expansion of the Universe to a look-back time more than 60% of the age of the Universe. These observations show an accelerating Universe which is currently best explained by a cosmological constant or other form of dark energy with an equation of state near w = p/rho = -1. While there are many possible remaining systematic effects, none appears large enough to challenge these current results. Future experiments are planned to better characterize the equation of state of the dark energy leading to the observed acceleration by observing hundreds or even thousands of objects. These experiments will need to carefully control systematic errors to ensure future conclusions are not dominated by effects unrelated to cosmology.

Saul Perlmutter; Brian P. Schmidt

2003-03-18T23:59:59.000Z

26

Cosmological shock waves  

E-Print Network (OSTI)

Large-scale structure formation, accretion and merging processes, AGN activity produce cosmological gas shocks. The shocks convert a fraction of the energy of gravitationally accelerated flows to internal energy of the gas. Being the main gas-heating agent, cosmological shocks could amplify magnetic fields and accelerate energetic particles via the multi-fluid plasma relaxation processes. We first discuss the basic properties of standard single-fluid shocks. Cosmological plasma shocks are expected to be collisionless. We then review the plasma processes responsible for the microscopic structure of collisionless shocks. A tiny fraction of the particles crossing the shock is injected into the non-thermal energetic component that could get a substantial part of the ram pressure power dissipated at the shock. The energetic particles penetrate deep into the shock upstream producing an extended shock precursor. Scaling relations for postshock ion temperature and entropy as functions of shock velocity in strong collisionless multi-fluid shocks are discussed. We show that the multi-fluid nature of collisionless shocks results in excessive gas compression, energetic particle acceleration, precursor gas heating, magnetic field amplification and non-thermal emission. Multi-fluid shocks provide a reduced gas entropy production and could also modify the observable thermodynamic scaling relations for clusters of galaxies.

A. M. Bykov; K. Dolag; F. Durret

2008-01-07T23:59:59.000Z

27

Cosmological Consequences of String Axions  

E-Print Network (OSTI)

2005 Cosmological Consequences of String Axions ? Ben Kain †for the model independent string axion we consider thefor two additional string axions. We do so independent of

Kain, Ben

2005-01-01T23:59:59.000Z

28

The South Pole Telescope  

E-Print Network (OSTI)

A new 10 meter diameter telescope is being constructed for deployment at the NSF South Pole research station. The telescope is designed for conducting large-area millimeter and sub-millimeter wave surveys of faint, low contrast emission, as required to map primary and secondary anisotropies in the cosmic microwave background. To achieve the required sensitivity and resolution, the telescope design employs an off-axis primary with a 10m diameter clear aperture. The full aperture and the associated optics will have a combined surface accuracy of better than 20 microns rms to allow precision operation in the submillimeter atmospheric windows. The telescope will be surrounded with a large reflecting ground screen to reduce sensitivity to thermal emission from the ground and local interference. The optics of the telescope will support a square degree field of view at 2mm wavelength and will feed a new 1000-element micro-lithographed planar bolometric array with superconducting transition-edge sensors and frequency-multiplexed readouts. The first key project will be to conduct a survey over approximately 4000 degrees for galaxy clusters using the Sunyaev-Zel'dovich Effect. This survey should find many thousands of clusters with a mass selection criteria that is remarkably uniform with redshift. Armed with redshifts obtained from optical and infrared follow-up observations, it is expected that the survey will enable significant constraints to be placed on the equation of state of the dark energy.

SPT Collaboration; J. E. Ruhl; P. A. R. Ade; J. E. Carlstrom; H. M. Cho; T. Crawford; M. Dobbs; C. H. Greer; N. W. Halverson; W. L. Holzapfel; T. M. Lantin; A. T. Lee; J. Leong; E. M. Leitch; W. Lu; M. Lueker; J. Mehl; S. S. Meyer; J. J. Mohr; S. Padin; T. Plagge; C. Pryke; D. Schwan; M. K. Sharp; M. C. Runyan; H. Spieler; Z. Staniszewski; A. A. Stark

2004-11-04T23:59:59.000Z

29

Particle Data Group - Astrophysics and Cosmology  

NLE Websites -- All DOE Office Websites (Extended Search)

Astrophysical Constants and Parameters Experimental tests of gravitational theory Big-Bang cosmology Big-Bang nucleosynthesis Cosmological parameters Dark matter Cosmic...

30

Chaplygin DGP cosmologies  

E-Print Network (OSTI)

A new class of braneworld models displaying late-time phantom acceleration without resorting to a phantom fluid is presented. In this scenario expansion is fuelled by dark matter together with some effective dark energy capable of crossing the phantom divide. Unlike a previous proposal of this nature, in these models the effective phantom behaviour remains valid at all redshifts for some choices of the free parameters of the models. The construction is based on the generalised Chaplygin gas, and the cosmological history interpolates between a standard CDM-like behaviour at early times and a de Sitter-like behaviour at late times, so no future singularity is reached.

Mariam Bouhmadi-López; Ruth Lazkoz

2007-06-26T23:59:59.000Z

31

Inflationary Axion Cosmology  

DOE R&D Accomplishments (OSTI)

If Peccei-Quinn (PQ) symmetry is broken after inflation, the initial axion angle is a random variable on cosmological scales; based on this fact, estimates of the relic-axion mass density give too large a value if the axion mass is less than about 10-6 eV. This bound can be evaded if the Universe underwent inflation after PQ symmetry breaking and if the observable Universe happens to be a region where the initial axion angle was atypically small, .1 . (ma/10-6eV)0.59. We show consideration of fluctuations induced during inflation severely constrains the latter alternative.

Wilczek, Frank; Turner, Michael S.

1990-09-00T23:59:59.000Z

32

Spinning fluid cosmology  

E-Print Network (OSTI)

The dynamics of a spinning fluid in a flat cosmological model is investigated. The space-time is itself generated by the spinning fluid which is characterized by an energy-momentum tensor consisting a sum of the usual perfect-fluid energy-momentum tensor and some Belinfante-Rosenfeld tensors. It is shown that the equations of motion admit a solution for which the fluid four-velocity and four-momentum are not co-linear in general. The momentum and spin densities of the fluid are expressed in terms of the scale factor.

Morteza Mohseni

2008-07-22T23:59:59.000Z

33

Spinning fluid cosmology  

E-Print Network (OSTI)

The dynamics of a spinning fluid in a flat cosmological model is investigated. The space-time is itself generated by the spinning fluid which is characterized by an energy-momentum tensor consisting a sum of the usual perfect-fluid energy-momentum tensor and some Belinfante-Rosenfeld tensors. It is shown that the equations of motion admit a solution for which the fluid four-velocity and four-momentum are not co-linear in general. The momentum and spin densities of the fluid are expressed in terms of the scale factor.

Mohseni, Morteza

2008-01-01T23:59:59.000Z

34

Cosmology: Recent and future developments  

Science Conference Proceedings (OSTI)

The precision with which the cosmological parameters have been determined has made dramatic progress in just the last two years. The author reviews this recent observational progress, highlights some of the key questions facing cosmology in the new millennium, and briefly discusses some of the projects now being mounted or contemplated to address them.

Joshua A. Frieman

2003-01-15T23:59:59.000Z

35

Cosmological models with isotropic singularities  

E-Print Network (OSTI)

In 1985 Goode and Wainwright devised the concept of an isotropic singularity. Since that time, numerous authors have explored the interesting consequences, in mathematical cosmology, of assuming the existence of this type of singularity. In this paper, we collate all examples of cosmological models which are known to admit an isotropic singularity, and make a number of observations regarding their general characteristics.

Susan M. Scott; Geoffery Ericksson

1998-12-07T23:59:59.000Z

36

Imaging Atmospheric Cerenkov Telescopes: Techniques and Results  

E-Print Network (OSTI)

The hunt for cosmic TeV particle accelerators is prospering through Imaging Atmospheric Cerenkov Telescopes. We face challenges such as low light levels and MHz trigger rates, and the need to distinguish between particle air showers stemming from primary gamma rays and those due to the hadronic cosmic ray background. Our test beam is provided by the Crab Nebula, a steady accelerator of particles to energies beyond 20 TeV. Highly variable gamma-ray emission, coincident with flares at longer wavelengths, is revealing the particle acceleration mechanisms at work in the relativistic jets of Active Galaxies. These 200 GeV to 20 TeV photons propagating over cosmological distances allow us to place a limit on the infra-red background linked to galaxy formation and, some speculate, to the decay of massive relic neutrinos. Gamma rays produced in neutralino annihilation or the evaporation of primordial black holes may also be detectable. These phenomena and a zoo of astrophysical objects will be the targets of the next generation multi-national telescope facilities.

S. M. Bradbury

2001-01-30T23:59:59.000Z

37

Nonlinear Noise in Cosmology  

E-Print Network (OSTI)

This paper derives and analyzes exact, nonlocal Langevin equations appropriate in a cosmological setting to describe the interaction of some collective degree of freedom with a surrounding ``environment.'' Formally, these equations are much more general, involving as they do a more or less arbitrary ``system,'' characterized by some time-dependent potential, which is coupled via a nonlinear, time-dependent interaction to a ``bath'' of oscillators with time-dependent frequencies. The analysis reveals that, even in a Markov limit, which can often be justified, the time dependences and nonlinearities can induce new and potentially significant effects, such as systematic and stochastic mass renormalizations and state-dependent ``memory'' functions, aside from the standard ``friction'' of a heuristic Langevin description. One specific example is discussed in detail, namely the case of an inflaton field, characterized by a Landau-Ginsburg potential, that is coupled quadratically to a bath of scalar ``radiation.'' T...

Habib, S; Habib, Salman; Kandrup, Henry E.

1992-01-01T23:59:59.000Z

38

Fast Fourier transform telescope  

Science Conference Proceedings (OSTI)

We propose an all-digital telescope for 21 cm tomography, which combines key advantages of both single dishes and interferometers. The electric field is digitized by antennas on a rectangular grid, after which a series of fast Fourier transforms recovers simultaneous multifrequency images of up to half the sky. Thanks to Moore's law, the bandwidth up to which this is feasible has now reached about 1 GHz, and will likely continue doubling every couple of years. The main advantages over a single dish telescope are cost and orders of magnitude larger field-of-view, translating into dramatically better sensitivity for large-area surveys. The key advantages over traditional interferometers are cost (the correlator computational cost for an N-element array scales as Nlog{sub 2}N rather than N{sup 2}) and a compact synthesized beam. We argue that 21 cm tomography could be an ideal first application of a very large fast Fourier transform telescope, which would provide both massive sensitivity improvements per dollar and mitigate the off-beam point source foreground problem with its clean beam. Another potentially interesting application is cosmic microwave background polarization.

Tegmark, Max; Zaldarriaga, Matias [Department of Physics and MIT Kavli Institute, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Center for Astrophysics, Harvard University, Cambridge, Massachusetts 02138 (United States)

2009-04-15T23:59:59.000Z

39

FISICA: The Florida Image Slicer for Infrared Cosmology & Astrophysics  

E-Print Network (OSTI)

We report on the design, fabrication, and on-sky performance of the Florida Image Slicer for Infrared Cosmology and Astrophysics (FISICA)- a fully-cryogenic all-reflective image-slicing integral field unit for the FLAMINGOS near-infrared spectrograph. Designed to accept input beams near f/15, FISICA with FLAMINGOS provides R \\sim 1300 spectra over a 16x33-arcsec field-of-view on the Cassegrain f/15 focus of the KPNO 4-meter telescope, or a 6x12-arcsec field-of-view on the Nasmyth or Bent Cassegrain foci of the Gran Telescopio Canarias 10.4-meter telescope. FISICA accomplishes this using three sets of "monolithic" powered mirror arrays, each with 22 mirrored surfaces cut into a single piece of aluminum. We review the optical and opto-mechanical design and fabrication of FISICA, as well as laboratory test results for FISICA integrated with the FLAMINGOS instrument. Finally, we present performance results from observations with FISICA at the KPNO 4-m telescope and comparisons of FISICA performance to other available IFUs on 4-m to 8-m-class telescopes.

Stephen Eikenberry; S. Nicholas Raines; Nicolas Gruel; Richard Elston; Rafael Guzman; Jeff Julian; Glenn Boreman; Paul Glenn; Greg Hull-Allen; Jeff Hoffmann; Michael Rodgers; Kevin Thompson; Scott Flint; Lovell Comstock; Bruce Myrick

2006-04-27T23:59:59.000Z

40

Precision Cosmology and the Landscape  

E-Print Network (OSTI)

After reviewing the cosmological constant problem - why is Lambda not huge? - I outline the two basic approaches that had emerged by the late 1980s, and note that each made a clear prediction. Precision cosmological experiments now indicate that the cosmological constant is nonzero. This result strongly favors the environmental approach, in which vacuum energy can vary discretely among widely separated regions in the universe. The need to explain this variation from first principles constitutes an observational constraint on fundamental theory. I review arguments that string theory satisfies this constraint, as it contains a dense discretuum of metastable vacua. The enormous landscape of vacua calls for novel, statistical methods of deriving predictions, and it prompts us to reexamine our description of spacetime on the largest scales. I discuss the effects of cosmological dynamics, and I speculate that weighting vacua by their entropy production may allow for prior-free predictions that do not resort to explicitly anthropic arguments.

Raphael Bousso

2006-10-18T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


41

Inflationary cosmology and fundamental physics  

E-Print Network (OSTI)

This thesis is a collection of several papers at the interface between cosmology, particle physics, and field theory. In the first half, we examine topics that are directly related to inflation: axions, string theory, and ...

Hertzberg, Mark Peter

2010-01-01T23:59:59.000Z

42

Particle Production in Matrix Cosmology  

E-Print Network (OSTI)

We consider cosmological particle production in 1+1 dimensional string theory. The process is described most efficiently in terms of anomalies, but we also discuss the explicit mode expansions. In matrix cosmology the usual vacuum ambiguity of quantum fields in time-dependent backgrounds is resolved by the underlying matrix model. This leads to a finite energy density for the "in" state which cancels the effect of anomalous particle production.

Sumit R. Das; Joshua L. Davis; Finn Larsen; Partha Mukhopadhyay

2004-03-28T23:59:59.000Z

43

Cosmological milestones and energy conditions  

E-Print Network (OSTI)

Until recently, the physically relevant singularities occurring in FRW cosmologies had traditionally been thought to be limited to the "big bang", and possibly a "big crunch". However, over the last few years, the zoo of cosmological singularities considered in the literature has become considerably more extensive, with "big rips" and "sudden singularities" added to the mix, as well as renewed interest in non-singular cosmological events such as "bounces" and "turnarounds". In this talk, we present an extensive catalogue of such cosmological milestones, both at the kinematical and dynamical level. First, using generalized power series, purely kinematical definitions of these cosmological events are provided in terms of the behaviour of the scale factor a(t). The notion of a "scale-factor singularity" is defined, and its relation to curvature singularities (polynomial and differential) is explored. Second, dynamical information is extracted by using the Friedmann equations (without assuming even the existence of any equation of state) to place constraints on whether or not the classical energy conditions are satisfied at the cosmological milestones. Since the classification is extremely general, and modulo certain technical assumptions complete, the corresponding results are to a high degree model-independent.

Celine Cattoen; Matt Visser

2006-09-18T23:59:59.000Z

44

New ekpyrotic cosmology  

SciTech Connect

In this paper, we present a new scenario of the early universe that contains a pre-big bang ekpyrotic phase. By combining this with a ghost condensate, the theory explicitly violates the null energy condition without developing any ghostlike instabilities. Thus the contracting universe goes through a nonsingular bounce and evolves smoothly into the expanding post-big bang phase. The curvature perturbation acquires a scale-invariant spectrum well before the bounce in this scenario. It is sourced by the scale-invariant entropy perturbation engendered by two ekpyrotic scalar fields, a mechanism recently proposed by Lehners et al. Since the background geometry is nonsingular at all times, the curvature perturbation remains nearly constant on superhorizon scales. It emerges from the bounce unscathed and imprints a scale-invariant spectrum of density fluctuations in the matter-radiation fluid at the onset of the hot big bang phase. The ekpyrotic potential can be chosen so that the spectrum has a red tilt, in accordance with the recent data from WMAP. As in the original ekpyrotic scenario, the model predicts a negligible gravity wave signal on all observable scales. As such ''new ekpyrotic cosmology'' provides a consistent and distinguishable alternative to inflation to account for the origin of the seeds of large-scale structure.

Buchbinder, Evgeny I.; Khoury, Justin [Perimeter Institute for Theoretical Physics, Waterloo, Ontario, N2L 2Y5 (Canada); Ovrut, Burt A. [Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6395 (United States)

2007-12-15T23:59:59.000Z

45

The Large Synoptic Survey Telescope  

NLE Websites -- All DOE Office Websites (Extended Search)

night sky. Below: The telescope depicted at its future site atop Cerro Pachn in Chile. (Top image by Todd Mason, Mason Productions Inc. LSST Corporation. Bottom image...

46

Timescape cosmology with radiation fluid  

E-Print Network (OSTI)

The timescape cosmology represents a potentially viable alternative to the standard homogeneous cosmology, without the need for dark energy. Although average cosmic evolution in the timescape scenario only differs substantially from that of Friedmann-Lemaitre model at relatively late epochs when the contribution from the energy density of radiation is negligible, a full solution of the Buchert equations to incorporate radiation is necessary to smoothly match parameters to the epoch of photon decoupling and to obtain constraints from cosmic microwave background data. Here we extend the matter-dominated solution found in earlier work to include radiation, providing series solutions at early times and an efficient numerical integration strategy for generating the complete solution. The numerical solution is used to directly calculate the scale of the sound horizon at decoupling, and at the baryon drag epoch. The constraints on these scales from the Planck satellite data yield bounds on the timescape cosmological...

Duley, James A G; Wiltshire, David L

2013-01-01T23:59:59.000Z

47

Stringy Model of Cosmological Dark Energy  

E-Print Network (OSTI)

A string field theory(SFT) nonlocal model of the cosmological dark energy providing w<-1 is briefly surveyed. We summarize recent developments and open problems, as well as point out some theoretical issues related with others applications of the SFT nonlocal models in cosmology, in particular, in inflation and cosmological singularity.

Irina Ya. Aref'eva

2007-10-16T23:59:59.000Z

48

Cosmological science enabled by Planck  

E-Print Network (OSTI)

Planck will be the first mission to map the entire cosmic microwave background (CMB) sky with mJy sensitivity and resolution better than 10'. The science enabled by such a mission spans many areas of astrophysics and cosmology. In particular it will lead to a revolution in our understanding of primary and secondary CMB anisotropies, the constraints on many key cosmological parameters will be improved by almost an order of magnitude (to sub-percent levels) and the shape and amplitude of the mass power spectrum at high redshift will be tightly constrained.

Martin White

2006-06-27T23:59:59.000Z

49

The Space Infrared Interferometric Telescope (SPIRIT): High-resolution imaging and spectroscopy in the far-infrared  

E-Print Network (OSTI)

We report results of a recently-completed pre-Formulation Phase study of SPIRIT, a candidate NASA Origins Probe mission. SPIRIT is a spatial and spectral interferometer with an operating wavelength range 25 - 400 microns. SPIRIT will provide sub-arcsecond resolution images and spectra with resolution R = 3000 in a 1 arcmin field of view to accomplish three primary scientific objectives: (1) Learn how planetary systems form from protostellar disks, and how they acquire their inhomogeneous composition; (2) characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets of different types form; and (3) learn how high-redshift galaxies formed and merged to form the present-day population of galaxies. Observations with SPIRIT will be complementary to those of the James Webb Space Telescope and the ground-based Atacama Large Millimeter Array. All three observatories could be operational contemporaneously.

David Leisawitz; Charles Baker; Amy Barger; Dominic Benford; Andrew Blain; Rob Boyle; Richard Broderick; Jason Budinoff; John Carpenter; Richard Caverly; Phil Chen; Steve Cooley; Christine Cottingham; Julie Crooke; Dave DiPietro; Mike DiPirro; Michael Femiano; Art Ferrer; Jacqueline Fischer; Jonathan P. Gardner; Lou Hallock; Kenny Harris; Kate Hartman; Martin Harwit; Lynne Hillenbrand; Tupper Hyde; Drew Jones; Jim Kellogg; Alan Kogut; Marc Kuchner; Bill Lawson; Javier Lecha; Maria Lecha; Amy Mainzer; Jim Mannion; Anthony Martino; Paul Mason; John Mather; Gibran McDonald; Rick Mills; Lee Mundy; Stan Ollendorf; Joe Pellicciotti; Dave Quinn; Kirk Rhee; Stephen Rinehart; Tim Sauerwine; Robert Silverberg; Terry Smith; Gordon Stacey; H. Philip Stahl; Johannes Staguhn; Steve Tompkins; June Tveekrem; Sheila Wall; Mark Wilson

2007-07-05T23:59:59.000Z

50

Science magazine names Supernova Cosmology Project "Breakthrough of the  

NLE Websites -- All DOE Office Websites (Extended Search)

December 17, 1998 December 17, 1998 Go to Berkeley Lab Home Page Contacts: Saul Perlmutter, (510) 486-5203, s_perlmutter@lbl.gov Paul Preuss, (510) 486-6249, paul_preuss@lbl.gov Lynn Yarris, (510) 486-5375, lcyarris@lbl.gov Additional Information: Down-to-Earth Benefits from Far-Out Science Supernova Cosmology Project Research Site Jan 98 news release: Universe To Last Forever Search for Omega: Will the Universe Last Forever Fate of the Universe and the Cosmological Constant Revolution in Telescopes: The Keck The oldest, farthest supernova NERSC: Computers and Cosmology Images: High-resolution versions of image on this page Still images from the Supernova Cosmology Project website Online movie clip BERKELEY, CA -- By observing distant, ancient exploding stars, physicists and astronomers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory and elsewhere have determined that the universe is expanding at an accelerating rate -- an observation that implies the existence of a mysterious, self-repelling property of space first proposed by Albert Einstein, which he called the cosmological constant. This extraordinary finding has been named Science magazine's "Breakthrough of the Year for 1998."

51

Electric Time in Quantum Cosmology  

E-Print Network (OSTI)

Effective quantum cosmology is formulated with a realistic global internal time given by the electric vector potential. New possibilities for the quantum behavior of space-time are found, and the high-density regime is shown to be very sensitive to the specific form of state realized.

Stephon Alexander; Martin Bojowald; Antonino Marciano; David Simpson

2012-12-10T23:59:59.000Z

52

Conformal formulation of cosmological futures  

E-Print Network (OSTI)

We summarise the new conformal framework of an Anisotropic Future Endless Universe and an Anisotropic Future Singularity. Both new definitions are motivated by, but not restricted to quiescent cosmology and the Weyl curvature hypothesis, which previously only possessed a framework for a classical initial state of the universe, namely the Isotropic Singularity. Some of the features of the framework are briefly discussed.

Philipp A Hoehn; Susan M Scott

2010-01-22T23:59:59.000Z

53

Median statistics cosmological parameter values  

E-Print Network (OSTI)

We present median statistics central values and ranges for 12 cosmological parameters, using 582 measurements (published during 1990-2010) collected by Croft & Dailey (2011). On comparing to the recent Planck collaboration Ade et al. 2013 estimates of 11 of these parameters, we find good consistency in nine cases.

Crandall, Sara

2013-01-01T23:59:59.000Z

54

Summary & Outlook: Particles and Cosmology  

E-Print Network (OSTI)

We review new results on strong and electroweak interactions, flavour physics, cosmic rays and cosmology, which were presented at this conference, focussing on physics beyond the Standard Models. Special emphasis is given to the Higgs sector of the Standard Model of Particle Physics and recent results on high-energy cosmic rays and their implications for dark matter.

Wilfried Buchmuller

2010-03-04T23:59:59.000Z

55

The world-wide telescope  

Science Conference Proceedings (OSTI)

Mining vast databases of astronomical data, this new online way to see the global structure of the universe promises to be not only a wonderful virtual telescope but an archetype for the evolution of computational science.

Jim Gray; Alex Szalay

2002-11-01T23:59:59.000Z

56

PHOTOMETRIC SUPERNOVA COSMOLOGY WITH BEAMS AND SDSS-II  

SciTech Connect

Supernova (SN) cosmology without spectroscopic confirmation is an exciting new frontier, which we address here with the Bayesian Estimation Applied to Multiple Species (BEAMS) algorithm and the full three years of data from the Sloan Digital Sky Survey II Supernova Survey (SDSS-II SN). BEAMS is a Bayesian framework for using data from multiple species in statistical inference when one has the probability that each data point belongs to a given species, corresponding in this context to different types of SNe with their probabilities derived from their multi-band light curves. We run the BEAMS algorithm on both Gaussian and more realistic SNANA simulations with of order 10{sup 4} SNe, testing the algorithm against various pitfalls one might expect in the new and somewhat uncharted territory of photometric SN cosmology. We compare the performance of BEAMS to that of both mock spectroscopic surveys and photometric samples that have been cut using typical selection criteria. The latter typically either are biased due to contamination or have significantly larger contours in the cosmological parameters due to small data sets. We then apply BEAMS to the 792 SDSS-II photometric SNe with host spectroscopic redshifts. In this case, BEAMS reduces the area of the {Omega}{sub m}, {Omega}{sub {Lambda}} contours by a factor of three relative to the case where only spectroscopically confirmed data are used (297 SNe). In the case of flatness, the constraints obtained on the matter density applying BEAMS to the photometric SDSS-II data are {Omega}{sup BEAMS}{sub m} = 0.194 {+-} 0.07. This illustrates the potential power of BEAMS for future large photometric SN surveys such as Large Synoptic Survey Telescope.

Hlozek, Renee [Oxford Astrophysics, Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH (United Kingdom); Kunz, Martin [Department de physique theorique, Universite de Geneve, 30, quai Ernest-Ansermet, CH-1211 Geneve 4 (Switzerland); Bassett, Bruce; Smith, Mat; Newling, James [African Institute for Mathematical Sciences, 68 Melrose Road, Muizenberg 7945 (South Africa); Varughese, Melvin [Department of Mathematics and Applied Mathematics, University of Cape Town, Rondebosch, Cape Town, 7700 (South Africa); Kessler, Rick; Frieman, Joshua [The Kavli Institute for Cosmological Physics, The University of Chicago, 933 East 56th Street, Chicago, IL 60637 (United States); Bernstein, Joseph P.; Kuhlmann, Steve; Marriner, John [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Campbell, Heather; Lampeitl, Hubert; Nichol, Robert C. [Institute of Cosmology and Gravitation, Dennis Sciama Building Burnaby Road Portsmouth PO1 3FX (United Kingdom); Dilday, Ben [Las Cumbres Observatory Global Telescope Network, 6740 Cortona Drive, Suite 102, Goleta, CA 93117 (United States); Falck, Bridget; Riess, Adam G. [Department of Physics and Astronomy, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218 (United States); Sako, Masao [Department of Physics and Astronomy, University of Pennsylvania, 203 South 33rd Street, Philadelphia, PA 19104 (United States); Schneider, Donald P., E-mail: rhlozek@astro.princeton.edu [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)

2012-06-20T23:59:59.000Z

57

Cosmology, Thermodynamics and Matter Creation  

E-Print Network (OSTI)

Several approaches to the matter creation problem in the context of cosmological models are summarily reviewed. A covariant formulation of the general relativistic imperfect simple fluid endowed with a process of matter creation is presented. By considering the standard big bang model, it is shown how the recent results of Prigogine et alii \\cite{1} can be recovered and, at the same time their limits of validity are explicited.

J. A. S. Lima; M. O. Calvao; I. Waga

2007-08-24T23:59:59.000Z

58

Quantum Weak Measurements and Cosmology  

E-Print Network (OSTI)

The indeterminism of quantum mechanics generally permits the independent specification of both an initial and a final condition on the state. Quantum pre-and-post-selection of states opens up a new, experimentally testable, sector of quantum mechanics, when combined with statistical averages of identical weak measurements. In this paper I apply the theory of weak quantum measurements combined with pre-and-post-selection to cosmology. Here, pre-selection means specifying the wave function of the universe or, in a popular semi-classical approximation, the initial quantum state of a subset of quantum fields propagating in a classical back-ground spacetime. The novel feature is post-selection: the additional specification of a condition on the quantum state in the far future. I discuss "natural" final conditions, and show how they may lead to potentially large and observable effects at the present cosmological epoch. I also discuss how pre-and-post-selected quantum contrast to the expectation value of the stress-energy-momentum tensor, resolving a vigorous debate from the 1970's. The paper thus provides a framework for computing large-scale cosmological effects arising from this new sector of quantum mechanics. A simple experimental test is proposed.

Paul Davies

2013-09-03T23:59:59.000Z

59

Timescape cosmology with radiation fluid  

E-Print Network (OSTI)

The timescape cosmology represents a potentially viable alternative to the standard homogeneous cosmology, without the need for dark energy. Although average cosmic evolution in the timescape scenario only differs substantially from that of Friedmann-Lemaitre model at relatively late epochs when the contribution from the energy density of radiation is negligible, a full solution of the Buchert equations to incorporate radiation is necessary to smoothly match parameters to the epoch of photon decoupling and to obtain constraints from cosmic microwave background data. Here we extend the matter-dominated solution found in earlier work to include radiation, providing series solutions at early times and an efficient numerical integration strategy for generating the complete solution. The numerical solution is used to directly calculate the scale of the sound horizon at decoupling, and at the baryon drag epoch. The constraints on these scales from the Planck satellite data yield bounds on the timescape cosmological parameters, which are found to also agree with the best-fit values from a recent analysis of SDSS-II supernova data, while avoiding the problem of a primordial lithium-7 abundance anomaly.

James A. G. Duley; M. Ahsan Nazer; David L. Wiltshire

2013-06-13T23:59:59.000Z

60

String Gas Cosmology and Non-Gaussianities  

E-Print Network (OSTI)

Recently it has been shown that string gas cosmology, an alternative model of the very early universe which does not involve a period of cosmological inflation, can give rise to an almost scale invariant spectrum of metric perturbations. Here we calculate the non-Gaussianities of the spectrum of cosmological fluctuations in string gas cosmology, and find that these non-Gaussianities depend linearly on the wave number and that their amplitude depends sensitively on the string scale. If the string scale is at the TeV scale, string gas cosmology could lead to observable non-Gaussianities, if it is close to the Planck scale, then the non-Gaussianities on current cosmological scales are negligible.

Bin Chen; Yi Wang; Wei Xue; Robert Brandenberger

2007-12-14T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


61

A small but nonzero cosmological constant  

E-Print Network (OSTI)

Recent astrophysical observations seem to indicate that the cosmological constant is small but nonzero and positive. The old cosmological constant problem asks why it is so small; we must now ask, in addition, why it is nonzero, and why it is positive. In this essay, we try to kill these three metaphorical birds with one stone. That stone is the unimodular theory of gravity, which is the canonical theory of gravity, except for the way the cosmological constant arises in the theory.

Y. Jack Ng (a; H. Van Dam (b

1999-01-01T23:59:59.000Z

62

Imperfect fluids, Lorentz violations, and Finsler cosmology  

Science Conference Proceedings (OSTI)

We construct a cosmological toy model based on a Finslerian structure of space-time. In particular, we are interested in a specific Finslerian Lorentz violating theory based on a curved version of Cohen and Glashow's very special relativity. The osculation of a Finslerian manifold to a Riemannian manifold leads to the limit of relativistic cosmology, for a specified observer. A modified flat Friedmann-Robertson-Walker cosmology is produced. The analogue of a zero energy particle unfolds some special properties of the dynamics. The kinematical equations of motion are affected by local anisotropies. Seeds of Lorentz violations may trigger density inhomogeneities to the cosmological fluid.

Kouretsis, A. P.; Stathakopoulos, M.; Stavrinos, P. C. [Section of Astrophysics, Astronomy and Mechanics, Department of Physics, Aristotle University of Thessaloniki, Thessaloniki 54124 (Greece); 1 Anastasiou Genadiou Street, 11474, Athens (Greece); Department of Mathematics, University of Athens, 15784 Greece (Greece)

2010-09-15T23:59:59.000Z

63

Large Synoptic Survey Telescope: Dark Energy Science Collaboration  

E-Print Network (OSTI)

This white paper describes the LSST Dark Energy Science Collaboration (DESC), whose goal is the study of dark energy and related topics in fundamental physics with data from the Large Synoptic Survey Telescope (LSST). It provides an overview of dark energy science and describes the current and anticipated state of the field. It makes the case for the DESC by laying out a robust analytical framework for dark energy science that has been defined by its members and the comprehensive three-year work plan they have developed for implementing that framework. The analysis working groups cover five key probes of dark energy: weak lensing, large scale structure, galaxy clusters, Type Ia supernovae, and strong lensing. The computing working groups span cosmological simulations, galaxy catalogs, photon simulations and a systematic software and computational framework for LSST dark energy data analysis. The technical working groups make the connection between dark energy science and the LSST system. The working groups have close linkages, especially through the use of the photon simulations to study the impact of instrument design and survey strategy on analysis methodology and cosmological parameter estimation. The white paper describes several high priority tasks identified by each of the 16 working groups. Over the next three years these tasks will help prepare for LSST analysis, make synergistic connections with ongoing cosmological surveys and provide the dark energy community with state of the art analysis tools. Members of the community are invited to join the LSST DESC, according to the membership policies described in the white paper. Applications to sign up for associate membership may be made by submitting the Web form at http://www.slac.stanford.edu/exp/lsst/desc/signup.html with a short statement of the work they wish to pursue that is relevant to the LSST DESC.

LSST Dark Energy Science Collaboration

2012-11-01T23:59:59.000Z

64

Scientific Objectives of Einstein Telescope  

E-Print Network (OSTI)

The advanced interferometer network will herald a new era in observational astronomy. There is a very strong science case to go beyond the advanced detector network and build detectors that operate in a frequency range from 1 Hz-10 kHz, with sensitivity a factor ten better in amplitude. Such detectors will be able to probe a range of topics in nuclear physics, astronomy, cosmology and fundamental physics, providing insights into many unsolved problems in these areas.

B. Sathyaprakash; M. Abernathy; F. Acernese; P. Ajith; B. Allen; P. Amaro-Seoane; N. Andersson; S. Aoudia; K. Arun; P. Astone; B. Krishnan; L. Barack; F. Barone; B. Barr; M. Barsuglia; M. Bassan; R. Bassiri; M. Beker; N. Beveridge; M. Bizouard; C. Bond; S. Bose; L. Bosi; S. Braccini; C. Bradaschia; M. Britzger; F. Brueckner; T. Bulik; H. J. Bulten; O. Burmeister; E. Calloni; P. Campsie; L. Carbone; G. Cella; E. Chalkley; E. Chassande-Mottin; S. Chelkowski; A. Chincarini; A. Di. Cintio; J. Clark; E. Coccia; C. N. Colacino; J. Colas; A. Colla; A. Corsi; A. Cumming; L. Cunningham; E. Cuoco; S. Danilishin; K. Danzmann; E. Daw; R. De. Salvo; W. Del. Pozzo; T. Dent; R. De. Rosa; L. Di. Fiore; M. Di. Paolo. Emilio; A. Di. Virgilio; A. Dietz; M. Doets; J. Dueck; M. Edwards; V. Fafone; S. Fairhurst; P. Falferi; M. Favata; V. Ferrari; F. Ferrini; F. Fidecaro; R. Flaminio; J. Franc; F. Frasconi; A. Freise; D. Friedrich; P. Fulda; J. Gair; M. Galimberti; G. Gemme; E. Genin; A. Gennai; A. Giazotto; K. Glampedakis; S. Gossan; R. Gouaty; C. Graef; W. Graham; M. Granata; H. Grote; G. Guidi; J. Hallam; G. Hammond; M. Hannam; J. Harms; K. Haughian; I. Hawke; D. Heinert; M. Hendry; I. Heng; E. Hennes; S. Hild; J. Hough; D. Huet; S. Husa; S. Huttner; B. Iyer; D. I. Jones; G. Jones; I. Kamaretsos; C. Kant Mishra; F. Kawazoe; F. Khalili; B. Kley; K. Kokeyama; K. Kokkotas; S. Kroker; R. Kumar; K. Kuroda; B. Lagrange; N. Lastzka; T. G. F. Li; M. Lorenzini; G. Losurdo; H. Lück; E. Majorana; V. Malvezzi; I. Mandel; V. Mandic; S. Marka; F. Marin; F. Marion; J. Marque; I. Martin; D. Mc. Leod; D. Mckechan; M. Mehmet; C. Michel; Y. Minenkov; N. Morgado; A. Morgia; S. Mosca; L. Moscatelli; B. Mours; H. Müller-Ebhardt; P. Murray; L. Naticchioni; R. Nawrodt; J. Nelson; R. O'. Shaughnessy; C. D. Ott; C. Palomba; A. Paoli; G. Parguez; A. Pasqualetti; R. Passaquieti; D. Passuello; M. Perciballi; F. Piergiovanni; L. Pinard; M. Pitkin; W. Plastino; M. Plissi; R. Poggiani; P. Popolizio; E. Porter; M. Prato; G. Prodi; M. Punturo; P. Puppo; D. Rabeling; I. Racz; P. Rapagnani; V. Re; J. Read; T. Regimbau; H. Rehbein; S. Reid; F. Ricci; F. Richard; C. Robinson; A. Rocchi; R. Romano; S. Rowan; A. Rüdiger; A. Samblowski; L. Santamaría; B. Sassolas; R. Schilling; P. Schmidt; R. Schnabel; B. Schutz; C. Schwarz; J. Scott; P. Seidel; A. M. Sintes; K. Somiya; C. F. Sopuerta; B. Sorazu; F. Speirits; L. Storchi; K. Strain; S. Strigin; P. Sutton; S. Tarabrin; B. Taylor; A. Thürin; K. Tokmakov; M. Tonelli; H. Tournefier; R. Vaccarone; H. Vahlbruch; J. F. J. van. den. Brand; C. Van. Den. Broeck; S. van. der. Putten; M. van. Veggel; A. Vecchio; J. Veitch; F. Vetrano; A. Vicere; S. Vyatchanin; P. Weßels; B. Willke; W. Winkler; G. Woan; A. Woodcraft; K. Yamamoto

2012-06-02T23:59:59.000Z

65

Code for Largest Cosmological Simulations Ever on GPUs Is Gordon Bell  

NLE Websites -- All DOE Office Websites (Extended Search)

Code for Largest Cosmological Simulations Ever on GPUs Is Gordon Bell Code for Largest Cosmological Simulations Ever on GPUs Is Gordon Bell Finalist Katie Elyce Jones - November 05, 2013 Zoom-in showing the clustering of dark matter, including the effect of massive neutrinos, as simulated on Titan. HACC uses modules with algorithms specific to different supercomputing architectures Advancements to instruments in observatories and satellites can stretch the eye of the observer billions of light-years away to the fringes of the observable universe. Images from sky surveys of galaxies, quasars, and other astronomical objects offer scientists clues about how the distribution of mass is influenced by dark energy, the repelling force guiding the accelerated expansion of the universe. But all the telescopes at scientists' disposal cannot begin to canvas the

66

Neutrinos in Cosmology and Astrophysics  

E-Print Network (OSTI)

We briefly review the recent developments in neutrino physics and astrophysics which have import for frontline research in nuclear physics. These developments, we argue, tie nuclear physics to exciting developments in observational cosmology and astrophysics in new ways. Moreover, the behavior of neutrinos in dense matter is itself a fundamental problem in many-body quantum mechanics, in some ways akin to well-known issues in nuclear matter and nuclei, and in some ways radically different, especially because of nonlinearity and quantum de-coherence. The self-interacting neutrino gas is the only many body system driven by the weak interactions.

A. B. Balantekin; G. M. Fuller

2013-03-15T23:59:59.000Z

67

A new perspective on early cosmology  

E-Print Network (OSTI)

We present a new perspective on early cosmology based on Loop Quantum Gravity. We use projected spinnetworks, coherent states and spinfoam techniques, to implement a quantum reduction of the full Kinematical Hilbert space of LQG, suitable to describe inhomogeneous cosmological models. Some preliminary results on the solutions of the Scalar constraint of the reduced theory are also presented.

Emanuele Alesci

2013-03-04T23:59:59.000Z

68

Symplectic method in quantum cosmology  

Science Conference Proceedings (OSTI)

In the present work, we study the quantum cosmology description of Friedmann-Robertson-Walker models in the presence of a generic perfect fluid and a cosmological constant, which may be positive or negative. We work in Schutz's variational formalism and the three-dimensional spatial sections may have positive, negative, or zero constant curvature. If one uses the scale factor and its canonically conjugated momentum as the phase space variables that describe the geometrical sector of these models, one obtains Wheeler-DeWitt equations with operator ordering ambiguities. In order to avoid those ambiguities and simplify the quantum treatment of the models, we follow references [Edesio M. Barbosa, Jr. and Nivaldo A. Lemos, Gen. Relativ. Gravit. 38, 1609 (2006).][Edesio M. Barbosa, Jr. and Nivaldo A. Lemos, Phys. Rev. D 78, 023504 (2008).] and introduce new phase space variables. We explicitly demonstrate, using the symplectic method, that the transformation leading from the old set of variables to the new one is canonical.

Silva, E. V. Correa; Monerat, G. A.; Oliveira-Neto, G.; Neves, C. [Departamento de Matematica e Computacao, Faculdade de Tecnologia, Universidade do Estado do Rio de Janeiro, Rodovia Presidente Dutra, Km 298, Polo Industrial, CEP 27537-000, Resende-RJ (Brazil); Ferreira Filho, L. G. [Departamento de Mecanica e Energia, Faculdade de Tecnologia, Universidade do Estado do Rio de Janeiro, Rodovia Presidente Dutra, Km 298, Polo Industrial, CEP 27537-000, Resende-RJ (Brazil)

2009-08-15T23:59:59.000Z

69

SLAC National Accelerator Laboratory - Bringing Telescope Tech...  

NLE Websites -- All DOE Office Websites (Extended Search)

Telescope Tech to X-ray Lasers By Glenn Roberts Jr July 10, 2012 Technology that helps ground-based telescopes cut through the haze of Earth's atmosphere to get a clearer view of...

70

Radiation Dominated Universe for Jordan-Brans-Dicke Cosmology  

E-Print Network (OSTI)

Jordan-Brans-Dicke cosmology with a standard kinetic term for the scalar field and no mass term has the same radiation dominated solution as standard Einstein cosmology without the cosmological constant. Because of this, the primordial nucleosynthesis (Big - Bang nucleosynthesis) result obtained for standard cosmology remains the same for Jordan-Brans-Dicke cosmology. We show that Jordan-Brans-Dicke cosmology with a mass term for the scalar field as well as explaining dark energy for the present era, can also explain radiation dominated cosmology for the primordial nucleosynthesis era.

M. Arik; L. Amon Susam

2010-06-22T23:59:59.000Z

71

Scalar perturbations in deflationary cosmological models  

E-Print Network (OSTI)

We consider scalar perturbations of energy--density for a class of cosmological models where an early phase of accelerated expansion evolves, without any fine--tuning for graceful exit, towards the standard Friedman eras of observed universe. The geometric procedure which generates such models agrees with results for string cosmology since it works if dynamics is dominated by a primordial fluid of extended massive objects. The main result is that characteristic scales of cosmological interest, connected with the extension of such early objects, are selected.}

S. Capozziello; G. Lambiase; G. Scarpetta

1998-06-09T23:59:59.000Z

72

From Microwave Anisotropies to Cosmology  

E-Print Network (OSTI)

Fluctuations in the temperature of the cosmic microwave background have now been detected over a wide range of angular scales, and a consistent picture seems to be emerging. This article describes some of the implications for cosmology. Analysis of all the published detections suggests the existence of a peak on degree scales of height 2.4 to 10 (90%CL) relative to the amplitude of the power spectrum at large angular scales. This result confirms an early prediction, implies that the universe did in fact recombine, and limits theories of structure formation. Illustrative examples are provided of how the comparison of microwave background and large-scale structure data will be a potentially powerful means of answering fundamental questions about the universe.

Douglas Scott; Joe Silk; Martin White

1995-05-04T23:59:59.000Z

73

Generating Cosmological Gaussian Random Fields  

E-Print Network (OSTI)

We present a generic algorithm for generating Gaussian random initial conditions for cosmological simulations on periodic rectangular lattices. We show that imposing periodic boundary conditions on the real-space correlator and choosing initial conditions by convolving a white noise random field results in a significantly smaller error than the traditional procedure of using the power spectrum. This convolution picture produces exact correlation functions out to separations of L/2, where L is the box size, which is the maximum theoretically allowed. This method also produces tophat sphere fluctuations which are exact at radii $ R \\le L/4 $. It is equivalent to windowing the power spectrum with the simulation volume before discretizing, thus bypassing sparse sampling problems. The mean density perturbation in the volume is no longer constrained to be zero, allowing one to assemble a large simulation using a series of smaller ones. This is especially important for simulations of Lyman-$\\alpha$ systems where sma...

Pen, U L

1997-01-01T23:59:59.000Z

74

Higgs Particle Mass in Cosmology  

E-Print Network (OSTI)

A version of the Standard Model is considered, where the electroweak symmetry breaking is provided by cosmological initial data given for the zeroth Fourier harmonic of the Higgs field $$. The initial data symmetry breaking mechanism removes the Higgs field contribution to the vacuum energy density, possible creation of monopoles, and tachion behavior at high energies, if one imposes an ``inertial'' condition on the Higgs potential $\\textsf{V}_{\\rm Higgs}()=0$. The requirement of zero radiative corrections to this {\\em inertial} condition coincides with the limiting point of the vacuum stability in the Standard Model. The latter together with the direct experimental limit gives the prediction for the mass of the Higgs boson to be in the range $114 < m_h \\lsim 134$ GeV.

A. B. Arbuzov; L. A. Glinka; V. N. Pervushin

2007-05-31T23:59:59.000Z

75

Dynamical System Analysis of Cosmologies with Running Cosmological Constant from Quantum Einstein Gravity  

E-Print Network (OSTI)

We discuss a mechanism that induces a time-dependent vacuum energy on cosmological scales. It is based on the instability induced renormalization triggered by the low energy quantum fluctuations in a Universe with a positive cosmological constant. We employ the dynamical systems approach to study the qualitative behavior of Friedmann-Robertson-Walker cosmologies where the cosmological constant is dynamically evolving according with this nonperturbative scaling at low energies. It will be shown that it is possible to realize a "two regimes" dark energy phases, where an unstable early phase of power-law evolution of the scale factor is followed by an accelerated expansion era at late times.

Bonanno, Alfio

2011-01-01T23:59:59.000Z

76

Constraining Palatini cosmological models using GRB data  

E-Print Network (OSTI)

New constraints on previously investigated Palatini cosmological models [arXiv:1109.3420] have been obtained by adding Gamma Ray Burst data [arXiv:1205.2954].

Michal Kamionka

2013-03-08T23:59:59.000Z

77

SLAC National Accelerator Laboratory - Astrophysics and Cosmology  

NLE Websites -- All DOE Office Websites (Extended Search)

Astrophysics and Cosmology A night time aerial image of one of the labs at SLAC SLAC astrophysicists and cosmologists play leading roles in the study of the high-energy universe,...

78

Entropy signature of the running cosmological constant  

E-Print Network (OSTI)

Renormalization group (RG) improved cosmologies based upon a RG trajectory of Quantum Einstein Gravity (QEG) with realistic parameter values are investigated using a system of cosmological evolution equations which allows for an unrestricted energy exchange between the vacuum and the matter sector. It is demonstrated that the scale dependence of the gravitational parameters, the cosmological constant in particular, leads to an entropy production in the matter system. The picture emerges that the Universe started out from a state of vanishing entropy, and that the radiation entropy observed today is essentially due to the coarse graining (RG flow) in the quantum gravity sector which is related to the expansion of the Universe. Furthermore, the RG improved field equations are shown to possess solutions with an epoch of power law inflation immediately after the initial singularity. The inflation is driven by the cosmological constant and ends automatically once the RG running has reduced the vacuum energy to the...

Bonanno, Alfio

2007-01-01T23:59:59.000Z

79

A small but nonzero cosmological constant  

E-Print Network (OSTI)

Recent astrophysical observations seem to indicate that the cosmological constant is small but nonzero and positive. The old cosmological constant problem asks why it is so small; we must now ask, in addition, why it is nonzero (and is in the range found by recent observations), and why it is positive. In this essay, we try to kill these three metaphorical birds with one stone. That stone is the unimodular theory of gravity, which is the ordinary theory of gravity, except for the way the cosmological constant arises in the theory. We argue that the cosmological constant becomes dynamical, and eventually, in terms of the cosmic scale factor $R(t)$, it takes the form $\\Lambda(t) = \\Lambda(t_0)(R(t_0)/R(t))^2$, but not before the epoch corresponding to the redshift parameter $z \\sim 1$.

Y. Jack Ng; H. van Dam

1999-11-13T23:59:59.000Z

80

Quantum cosmology and late-time singularities  

E-Print Network (OSTI)

The development of dark energy models has stimulated interest to cosmological singularities, which differ from the traditional Big Bang and Big Crunch singularities. We review a broad class of phenomena connected with soft cosmological singularities in classical and quantum cosmology. We discuss the classification of singularities from the geometrical point of view and from the point of view of the behaviour of finite size objects, crossing such singularities. We discuss in some detail quantum and classical cosmology of models based on perfect fluids (anti-Chaplygin gas and anti-Chaplygin gas plus dust), of models based on the Born-Infeld-type fields and of the model of a scalar field with a potential inversely proportional to the field itself. We dwell also on the phenomenon of the phantom divide line crossing in the scalar field models with cusped potentials. Then we discuss the Friedmann equations modified by quantum corrections to the effective action of the models under considerations and the influence of such modification on the nature and the existence of soft singularities. We review also quantum cosmology of models, where the initial quantum state of the universe is presented by the density matrix (mixed state). Finally, we discuss the exotic singularities arising in the brane-world cosmological models.

A. Yu. Kamenshchik

2013-07-22T23:59:59.000Z

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81

Cosmological Acceleration: Dark Energy or Modified Gravity?  

E-Print Network (OSTI)

We review the evidence for recently accelerating cosmological expansion or "dark energy", either a negative pressure constituent in General Relativity (Dark Energy) or modified gravity (Dark Gravity), without any Dark Energy constituent. If constituent Dark Energy does not exist, so that our universe is now dominated by pressure-free matter, Einstein gravity must be modified at low curvature. The vacuum symmetry of any Robertson-Walker universe then characterizes Dark Gravity as low- or high-curvature modifications of Einstein gravity. The dynamics of either kind of "dark energy" cannot be derived from the homogeneous expansion alone, but requires also observing the growth of inhomogeneities. Present and projected observations are all consistent with a small fine tuned cosmological constant, with nearly static Dark Energy, or with gravity modified at cosmological scales. The growth of cosmological fluctuations will potentially distinguish static "dark energy" from dynamic "dark energy" with equation of state $w(z)$ either changing rapidly or tracking the background matter. But to cosmologically distinguish $\\Lambda$CDM from modified gravity will require a weak lensing shear survey more ambitious than any now projected. Dvali-Gabadadze-Porrati modifications of Einstein gravity may also be detected in refined bservations in the solar system or at the intermediate Vainstein scale. Dark Energy's epicyclic character, failure to explain the original Cosmic Coincidence ("Why now?") without fine tuning, inaccessibility to laboratory or solar system tests, along with braneworld theories, now motivate future precision solar system, Vainstein-scale and cosmological-scale studies of Dark Gravity.

Sidney Bludman

2006-05-08T23:59:59.000Z

82

Conformal cosmological model and SNe Ia data  

SciTech Connect

Now there is a huge scientific activity in astrophysical studies and cosmological ones in particular. Cosmology transforms from a pure theoretical branch of science into an observational one. All the cosmological models have to pass observational tests. The supernovae type Ia (SNe Ia) test is among the most important ones. If one applies the test to determine parameters of the standard Friedmann-Robertson-Walker cosmological model one can conclude that observations lead to the discovery of the dominance of the {Lambda} term and as a result to an acceleration of the Universe. However, there are big mysteries connected with an origin and an essence of dark matter (DM) and the {Lambda} term or dark energy (DE). Alternative theories of gravitation are treated as a possible solution of DM and DE puzzles. The conformal cosmological approach is one of possible alternatives to the standard {Lambda}CDM model. As it was noted several years ago, in the framework of the conformal cosmological approach an introduction of a rigid matter can explain observational data without {Lambda} term (or dark energy). We confirm the claim with much larger set of observational data.

Zakharov, A. F., E-mail: zakharov@itep.ru [National Astronomical Observatories of Chinese Academy of Sciences (China); Pervushin, V. N. [Joint Institute for Nuclear Research, Bogoliubov Laboratory for Theoretical Physics (Russian Federation)

2012-11-15T23:59:59.000Z

83

Magnetic Bianchi type II string cosmological model in loop quantum cosmology  

E-Print Network (OSTI)

The loop quantum cosmology of the Bianchi type II string cosmological model in the presence of a homogeneous magnetic field is studied. We present the effective equations which provide modifications to the classical equations of motion due to quantum effects. The numerical simulations confirm that the big bang singularity is resolved by quantum gravity effects.

Victor Rikhvitsky; Bijan Saha; Mihai Visinescu

2013-12-09T23:59:59.000Z

84

Generating Cosmological Gaussian Random Fields  

E-Print Network (OSTI)

We present a generic algorithm for generating Gaussian random initial conditions for cosmological simulations on periodic rectangular lattices. We show that imposing periodic boundary conditions on the real-space correlator and choosing initial conditions by convolving a white noise random field results in a significantly smaller error than the traditional procedure of using the power spectrum. This convolution picture produces exact correlation functions out to separations of L/2, where L is the box size, which is the maximum theoretically allowed. This method also produces tophat sphere fluctuations which are exact at radii $ R \\le L/4 $. It is equivalent to windowing the power spectrum with the simulation volume before discretizing, thus bypassing sparse sampling problems. The mean density perturbation in the volume is no longer constrained to be zero, allowing one to assemble a large simulation using a series of smaller ones. This is especially important for simulations of Lyman-$\\alpha$ systems where small boxes with steep power spectra are routinely used. We also present an extension of this procedure which generates exact initial conditions for hierarchical grids at negligible cost.

Ue-Li Pen

1997-09-25T23:59:59.000Z

85

TERAPIXEL IMAGING OF COSMOLOGICAL SIMULATIONS  

SciTech Connect

The increasing size of cosmological simulations has led to the need for new visualization techniques. We focus on smoothed particle hydrodynamic (SPH) simulations run with the GADGET code and describe methods for visually accessing the entire simulation at full resolution. The simulation snapshots are rastered and processed on supercomputers into images that are ready to be accessed through a Web interface (GigaPan). This allows any scientist with a Web browser to interactively explore simulation data sets in both spatial and temporal dimensions and data sets which in their native format can be hundreds of terabytes in size or more. We present two examples, the first a static terapixel image of the MassiveBlack simulation, a P-GADGET SPH simulation with 65 billion particles, and the second an interactively zoomable animation of a different simulation with more than 1000 frames, each a gigapixel in size. Both are available for public access through the GigaPan Web interface. We also make our imaging software publicly available.

Feng Yu; Croft, Rupert A. C.; Di Matteo, Tiziana; Khandai, Nishikanta [Bruce and Astrid McWilliams Center for Cosmology, Carnegie Mellon University, Pittsburgh, PA 15213 (United States); Sargent, Randy; Nourbakhsh, Illah; Dille, Paul; Bartley, Chris [Robotics Institute, Carnegie Mellon University, Pittsburgh, PA 15213 (United States); Springel, Volker [Heidelberger Institut fuer Theoretische Studien, Schloss-Wolfsbrunnenweg 35, 69118 Heidelberg (Germany); Jana, Anirban [Pittsburgh Supercomputing Center, Pittsburgh, PA 15213 (United States); Gardner, Jeffrey, E-mail: yfeng1@andrew.cmu.edu [Physics Department, University of Washington, Seattle, WA 98195 (United States)

2011-12-01T23:59:59.000Z

86

BNL | Large Synoptic Survey Telescope (LSST)  

NLE Websites -- All DOE Office Websites (Extended Search)

Large Synoptic Survey Telescope Large Synoptic Survey Telescope About LSST Digital Sensor Array Brookhaven & Physics of the Universe LSST Project Website LSST: Providing an Unprecedented View of the Cosmos rendering of the LSST site in Chile A revolutionary 3.2 gigapixel camera mounted in a massive ground-based telescope will produce unprecedented views of the cosmos, driving discoveries with the widest, densest, and most complete images of our universe ever captured. New Visions The Large Synoptic Survey Telescope (LSST) will peer into space as no other telescope can. This new facility will create an unparalleled wide-field astronomical survey of our universe - wider and deeper in volume than all previous telescopes combined. The combination of a 3200 megapixel camera sensor array, a powerful supercomputer, a cutting-edge data processing and

87

The ANTARES underwater neutrino telescope  

E-Print Network (OSTI)

ANTARES is the first undersea neutrino telescope. It is in its complete configuration since May 2008 at about 2.5 km below the sea surface close to Marseille. Data from 12 lines are being analyzed and are producing first results. Here we discuss first analysis results for 5 lines and 10 lines, and we also comment on the performance of the full detector. We show that the detector has capabilities for discriminating upgoing neutrino events from the much larger amount of downgoing atmospheric muons and that data and simulation are in good agreement. We then discuss the physics reach of the detector for what concerns point-like source and dark matter searches.

Teresa Montaruli; for the ANTARES Collaboration

2008-10-21T23:59:59.000Z

88

The Universe Adventure - The Cosmological Principle  

NLE Websites -- All DOE Office Websites (Extended Search)

Cosmological Principle Cosmological Principle The distribution of matter across the universe is approximately even. The distribution of matter across the Universe is approximately even, homogeneous, when considered at large scales. Albert Einstein's theory of General Relativity permits many possible types of universes. In applying the theory to describe the dynamics of our Universe, Einstein made a central empirical assumption to limit the number of possible solutions to the equations. He assumed that on very large scales the distribution of matter in the Universe is constant, making the Universe appear smooth. This idea is a form of the modern cosmological principle. This principle is not exact since much of the Universe's matter is found clustered together in planets, stars, and galaxies, but when considered at

89

Higgs mass determined by cosmological parameters  

E-Print Network (OSTI)

Postulating that all massless elementary fields have conformal scaling symmetry removes a conflict between gravitational theory and the standard model of elementary quantum fields. If the scalar field essential to SU(2) symmetry breaking has conformal symmetry, it must depend explicitly on the Ricci curvature scalar of gravitational theory. This has profound consequences for both cosmology and elementary particle physics, since cosmological data determine scalar field parameters. A modified Friedmann equation is derived and solved numerically. The theory is consistent with all relevant data for supernovae redshifts below $z=1$. The implied value of the cosmological constant implies extremely small Higgs mass, far below current empirical lower bounds. Detection of a Higgs boson with large mass would falsify this argument.

R. K. Nesbet

2008-11-25T23:59:59.000Z

90

A MEASUREMENT OF THE CORRELATION OF GALAXY SURVEYS WITH CMB LENSING CONVERGENCE MAPS FROM THE SOUTH POLE TELESCOPE  

Science Conference Proceedings (OSTI)

We compare cosmic microwave background lensing convergence maps derived from South Pole Telescope (SPT) data with galaxy survey data from the Blanco Cosmology Survey, WISE, and a new large Spitzer/IRAC field designed to overlap with the SPT survey. Using optical and infrared catalogs covering between 17 and 68 deg{sup 2} of sky, we detect a correlation between the SPT convergence maps and each of the galaxy density maps at >4{sigma}, with zero correlation robustly ruled out in all cases. The amplitude and shape of the cross-power spectra are in good agreement with theoretical expectations and the measured galaxy bias is consistent with previous work. The detections reported here utilize a small fraction of the full 2500 deg{sup 2} SPT survey data and serve as both a proof of principle of the technique and an illustration of the potential of this emerging cosmological probe.

Bleem, L. E.; Becker, M. R.; Benson, B. A.; Carlstrom, J. E.; Chang, C. L.; Crawford, T. M.; Crites, A. T. [Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Van Engelen, A.; Holder, G. P.; De Haan, T.; Dobbs, M. A. [Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8 (Canada); Aird, K. A. [University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Armstrong, R. [National Center for Supercomputing Applications, University of Illinois, 1205 West Clark Street, Urbana, IL 61801 (United States); Ashby, M. L. N. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Biesiadzinski, T. [Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, MI 48109 (United States); Brodwin, M. [Department of Physics and Astronomy, University of Missouri, 5110 Rockhill Road, Kansas City, MO 64110 (United States); Busha, M. T. [Institute for Theoretical Physics, University of Zuerich, Zuerich (Switzerland); Cho, H. M. [NIST Quantum Devices Group, 325 Broadway, Mailcode 817.03, Boulder, CO 80305 (United States); Desai, S. [Department of Physics, Ludwig-Maximilians-Universitaet, Scheinerstr. 1, 81679 Muenchen (Germany); Dore, O. [Division of Physics, Mathematics, and Astronomy, California Institute of Technology, MS 249-17, 1216 East California Blvd., Pasadena, CA 91125 (United States); and others

2012-07-01T23:59:59.000Z

91

Thermodynamics of Ideal Gas in Cosmology  

E-Print Network (OSTI)

The equation of state and the state functions for the gravitational source are necessary conditions for solving cosmological model and stellar structure. The usual treatments are directly based on the laws of thermodynamics, and the physical meanings of some concepts are obscure. This letter show that, we can actually derive all explicit fundamental state functions for the ideal gas in the context of cosmology via rigorous dynamical and statistical calculation. These relations have clear physical meanings, and are valid in both non-relativistic and ultra-relativistic cases. Some features of the equation of state are important for a stable structure of a star with huge mass.

Ying-Qiu Gu

2007-08-22T23:59:59.000Z

92

Microscopic surface structure of C/SiC composite mirrors for space cryogenic telescopes  

E-Print Network (OSTI)

We report on the microscopic surface structure of carbon-fiber-reinforced silicon carbide (C/SiC) composite mirrors that have been improved for the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and other cooled telescopes. The C/SiC composite consists of carbon fiber, silicon carbide, and residual silicon. Specific microscopic structures are found on the surface of the bare C/SiC mirrors after polishing. These structures are considered to be caused by the different hardness of those materials. The roughness obtained for the bare mirrors is 20 nm rms for flat surfaces and 100 nm rms for curved surfaces. It was confirmed that a SiSiC slurry coating is effective in reducing the roughness to 2 nm rms. The scattering properties of the mirrors were measured at room temperature and also at 95 K. No significant change was found in the scattering properties through cooling, which suggests that the microscopic surface structure is stable with changes in temperature down to cryogenic values. The C/SiC mirror with the SiSiC slurry coating is a promising candidate for the SPICA telescope.

Keigo Enya; Takao Nakagawa; Hidehiro Kaneda; Takashi Onaka; Tuyoshi Ozaki; Masami Kume

2007-07-10T23:59:59.000Z

93

Cosmological singularities in Bakry-Émery spacetimes  

E-Print Network (OSTI)

We consider spacetimes consisting of a manifold with Lorentzian metric and a weight function or scalar field. These spacetimes admit a Bakry-\\'Emery-Ricci tensor which is a natural generalization of the Ricci tensor. We impose an energy condition on the Bakry-\\'Emery-Ricci tensor and obtain singularity theorems of a cosmological type, both for zero and for positive cosmological constant. That is, we find conditions under which every timelike geodesic is incomplete. These conditions are given by "open" inequalities, so we examine the borderline (equality) cases and show that certain singularities are avoided in these cases only if the geometry is rigid; i.e., if it splits as a Lorentzian product or, for a positive cosmological constant, a warped product, and the weight function is constant along the time direction. Then the product case is future timelike geodesically complete while, in the warped product case, worldlines of conformally static observers are complete. Our results answer a question posed by J Case. We then apply our results to the cosmology of scalar-tensor gravitation theories. We focus on the Brans-Dicke family of theories in 4 spacetime dimensions, where we obtain "Jordan frame" singularity theorems for big bang singularities.

Gregory J Galloway; Eric Woolgar

2013-12-12T23:59:59.000Z

94

Primordial magnetic field limits from cosmological data  

SciTech Connect

We study limits on a primordial magnetic field arising from cosmological data, including that from big bang nucleosynthesis, cosmic microwave background polarization plane Faraday rotation limits, and large-scale structure formation. We show that the physically relevant quantity is the value of the effective magnetic field, and limits on it are independent of how the magnetic field was generated.

Kahniashvili, Tina [McWilliams Center for Cosmology and Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213 (United States); Department of Physics, Laurentian University, Ramsey Lake Road, Sudbury, Ontario P3E 2C (Canada); Abastumani Astrophysical Observatory, Ilia State University, 2A Kazbegi Ave, Tbilisi, GE-0160 (Georgia); Tevzadze, Alexander G. [Abastumani Astrophysical Observatory, Ilia State University, 2A Kazbegi Ave, Tbilisi, GE-0160 (Georgia); Faculty of Exact and Natural Sciences, Tbilisi State University, 1 Chavchavadze Avenue, Tbilisi, GE-0128 (Georgia); Sethi, Shiv K. [McWilliams Center for Cosmology and Department of Physics, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, Pennsylvania 15213 (United States); Raman Research Institute, Sadashivanagar, Bangalore 560080 (India); Pandey, Kanhaiya [Raman Research Institute, Sadashivanagar, Bangalore 560080 (India); Ratra, Bharat [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States)

2010-10-15T23:59:59.000Z

95

Encoding cosmological futures with conformal structures  

E-Print Network (OSTI)

Quiescent cosmology and the Weyl curvature hypothesis possess a mathematical framework, namely the definition of an Isotropic Singularity, but only for the initial state of the universe. A complementary framework is necessary to also encode appropriate cosmological futures. In order to devise a new framework we analyse the relation between regular conformal structures and (an)isotropy, the behaviour and role of a monotonic conformal factor which is a function of cosmic time, as well as four example cosmologies for further guidance. Finally, we present our new definitions of an Anisotropic Future Endless Universe and an Anisotropic Future Singularity which offer a promising realisation for the new framework. Their irregular, degenerate conformal structures differ significantly from those of the Isotropic Singularity. The combination of the three definitions together could then provide the first complete formalisation of the quiescent cosmology concept. For completeness we also present the new definitions of an Isotropic Future Singularity and a Future Isotropic Universe. The relation to other approaches, in particular to the somewhat dual dynamical systems approach, and other asymptotic scenarios is briefly discussed.

Philipp A Hoehn; Susan M Scott

2010-01-18T23:59:59.000Z

96

Cosmological parameter estimation from CMB experiments  

Science Conference Proceedings (OSTI)

I review the general aspects of cosmological parameter estimation from observations of the cosmic microwave background (CMB) temperature anisotropies in the framework of inflationary adiabatic models. The most recent CMB datasets are starting to give good constraints on the relevant parameters of inflationary adiabatic models. They point toward a model consistent with the basic predictions of inflation: a nearly flat universe

Amedeo Balbi

2001-01-01T23:59:59.000Z

97

NIST Telescope Calibration May Help Explain Mystery of ...  

Science Conference Proceedings (OSTI)

... They will use this information to calibrate a much larger telescope–the Large Synoptic Survey Telescope, planned for construction in Chile. ...

2011-01-05T23:59:59.000Z

98

Measuring Neutrinos with the ANTARES Telescope  

Science Conference Proceedings (OSTI)

The ANTARES underwater neutrino telescope has been taking data since construction began in 2006. The telescope, completed in May of 2008, detects the Cerenkov radiation of charged leptons produced by high energy neutrinos interacting in or around the detector. The lepton trajectory is reconstructed with high precision, revealing the direction of the incoming neutrino. The performance of the detector will be discussed and recent data showing muons, electromagnetic showers and atmospheric neutrinos will be presented. Studies have been underway to search for neutrino point sources in the ANTARES data since 2007. Results from these studies will be presented, and the sensitivity of the telescope will be discussed.

Reed, Corey [National Institute for Subatomic Physics (Nikhef), Amsterdam (Netherlands)

2009-12-17T23:59:59.000Z

99

SCIENTIFIC EFFICIENCY OF GROUND-BASED TELESCOPES  

SciTech Connect

I scanned the six major astronomical journals of 2008 for all 1589 papers that are based on new data obtained from ground-based optical/IR telescopes worldwide. Then I collected data on numbers of papers, citations to them in 3+ years, the most-cited papers, and annual operating costs. These data are assigned to four groups by telescope aperture. For instance, while the papers from telescopes with an aperture >7 m average 1.29 more citations than those with an aperture of 2 to <4 m, this represents a small return for a factor of four difference in operating costs. Among the 17 papers that have received {>=}100 citations in 3+ years, only half come from the large (>7 m) telescopes. I wonder why the large telescopes do so relatively poorly and suggest possible reasons. I also found that papers based on archival data, such as the Sloan Digital Sky Survey, produce 10.6% as many papers and 20.6% as many citations as those based on new data. Also, the 577.2 papers based on radio data produced 36.3% as many papers and 33.6% as many citations as the 1589 papers based on optical/IR telescopes.

Abt, Helmut A., E-mail: abt@noao.edu [Kitt Peak National Observatory, P.O. Box 26732, Tucson, AZ 85726-6732 (United States)

2012-10-01T23:59:59.000Z

100

Conformal Structures Admitted by a Class of FRW Cosmologies  

E-Print Network (OSTI)

In this paper we demonstrate that there are large classes of Friedmann-Robertson-Walker (FRW) cosmologies that admit isotropic conformal structures of Quiescent Cosmology. FRW models have long been known to admit singularities such as Big Bangs and Big Crunches [1, 2] but recently it has been shown that there are other cosmological structures that these solutions contain. These structures are Big Rips, Sudden Singularities and Extremality Events [1, 2]. Within the Quiescent Cosmology framework [3] there also exist structures consistent with a cosmological singularity known as the Isotropic Past Singularity (IPS) [4, 5]. There also exists a cosmological final state known as a Future Isotropic Universe (FIU) [4], which strictly speaking, doesn't fit with the fundamental ideals of Quiescent Cosmology. In this paper, we compare the cosmological events of a large class of FRW solutions to the conformal structures of Quiescent Cosmology [4]. In the first section of this paper we present the relevant background information and our motivation. In the second section of this paper we construct conformal relationships for relevant FRW models. The third section contains a thorough discussion of a class of FRW solutions that cannot represent any of the previously constructed isotropic conformal structures from Quiescent Cosmology. The final section contains our remarks and future outlook for further study of this field.

Philip Threlfall; Susan M. Scott

2012-11-26T23:59:59.000Z

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101

Cosmology Becomes Data-driven Science Cosmology, our study of the nature, formation, and evolution of  

E-Print Network (OSTI)

), two powerful but competing models were in the air: the big bang and the steady state models by the flood of data from telescopes on Earth and in space. Observations have amply and thoroughly confirmed the big bang model as essentially correct. The Hubble Space Telescope and many other instruments have now

Landweber, Laura

102

High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes  

E-Print Network (OSTI)

We present the results of high precision measurements of the thermal expansion of the sintered SiC, SiC-100, intended for use in cryogenic space-telescopes, in which minimization of thermal deformation of the mirror is critical and precise information of the thermal expansion is needed for the telescope design. The temperature range of the measurements extends from room temperature down to $\\sim$ 10 K. Three samples, #1, #2, and #3 were manufactured from blocks of SiC produced in different lots. The thermal expansion of the samples was measured with a cryogenic dilatometer, consisting of a laser interferometer, a cryostat, and a mechanical cooler. The typical thermal expansion curve is presented using the 8th order polynomial of the temperature. For the three samples, the coefficients of thermal expansion (CTE), $\\bar{\\alpha}_{#1}$, $\\bar{\\alpha}_{#2}$, and $\\bar{\\alpha}_{#3}$ were derived for temperatures between 293 K and 10 K. The average and the dispersion (1 $\\sigma$ rms) of these three CTEs are 0.816 and 0.002 ($\\times 10^{-6}$/K), respectively. No significant difference was detected in the CTE of the three samples from the different lots. Neither inhomogeneity nor anisotropy of the CTE was observed. Based on the obtained CTE dispersion, we performed an finite-element-method (FEM) analysis of the thermal deformation of a 3.5 m diameter cryogenic mirror made of six SiC-100 segments. It was shown that the present CTE measurement has a sufficient accuracy well enough for the design of the 3.5 m cryogenic infrared telescope mission, the Space Infrared telescope for Cosmology and Astrophysics (SPICA).

K. Enya; N. Yamada; T. Onaka; T. Nakagawa; H. Kaneda; M. Hirabayashi; Y. Toulemont; D. Castel; Y. Kanai; N. Fujishiro

2007-04-12T23:59:59.000Z

103

A Cosmology Forecast Toolkit -- CosmoLib  

E-Print Network (OSTI)

The package CosmoLib is a combination of a cosmological Boltzmann code and a simulation toolkit to forecast the constraints on cosmological parameters from future observations. In this paper we describe the released linear-order part of the package. We discuss the stability and performance of the Boltzmann code. This is written in Newtonian gauge and including dark energy perturbations. In CosmoLib the integrator that computes the CMB angular power spectrum is optimized for a $\\ell$-by-$\\ell$ brute-force integration, which is useful for studying inflationary models predicting sharp features in the primordial power spectrum of metric fluctuations. The numerical code and its documentation are available at http://www.cita.utoronto.ca/~zqhuang/CosmoLib.

Zhiqi Huang

2012-01-28T23:59:59.000Z

104

Simple Cosmological Model with Relativistic Gas  

E-Print Network (OSTI)

We construct simple and useful approximation for the relativistic gas of massive particles. The equation of state is given by an elementary function and admits analytic solution of the Friedmann equation, including more complex cases when the relativistic gas of massive particles is considered together with radiation or with dominating cosmological constant. The model of relativistic gas may be interesting for the description of primordial Universe, especially as a candidate for the role of a Dark Matter.

Guilherme de Berredo-Peixoto; Ilya L. Shapiro; Flavia Sobreira

2004-12-11T23:59:59.000Z

105

Shock Waves and Cosmological Matrix Models  

E-Print Network (OSTI)

We find the shock wave solutions in a class of cosmological backgrounds with a null singularity, each of these backgrounds admits a matrix description. A shock wave solution breaks all supersymmetry meanwhile indicates that the interaction between two static D0-branes cancel, thus provides basic evidence for the matrix description. The probe action of a D0-brane in the background of another suggests that the usual perturbative expansion of matrix model breaks down.

Miao Li; Wei Song

2005-07-19T23:59:59.000Z

106

Forecasting Cosmological Constraints from Redshift Surveys  

E-Print Network (OSTI)

Observations of redshift-space distortions in spectroscopic galaxy surveys offer an attractive method for observing the build-up of cosmological structure, which depends both on the expansion rate of the Universe and our theory of gravity. In this paper we present a formalism for forecasting the constraints on the growth of structure which would arise in an idealized survey. This Fisher matrix based formalism can be used to study the power and aid in the design of future surveys.

Martin White; Yong-Seon Song; Will J. Percival

2008-10-08T23:59:59.000Z

107

Consistent probabilities in loop quantum cosmology  

E-Print Network (OSTI)

A fundamental issue for any quantum cosmological theory is to specify how probabilities can be assigned to various quantum events or sequences of events such as the occurrence of singularities or bounces. In previous work, we have demonstrated how this issue can be successfully addressed within the consistent histories approach to quantum theory for Wheeler-DeWitt-quantized cosmological models. In this work, we generalize that analysis to the exactly solvable loop quantization of a spatially flat, homogeneous and isotropic cosmology sourced with a massless, minimally coupled scalar field known as sLQC. We provide an explicit, rigorous and complete decoherent histories formulation for this model and compute the probabilities for the occurrence of a quantum bounce vs. a singularity. Using the scalar field as an emergent internal time, we show for generic states that the probability for a singularity to occur in this model is zero, and that of a bounce is unity, complementing earlier studies of the expectation values of the volume and matter density in this theory. We also show from the consistent histories point of view that all states in this model, whether quantum or classical, achieve arbitrarily large volume in the limit of infinite `past' or `future' scalar `time', in the sense that the wave function evaluated at any arbitrary fixed value of the volume vanishes in that limit. Finally, we briefly discuss certain misconceptions concerning the utility of the consistent histories approach in these models.

David A. Craig; Parampreet Singh

2013-06-26T23:59:59.000Z

108

Planck 2013 results. XVI. Cosmological parameters  

E-Print Network (OSTI)

We present the first results based on Planck measurements of the CMB temperature and lensing-potential power spectra. The Planck spectra at high multipoles are extremely well described by the standard spatially-flat six-parameter LCDM cosmology. In this model Planck data determine the cosmological parameters to high precision. We find a low value of the Hubble constant, H0=67.3+/-1.2 km/s/Mpc and a high value of the matter density parameter, Omega_m=0.315+/-0.017 (+/-1 sigma errors) in excellent agreement with constraints from baryon acoustic oscillation (BAO) surveys. Including curvature, we find that the Universe is consistent with spatial flatness to percent-level precision using Planck CMB data alone. We present results from an analysis of extensions to the standard cosmology, using astrophysical data sets in addition to Planck and high-resolution CMB data. None of these models are favoured significantly over standard LCDM. The deviation of the scalar spectral index from unity is insensitive to the additi...

Ade, P A R; Armitage-Caplan, C; Arnaud, M; Ashdown, M; Atrio-Barandela, F; Aumont, J; Baccigalupi, C; Banday, A J; Barreiro, R B; Bartlett, J G; Battaner, E; Benabed, K; Benoît, A; Benoit-Lévy, A; Bernard, J -P; Bersanelli, M; Bielewicz, P; Bobin, J; Bock, J J; Bonaldi, A; Bond, J R; Borrill, J; Bouchet, F R; Bridges, M; Bucher, M; Burigana, C; Butler, R C; Calabrese, E; Cappellini, B; Cardoso, J -F; Catalano, A; Challinor, A; Chamballu, A; Chary, R -R; Chen, X; Chiang, L -Y; Chiang, H C; Christensen, P R; Church, S; Clements, D L; Colombi, S; Colombo, L P L; Couchot, F; Coulais, A; Crill, B P; Curto, A; Cuttaia, F; Danese, L; Davies, R D; Davis, R J; de Bernardis, P; de Rosa, A; de Zotti, G; Delabrouille, J; Delouis, J -M; Désert, F -X; Dickinson, C; Diego, J M; Dolag, K; Dole, H; Donzelli, S; Doré, O; Douspis, M; Dunkley, J; Dupac, X; Efstathiou, G; Elsner, F; Enßlin, T A; Eriksen, H K; Finelli, F; Forni, O; Frailis, M; Fraisse, A A; Franceschi, E; Gaier, T C; Galeotta, S; Galli, S; Ganga, K; Giard, M; Giardino, G; Giraud-Héraud, Y; Gjerløw, E; González-Nuevo, J; Górski, K M; Gratton, S; Gregorio, A; Gruppuso, A; Gudmundsson, J E; Haissinski, J; Hamann, J; Hansen, F K; Hanson, D; Harrison, D; Henrot-Versillé, S; Hernández-Monteagudo, C; Herranz, D; Hildebrandt, S R; Hivon, E; Hobson, M; Holmes, W A; Hornstrup, A; Hou, Z; Hovest, W; Huffenberger, K M; Jaffe, T R; Jaffe, A H; Jewell, J; Jones, W C; Juvela, M; Keihänen, E; Keskitalo, R; Kisner, T S; Kneissl, R; Knoche, J; Knox, L; Kunz, M; Kurki-Suonio, H; Lagache, G; Lähteenmäki, A; Lamarre, J -M; Lasenby, A; Lattanzi, M; Laureijs, R J; Lawrence, C R; Leach, S; Leahy, J P; Leonardi, R; León-Tavares, J; Lesgourgues, J; Lewis, A; Liguori, M; Lilje, P B; Linden-Vørnle, M; López-Caniego, M; Lubin, P M; Macías-Pérez, J F; Maffei, B; Maino, D; Mandolesi, N; Maris, M; Marshall, D J; Martin, P G; Martínez-González, E; Masi, S; Matarrese, S; Matthai, F; Mazzotta, P; Meinhold, P R; Melchiorri, A; Melin, J -B; Mendes, L; Menegoni, E; Mennella, A; Migliaccio, M; Millea, M; Mitra, S; Miville-Deschênes, M -A; Moneti, A; Montier, L; Morgante, G; Mortlock, D; Moss, A; Munshi, D; Naselsky, P; Nati, F; Natoli, P; Netterfield, C B; Nørgaard-Nielsen, H U; Noviello, F; Novikov, D; Novikov, I; O'Dwyer, I J; Osborne, S; Oxborrow, C A; Paci, F; Pagano, L; Pajot, F; Paoletti, D; Partridge, B; Pasian, F; Patanchon, G; Pearson, D; Pearson, T J; Peiris, H V; Perdereau, O; Perotto, L; Perrotta, F; Pettorino, V; Piacentini, F; Piat, M; Pierpaoli, E; Pietrobon, D; Plaszczynski, S; Platania, P; Pointecouteau, E; Polenta, G; Ponthieu, N; Popa, L; Poutanen, T; Pratt, G W; Prézeau, G; Prunet, S; Puget, J -L; Rachen, J P; Reach, W T; Rebolo, R; Reinecke, M; Remazeilles, M; Renault, C; Ricciardi, S; Riller, T; Ristorcelli, I; Rocha, G; Rosset, C; Roudier, G; Rowan-Robinson, M; Rubiño-Martín, J A; Rusholme, B; Sandri, M; Santos, D; Savelainen, M; Savini, G; Scott, D; Seiffert, M D; Shellard, E P S; Spencer, L D; Starck, J -L; Stolyarov, V; Stompor, R; Sudiwala, R; Sunyaev, R; Sureau, F; Sutton, D; Suur-Uski, A -S; Sygnet, J -F; Tauber, J A; Tavagnacco, D; Terenzi, L; Toffolatti, L; Tomasi, M; Tristram, M; Tucci, M; Tuovinen, J; Türler, M; Umana, G; Valenziano, L; Valiviita, J; Van Tent, B; Vielva, P; Villa, F; Vittorio, N; Wade, L A; Wandelt, B D; Wehus, I K; White, M; White, S D M; Wilkinson, A; Yvon, D; Zacchei, A; Zonca, A

2013-01-01T23:59:59.000Z

109

Decaying Higgs Fields and Cosmological Dark Energy  

E-Print Network (OSTI)

The observed dark energy in the universe might give particles inertial mass. We investigate one realization of this idea, that the dark energy field might be a decayed scalar component of a supermultiplet field in the early universe that creates inertial mass through spontaneous symmetry breaking, e.g. a Higgs field. To investigate this possibility, the cosmological Friedmann equation of energy balance is augmented in a standard way to incorporate a minimally coupled cosmological Higgs. For epochs where the expansion of the universe is driven by matter and radiation and not the scalar field, the observed hidden nature of the Higgs field can be codified into a single differential equation that we call the "hidden higgs" condition. The resulting differential equation is solved for the time dependant scalar field and a simple and interesting solution is found analytically. Such a Higgs field decays from Planck scale energies rapidly and approximately exponentially from onset, leaving only the initially negligible constant term of the potential as a final cosmological constant. Such evolution replaces the hierarchy problem with the problem of explaining why such evolution is physically justified.

Robert J. Nemiroff; Bijunath Patla

2004-09-27T23:59:59.000Z

110

Isotropic singularities in shear-free perfect fluid cosmologies  

E-Print Network (OSTI)

We investigate barotropic perfect fluid cosmologies which admit an isotropic singularity. From the General Vorticity Result of Scott, it is known that these cosmologies must be irrotational. In this paper we prove, using two different methods, that if we make the additional assumption that the perfect fluid is shear-free, then the fluid flow must be geodesic. This then implies that the only shear-free, barotropic, perfect fluid cosmologies which admit an isotropic singularity are the FRW models.

Geoffery Ericksson; Susan M. Scott

2001-08-02T23:59:59.000Z

111

A Cosmology Calculator for the World Wide Web  

E-Print Network (OSTI)

A cosmology calculator that computes times and distances as a function of redshift for user-defined cosmological parameters is available on the World Wide Web. This note gives the formulae used by the cosmology calculator and discusses some of its implementation. A version of the calculator that allows one to specify the equation of state parameter w and w' and neutrino masses, and a version for converting the light travel times usually given in the popular press into redshifts are also available.

Edward L. Wright

2006-09-20T23:59:59.000Z

112

Constraining gravitational and cosmological parameters with astrophysical data  

E-Print Network (OSTI)

We use astrophysical data to shed light on fundamental physics by constraining parametrized theoretical cosmological and gravitational models. Gravitational parameters are those constants that parametrize possible departures ...

Mao, Yi, Ph. D. Massachusetts Institute of Technology

2008-01-01T23:59:59.000Z

113

A new multidimensional AMR Hydro+Gravity Cosmological code  

E-Print Network (OSTI)

A new cosmological multidimensional hydrodynamic and N-body code based on an Adaptive Mesh Refinement scheme is described and tested. The hydro part is based on modern high-resolution shock-capturing techniques, whereas N-body approach is based on the Particle Mesh method. The code has been specifically designed for cosmological applications. Tests including shocks, strong gradients, and gravity have been considered. A cosmological test based on Santa Barbara cluster is also presented. The usefulness of the code is discussed. In particular, this powerful tool is expected to be appropriate to describe the evolution of the hot gas component located inside asymmetric cosmological structures.

Vicent Quilis

2004-05-20T23:59:59.000Z

114

Birth of the Universe, Direct Numerical Simulations of Cosmological...  

NLE Websites -- All DOE Office Websites (Extended Search)

Simulations of Cosmological Reionization November 30, 2011 Tweet EmailPrint In this video from SC11, Michael Norman (SDSC), Joseph Insley (MCS), and Rick Wagner (SDSC) describe...

115

Positioning system of the ANTARES Neutrino Telescope  

E-Print Network (OSTI)

Completed in May 2008, the ANTARES neutrino telescope is located 40 km off the coast of Toulon, at a depth of about 2500 m. The telescope consists of 12 detect or lines housing a total of 884 optical modules. Each line is anchored to the seabed and pulled taught by the buoyancy of the individual optical modules and a top buoy. Due to the fluid nature of the sea-water detecting medium and the flexible nature of the detector lines, the optical modules of the ANTARES telescope can suffer from deviations of up to several meters from the vertical and as such, real time positioning is needed. Real time positioning of the ANTARES telescope is achieved by a combination of an acoustic positioning system and a lattice of tiltmeters and compasses. These independent and complementary systems are used to compute a global fit to each individual detector line, allowing us to construct a 3 dimensional picture of the ANTARES neutrino telescope with an accuracy of less than 10 cm. In this paper we describe the positioning syst...

Brown, Anthony M

2009-01-01T23:59:59.000Z

116

Mirror Development for the Cherenkov Telescope Array  

E-Print Network (OSTI)

The Cherenkov Telescope Array (CTA) is a planned observatory for very-high energy gamma-ray astronomy. It will consist of several tens of telescopes of different sizes, with a total mirror area of up to 10,000 square meters. Most mirrors of current installations are either polished glass mirrors or diamond-turned aluminium mirrors, both labour intensive technologies. For CTA, several new technologies for a fast and cost-efficient production of light-weight and reliable mirror substrates have been developed and industrial pre-production has started for most of them. In addition, new or improved aluminium-based and dielectric surface coatings have been developed to increase the reflectance over the lifetime of the mirrors compared to those of current Cherenkov telescope instruments.

Förster, A; Baba, H; Bähr, J; Bonardi, A; Bonnoli, G; Brun, P; Canestrari, R; Chadwick, P; Chikawa, M; Carton, P -H; De Souza, V; Dipold, J; Doro, M; Durand, D; Dyrda, M; Giro, E; Glicenstein, J -F; Hanabata, Y; Hayashida, M; Hrabovski, M; Jeanney, C; Kagaya, M; Katagiri, H; Lessio, L; MANDAT, D; Mariotti, M; Medina, C; Micha?owski, J; Micolon, P; Nakajima, D; Niemiec, J; Nozato, A; Palatka, M; Pareschi, G; Pech, M; Peyaud, B; Pühlhofer, G; Rataj, M; Rodeghiero, G; Rojas, G; Rousselle, J; Sakonaka, R; Schovanek, P; Seweryn, K; Schultz, C; Shu, S; Stinzing, F; Stodulski, M; Teshima, M; Travniczek, P; Van Eldik, C; Vassiliev, V; Wi?niewski, ?; Wörnlein, A; Yoshida, T

2013-01-01T23:59:59.000Z

117

Microscopic surface structure of C/SiC composite mirrors for space cryogenic telescopes  

E-Print Network (OSTI)

We report on the microscopic surface structure of carbon-fiber-reinforced silicon carbide (C/SiC) composite mirrors that have been improved for the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and other cooled telescopes. The C/SiC composite consists of carbon fiber, silicon carbide, and residual silicon. Specific microscopic structures are found on the surface of the bare C/SiC mirrors after polishing. These structures are considered to be caused by the different hardness of those materials. The roughness obtained for the bare mirrors is 20 nm rms for flat surfaces and 100 nm rms for curved surfaces. It was confirmed that a SiSiC slurry coating is effective in reducing the roughness to 2 nm rms. The scattering properties of the mirrors were measured at room temperature and also at 95 K. No significant change was found in the scattering properties through cooling, which suggests that the microscopic surface structure is stable with changes in temperature down to cryogenic values. The C/SiC ...

Enya, Keigo; Kaneda, Hidehiro; Onaka, Takashi; Ozaki, Tuyoshi; Kume, Masami

2007-01-01T23:59:59.000Z

118

The Robinson Gravitational Wave Background Telescope (BICEP): a bolometric large angular scale CMB polarimeter  

E-Print Network (OSTI)

The Robinson Telescope (BICEP) is a ground-based millimeter-wave bolometric array designed to study the polarization of the cosmic microwave background radiation (CMB) and galactic foreground emission. Such measurements probe the energy scale of the inflationary epoch, tighten constraints on cosmological parameters, and verify our current understanding of CMB physics. Robinson consists of a 250-mm aperture refractive telescope that provides an instantaneous field-of-view of 17 degrees with angular resolution of 55 and 37 arcminutes at 100 GHz and 150 GHz, respectively. Forty-nine pair of polarization-sensitive bolometers are cooled to 250 mK using a 4He/3He/3He sorption fridge system, and coupled to incoming radiation via corrugated feed horns. The all-refractive optics is cooled to 4 K to minimize polarization systematics and instrument loading. The fully steerable 3-axis mount is capable of continuous boresight rotation or azimuth scanning at speeds up to 5 deg/s. Robinson has begun its first season of observation at the South Pole. Given the measured performance of the instrument along with the excellent observing environment, Robinson will measure the E-mode polarization with high sensitivity, and probe for the B-modes to unprecedented depths. In this paper we discuss aspects of the instrument design and their scientific motivations, scanning and operational strategies, and the results of initial testing and observations.

K. W. Yoon; P. A. R. Ade; D. Barkats; J. O. Battle; E. M. Bierman; J. J. Bock; J. A. Brevik; H. C. Chiang; A. Crites; C. D. Dowell; L. Duband; G. S. Griffin; E. F. Hivon; W. L. Holzapfel; V. V. Hristov; B. G. Keating; J. M. Kovac; C. L. Kuo; A. E. Lange; E. M. Leitch; P. V. Mason; H. T. Nguyen; N. Ponthieu; Y. D. Takahashi; T. Renbarger; L. C. Weintraub; D. Woolsey

2006-06-12T23:59:59.000Z

119

Polarimeter Receiver Prototyping and Testing for the South Pole Telescope Upgrade  

E-Print Network (OSTI)

Experimental evidence has so far been supportive for the inflationary Big Bang model of cosmology, while imposing other mysteries, such as the fact that dark matter and dark energy actually consist of 95 % of the observable universe. The forthcoming upgrade of the South Pole Telescope, planned for 2010, will include a polarimeter with increased sensitivity. Measurements of the CMB polarization anisotropy to a high accuracy will describe the angular power spectrum of the B-mode polarization, which will help unravel some of the mysteries. We prototype and test a digital frequency multiplexed readout system for the SPT upgrade. The digital system has the advantage of being able to reconstruct the phase of the signals. We characterize the performance of the readout and we compare it to the theoretical expectations. The noise is found to be statistically insignificant (insert quantitative proof), and the system performs as expected, significantly better than the previous implementation. We conclude that the digital fMux readout system should be sent to the South Pole Telescope. 1

Constantinos Melachrinos

2009-01-01T23:59:59.000Z

120

Cosmological Parameters and Quintessence From Radio Galaxies  

E-Print Network (OSTI)

FRIIb radio galaxies provide a tool to determine the coordinate distance to sources at redshifts from zero to two. The coordinate distance depends on the present values of global cosmological parameters, quintessence, and the equation of state of quintessence. The coordinate distance provides one of the cleanest determinations of global cosmological parameters because it does not depend on the clustering properties of any of the mass-energy components present in the universe. Two complementary methods that provide direct determinations of the coordinate distance to sources with redshifts out to one or two are the modified standard yardstick method utilizing FRIIb radio galaxies, and the modified standard candle method utilizing type Ia supernovae. These two methods are compared here, and are found to be complementary in many ways. The two methods do differ in some regards; perhaps the most significant difference is that the radio galaxy method is completely independent of the local distance scale and independent of the properties of local sources, while the supernovae method is very closely tied to the local distance scale and the properties of local sources. FRIIb radio galaxies provide one of the very few reliable probes of the coordinate distance to sources with redshifts out to two. This method indicates that the current value of the density parameter in non-relativistic matter, ?m, must be low, irrespective of whether the universe is spatially flat, and of whether a significant cosmological constant or quintessence pervades the universe at the present epoch. The effect of quintessence, with equation of state w, is considered. FRIIb radio galaxies indicate that the universe is currently accelerating in its expansion if the primary components of the universe at the present epoch are non-relativistic matter and quintessence, and the universe is spatially flat. 1.

A. Daly; Erick J. Guerra

2001-01-01T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


121

The cosmological simulation code GADGET-2  

E-Print Network (OSTI)

We discuss the cosmological simulation code GADGET-2, a new massively parallel TreeSPH code, capable of following a collisionless fluid with the N-body method, and an ideal gas by means of smoothed particle hydrodynamics (SPH). Our implementation of SPH manifestly conserves energy and entropy in regions free of dissipation, while allowing for fully adaptive smoothing lengths. Gravitational forces are computed with a hierarchical multipole expansion, which can optionally be applied in the form of a TreePM algorithm, where only short-range forces are computed with the `tree'-method while long-range forces are determined with Fourier techniques. Time integration is based on a quasi-symplectic scheme where long-range and short-range forces can be integrated with different timesteps. Individual and adaptive short-range timesteps may also be employed. The domain decomposition used in the parallelisation algorithm is based on a space-filling curve, resulting in high flexibility and tree force errors that do not depend on the way the domains are cut. The code is efficient in terms of memory consumption and required communication bandwidth. It has been used to compute the first cosmological N-body simulation with more than 10^10 dark matter particles, reaching a homogeneous spatial dynamic range of 10^5 per dimension in a 3D box. It has also been used to carry out very large cosmological SPH simulations that account for radiative cooling and star formation, reaching total particle numbers of more than 250 million. We present the algorithms used by the code and discuss their accuracy and performance using a number of test problems. GADGET-2 is publicly released to the research community.

Volker Springel

2005-05-02T23:59:59.000Z

122

Energy Conservation in Flat FRW Cosmology  

E-Print Network (OSTI)

The consequence of energy conservation in the flat Friedmannn-Robertson-Walker (FRW) cosmology is a strictly positive accelerating expansion. A mechanism is proposed for this expansion due to the effect of the attractive (negative) gravitational potential of matter as it is being included within the expanding horizon, and the offsetting work of metric expansion, which takes place at sub-luminal speed. In our semi-classical treatment, we deal with a quintic as the equation for the scale parameter. Implications for modeling the earliest parts of the primordial expansion are discussed.

Steven Maxson

2009-01-07T23:59:59.000Z

123

About non standard Lagrangians in cosmology  

Science Conference Proceedings (OSTI)

A review of non standard Lagrangians present in modern cosmological models will be considered. Well known example of non standard Lagrangian is Dirac-Born-Infeld (DBI) type Lagrangian for tachyon field. Another type of non standard Lagrangian under consideration contains scalar field which describes open p-adic string tachyon and is called p-adic string theory Lagrangian. We will investigate homogenous cases of both DBI and p-adic fields and obtain Lagrangians of the standard type which have the same equations of motions as aforementioned non standard one.

Dimitrijevic, Dragoljub D.; Milosevic, Milan [Department of Physics, Faculty of Science and Mathematics, University of Nis, Visegradska 33, P.O. Box 224, 18000 Nis (Serbia)

2012-08-17T23:59:59.000Z

124

Cosmological implications of light element abundances: Theory  

DOE Green Energy (OSTI)

Primordial nucleosynthesis provides (with the microwave background radiation) one of the two quantitative experimental tests of the hot Big Bang cosmological model (versus alternative explanations for the observed Hubble expansion). The standard homogeneous-isotopic calculation fits the light element abundances ranging from [sup 1]H at 76% and [sup 4]He at 24% by mass through [sup 2]H and [sup 3]He at parts in 10[sup 5] down to [sup 7]Li at parts in 10[sup 10]. It is also noted how the recent Large Electron Positron Collider (and Stanford Linear Collider) results on the number of neutrinos (N[sub [nu

Schramm, D.N. (Univ. of Chicago, IL (United States) Fermi National Accelerator Lab., Batavia, IL (United States))

1993-06-01T23:59:59.000Z

125

Dependent component analysis for cosmology: a case study  

Science Conference Proceedings (OSTI)

In this paper, we discuss various dependent component analysis approaches available in the literature and study their performances on the problem of separation of dependent cosmological sources from multichannel microwave radiation maps of the sky. Realisticaly ... Keywords: cosmic microwave background radiation, cosmological source separation, dependent component analysis

Ercan E. Kuruoglu

2010-09-01T23:59:59.000Z

126

Exact cosmological solutions of models with an interacting dark sector  

E-Print Network (OSTI)

We extend the First Order Formalism for cosmological models, developed including an interaction between a fermionic and a scalar field. Cosmological exact solutions, describing universes filled with interacting dark energy and dark matter, have been obtained. We suggest some alternative couplings that yield solutions for the scalar field that could model the present expansion of our universe.

Pavan, A B; Micheletti, S; Ferreira, E G M; de Souza, J C C

2011-01-01T23:59:59.000Z

127

The TACTIC atmospheric Cherenkov Imaging telescope  

E-Print Network (OSTI)

The TACTIC $\\gamma$-ray telescope, equipped with a light collector of area $\\sim$9.5m$^2$ and a medium resolution imaging camera of 349-pixels, has been in operation at Mt.Abu, India since 2001. This paper describes the main features of its various subsystems and its overall performance with regard to (a) tracking accuracy of its 2-axes drive system, (b) spot size of the light collector, (c) back-end signal processing electronics and topological trigger generation scheme, (d) data acquisition and control system and (e) relative and absolute gain calibration methodology. Using a trigger field of view of 11$\\times$11 pixels ($\\sim$ 3.4$^\\circ$$\\times3.4^\\circ$), the telescope records a cosmic ray event rate of $\\sim$2.5 Hz at a typical zenith angle of 15$^\\circ$. Monte Carlo simulation results are also presented in the paper for comparing the expected performance of the telescope with actual observational results. The consistent detection of a steady signal from the Crab Nebula above $\\sim$1.2 TeV energy, at a sensitivity level of $\\sim5.0\\sigma$ in $\\sim$25 h, alongwith excellent matching of its energy spectrum with that obtained by other groups, reassures that the performance of the TACTIC telescope is quite stable and reliable. Furthermore, encouraged by the detection of strong $\\gamma$-ray signals from Mrk 501 (during 1997 and 2006 observations) and Mrk 421 (during 2001 and 2005-2006 observations), we believe that there is considerable scope for the TACTIC telescope to monitor similar TeV $\\gamma$-ray emission activity from other active galactic nuclei on a long term basis.

R. Koul; A. K. Tickoo; S. K. Kaul; S. R. Kaul; N. Kumar; K. K. Yadav; N. Bhatt; K. Venugopal; H. C. Goyal; M. Kothari; P. Chandra; R. C. Rannot; V. K. Dhar; M. K. Koul; R. K. Kaul; S. Kotwal; K. Chanchalani; S. Thoudam; N. Chouhan; M. Sharma; S. Bhattacharyya; S. Sahayanathan

2007-06-14T23:59:59.000Z

128

Evolution of Dust Extinction and Supernova Cosmology  

E-Print Network (OSTI)

We have made a quantitative calculation for the systematic evolution of average extinction by interstellar dust in host galaxies of high-redshift Type Ia supernovae, by using a realistic model of photometric and chemical evolution of galaxies and supernova rate histories in various galaxy types. We find that average B band extinction at z \\sim 0.5 is typically 0.1-0.2 mag larger than present, under a natural assumption that dust optical depth is proportional to gas column density and gas metallicity. This systematic evolution causes average reddening with E(B-V) \\sim 0.025-0.05 mag with the standard extinction curve, and this is comparable with the observational uncertainty of the reddening of high-redshift supernovae. Therefore, our result does not contradict the observations showing no significant reddening in high-z supernovae. However, the difference in apparent magnitude between an open universe and a \\Lambda-dominated flat universe is only \\sim 0.2 mag at z \\sim 0.5, and hence this systematic evolution of extinction should be taken into account in a reliable measurement of cosmological parameters. Considering this uncertainty, we show that it is difficult to discriminate between an open and \\Lambda-dominated flat cosmologies from the current data.

Tomonori Totani; Chiaki Kobayashi

1999-10-04T23:59:59.000Z

129

Constraints on cosmological parameters from MAXIMA-1  

SciTech Connect

We set new constraints on a seven-dimensional space of cosmological parameters within the class of inflationary adiabatic models. We use the angular power spectrum of the cosmic microwave background measured over a wide range of l in the first flight of the MAXIMA balloon-borne experiment (MAXIMA-1) and the low-l results from the COBE Differential Microwave Radiometer experiment. We find constraints on the total energy density of the universe, Omega = 1.0(-0.30)(+0.15), the physical density of baryons, Omega (b)h(2) = 0.03 +/- 0.01, the physical density of cold dark matter, Omega (cdm)h(2) = 0.2(-0.1)(+0.2), and the spectral index of primordial scalar fluctuations, n(s) = 1.08 +/- 0.1,all at the 95 percent confidence level. By combining our results with measurements of high-redshift supernovae we constrain the value of the cosmological constant and the fractional amount of pressureless matter in the universe to 0.45<(Lambda)<0.75 and 0.25

Balbi, A.; Ade, P.; Bock, J.; Borrill, J.; Boscaleri, A.; DeBernardis, P.; Ferreira, P.G.; Hanany, S.; Hristov, V.; Jaffe, A.H.; Lee,A.T.; Oh, S.; Pascale; E.; Rabii, B.; Richards, R.L.; Smoot, G.F.; Stompor, R.; Winant, C.D.; Wu, J.H.P.

2006-05-08T23:59:59.000Z

130

An Analog Trigger System for Atmospheric Cherenkov Telescopes  

E-Print Network (OSTI)

Arrays of Cherenkov telescopes typically use multi-level trigger schemes to keep the rate of random triggers from the night sky background low. At a first stage, individual telescopes produce a trigger signal from the pixel information in the telescope camera. The final event trigger is then formed by combining trigger signals from several telescopes. In this poster, we present a possible scheme for the Cherenkov Telescope Array telescope trigger, which is based on the analog pulse information of the pixels in a telescope camera. Advanced versions of all components of the system have been produced and working prototypes have been tested, showing a performance that meets the original specifications. Finally, issues related to integrating the trigger system in a telescope camera and in the whole array will be dealt with.

Barcelo, M; Bigas, O Blanch; Boix, J; Delgado, C; Herranz, D; Lopez-Coto, R; Martinez, G

2013-01-01T23:59:59.000Z

131

THE SPITZER SPACE TELESCOPE MISSION M. W. Werner,1  

E-Print Network (OSTI)

with a cryogenic telescope in space with the great imaging and spectroscopic power of modern detector arraysTHE SPITZER SPACE TELESCOPE MISSION M. W. Werner,1 T. L. Roellig,2 F. J. Low,3 G. H. Rieke,3 M2 Receivved 2004 March 26; accepted 2004 May 26 ABSTRACT The Spitzer Space Telescope, NASA's Great

Galis, Frietson

132

Detection of Galaxy Cluster Motions with the Kinematic Sunyaev-Zel'dovich Effect  

E-Print Network (OSTI)

Using high-resolution microwave sky maps made by the Atacama Cosmology Telescope, we for the first time detect motions of galaxy clusters and groups via microwave background temperature distortions due to the kinematic Sunyaev-Zel'dovich effect. Galaxy clusters are identified by their constituent luminous galaxies observed by the Baryon Oscillation Spectroscopic Survey, part of the Sloan Digital Sky Survey III. The mean pairwise momentum of clusters is measured at a statistical significance of 3.8 sigma, and the signal is consistent with the growth of cosmic structure in the standard model of cosmology.

Hand, Nick; Aubourg, Eric; Battaglia, Nick; Battistelli, Elia S; Bizyaev, Dmitry; Bond, J Richard; Brewington, Howard; Brinkmann, Jon; Brown, Benjamin R; Das, Sudeep; Dawson, Kyle S; Devlin, Mark J; Dunkley, Joanna; Dunner, Rolando; Eisenstein, Daniel J; Fowler, Joseph W; Gralla, Megan B; Hajian, Amir; Halpern, Mark; Hilton, Matt; Hincks, Adam D; Hlozek, Renee; Hughes, John P; Infante, Leopoldo; Irwin, Kent D; Kosowsky, Arthur; Lin, Yen-Ting; Malanushenko, Elena; Malanushenko, Viktor; Marriage, Tobias A; Marsden, Danica; Menanteau, Felipe; Moodley, Kavilan; Niemack, Michael D; Nolta, Michael R; Oravetz, Daniel; Page, Lyman A; Palanque-Delabrouille, Nathalie; Pan, Kaike; Reese, Erik D; Schlegel, David J; Schneider, Donald P; Sehgal, Neelima; Shelden, Alaina; Sievers, Jon; Sifon, Cristobal; Simmons, Audrey; Snedden, Stephanie; Spergel, David N; Staggs, Suzanne T; Swetz, Daniel S; Switzer, Eric R; Trac, Hy; Weaver, Benjamin A; Wollack, Edward J; Yeche, Christophe; Zunckel, Caroline

2012-01-01T23:59:59.000Z

133

Asymptotic analysis of perturbed dust cosmologies to second order  

E-Print Network (OSTI)

Nonlinear perturbations of Friedmann-Lemaitre cosmologies with dust and a positive cosmological constant have recently attracted considerable attention. In this paper our first goal is to compare the evolution of the first and second order perturbations by determining their asymptotic behaviour at late times in ever-expanding models. We show that in the presence of spatial curvature K or a positive cosmological constant, the density perturbation approaches a finite limit both to first and second order, but the rate of approach depends on the model, being power law in the scale factor if the cosmological constant is positive but logarithmic if it is zero and and Kdoes not die away, i.e. it contributes on an equal footing as the growing mode to the asymptotic expression for the density perturbation. On the other hand, the future asymptotic regime of the Einstein-de Sitter universe (for which the cosmological constant and the spatial curvature are both zero) is completely different, as exemplified by the density perturbation which diverges; moreover, the second order perturbation diverges faster than the first order perturbation, which suggests that the Einstein-de Sitter universe is unstable to perturbations, and that the perturbation series do not converge towards the future. We conclude that the presence of spatial curvature or a cosmological constant stabilizes the perturbations. Our second goal is to derive an explicit expression for the second order density perturbation that can be used to study the effects of including a cosmological constant and spatial curvature.

Claes Uggla; John Wainwright

2013-03-19T23:59:59.000Z

134

Cosmological evolution of the cosmological plasma with interpartial scalar interaction. II. Formulation of mathematical model  

E-Print Network (OSTI)

On the basis of the relativistic kinetic theory the relativistic statistical systems with scalar interaction particles are investigated. The self-consistent system of the equations describing self-gravitating plasma with interpartial scalar interaction is formulated, macroscopical laws of preservation are received. The closed system of the equations describing cosmological models to which the matter is presented by plasma with interpartial scalar interaction is received.

Yu. G. Ignat'ev

2013-07-09T23:59:59.000Z

135

A Critique of Supernova Data Analysis in Cosmology  

E-Print Network (OSTI)

Observational astronomy has shown significant growth over the last decade and made important contributions to cosmology. A major paradigm shift in cosmology was brought about by the observations of Type Ia supernovae. The notion that the universe is accelerating has led to several theoretical challenges. Unfortunately, although the supernovae data-sets of high quality are being produced, their statistical analysis leaves much to be desired. Instead of using the data to test the model directly, several studies seem to concentrate on assuming the model to be correct and limiting themselves to estimating model parameters and internal errors. As shown here, the important purpose of testing a cosmological theory is thereby vitiated.

Vishwakarma, Ram Gopal

2010-01-01T23:59:59.000Z

136

A Critique of Supernova Data Analysis in Cosmology  

E-Print Network (OSTI)

Observational astronomy has shown significant growth over the last decade and has made important contributions to cosmology. A major paradigm shift in cosmology was brought about by observations of Type Ia supernovae. The notion that the universe is accelerating has led to several theoretical challenges. Unfortunately, although high quality supernovae data-sets are being produced, their statistical analysis leaves much to be desired. Instead of using the data to directly test the model, several studies seem to concentrate on assuming the model to be correct and limiting themselves to estimating model parameters and internal errors. As shown here, the important purpose of testing a cosmological theory is thereby vitiated.

Ram Gopal Vishwakarma; Jayant V. Narlikar

2010-10-25T23:59:59.000Z

137

Physics and Cosmology : the Milli-Electron-Volt Scale  

E-Print Network (OSTI)

A short review about vacuum energy and the cosmological constant is presented. The observed acceleration of the universe introduces a new meV energy scale. The problem is that, theoretically, the predicted vacuum energy is many orders of magnitude larger than $10^{-3}$ eV. The problem is a link between two Standard Models, namely the Standard Model of Particles and their Interactions (where the vacuum energy appears) and the Standard Cosmological Model (where a cosmological constant is a good fit to data), and perhaps it is a clue in our search for new physics.

Eduard Masso

2009-02-27T23:59:59.000Z

138

Absence of Black Holes Information Paradox in Group Field Cosmology  

E-Print Network (OSTI)

In this paper we will analyse the black hole information paradox in group field cosmology. We will first construct a group field cosmology with third quantized gauge symmetry. Then we will argue that that in this group field cosmology the process that change the topology of spacetime are unitarity process. Thus, the information paradox from this perspective appears only because we are using a second quantized formalism to explain a third quantized process. A similar paradox would also occur if we analyse a second quantized process in first quantized formalism. Hence, we will demonstrated that in reality there is no information paradox but only a breakdown of the second quantized formalism.

Mir Faizal

2013-01-02T23:59:59.000Z

139

Cosmological perturbations in singularity-free, deflationary models  

E-Print Network (OSTI)

We consider scalar perturbations of energy-density for a class of cosmological models where an early phase of accelerated expansion evolves, without any fine-tuning for graceful exit, towards the standard Friedman eras of observed universe. The quantum geometric procedure which generates such models agrees with results for string cosmology since it works if dynamics is dominated by a primordial fluid of extended massive objects. The main result is that characteristic scales of cosmological interest, connected with the extension of such early objects, are selected.

S. Capozziello; G. Lambiase; G. Scarpetta

1998-05-13T23:59:59.000Z

140

Ultra Violet Imaging Telescope (UVIT) on ASTROSAT  

E-Print Network (OSTI)

Ultra Violet Imaging Telescope on ASTROSAT Satellite mission is a suite of Far Ultra Violet (FUV 130 to 180 nm), Near Ultra Violet (NUV 200 to 300 nm) and Visible band (VIS 320 to 550nm) imagers. ASTROSAT is the first multi wavelength mission of INDIA. UVIT will image the selected regions of the sky simultaneously in three channels and observe young stars, galaxies, bright UV Sources. FOV in each of the 3 channels is about 28 arc-minute. Targeted angular resolution in the resulting UV images is better than 1.8 arc-second (better than 2.0 arc-second for the visible channel). Two identical co-aligned telescopes (T1, T2) of Ritchey-Chretien configuration (Primary mirror of 375 mm diameter) collect celestial radiation and feed to the detector system via a selectable filter on a filter wheel mechanism; gratings are available in filter wheels of FUV and NUV channels for slit-less low resolution spectroscopy. The detector system for each of the 3 channels is generically identical. One of the telescopes images in the...

Kumar, Amit; Hutchings, J; Kamath, P U; Kathiravan, S; Mahesh, P K; Murthy, J; S, Nagbhushana; Pati, A K; Rao, M N; Rao, N K; Sriram, S; Tandon, S N

2012-01-01T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


141

A Cosmic Ray Telescope For Educational Purposes  

SciTech Connect

Cosmic ray detectors are widely used, for educational purposes, in order to motivate students to the physics of elementary particles and astrophysics. Using a 'telescope' of scintillation counters, the directional characteristics, diurnal variation, correlation with solar activity, can be determined, and conclusions about the composition, origin and interaction of elementary particles with the magnetic field of earth can be inferred. A telescope was built from two rectangular scintillator panels with dimensions: 91.6x1.9x3.7 cm{sup 3}. The scintillators are placed on top of each other, separated by a fixed distance of 34.6 cm. They are supported by a wooden frame which can be rotated around a horizontal axis. Direction is determined by the coincidence of the signals of the two PMTs. Standard NIM modules are used for readout. This device is to be used in the undergraduate nuclear and particle physics laboratory. The design and construction of the telescope as well as some preliminary results are presented.

Voulgaris, G.; Kazanas, S.; Chamilothoris, I. [Department of Physics, National and Kapodistrian University of Athens (Greece)

2010-01-21T23:59:59.000Z

142

Extending the Sensitivity of Air Cerenkov Telescopes  

E-Print Network (OSTI)

Over the last decade, the Imaging Air Cerenkov technique has proven itself to be an extremely powerful means to study very energetic gamma-radiation from a number of astrophysical sources in a regime which is not practically accessible to satellite-based instruments. The further development of this approach in recent years has generally concentrated on increasing the density of camera pixels, increasing the mirror area and using multiple telescopes. Here we present a practical method to substantially improve the sensitivity of Atmospheric Cerenkov Telescopes using wide-field cameras with a relatively course density of photomultiplier tubes. The 2-telescope design considered here is predicted to be more than ~3 times more sensitive than existing/planned arrays in the regime above 300 GeV for continuously emitting sources; up to ~10 times more sensitive for hour-scale emission (relevant for episodic sources, such as AGN); significantly more sensitive in the regime above 10 TeV; and possessing a sky coverage which is roughly an order of magnitude larger than existing instruments. It should be possible to extend this approach for even further improvement in sensitivity and sky coverage.

I. de la Calle Perez; S. D. Biller

2006-02-13T23:59:59.000Z

143

Environment-induced superselection in cosmology  

SciTech Connect

Interaction between a quantum system and its environment can be often regarded as a measurement, in the course of which one of the system observables influences the evolution of the external degrees of freedom and is thus monitored'' by the environment. This causes the system to decohere.'' Loss of quantum coherence erases part of the density matrix responsible for the correlations between the eigenstates of the monitored observables. This mechanism is very efficient even in the limit of weak coupling to the environment. The classical limit of quantum theory -- that is, both classical irreversible equations of motion and classical states (trajectories in phase space rather than their superpositions) obtains in the limit in which the coupling strength and the Planck constant simultaneously tend to zero. Transition from quantum to classical in the inflationary cosmological model can be justified in the framework of environment induced susperselection. 24 refs., 2 figs.

Zurek, W.H.

1990-01-01T23:59:59.000Z

144

Green's function of the cosmological thermalization problem  

E-Print Network (OSTI)

Energy release in the early Universe leads to spectral distortions of the cosmic microwave background (CMB) which in the future might allow probing different physical processes in the pre-recombination (z>~10^3) epoch. Depending on the energy injection history, the associated distortion partially thermalizes due to the combined action of Compton scattering, double Compton scattering and Bremsstrahlung emission, a problem that in general is hard to solve. Various analytic approximations describing the resulting distortion exist, however, for small distortions and fixed background cosmology the Green's function of the problem can be computed numerically. Here we show that this approach gives very accurate results for general thermal histories, allowing fast and quasi-exact computation of the spectral distortion given the energy release rate. Our method can thus be used to forecast possible constraints on early-universe physics obtained from future measurements of the CMB spectrum.

Chluba, Jens

2013-01-01T23:59:59.000Z

145

Scaling cosmological solutions with Horndeski Lagrangian  

E-Print Network (OSTI)

We find the most general coupled scalar field Lagrangian linear in $\\Box\\phi$ and with a general kinetic term that contains cosmological scaling solutions, i.e. solutions on which the ratio of matter to field density and the equation of state remains constant. Scaling solutions of this kind may help solving the coincidence problem since in this case the presently observed ratio of matter to dark energy does not depend on initial conditions but rather on the theoretical parameters. Extending previous results we find that it is impossible to join in a single solution a matter era and the scaling attractor. This is an additional step towards finding the most general scaling Lagrangian within the Horndeski class, i.e. general scalar-tensor models with second order equations of motion.

Gomes, A R

2013-01-01T23:59:59.000Z

146

Precision cosmology defeats void models for acceleration  

SciTech Connect

The suggestion that we occupy a privileged position near the center of a large, nonlinear, and nearly spherical void has recently attracted much attention as an alternative to dark energy. Putting aside the philosophical problems with this scenario, we perform the most complete and up-to-date comparison with cosmological data. We use supernovae and the full cosmic microwave background spectrum as the basis of our analysis. We also include constraints from radial baryonic acoustic oscillations, the local Hubble rate, age, big bang nucleosynthesis, the Compton y distortion, and for the first time include the local amplitude of matter fluctuations, {sigma}{sub 8}. These all paint a consistent picture in which voids are in severe tension with the data. In particular, void models predict a very low local Hubble rate, suffer from an ''old age problem,'' and predict much less local structure than is observed.

Moss, Adam; Zibin, James P.; Scott, Douglas [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z1 (Canada)

2011-05-15T23:59:59.000Z

147

String spectra near some null cosmological singularities  

Science Conference Proceedings (OSTI)

We construct cosmological spacetimes with null Kasner-like singularities as purely gravitational solutions with no other background fields turned on. These can be recast as anisotropic plane-wave spacetimes by coordinate transformations. We analyze string quantization to find the spectrum of string modes in these backgrounds. The classical string modes can be solved for exactly in these time-dependent backgrounds, which enables a detailed study of the near-singularity string spectrum, (time-dependent) oscillator masses, and wave functions. We find that for low-lying string modes (finite oscillation number), the classical near-singularity string mode functions are nondivergent for various families of singularities. Furthermore, for any infinitesimal regularization of the vicinity of the singularity, we find a tower of string modes of ultrahigh oscillation number which propagate essentially freely in the background. The resulting picture suggests that string interactions are non-negligible near the singularity.

Madhu, Kallingalthodi [Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400005 (India); Narayan, K. [Chennai Mathematical Institute, SIPCOT IT Park, Padur PO, Siruseri 603103 (India)

2009-06-15T23:59:59.000Z

148

Radion Physics, Stability and Cosmological issues  

Science Conference Proceedings (OSTI)

Moduli fields are a known ingredient of models that involve extra compact dimensions, as the Kaluza-Klein theories, String theory, and models with compact extra dimensions. They are scalar fields that emerge when the configuration of the compact space is perturbed. The radion is a particular example of this type of fields, which is associated to the variations of the total volume of compact space. Radions usually couple to all other fields, affecting the definition of coupling constants and gravity strength. They also modify gravitational potentials in a way that may be tested in table top experiments. Usually, these fields are run away modes which manifest the difficulties to stabilize the shape of the compact manifold of extra space. This is feature that can be a threat for cosmology on the early Universe. Here we provide a brief discussion of these general aspects of the radion physics.

Perez-Lorenzana, Abdel [Departamento de Fisica, Centro de Investigacion y de Estudios Avanzados del I.P.N. Apdo. Post. 14-740, 07000, Mexico, D.F. (Mexico); Santos, Eli [Centro de Estudios en Fisica y Matematicas Basicas y Aplicadas, UNACH, 4a Oriente Norte 1428, C.P. 29000 Tuxtla Gutierrez, Chiapas (Mexico); Instituto de Fisica y Matematicas, Universidad Michoacana de San Nicolas de Hidalgo Edificio C-3, Ciudad Universitaria, CP. 58040 Morelia, Michoacan (Mexico)

2010-07-12T23:59:59.000Z

149

The Cosmology of Composite Inelastic Dark Matter  

SciTech Connect

Composite dark matter is a natural setting for implementing inelastic dark matter - the O(100 keV) mass splitting arises from spin-spin interactions of constituent fermions. In models where the constituents are charged under an axial U(1) gauge symmetry that also couples to the Standard Model quarks, dark matter scatters inelastically off Standard Model nuclei and can explain the DAMA/LIBRA annual modulation signal. This article describes the early Universe cosmology of a minimal implementation of a composite inelastic dark matter model where the dark matter is a meson composed of a light and a heavy quark. The synthesis of the constituent quarks into dark hadrons results in several qualitatively different configurations of the resulting dark matter composition depending on the relative mass scales in the system.

Spier Moreira Alves, Daniele; Behbahani, Siavosh R.; /SLAC /Stanford U., ITP; Schuster, Philip; Wacker, Jay G.; /SLAC

2011-08-19T23:59:59.000Z

150

Projective Structures in Loop Quantum Cosmology  

E-Print Network (OSTI)

Projective structures have successfully been used for the construction of measures in the framework of loop quantum gravity. In the present paper we establish such a structure for the space $R \\sqcup R_Bohr$ recently constructed in the context of homogeneous isotropic loop quantum cosmology. This space has the advantage to be canonically embedded into the quantum configuration space of the full theory, but, in contrast to the traditional space $R_Bohr$, there exists no Haar measure on $R \\sqcup R_Bohr$. The introduced projective structure, however, allows to construct a family of canonical measures on $R \\sqcup R_Bohr$ whose corresponding Hilbert spaces of square integrable functions we finally investigate.

Maximilian Hanusch

2013-09-03T23:59:59.000Z

151

BRST technique for the cosmological density matrix  

E-Print Network (OSTI)

The microcanonical density matrix in closed cosmology has a natural definition as a projector on the space of solutions of Wheeler-DeWitt equations, which is motivated by the absence of global non-vanishing charges and energy in spatially closed gravitational systems. Using the BRST/BFV formalism in relativistic phase space of gauge and ghost variables we derive the path integral representation for this projector and the relevant statistical sum. This derivation circumvents the difficulties associated with the open algebra of noncommutative quantum Dirac constraints and the construction/regularization of the physical inner product in the subspace of BRS singlets. This inner product is achieved via the Batalin-Marnelius gauge fixing in the space of BRS-invariant states, which in its turn is shown to be a result of truncation of the BRST/BFV formalism to the "matter" sector of relativistic phase space.

Andrei O. Barvinsky

2013-08-14T23:59:59.000Z

152

Emergent universe in spatially flat cosmological model  

E-Print Network (OSTI)

The scenario of an emergent universe provides a promising resolution to the big bang singularity in universes with positive or negative spatial curvature. It however remains unclear whether the scenario can be successfully implemented in a spatially flat universe which seems to be favored by present cosmological observations. In this paper, we study the stability of Einstein static state solutions in a spatially flat Shtanov-Sahni braneworld scenario. With a negative dark radiation term included and assuming a scalar field as the only matter energy component, we find that the universe can stay at an Einstein static state past eternally and then evolve to an inflation phase naturally as the scalar field climbs up its potential slowly. In addition, we also propose a concrete potential of the scalar field that realizes this scenario.

Kaituo Zhang; Puxun Wu; Hongwei Yu

2013-11-16T23:59:59.000Z

153

Verifying the Cosmological Utility of Type Ia Supernovae: Implications of a Dispersion in the Ultraviolet Spectra  

SciTech Connect

We analyze the mean rest-frame ultraviolet (UV) spectrum of Type Ia Supernovae (SNe) and its dispersion using high signal-to-noise ratio Keck-I/LRIS-B spectroscopy for a sample of 36 events at intermediate redshift (z=0.5) discovered by the Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS). We introduce a new method for removing host galaxy contamination in our spectra, exploiting the comprehensive photometric coverage of the SNLS SNe and their host galaxies, thereby providing the first quantitative view of the UV spectral properties of a large sample of distant SNe Ia. Although the mean SN Ia spectrum has not evolved significantly over the past 40percent of cosmic history, precise evolutionary constraints are limited by the absence of a comparable sample of high-quality local spectra. The mean UV spectrum of our z~;;=0.5 SNe Ia and its dispersion is tabulated for use in future applications. Within the high-redshift sample, we discover significant UV spectral variations and exclude dust extinction as the primary cause by examining trends with the optical SN color. Although progenitor metallicity may drive some of these trends, the variations we see are much larger than predicted in recent models and do not follow expected patterns. An interesting new result is a variation seen in the wavelength of selected UV features with phase. We also demonstrate systematic differences in the SN Ia spectral features with SN light curve width in both the UV and the optical. We show that these intrinsic variations could represent a statistical limitation in the future use of high-redshift SNe Ia for precision cosmology. We conclude that further detailed studies are needed, both locally and at moderate redshift where the rest-frame UV can be studied precisely, in order that future missions can confidently be planned to fully exploit SNe Ia as cosmological probes.

Nugent, Peter E; Ellis, R.S.; Sullivan, M.; Nugent, P.E.; Howell, D.A.; Gal-Yam, A.; Astier, P.; Balam, D.; Balland, C.; Basa, S.; Carlberg, R.; Conley, A.; Fouchez, D.; Guy, J.; Hardin, D.; Hook, I.; Pain, R.; Perrett, K.; Pritchet, C.J.; Regnault, N.

2008-02-28T23:59:59.000Z

154

A new type of second order cosmological lagrangians  

E-Print Network (OSTI)

We investigate a possible connection between Galileon gravity and teleparallel gravity. We also propose a new type of second order cosmological lagrangian and study a some of its properties.

P. Tretyakov

2013-02-26T23:59:59.000Z

155

Cosmology and Astrophysical Constraints of Gauss-Bonnet Dark Energy  

E-Print Network (OSTI)

Cosmological consequences of a string-motivated dark energy scenario featuring a scalar field coupled to the Gauss-Bonnet invariant are investigated. We study the evolution of the universe in such a model, identifying its key properties. The evolution of the homogeneous background and cosmological perturbations, both at large and small scales, are calculated. The impact of the coupling on galaxy distributions and the cosmic microwave background is examined. We find the coupling provides a mechanism to viably onset the late acceleration, to alleviate the coincidence problem, and furthermore to effectively cross the phantom divide at the present while avoiding a Big Rip in the future. We show the model could explain the present cosmological observations, and discuss how various astrophysical and cosmological data, from the Solar system, supernovae Ia, cosmic microwave background radiation and large scale structure constrain it.

Tomi Koivisto; David F. Mota

2006-06-04T23:59:59.000Z

156

Dynamical eigenfunctions and critical density in loop quantum cosmology  

E-Print Network (OSTI)

We offer a new, physically transparent argument for the existence of the critical, universal maximum matter density in loop quantum cosmology for the case of a flat Friedmann-Lemaitre-Robertson-Walker cosmology with scalar matter. The argument is based on the existence of a sharp exponential ultraviolet cutoff in momentum space on the eigenfunctions of the quantum cosmological dynamical evolution operator (the gravitational part of the Hamiltonian constraint), attributable to the fundamental discreteness of spatial volume in loop quantum cosmology. The existence of the cutoff is proved directly from recently found exact solutions for the eigenfunctions for this model. As a consequence, the operators corresponding to the momentum of the scalar field and the spatial volume approximately commute. The ultraviolet cutoff then implies that the scalar momentum, though not a bounded operator, is in effect bounded on subspaces of constant volume, leading to the upper bound on the expectation value of the matter densit...

Craig, David A

2012-01-01T23:59:59.000Z

157

The Darboux Transformation and Exactly Solvable Cosmological Models  

E-Print Network (OSTI)

We present a simple and effective method for constructing exactly solvable cosmological models containing inflation with exit. This method does not involve any parameter fitting. We discuss the problems arising with solutions that violate the weak energy condition.

A. V. Yurov; S. D. Vereshchagin

2005-02-10T23:59:59.000Z

158

Applicability of the linearly perturbed FRW metric and Newtonian cosmology  

E-Print Network (OSTI)

It has been argued that the effect of cosmological structure formation on the average expansion rate is negligible, because the linear approximation to the metric remains applicable in the regime of non-linear density perturbations. We discuss why the arguments based on the linear theory are not valid. We emphasise the difference between Newtonian gravity and the weak field, small velocity limit of general relativity in the cosmological setting.

Syksy Rasanen

2010-02-25T23:59:59.000Z

159

The dual-mirror Small Size Telescope for the Cherenkov Telescope Array  

E-Print Network (OSTI)

In this paper, the development of the dual mirror Small Size Telescopes (SST) for the Cherenkov Telescope Array (CTA) is reviewed. Up to 70 SST, with a primary mirror diameter of 4 m, will be produced and installed at the CTA southern site. These will allow investigation of the gamma-ray sky at the highest energies accessible to CTA, in the range from about 1 TeV to 300 TeV. The telescope presented in this contribution is characterized by two major innovations: the use of a dual mirror Schwarzschild-Couder configuration and of an innovative camera using as sensors either multi-anode photomultipliers (MAPM) or silicon photomultipliers (SiPM). The reduced plate-scale of the telescope, achieved with the dual-mirror optics, allows the camera to be compact (40 cm in diameter), and low-cost. The camera, which has about 2000 pixels of size 6x6 mm^2, covers a field of view of 10{\\deg}. The dual mirror telescopes and their cameras are being developed by three consortia, ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana, Italy/INAF), GATE (Gamma-ray Telescope Elements, France/Paris Observ.) and CHEC (Compact High Energy Camera, universities in UK, US and Japan) which are merging their efforts in order to finalize an end-to-end design that will be constructed for CTA. A number of prototype structures and cameras are being developed in order to investigate various alternative designs. In this contribution, these designs are presented, along with the technological solutions under study.

G. Pareschi; G. Agnetta; L. A. Antonelli; D. Bastieri; G. Bellassai; M. Belluso; C. Bigongiari; S. Billotta; B. Biondo; G. Bonanno; G. Bonnoli; P. Bruno; A. Bulgarelli; R. Canestrari; M. Capalbi; P. Caraveo; A. Carosi; E. Cascone; O. Catalano; M. Cereda; P. Conconi; V. Conforti; G. Cusumano; V. De Caprio; A. De Luca; A. Di Paola; F. Di Pierro; D. Fantinel; M. Fiorini; D. Fugazza; D. Gardiol; M. Ghigo; F. Gianotti; S. Giarrusso; E. Giro; A. Grillo; D. Impiombato; S. Incorvaia; A. La Barbera; N. La Palombara; V. La Parola; G. La Rosa; L. Lessio; G. Leto; S. Lombardi; F. Lucarelli; M. C. Maccarone; G. Malaguti; G. Malaspina; V. Mangano; D. Marano; E. Martinetti; R. Millul; T. Mineo; A. MistÒ; C. Morello; G. Morlino; M. R. Panzera; G. Rodeghiero; P. Romano; F. Russo; B. Sacco; N. Sartore; J. Schwarz; A. Segreto; G. Sironi; G. Sottile; A. Stamerra; E. Strazzeri; L. Stringhetti; G. Tagliaferri; V. Testa; M. C. Timpanaro; G. Toso; G. Tosti; M. Trifoglio; P. Vallania; S. Vercellone; V. Zitelli; For The Astri Collaboration; J. P. Amans; C. Boisson; C. Costille; J. L. Dournaux; D. Dumas; G. Fasola; O. Hervet; J. M. Huet; P. Laporte; C. Rulten; H. Sol; A. Zech; For The Gate Collaboration; R. White; J. Hinton; D. Ross; J. Sykes; S. Ohm; J. Schmoll; P. Chadwick; T. Greenshaw; M. Daniel; G. Cotter; G. S. Varner; S. Funk; J. Vandenbroucke; L. Sapozhnikov; J. Buckley; P. Moore; D. Williams; S. Markoff; J. Vink; D. Berge; N. Hidaka; A. Okumura; H. Tajima; For The Chec Collaboration; For The Cta Consortium

2013-07-18T23:59:59.000Z

160

Very Large Aperture Diffractive Space Telescope  

DOE Patents (OSTI)

A very large (10's of meters) aperture space telescope including two separate spacecraft--an optical primary functioning as a magnifying glass and an optical secondary functioning as an eyepiece. The spacecraft are spaced up to several kilometers apart with the eyepiece directly behind the magnifying glass ''aiming'' at an intended target with their relative orientation determining the optical axis of the telescope and hence the targets being observed. The magnifying glass includes a very large-aperture, very-thin-membrane, diffractive lens, e.g., a Fresnel lens, which intercepts incoming light over its full aperture and focuses it towards the eyepiece. The eyepiece has a much smaller, meter-scale aperture and is designed to move along the focal surface of the magnifying glass, gathering up the incoming light and converting it to high quality images. The positions of the two space craft are controlled both to maintain a good optical focus and to point at desired targets.

Hyde, Roderick Allen

1998-04-20T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
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161

The ROTSE-IIIa Telescope System  

E-Print Network (OSTI)

We report on the current operating status of the ROTSE-IIIa telescope, currently undergoing testing at Los Alamos National Laboratories in New Mexico. It will be shipped to Siding Spring Observatory, Australia, in first quarter 2002. ROTSE-IIIa has been in automated observing mode since early October, 2001, after completing several weeks of calibration and check-out observations. Calibrated lists of objects in ROTSE-IIIa sky patrol data are produced routinely in an automated pipeline, and we are currently automating analysis procedures to compile these lists, eliminate false detections, and automatically identify transient and variable objects. The manual application of these procedures has already led to the detection of a nova that rose over six magnitudes in two days to a maximum detected brightness of m_R~13.9 and then faded two magnitudes in two weeks. We also readily identify variable stars, includings those suspected to be variables from the Sloan Digital Sky Survey. We report on our system to allow public monitoring of the telescope operational status in real time over the WWW.

D. A. Smith; C. Akerlof; M. C. B. Ashley; D. Casperson; G. Gisler; R. Kehoe; S. Marshall; K. McGowan; T. McKay; M. A. Phillips; E. Rykoff; W. T. Vestrand; P. Wozniak; J. Wren

2002-04-24T23:59:59.000Z

162

The ANTARES neutrino telescope: a status report  

E-Print Network (OSTI)

ANTARES is a large volume neutrino telescope currently under construction off La Seyne-sur-mer, France, at 2475m depth. Neutrino telescopes aim at detecting neutrinos as a new probe for a sky study at energies greater than 1 TeV. The detection principle relies on the observation, using photomultipliers, of the Cherenkov light emitted by charged leptons induced by neutrino interactions in the surrounding detector medium. Since late January 2007, the ANTARES detector consists of 5 lines, comprising 75 optical detectors each, connected to the shore via a 40 km long undersea cable. The data from these lines not only allow an extensive study of the detector properties but also the reconstruction of downward going cosmic ray muons and the search for the first upward going neutrino induced muons.The operation of these lines follows on from that of the ANTARES instrumentation line, which has provided data for more than a year on the detector stability and the environmental conditions. The full 12 line detector is planned to be fully operational early 2008.

A. Kouchner; for the Antares collaboration

2007-10-01T23:59:59.000Z

163

Neutron Stars and the Cosmological Constant Problem  

E-Print Network (OSTI)

The gravitational aether theory is a modification of general relativity that decouples vacuum energy from gravity, and thus can potentially address the cosmological constant problem. The classical theory is distinguishable from general relativity only in the presence of relativistic pressure (or vorticity). Since the interior of neutron stars has high pressure and as their mass and radius can be measured observationally, they are the perfect laboratory for testing the validity of the aether theory. In this paper, we solve the equations of stellar structure for the gravitational aether theory and find the predicted mass-radius relation of non-rotating neutron stars using two different realistic proposals for the equation of state of nuclear matter. We find that the maximum neutron star mass predicted by the aether theory is 12% - 16% less than the maximum mass predicted by general relativity assuming these two equations of state. We also show that the effect of aether is similar to modifying the equation of state in general relativity. The effective pressure of the neutron star given by the aether theory at a fiducial density differs from the values given by the two nuclear equations of state to an extent that can be constrained using future gravitational wave observations of neutron stars in compact systems. This is a promising way to test the aether theory if further progress is made in constraining the equation of state of nuclear matter in densities above the nuclear saturation density.

Farbod Kamiab; Niayesh Afshordi

2011-04-29T23:59:59.000Z

164

Cosmological properties of a gauged axion  

SciTech Connect

We analyze the most salient cosmological features of axions in extensions of the standard model with a gauged anomalous extra U(1) symmetry. The model is built by imposing the constraint of gauge invariance in the anomalous effective action, which is extended with Wess-Zumino counterterms. These generate axionlike interactions of the axions to the gauge fields and a gauged shift symmetry. The scalar sector is assumed to acquire a nonperturbative potential after inflation, at the electroweak phase transition, which induces a mixing of the Stueckelberg field of the model with the scalars of the electroweak sector, and at the QCD phase transition. We discuss the possible mechanisms of sequential misalignments which could affect the axions of these models, and generated, in this case, at both transitions. We compute the contribution of these particles to dark matter, quantifying their relic densities as a function of the Stueckelberg mass. We also show that models with a single anomalous U(1) in general do not account for the dark energy, due to the presence of mixed U(1)-SU(3) anomalies.

Coriano, Claudio; Mariano, Antonio [Dipartimento di Fisica, Universita del Salento, Via Arnesano 73100 Lecce (Italy) and INFN Sezione di Lecce, Via Arnesano 73100 Lecce (Italy); Guzzi, Marco [Department of Physics, Southern Methodist University, Dallas Texas 75275 (United States); Lazarides, George [Physics Division, School of Technology, Aristotle University of Thessaloniki, Thessaloniki 54124 (Greece)

2010-09-15T23:59:59.000Z

165

A Short and Personal History of the Spitzer Space Telescope  

E-Print Network (OSTI)

The Spitzer Space Telescope, born as the Shuttle Infrared Telescope Facility (SIRTF) and later the Space Infrared Telescope Facility (still SIRTF), was under discussion and development within NASA and the scientific community for more than 30 years prior to its launch in 2003. This brief history chronicles a few of the highlights and the lowlights of those 30 years from the authors personal perspective. A much more comprehensive history of SIRTF/Spitzer has been written by George Rieke (2006).

Michael Werner

2005-03-29T23:59:59.000Z

166

Status of the second phase of the MAGIC telescope  

E-Print Network (OSTI)

The MAGIC 17m diameter Cherenkov telescope will be upgraded with a second telescope with advanced photon detectors and ultra fast readout within the year 2007. The sensitivity of MAGIC-II, the two telescope system, will be improved by a factor of 2. In addition the energy threshold will be reduced and the energy and angular resolution will be improved. The design, status and expected performance of MAGIC-II is presented here.

Florian Goebel; for the MAGIC collaboration

2007-09-17T23:59:59.000Z

167

The discovery of high-redshift supernovae and their cosmological implications  

SciTech Connect

In this thesis the author discusses the methodology for doing photometry: from procedure of extracting supernova counts from images that contain combined supernova plus galaxy flux, to standard star calibration, to additional instrumental corrections that arise due to the multiple telescopes used for observations. He discusses the different sources of photometric error and their correlations, and the construction of the covariance matrix for all the points in the light curve. He then describes the K corrections which account for the redshifting of spectra that are necessary to compare the photometry of the high-redshift data with those from nearby (z < 0.1) supernovae. Finally, he uses the first seven of the supernovae to test the hypothesis that they live in an under-dense bubble where the locally measured Hubble constant differs significantly from the true Hubble constant. He also uses the data to place limits on the value of the Hubble constant. Discussions of several other important aspects of the data analysis are or will be included in other papers. These topics include a description of how the covariance matrix is used to generate light-curve fits, a discussion of non-photometric systematic errors that also effect the measurements, and a discussion of the application of the supernovae to address other scientific/cosmological problems.

Kim, A.G. [Univ. of California, Berkeley, CA (United States). Dept. of Physics]|[Lawrence Berkeley National Lab., CA (United States). Physics Div.

1997-09-01T23:59:59.000Z

168

Dynamics and constraints of the unified dark matter flat cosmologies  

SciTech Connect

We study the dynamics of the scalar field Friedmann-Lemaitre-Robertson-Walker flat cosmological models within the framework of the unified dark matter (UDM) scenario. In this model we find that the main cosmological functions such as the scale factor of the Universe, the scalar field, the Hubble flow, and the equation of state parameter are defined in terms of hyperbolic functions. These analytical solutions can accommodate an accelerated expansion, equivalent to either the dark energy or the standard {lambda} models. Performing a joint likelihood analysis of the recent supernovae type Ia data and the baryonic acoustic oscillations traced by the Sloan Digital Sky Survey galaxies, we place tight constraints on the main cosmological parameters of the UDM cosmological scenario. Finally, we compare the UDM scenario with various dark energy models namely {lambda} cosmology, parametric dark energy model and variable Chaplygin gas. We find that the UDM scalar field model provides a large and small scale dynamics which are in fair agreement with the predictions by the above dark energy models although there are some differences especially at high redshifts.

Basilakos, Spyros [Academy of Athens, Research Center for Astronomy and Applied Mathematics, Soranou Efesiou 4, GR-11527, Athens (Greece); Lukes-Gerakopoulos, Georgios [Academy of Athens, Research Center for Astronomy and Applied Mathematics, Soranou Efesiou 4, GR-11527, Athens (Greece); University of Athens, Department of Physics, Section of Astrophysics, Astronomy and Mechanics (Greece)

2008-10-15T23:59:59.000Z

169

Measurements of Secondary Cosmic Microwave Background Anisotropies with the South Pole Telescope  

E-Print Network (OSTI)

We report cosmic microwave background (CMB) power spectrum measurements from the first 100 sq. deg. field observed by the South Pole Telescope (SPT) at 150 and 220 GHz. On angular scales where the primary CMB anisotropy is dominant, ell ~ 50 at both frequencies. We combine the 150 and 220 GHz data to remove the majority of the point source power, and use the point source subtracted spectrum to detect Sunyaev-Zel'dovich (SZ) power at 2.6 sigma. At ell=3000, the SZ power in the subtracted bandpowers is 4.2 +/- 1.5 uK^2, which is significantly lower than the power predicted by a fiducial model using WMAP5 cosmological parameters. This discrepancy may suggest that contemporary galaxy cluster models overestimate the thermal pressure of intracluster gas. Alternatively, this result can be interpreted as evidence for lower values of sigma8. When combined with an estimate of the kinetic SZ contribution, the measured SZ amplitude shifts sigma8 from the primary CMB anisotropy derived constraint of 0.794 +/- 0.028 down t...

Lueker, M; Schaffer, K K; Zahn, O; Ade, P A R; Aird, K A; Benson, B A; Bleem, L E; Carlstrom, J E; Chang, C L; Cho, H M; Crawford, T M; Crites, A T; de Haan, T; Dobbs, M A; George, E M; Hall, N R; Halverson, N W; Holder, G P; Holzapfel, W L; Hrubes, J D; Joy, M; Keisler, R; Knox, L; Lee, A T; Leitch, E M; McMahon, J J; Mehl, J; Meyer, S S; Mohr, J J; Montroy, T E; Padin, S; Plagge, T; Pryke, C; Ruhl, J E; Shaw, L; Shirokoff, E; Spieler, H G; Staniszewski, Z; Stark, A A; Vanderlinde, K; Vieira, J D; Williamson, R

2009-01-01T23:59:59.000Z

170

What does cosmology tell us about particle physics beyond the Standard Model?  

Science Conference Proceedings (OSTI)

Cosmology demands particle physics beyond the Standard Model: we need to explain the nature of dark matter and dark energy

Eiichiro Komatsu

2012-01-01T23:59:59.000Z

171

On some physical aspects of isotropic cosmology in Riemann-Cartan spacetime  

E-Print Network (OSTI)

Isotropic cosmology built in the framework of the Poincar\\'e gauge theory of gravity based on sufficiently general expression of gravitational Lagrangian is considered. The derivation of cosmological equations and equations for torsion functions in the case of the most general homogeneous isotropic models is given. Physical aspects of isotropic cosmology connected with possible solution of dark energy problem and problem of cosmological singularity are discussed.

A. V. Minkevich; A. S. Garkun; V. I. Kudin

2013-02-11T23:59:59.000Z

172

Theoretical Research in Cosmology, High-Energy Physics and String Theory  

Science Conference Proceedings (OSTI)

The research was in the area of Theoretical Physics: Cosmology, High-Energy Physics and String Theory

Ng, Y Jack; Dolan, Louise; Mersini-Houghton, Laura; Frampton, Paul

2013-07-29T23:59:59.000Z

173

Thermalization of Starlight in the Steady-State Cosmology  

E-Print Network (OSTI)

We investigate the fate of starlight in the Steady-State Cosmology. We discover that it is largely unaffected by the presence of ions in intergalactic space as it gets progressively red-shifted from the visible all the way down to the plasma frequency of the intergalactic matter. At that point, after about 450 Gyr - and contrary to previously published claims - the radiation will be thermalized. Under the assumptions adopted by Gold, Bondi, Hoyle, Narlikar, Burbidge and others concerning the creation of matter in the Steady-State Cosmology, and using reasonable estimates for the baryonic mass-density and mass-fraction of 4He, the analysis predicts a universal radiation field matching the CMB, i.e. having a black-body spectrum and temperature of about 2.7 K. The Steady-state Cosmology predicts that this radiation field will appear to originate from the intergalactic plasma.

M. Ibison

2009-10-15T23:59:59.000Z

174

Cosmological toolkit project featured on DOE energy website | Argonne  

NLE Websites -- All DOE Office Websites (Extended Search)

Cosmological toolkit project featured on DOE energy website Cosmological toolkit project featured on DOE energy website October 2, 2013 Tweet EmailPrint Researchers from Argonne National Laboratory, in partnership with Fermilab and Lawrence Berkeley National Laboratory, are developing a state-of-the-art toolkit for analyzing cosmological simulation data. The work was recently featured on the DOE website Energy.gov. Leading the Argonne team are Salman Habib, senior physicist and computational scientist in Argonne's High Energy Physics and Mathematics and Computer Science Divisions, and Ravi Madduri, project manager in the MCS Division. The multilaboratory team seeks to create an open platform with a web-based front end that will allow scientists to transfer, search, and analyze the complex data being generated by galaxy-formation simulations. Key to this

175

Quiescent cosmology and the final state of the universe  

E-Print Network (OSTI)

It has long been a primary objective of cosmology to understand the apparent isotropy in our universe and to provide a mathematical formulation for its evolution. A school of thought for its explanation is quiescent cosmology, which already possesses a mathematical framework, namely the definition of an Isotropic Singularity, but only for the initial state of the universe. A complementary framework is necessary in order to also describe possible final states of the universe. Our new definitions of an Anisotropic Future Endless Universe and an Anisotropic Future Singularity, whose structure and properties differ significantly from those of the Isotropic Singularity, offer a promising realisation for this framework. The combination of the three definitions together may then provide the first complete formalisation of the quiescent cosmology concept.

Philipp A Hoehn; Susan M Scott

2010-01-18T23:59:59.000Z

176

Thermodynamics of de Sitter Black Holes: Thermal Cosmological Constant  

E-Print Network (OSTI)

We study the thermodynamic properties associated with the black hole event horizon and the cosmological horizon for black hole solutions in asymptotically de Sitter spacetimes. We examine thermodynamics of these horizons on the basis of the conserved charges according to Teitelboim's method. In particular, we have succeeded in deriving the generalized Smarr formula among thermodynamical quantities in a simple and natural way. We then show that cosmological constant must decrease when one takes into account the quantum effect. These observations have been obtained if and only if cosmological constant plays the role of a thermodynamical state variable. We also touch upon the relation between inflation of our universe and a phase transition of black holes.

Yuichi Sekiwa

2006-02-25T23:59:59.000Z

177

Crisis in Cosmology : Observational Constraints on Omega and H_0  

E-Print Network (OSTI)

Thanks to new technology of observations and fresh inputs from particle physics, cosmology has advanced on both observational and theoretical fronts. It is therefore opportune that we take stock of the cosmological situation today and examine the observational and theoretical constraints as they are now. The bottom line in this review is that despite the availability of the cosmological constant as an extra parameter for flat Friedmann models, the allowed parameter space for such models is very small. The observations that we consider here include the ages of globular clusters, measurement of Hubble's constant, abundance of rich clusters of galaxies, fraction of mass contributed by baryons in rich clusters and abundance of high redshift objects.

J. S. Bagla; T. Padmanabhan; J. V. Narlikar

1995-11-22T23:59:59.000Z

178

COSMOLOGICAL POST-NEWTONIAN APPROXIMATION COMPARED WITH PERTURBATION THEORY  

Science Conference Proceedings (OSTI)

We compare the cosmological first-order post-Newtonian (1PN) approximation with the relativistic cosmological linear perturbation theory in a zero-pressure medium with the cosmological constant. We compare equations and solutions in several different gauge conditions available in both methods. In the PN method we have perturbation equations for density, velocity, and gravitational potential independently of the gauge condition to 1PN order. However, correspondences with these 1PN equations are available only in certain gauge conditions in the perturbation theory. Equations of perturbed velocity and the perturbed gravitational potential in the zero-shear gauge exactly coincide with the Newtonian equations, which remain valid even to 1PN order (the same is true for perturbed velocity identified in the comoving gauge), and equations of perturbed density in the zero-shear gauge and the uniform-expansion gauge coincide to 1PN order. We identify other correspondences available in different gauge conditions of the perturbation theory.

Noh, Hyerim [Korea Astronomy and Space Science Institute, Daejon 305-348 (Korea, Republic of); Hwang, Jai-chan [Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 702-701 (Korea, Republic of)

2012-10-01T23:59:59.000Z

179

Deployment of a Pair of 3 M telescopes in Utah  

SciTech Connect

Two 3 m telescopes are being installed in Grantsville Utah. They are intended for the testing of various approaches to the implementation of intensity interferometry using Cherenkov Telescopes in large arrays as receivers as well as for the testing of novel technology cameras and electronics for ground based gamma-ray astronomy.

Finnegan, G.; Adams, B.; Butler, K.; Cardoza, J.; Colin, P.; Hui, C. M.; Kieda, D.; Kirkwood, D.; Kress, D.; Kress, M.; LeBohec, S.; McGuire, C.; Newbold, M.; Nunez, P.; Pham, K. [University of Utah, Department of Physics, Salt Lake City, Utah 84112 (United States)

2008-12-24T23:59:59.000Z

180

Searching for Transient Pulses with the ETA Radio Telescope  

Science Conference Proceedings (OSTI)

Array-based, direct-sampling radio telescopes have computational and communication requirements unsuited to conventional computer and cluster architectures. Synchronization must be strictly maintained across a large number of parallel data streams, from ... Keywords: Direct sampling radio telescope array, FPGA cluster computing, RFI mitigation, signal dedispersion

C. D. Patterson; S. W. Ellingson; B. S. Martin; K. Deshpande; J. H. Simonetti; M. Kavic; S. E. Cutchin

2009-01-01T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
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181

Optimal Networks of Future Gravitational-Wave Telescopes  

E-Print Network (OSTI)

We aim to find the optimal site locations for a hypothetical network of 1-3 triangular gravitational-wave telescopes. We define the following N-telescope figures of merit and construct three corresponding metrics: (a) capability of reconstructing the signal polarization; (b) accuracy in source localization; and (c) accuracy in reconstructing the parameters of a standard binary source. We also define a combined metric that takes into account the three figures of merit with practically equal weight. After constructing a geomap of possible telescope sites, we give the optimal 2-telescope networks for the four figures of merit separately in example cases where the location of the first telescope has been predetermined. We found that the optimal site locations for a second telescope based on the combined metric form a +/-7 deg annulus at an angular distance of ~130 deg from the location of the first telescope. Based on this result we conclude that placing the first telescope to Australia provides the most options ...

Raffai, Peter; Heng, Ik Siong; Kelecsenyi, Nandor; Logue, Josh; Marka, Zsuzsa; Marka, Szabolcs

2013-01-01T23:59:59.000Z

182

Cosmological mass limits on neutrinos, axions, and other light particles  

E-Print Network (OSTI)

The small-scale power spectrum of the cosmological matter distribution together with other cosmological data provides a sensitive measure of the hot dark matter fraction, leading to restrictive neutrino mass limits. We extend this argument to generic cases of low-mass thermal relics. We vary the cosmic epoch of thermal decoupling, the radiation content of the universe, and the new particle's spin degrees of freedom. Our treatment covers various scenarios of active plus sterile neutrinos or axion-like particles. For three degenerate massive neutrinos, we reproduce the well-known limit of m_nu solar eV-mass axions to be discovered by the CAST experiment.

Steen Hannestad; Georg Raffelt

2003-12-11T23:59:59.000Z

183

Cosmological Solutions in Biconnection and Bimetric Gravity Theories  

E-Print Network (OSTI)

We show how generic off--diagonal cosmological solutions depending, in general, on all spacetime coordinates can be constructed in massive gravity using the anholonomic frame deformation method. Such metrics describe the late time acceleration due to effective cosmological terms induced by nonlinear off--diagonal interactions and graviton mass and include matter, graviton mass and other effective sources modelling nonlinear gravitational and matter fields interactions with polarization of physical constants and deformations of metrics, which may explain certain dark energy and dark matter effects.

Sergiu I. Vacaru

2013-04-02T23:59:59.000Z

184

General properties of cosmological models with an Isotropic Singularity  

E-Print Network (OSTI)

Much of the published work regarding the Isotropic Singularity is performed under the assumption that the matter source for the cosmological model is a barotropic perfect fluid, or even a perfect fluid with a $\\gamma$-law equation of state. There are, however, some general properties of cosmological models which admit an Isotropic Singularity, irrespective of the matter source. In particular, we show that the Isotropic Singularity is a point-like singularity and that vacuum space-times cannot admit an Isotropic Singularity. The relationships between the Isotropic Singularity, and the energy conditions, and the Hubble parameter is explored. A review of work by the authors, regarding the Isotropic Singularity, is presented.

Geoffery Ericksson; Susan M. Scott

2003-02-25T23:59:59.000Z

185

Towards a holographic theory of cosmology -- threads in a tapestry  

E-Print Network (OSTI)

In this Essay we address several fundamental issues in cosmology: What is the nature of dark energy and dark matter? Why is the dark sector so different from ordinary matter? Why is the effective cosmological constant non-zero but so incredibly small? What is the reason behind the emergence of a critical acceleration parameter of magnitude $10^{-8} cm/sec^2$ in galactic dynamics? We suggest that the holographic principle is the linchpin in a unified scheme to understand these various issues.

Y. Jack Ng

2013-05-16T23:59:59.000Z

186

Interplanetary Measures Can Not Bound the Cosmological Constant  

E-Print Network (OSTI)

The effect of a cosmological constant on the precession of the line of apsides is O(\\Lambda c^2 r^3/GM) which is 3(H_\\circ P)^2/8\\pi^2 \\approx 10^{-23} for a vacuum-dominated Universe with Hubble constant H_\\circ = 65 km/sec/Mpc and for the orbital period P = 88 days of Mercury. This is unmeasurably small, so planetary perturbations cannot be used to limit the cosmological constant, contrary to the suggestion by Cardona & Tejeiro (1998).

Edward L. Wright

1998-05-21T23:59:59.000Z

187

Troubles with quantum anisotropic cosmological models: loss of unitarity  

E-Print Network (OSTI)

The anisotropic Bianchi I cosmological model coupled with perfect fluid is quantized in the minisuperspace. The perfect fluid is described by using the Schutz formalism which allows to attribute dynamical degrees of freedom to matter. It is shown that the resulting model is non-unitary. This breaks the equivalence between the many-worlds and dBB interpretations of quantum mechanics.

F. G. Alvarenga; A. B. Batista; J. C. Fabris; S. V. B. Goncalves

2004-02-25T23:59:59.000Z

188

Problems of Cosmological Variability of Fundamental Physical Constants  

E-Print Network (OSTI)

of the fundamental constants which govern most of the common phenomena and are usually given in the handbooks. NoteProblems of Cosmological Variability of Fundamental Physical Constants #3; D. A. Varshalovich, A. Y and astronomical observations aimed at testing the possible space-time variability of fundamental physical

189

FRW quantum cosmology with a generalized Chaplygin gas  

SciTech Connect

Cosmologies with a Chaplygin gas have recently been explored with the objective of explaining the transition from a dust dominated epoch towards an accelerating expansion stage. In this context, we consider the hypothesis that this transition involves a quantum mechanical process. Our analysis is entirely analytical, with the objective of finding explicit mathematical expressions for the different quantum mechanical states and their cosmological implications. We employ a Friedmann-Robertson-Walker (FRW) minisuperspace model, characterized by two Lorentzian sectors, separated by a classically forbidden region. This is the configuration associated with the evolution of a generalized Chaplygin gas in a FRW universe. The Hartle-Hawking and Vilenkin wave functions are then computed, together with the transition amplitudes towards the accelerating epoch. Furthermore, for specific initial conditions we found that the generalized Chaplygin gas parameters become related through an expression involving an integer n. We also introduce a phenomenological association between some brane-world scenarios and a FRW minisuperspace cosmology with a generalized Chaplygin gas. The aim is to promote a discussion and subsequent research on the quantum creation of brane cosmologies from such a perspective. Additional results in this paper suggest that the brane tension would become related with the generalized Chaplygin gas parameters through another expression involving an integer.

Bouhmadi-Lopez, Mariam; Moniz, Paulo Vargas [Institute of Cosmology and Gravitation, University of Portsmouth, Mercantile House, Hampshire Terrace, Portsmouth PO1 2EG (United Kingdom); Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London E1 4NS (United Kingdom)

2005-03-15T23:59:59.000Z

190

An Alternative Solution to the Cosmological Constant Problem  

E-Print Network (OSTI)

In this paper it is analyzed the consecuences of a (1,1) dimensional space time at Planck scales. With this hypothesis is proposed an alternative solution to the density energy and the coincidence problem of the cosmological constant. Similarly it is predicted that the density of the dark energy is 4/9 of the critical density in the Universe.

Angel, Garcia Aspeitia Miguel

2010-01-01T23:59:59.000Z

191

Dark Energy: The Cosmological Challenge of the T. Padmanabhan  

E-Print Network (OSTI)

Dark Energy: The Cosmological Challenge of the Millennium T. Padmanabhan IUCAA, Pune Observational. It is made of a very exotic species called dark energy which exerts negative pressure. This is more esoteric per cent dark 1 #12;energy. The key direct evidence, however, came in late ninetees from the analysis

Udgaonkar, Jayant B.

192

Kaluza-Klein Cosmology With Modified Holographic Dark Energy  

E-Print Network (OSTI)

We investigate the compact Kaluza-Klein cosmology in which modified holographic dark energy is interacting with dark matter. Using this scenario, we evaluate equation of state parameter as well as equation of evolution of the modified holographic dark energy. Further, it is shown that the generalized second law of thermodynamics holds without any constraint.

M. Sharif; Farida Khanum

2011-06-13T23:59:59.000Z

193

Three fluid cosmological model using Lie and Noether symmetries  

E-Print Network (OSTI)

We employ a three fluid model in order to construct a cosmological model in the Friedmann Robertson Walker flat spacetime, which contains three types of matter dark energy, dark matter and a perfect fluid with a linear equation of state. Dark matter is described by dust and dark energy with a scalar field with potential V({\\phi}). In order to fix the scalar field potential we demand Lie symmetry invariance of the field equations, which is a model-independent assumption. The requirement of an extra Lie symmetry selects the exponential scalar field potential. The further requirement that the analytic solution is invariant under the point transformation generated by the Lie symmetry eliminates dark matter and leads to a quintessence and a phantom cosmological model containing a perfect fluid and a scalar field. Next we assume that the Lagrangian of the system admits an extra Noether symmetry. This new assumption selects the scalar field potential to be exponential and forces the perfect fluid to be stiff. Furthermore the existence of the Noether integral allows for the integration of the dynamical equations. We find new analytic solutions to quintessence and phantom cosmologies which contain all three fluids. Using these solutions one is able to compute analytically all main cosmological functions, such as the scale factor, the scalar field, the Hubble expansion rate, the deceleration parameter etc.

Michael Tsamparlis; Andronikos Paliathanasis

2011-11-23T23:59:59.000Z

194

Cosmological Constraints from the SDSS maxBCG Cluster Catalog  

Science Conference Proceedings (OSTI)

We use the abundance and weak lensing mass measurements of the SDSS maxBCG cluster catalog to simultaneously constrain cosmology and the richness-mass relation of the clusters. Assuming a flat {Lambda}CDM cosmology, we find {sigma}{sub 8}({Omega}{sub m}/0.25){sup 0.41} = 0.832 {+-} 0.033 after marginalization over all systematics. In common with previous studies, our error budget is dominated by systematic uncertainties, the primary two being the absolute mass scale of the weak lensing masses of the maxBCG clusters, and uncertainty in the scatter of the richness-mass relation. Our constraints are fully consistent with the WMAP five-year data, and in a joint analysis we find {sigma}{sub 8} = 0.807 {+-} 0.020 and {Omega}{sub m} = 0.265 {+-} 0.016, an improvement of nearly a factor of two relative to WMAP5 alone. Our results are also in excellent agreement with and comparable in precision to the latest cosmological constraints from X-ray cluster abundances. The remarkable consistency among these results demonstrates that cluster abundance constraints are not only tight but also robust, and highlight the power of optically-selected cluster samples to produce precision constraints on cosmological parameters.

Rozo, Eduardo; /CCAPP; Wechsler, Risa H.; /KIPAC, Menlo Park /SLAC; Rykoff, Eli S.; /UC, Santa Barbara; Annis, James T.; /Fermilab; Becker, Matthew R.; /Chicago U. /KICP, Chicago; Evrard, August E.; /Michigan U. /Michigan U., MCTP; Frieman, Joshua A.; /Fermilab /KICP, Chicago /Chicago U.; Hansen, Sarah M.; /UC, Santa Cruz; Hao, Jia; /Michigan U.; Johnston, David E.; /Northwestern U.; Koester, Benjamin P.; /KICP, Chicago /Chicago U.; McKay, Timothy A.; /Michigan U. /Michigan U., MCTP; Sheldon, Erin S.; /Brookhaven; Weinberg, David H.; /CCAPP /Ohio State U.

2009-08-03T23:59:59.000Z

195

The quantization of unimodular gravity and the cosmological constant problem  

E-Print Network (OSTI)

A quantization of unimodular gravity is described, which results in a quantum effective action which is also unimodular, ie a function of a metric with fixed determinant. A consequence is that contributions to the energy momentum tensor of the form of the metric times a spacetime constant, whether classical or quantum, are not sources of curvature in the equations of motion derived from the quantum effective action. This solves the first cosmological constant problem, which is suppressing the enormous contributions to the cosmological constant coming from quantum corrections. We discuss several forms of uniodular gravity and put two of them, including one proposed by Henneaux and Teitelboim, in constrained Hamiltonian form. The path integral is constructed from the latter. Furthermore, the second cosmological constant problem, which is why the measured value is so small, is also addressed by this theory. We argue that a mechanism first proposed by Ng and van Dam for suppressing the cosmological constant by quantum effects obtains at the semiclassical level.

Lee Smolin

2009-04-30T23:59:59.000Z

196

Comments on the Quasi-Steady-State Cosmology  

E-Print Network (OSTI)

The Quasi-Steady-State Cosmology as proposed by Hoyle, Burbidge and Narlikar does not fit the observed facts of the Universe. In particular, it predicts that 75-90\\% of the radio sources in the brightest sample that shows steeper than Euclidean source counts should be blueshifted.

Edward L. Wright

1994-10-20T23:59:59.000Z

197

Real-time condition assessment of RAPTOR telescope systems  

Science Conference Proceedings (OSTI)

The RAPid Telescopes for Optical Response (RAPTOR) observatory network consists of several robotic astronomical telescopes primarily designed to search for astrophysical transients called a gamma-ray bursts (GRBs). Although intrinsically bright, GRBs are difficult to detect because of their short duration. Typically, they are first observed by satellites that then relay the coordinates of the GRB to a ground station which, in turn, distributes the coordinates over the internet so that ground based observers can perform follow-up observations. Typically the ground based observations begin after the GRB has ended and only residual emiSSion (the 'afterglow') is left. However, if the satellite relays the GRB coordinates quickly enough, a 'fast' robotic telescope on the ground may be able to catch the GRB in progress. The RAPTOR telescope system is one of only a few in the world to have accomplished this feat. In order to achieve these results, the RAPTOR telescopes must operate autonomously at a high duty-cycle and in peak operating condition. Currently the telescopes are maintained in an ad hoc manner, often in a run-to-failure mode. The RAPTOR project could benefit greatly from a structural health monitoring (SHM) system, especially as more complex units are added to the suite of telescopes. This paper will summarize preliminary results from an SHM study performed on one of the RAPTOR telescopes. Damage scenarios that are of concern and that have been previously observed are first summarized. Then a specific study of damage to the telescope drive mechanism is presented where the data acquisition system is first described. Next, damage detection algorithms are developed with LANL's new publically available software SHMTools and the results of this process are discussed in detail. The paper will conclude with a summary of future planned refinemenls of the RAPTOR SHM system.

Stull, Chris [Los Alamos National Laboratory; Taylor, Stuart [Los Alamos National Laboratory; Wren, James [Los Alamos National Laboratory; Farrar, Charles [Los Alamos National Laboratory; Park, Gyuhae [Los Alamos National Laboratory

2010-11-30T23:59:59.000Z

198

A retrospective of the GREGOR solar telescope in scientific literature  

E-Print Network (OSTI)

In this review, we look back upon the literature, which had the GREGOR solar telescope project as its subject including science cases, telescope subsystems, and post-focus instruments. The articles date back to the year 2000, when the initial concepts for a new solar telescope on Tenerife were first presented at scientific meetings. This comprehensive bibliography contains literature until the year 2012, i.e., the final stages of commissioning and science verification. Taking stock of the various publications in peer-reviewed journals and conference proceedings also provides the "historical" context for the reference articles in this special issue of Astronomische Nachrichten/Astronomical Notes.

Denker, C; Feller, A; Arlt, K; Balthasar, H; Bauer, S -M; González, N Bello; Berkefeld, T; Caligari, P; Collados, M; Fischer, A; Granzer, T; Hahn, T; Halbgewachs, C; Heidecke, F; Hofmann, A; Kentischer, T; Klva?a, M; Kneer, F; Lagg, A; Nicklas, H; Popow, E; Puschmann, K G; Rendtel, J; Schmidt, D; Schmidt, W; Sobotka, M; Solanki, S K; Soltau, D; Staude, J; Strassmeier, K G; Volkmer, R; Waldmann, T; Wiehr, E; Wittmann, A D; Woche, M

2012-01-01T23:59:59.000Z

199

Pre-Big Bang, vacuum and noncyclic cosmologies  

E-Print Network (OSTI)

WMAP and Planck open the way to unprecedented Big Bang phenomenology, potentially allowing to test the standard Big Bang model as well as less conventional approaches including noncyclic pre-Big Bang cosmologies that would incorporate a new fundamental scale beyond the Planck scale and, possibly, new ultimate constituents of matter. Alternatives to standard physics can be considered from a cosmological point of view concerning vacuum structure, the nature of space-time, the origin and evolution of our Universe, the validity of quantum field theory and conventional symmetries, solutions to the cosmological constant problem, inflationary scenarios, dark matter and dark energy, the interpretation of string-like theories... Lorentz-like symmetries for the properties of matter (standard or superbradyonic) can then be naturally stable space-time configurations resulting from general cosmological scenarios that incorporate physics beyond the Planck scale and describe the formation and evolution of the present vacuum. But an even more primordial question seems to be that of the origin of half-integer spins, that cannot be generated through orbital angular momentum in the usual real space-time. It turns out that the use of a spinorial space-time with two complex coordinates instead of the conventional four real ones presents several attractive features. Taking the cosmic time to be the modulus of a SU(2) spinor leads by purely geometric means to a naturally expanding universe, with a ratio between cosmic relative velocities and distances equal to the inverse of the age of the Universe. No reference to standard matter, hidden fields, gravitation or relativity is required to get such a result that looks quite reasonable from an observational point of view. We discuss basic ideas and phenomenological issues for noncyclic pre-Big Bang cosmologies in the present context.

Luis Gonzalez-Mestres

2012-12-12T23:59:59.000Z

200

The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission  

SciTech Connect

The Large Area Telescope (Fermi/LAT, hereafter LAT), the primary instrument on the Fermi Gamma-ray Space Telescope (Fermi) mission, is an imaging, wide field-of-view (FoV), high-energy {gamma}-ray telescope, covering the energy range from below 20 MeV to more than 300 GeV. The LAT was built by an international collaboration with contributions from space agencies, high-energy particle physics institutes, and universities in France, Italy, Japan, Sweden, and the United States. This paper describes the LAT, its preflight expected performance, and summarizes the key science objectives that will be addressed. On-orbit performance will be presented in detail in a subsequent paper. The LAT is a pair-conversion telescope with a precision tracker and calorimeter, each consisting of a 4 x 4 array of 16 modules, a segmented anticoincidence detector that covers the tracker array, and a programmable trigger and data acquisition system. Each tracker module has a vertical stack of 18 (x, y) tracking planes, including two layers (x and y) of single-sided silicon strip detectors and high-Z converter material (tungsten) per tray. Every calorimeter module has 96 CsI(Tl) crystals, arranged in an eight-layer hodoscopic configuration with a total depth of 8.6 radiation lengths, giving both longitudinal and transverse information about the energy deposition pattern. The calorimeter's depth and segmentation enable the high-energy reach of the LAT and contribute significantly to background rejection. The aspect ratio of the tracker (height/width) is 0.4, allowing a large FoV (2.4 sr) and ensuring that most pair-conversion showers initiated in the tracker will pass into the calorimeter for energy measurement. Data obtained with the LAT are intended to (1) permit rapid notification of high-energy {gamma}-ray bursts and transients and facilitate monitoring of variable sources, (2) yield an extensive catalog of several thousand high-energy sources obtained from an all-sky survey, (3) measure spectra from 20 MeV to more than 50 GeV for several hundred sources, (4) localize point sources to 0.3-2 arcmin, (5) map and obtain spectra of extended sources such as SNRs, molecular clouds, and nearby galaxies, (6) measure the diffuse isotropic {gamma}-ray background up to TeV energies, and (7) explore the discovery space for dark matter.

Atwood, W.B.; /UC, Santa Cruz; Abdo, Aous A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Anderson, B. /UC, Santa Cruz; Axelsson, M.; /Stockholm U.; Baldini, L.; /INFN, Pisa; Ballet, J.; /DAPNIA, Saclay; Band, D.L.; /NASA, Goddard /NASA, Goddard; Barbiellini, Guido; /INFN, Trieste /Trieste U.; Bartelt, J.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bastieri, Denis; /INFN, Padua /Padua U.; Baughman, B.M.; /Ohio State U.; Bechtol, K.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bederede, D.; /DAPNIA, Saclay; Bellardi, F.; /INFN, Pisa; Bellazzini, R.; /INFN, Pisa; Berenji, B.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Bignami, G.F.; /Pavia U.; Bisello, D.; /INFN, Padua /Padua U.; Bissaldi, E.; /Garching, Max Planck Inst., MPE; Blandford, R.D.; /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /INFN, Perugia /Perugia U. /NASA, Goddard /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /INFN, Pisa /INFN, Pisa /Bari U. /INFN, Bari /Ecole Polytechnique /Washington U., Seattle /INFN, Padua /Padua U. /Bari U. /INFN, Bari /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /IASF, Milan /IASF, Milan /Kalmar U. /Royal Inst. Tech., Stockholm /DAPNIA, Saclay /ASI, Rome /INFN, Pisa /INFN, Perugia /Perugia U. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /George Mason U. /Naval Research Lab, Wash., D.C. /NASA, Goddard /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /DAPNIA, Saclay /NASA, Goddard /INFN, Perugia /Perugia U. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Montpellier U. /Stanford U., HEPL /KIPAC, Menlo Park /Stanford U., Phys. Dept.; /more authors..

2009-05-15T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


201

The Solar Optical Telescope for the Hinode Mission: An Overview  

E-Print Network (OSTI)

The Solar Optical Telescope (SOT) aboard the Hinode satellite (formerly called Solar-B) consists of the Optical Telescope Assembly (OTA) and the Focal Plane Package (FPP). The OTA is a 50 cm diffraction-limited Gregorian telescope, and the FPP includes the narrow-band (NFI) and wide-band (BFI) filtergraphs, plus the Stokes spectro-polarimeter (SP). SOT provides unprecedented high resolution photometric and vector magnetic images of the photosphere and chromosphere with a very stable point spread function, and is equipped with an image stabilization system that reduces the error to less than 0.01 arcsec rms. Together with the other two instruments on Hinode (the X-Ray Telescope (XRT) and EUV Imaging Spectrometer (EIS)), SOT is poised to address many fundamental questions about solar magneto-hydrodynamics. Note that this is an overview, and the details of the instrument are presented in a series of companion papers.

S. Tsuneta

2007-11-12T23:59:59.000Z

202

Verifying the Cosmological Utility of Type Ia Supernovae:Implications of a Dispersion in the Ultraviolet Spectra  

SciTech Connect

We analyze the mean rest-frame ultraviolet (UV) spectrum ofType Ia Supernovae(SNe) and its dispersion using high signal-to-noiseKeck-I/LRIS-B spectroscopyfor a sample of 36 events at intermediateredshift (z=0.5) discoveredby the Canada-France-Hawaii TelescopeSupernova Legacy Survey (SNLS). Weintroduce a new method for removinghost galaxy contamination in our spectra,exploiting the comprehensivephotometric coverage of the SNLS SNe and theirhost galaxies, therebyproviding the first quantitative view of the UV spectralproperties of alarge sample of distant SNe Ia. Although the mean SN Ia spectrumhas notevolved significantly over the past 40 percent of cosmic history,preciseevolutionary constraints are limited by the absence of acomparable sample ofhigh quality local spectra. The mean UV spectrum ofour z 0.5 SNe Ia and itsdispersion is tabulated for use in futureapplications. Within the high-redshiftsample, we discover significant UVspectral variations and exclude dust extinctionas the primary cause byexamining trends with the optical SN color. Although progenitormetallicity may drive some of these trends, the variations we see aremuchlarger than predicted in recent models and do not follow expectedpatterns.An interesting new result is a variation seen in the wavelengthof selected UVfeatures with phase. We also demonstrate systematicdifferences in the SN Iaspectral features with SN lightcurve width inboth the UV and the optical. Weshow that these intrinsic variations couldrepresent a statistical limitation in thefuture use of high-redshift SNeIa for precision cosmology. We conclude thatfurther detailed studies areneeded, both locally and at moderate redshift wherethe rest-frame UV canbe studied precisely, in order that future missions canconfidently beplanned to fully exploit SNe Ia as cosmological probes.

Ellis, R.S.; Sullivan, M.; Nugent, P.E.; Howell, D.A.; Gal-Yam,A.; Astier, P.; Balam, D.; Balland, C.; Basa, S.; Carlberg, R.G.; Conley,A.; Fouchez, D.; Guy, J.; Hardin, D.; Hook, I.; Pain, R.; Perrett, K.; Pritchet, C.J.; Regnault, N.

2007-11-02T23:59:59.000Z

203

Geomagnetic Effects on the Performance of Atmospheric Cerenkov Telescopes  

E-Print Network (OSTI)

Atmospheric Cerenkov telescopes are used to detect electromagnetic showers from primary gamma rays of energy > 300 GeV and to discriminate these from cascades due to hadrons using the shape and orientation of the Cerenkov images. The geomagnetic field affects the development of showers and diffuses and distorts the images. When the component of the field normal to the shower axis is sufficiently large (> 0.4 G) the performance of gamma ray telescopes may be affected.

P. M. Chadwick; K. Lyons; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; S. E. Shaw; K. E. Turver

1999-06-08T23:59:59.000Z

204

The Sloan Digital Sky Survey Monitor Telescope Pipeline  

E-Print Network (OSTI)

The photometric calibration of the Sloan Digital Sky Survey (SDSS) is a multi-step process which involves data from three different telescopes: the 1.0-m telescope at the US Naval Observatory (USNO), Flagstaff Station, Arizona (which was used to establish the SDSS standard star network); the SDSS 0.5-m Photometric Telescope (PT) at the Apache Point Observatory (APO), New Mexico (which calculates nightly extinctions and calibrates secondary patch transfer fields); and the SDSS 2.5-m telescope at APO (which obtains the imaging data for the SDSS proper). In this paper, we describe the Monitor Telescope Pipeline, MTPIPE, the software pipeline used in processing the data from the single-CCD telescopes used in the photometric calibration of the SDSS (i.e., the USNO 1.0-m and the PT). We also describe transformation equations that convert photometry on the USNO-1.0m u'g'r'i'z' system to photometry the SDSS 2.5m ugriz system and the results of various validation tests of the MTPIPE software. Further, we discuss the semi-automated PT factory, which runs MTPIPE in the day-to-day standard SDSS operations at Fermilab. Finally, we discuss the use of MTPIPE in current SDSS-related projects, including the Southern u'g'r'i'z' Standard Star project, the u'g'r'i'z' Open Star Clusters project, and the SDSS extension (SDSS-II).

D. L. Tucker; S. Kent; M. W. Richmond; J. Annis; J. A. Smith; S. S. Allam; C. T. Rodgers; J. L. Stute; J. K. Adelman-McCarthy; J. Brinkmann; M. Doi; D. Finkbeiner; M. Fukugita; J. Goldston; B. Greenway; J. E. Gunn; J. S. Hendry; D. W. Hogg; S. -I. Ichikawa; Z. Ivezic; G. R. Knapp; H. Lampeitl; B. C. Lee; H. Lin; T. A. McKay; A. Merrelli; J. A. Munn; E. H. Neilsen, Jr.; H. J. Newberg; G. T. Richards; D. J. Schlegel; C. Stoughton; A. Uomoto; B. Yanny

2006-08-26T23:59:59.000Z

205

Cosmological evolution of the cosmological plasma with interpartial scalar interaction. III. Model with the attraction of the like scalar charged particles  

E-Print Network (OSTI)

On the basis of the relativistic kinetic theory the mathematical model of cosmological plasmas with an attraction of the like charged scalar particles is formulated. It is shown, that cosmological the model, based on a classical scalar field with an attraction, is unsatisfactory, that leads to necessity of attraction of phantom models of a scalar field for systems with an attraction.

Yu. G. Ignat'ev

2013-07-09T23:59:59.000Z

206

Large Synoptic Survey Telescope (LSST) Posters from the 215th Meeting of the American Astronomical Society  

DOE Data Explorer (OSTI)

The 8.4 meter Large LSST will survey the entire visible sky deeply in multiple colors every week with its three-billion pixel digital camera, probing the mysteries of Dark Matter and Dark Energy, and opening a movie-like window on objects that change or move rapidly: exploding supernovae, potentially hazardous near-Earth asteroids, and distant Kuiper Belt Objects. [Copied from http://www.lsst.org/lsst/about]

The LSST is still in the design and development phase and will be ready for its scientific work approximately four years after construction starts in Chile. The scientific posters prepared by members of the LSST Project Team for the 215 meeting of the American Astronomical Society in January of 2010 provide a detailed, technical look at the project components. Titles of posters available online include:

  • LSST Observatory and Science Opportunities
  • The LSST: A System of Systems
  • LSST: from Science Drivers to Data Products
  • LSST Education and Public Outreach
  • LSST Operations Simulator
  • Simulating the LSST
  • Inventorying the Solar System with LSST
  • Stellar Population Science with LSST
  • Eclipsing Binary Science with the Large Synoptic Survey Telescope
  • Mapping Milky Way and Local Volume Structure with LSST
  • Galaxy Evolution with LSST
  • Photometric Redshift Performance of LSST
  • LSST Cosmological Probes
  • Probing Dark Energy with Weak Lensing: Ground versus Space
  • Strong Gravitational Lensing with LSST
  • AGN Science with the LSST
  • Exploring the Transient and Variable Universe with LSST
  • Investigation of LSST RR Lyrae Lightcurve Recovery
  • Calibation of LSST Instrument and Data
  • White Dwarf Starts as LSST Calibrators
  • The Camera for LSST and its Focal Plane Array
  • LSST Telescope and Optics Status
  • Data Management R&D for the LSST Project
  • The Spectrum of LSST Data Analysis Challenges: Kiloscale to Petascale
  • Accelerating LSST Source Catalog Simulations with Graphics Processing Units

LSST Project Team Members

207

Non-Abelian Einstein-Born-Infeld-Dilaton Cosmology  

E-Print Network (OSTI)

The non-abelian Einstein-Born-Infeld-Dilaton theory, which rules the dynamics of tensor-scalar gravitation coupled to a $su(2)$-valued gauge field ruled by Born-Infeld lagrangian, is studied in a cosmological framework. The microscopic energy exchange between the gauge field and the dilaton which results from a non-universality of the coupling to gravity modifies the usual behaviour of tensor-scalar theories coupled to matter fluids. General cosmological evolutions are derived for different couplings to gravitation and a comparison to universal coupling is highlighted. Evidences of cosmic acceleration are presented when the evolution is interpreted in the Jordan physical frame of a matter respecting the weak equivalence principle. The importance for the mechanism of cosmic acceleration of the dynamics of the Born-Infeld gauge field, the attraction role of the matter fluid and the non-universality of the gravitational couplings is briefly outlined.

A. Fuzfa; J. -M. Alimi

2005-11-16T23:59:59.000Z

208

Cosmological and astrophysical constraints on superconducting cosmic strings  

E-Print Network (OSTI)

We investigate the cosmological and astrophysical constraints on superconducting cosmic strings (SCSs). SCS loops emit strong bursts of electromagnetic waves, which might affect various cosmological and astrophysical observations. We take into account the effect on the CMB anisotropy, CMB blackbody spectrum, BBN, observational implications on radio wave burst and X-ray or gamma-ray events, and stochastic gravitational wave background measured by pulsar timing experiments. We then derive constraints on the parameters of SCS from current observations and estimate prospects for detecting SCS signatures in on-going observations. As a result, we find that these constraints exclude broad parameter regions, and also that on-going radio wave observations can probe large parameter space.

Koichi Miyamoto; Kazunori Nakayama

2012-12-30T23:59:59.000Z

209

Photon-Axion-Like Particle Coupling Constant and Cosmological Observations  

E-Print Network (OSTI)

We estimated the photon-pseudoscalar particle mixing constant from the effect of cosmological alignment and cosmological rotation of polarization plane of distant QSOs. This effect is explained in terms of birefringent phenomenon due to photon-pseudoscalar (axion-like) particle mixing in a cosmic magnetic field. On the contrary, one can estimate the strength of the cosmic magnetic field using the constraints on the photon-axion-like particle coupling constant from the CAST experiment and from SNe Ia dimming effect. In a result, the lower limit on the intergalactic ($z\\approx 1\\div 2$) magnetic field appears at the level of about $4\\times 10^{-10}\\div 10^{-11}$ G.

M. Yu. Piotrovich; Yu. N. Gnedin; T. M. Natsvlishvili

2008-05-23T23:59:59.000Z

210

Nuclear and particle physics, astrophysics and cosmology (NPAC) capability review  

Science Conference Proceedings (OSTI)

The present document represents a summary self-assessment of the status of the Nuclear and Particle Physics, Astrophysics and Cosmology (NPAC) capability across Los Alamos National Laboratory (LANL). For the purpose of this review, we have divided the capability into four theme areas: Nuclear Physics, Particle Physics, Astrophysics and Cosmology, and Applied Physics. For each theme area we have given a general but brief description of the activities under the area, a list of the Laboratory divisions involved in the work, connections to the goals and mission of the Laboratory, a brief description of progress over the last three years, our opinion of the overall status of the theme area, and challenges and issues.

Redondo, Antonio [Los Alamos National Laboratory

2010-01-01T23:59:59.000Z

211

Interacting Dark Energy in Ho?ava-Lifshitz Cosmology  

E-Print Network (OSTI)

In the usual Ho\\v{r}ava-Lifshitz cosmological models, the scalar field is responsible for dark matter. Using an additional scalar field, Saridakis \\cite{sari} has formulated Ho\\v{r}ava-Lifshitz cosmology with an effective dark energy sector. In the paper \\cite{sari} the scalar fields do not interact with each other, here we extend this work to the interacting case, where matter scalar field $\\phi$ interact with dark energy scalar field $\\sigma$. We will show that in contrast with \\cite{sari}, where $\\sigma$-filed is absent, we can obtain $w_d ^{\\rm eff}dark energy presenting phantom behaviour. This behaviour is pure effect of the interaction.

M R Setare

2009-09-02T23:59:59.000Z

212

Equation of state and singularities in FLRW cosmological models  

E-Print Network (OSTI)

We consider FLRW cosmological models with standard Friedmann equations, but leaving free the equation of state. We assume that the dark energy content of the universe is encoded in an equation of state $p=f(\\rho)$, which is expressed with most generality in the form of a power expansion. The inclusion of this expansion in Friedmann equations allows us to construct a perturbative solution and to relate the coefficients of the equation of state with the formation of singularities of different types.

L. Fernandez-Jambrina; R. Lazkoz

2010-01-18T23:59:59.000Z

213

Nonexpanding impulsive gravitational waves with an arbitrary cosmological constant  

E-Print Network (OSTI)

Exact solutions for nonexpanding impulsive waves in a background with nonzero cosmological constant are constructed using a `cut and paste' method. These solutions are presented using a unified approach which covers the cases of de Sitter, anti-de Sitter and Minkowski backgrounds. The metrics are presented in continuous and distributional forms, both of which are conformal to the corresponding metrics for impulsive pp-waves, and for which the limit as $\\Lambda\\to 0$ can be made explicitly.

J. Podolsky; J. B. Griffiths

1999-08-02T23:59:59.000Z

214

Brane World Cosmology In Jordan-Brans-Dicke Theory  

E-Print Network (OSTI)

We consider the embedding of 3+1 dimensional cosmology in 4+1 dimensional Jordan-Brans-Dicke theory. We show that exponentially growing and power law scale factors are implied. Whereas the 4+1 dimensional scalar field is approximately constant for each, the effective 3+1 dimensional scalar field is constant for exponentially growing scale factor and time dependent for power law scale factor.

M. Arik; D. Ciftci

2005-06-17T23:59:59.000Z

215

Self-Consistent Cosmological Simulations of DGP Braneworld Gravity  

Science Conference Proceedings (OSTI)

We perform cosmological N-body simulations of the Dvali-Gabadadze-Porrati braneworld model, by solving the full non-linear equations of motion for the scalar degree of freedom in this model, the brane bending mode. While coupling universally to matter, the brane-bending mode has self-interactions that become important as soon as the density field becomes non-linear. These self-interactions lead to a suppression of the field in high-density environments, and restore gravity to General Relativity. The code uses a multi-grid relaxation scheme to solve the non-linear field equation in the quasi-static approximation. We perform simulations of a flat self-accelerating DGP model without cosmological constant. However, the type of non-linear interactions of the brane-bending mode, which are the focus of this study, are generic to a wide class of braneworld cosmologies. The results of the DGP simulations are compared with standard gravity simulations assuming the same expansion history, and with DGP simulations using the linearized equation for the brane bending mode. This allows us to isolate the effects of the non-linear self-couplings of the field which are noticeable already on quasi-linear scales. We present results on the matter power spectrum and the halo mass function, and discuss the behavior of the brane bending mode within cosmological structure formation. We find that, independently of CMB constraints, the self-accelerating DGP model is strongly constrained by current weak lensing and cluster abundance measurements.

Schmidt, Fabian; /Chicago U., Astron. Astrophys. Ctr. /KICP, Chicago

2009-09-01T23:59:59.000Z

216

Thermodynamics of the apparent horizon in massive cosmology  

E-Print Network (OSTI)

Applying Clausius relation with energy-supply defined by the unified first law of thermodynamics formalism to the apparent horizon of a massive cosmological model proposed lately, the corrected entropic formula of the apparent horizon is obtained with the help of the modified Friedmann equations. This entropy-area relation, together with the identified internal energy, verifies the first law of thermodynamics for the apparent horizon with a volume change term for consistency. On the other hand, by means of the corrected entropy-area formula and the Clausius relation $\\delta Q=T dS$, the modified Friedmann equations governing the dynamical evolution of the universe are reproduced with the known energy density and pressure of massive graviton. The integration constant is found to correspond to a cosmological term which could be absorbed into the energy density of matter. Having established the correspondence of massive cosmology with the unified first law of thermodynamics on the apparent horizon, the validity of the generalized second law of thermodynamics is also discussed by assuming the thermal equilibrium between the apparent horizon and the matter field bounded by the apparent horizon. It is found that, in the limit $H_c\\rightarrow 0$ which recovers the Minkowski reference metric solution in the flat case, the generalized second law of thermodynamics holds if $\\alpha_3+4\\alpha_4<0$. Apart from that, even for the simplest model of dRGT massive cosmology with $\\alpha_3=\\alpha_4=0$, the generalized second law of thermodynamics could be violated.

Hui Li; Yi Zhang

2013-04-17T23:59:59.000Z

217

Specially Coupled Dark Energy in the Oscillating FRW Cosmology  

E-Print Network (OSTI)

We consider a four-dimensional flat-space Friedman universe, which is filled with two interacting ideal fluids (the coupling of dark energy with dark matter of special form). The gravitational equations of motion are solved. It is shown that in some cases there appears a periodic universe with finite-time cosmological singularities and also the universe becomes static in the remote future.

A. V. Timoshkin

2009-05-18T23:59:59.000Z

218

Post-Newtonian Celestial Dynamics in Cosmology: Field Equations  

E-Print Network (OSTI)

The present paper outlines theoretical principles of the post-Newtonian mechanics in the expanding universe. It is based upon the gauge-invariant theory of the Lagrangian perturbations of cosmological manifold caused by an isolated astronomical N-body system. We postulate that the background manifold is described by Friedman-Lemaitre-Robertson-Walker (FLRW) metric governed by two primary components - the dark matter and the dark energy. The dark matter is treated as an ideal fluid. The dark energy is described by a single scalar field with a potential which is hold unspecified as long as the theory permits. The Lagrangian of the dark matter and that of the scalar field are formulated in terms of the field variables. We use variational calculus to derive the gauge-invariant field equations of the post-Newtonian celestial mechanics of an isolated astronomical system in an expanding universe. These equations generalize the field equations of the post-Newtonian theory in asymptotically-flat spacetime by taking into account the cosmological effects explicitly. We introduce a new cosmological gauge which generalizes the harmonic gauge of the post-Newtonian theory in asymptotically-flat spacetime. This gauge significantly simplifies the gravitational field equations and allows finding out the approximations where the field equations can be fully decoupled and solved analytically. The residual gauge freedom is explored. The results of the present paper can be useful in the solar system for calculating more precise ephemerides of the solar system bodies on extremely long time intervals, in galactic astronomy to study the dynamics of clusters of galaxies, and in gravitational wave astronomy for discussing the impact of cosmology on generation and propagation of gravitational waves emitted by coalescing binaries and/or merging galactic nuclei.

Sergei Kopeikin; Alexander Petrov

2013-01-24T23:59:59.000Z

219

The Quantum Configuration Space of Loop Quantum Cosmology  

E-Print Network (OSTI)

The article gives an account of several aspects of the space known as the Bohr compactification of the line, featuring as the quantum configuration space in loop quantum cosmology, as well as of the corresponding configuration space realization of the so-called polymer representation. Analogies with loop quantum gravity are explored, providing an introduction to (part of) the mathematical structure of loop quantum gravity, in a technically simpler context.

J. M. Velhinho

2007-04-18T23:59:59.000Z

220

Neutron beta-decay, Standard Model and cosmology  

E-Print Network (OSTI)

The precise value of the neutron lifetime is of fundamental importance to particle physics and cosmology. The neutron lifetime recently obtained, 878.5 +/- 0.7stat +/- 0.3sys s, is the most accurate one to date. The new result for the neutron lifetime differs from the world average value by 6.5 standard deviations. The impact of the new result on testing of Standard Model and on data analysis for the primordial nucleosynthesis model is scrutinized.

A. P. Serebrov

2006-11-22T23:59:59.000Z

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221

Red Galaxies from Hot Halos in Cosmological Hydro Simulations  

E-Print Network (OSTI)

I highlight three results from cosmological hydrodynamic simulations that yield a realistic red sequence of galaxies: 1) Major galaxy mergers are not responsible for shutting off star-formation and forming the red sequence. Starvation in hot halos is. 2) Massive galaxies grow substantially (about a factor of 2 in mass) after being quenched, primarily via minor (1:5) mergers. 3) Hot halo quenching naturally explains why galaxies are red when they either (a) are massive or (b) live in dense environments.

Gabor, Jared

2012-01-01T23:59:59.000Z

222

FRW Quantum Cosmology with a Generalized Chaplygin Gas  

E-Print Network (OSTI)

Cosmologies with a Chaplygin gas have recently been explored with the objective of explaining the transition from a dust dominated epoch towards an accelerating expansion stage. We consider the hypothesis that the transition to the accelerated period involves a quantum mechanical process. Three physically admissible cases are possible. In particular, we identify a minisuperspace configuration with two Lorentzian sectors, separated by a classically forbidden region. The Hartle-Hawking and Vilenkin wave functions are computed, together with the transition amplitudes towards the accelerating epoch. Furthermore, it is found that for specific initial conditions, the parameters characterizing the generalized Chaplygin gas become related through an expression involving an integer $n$. We also introduce a phenomenological association between some brane-world scenarios and a FRW minisuperspace cosmology with a generalized Chaplygin gas. The aim is to promote a discussion and subsequent research on the quantum creation of brane cosmologies from such a perspective. Results suggest that the brane tension would become related with generalized Chaplygin gas parameters through another expression involving an integer.

Mariam Bouhmadi-Lopez; Paulo Vargas Moniz

2004-04-27T23:59:59.000Z

223

Conformal symmetry of gravity and the cosmological constant problem  

E-Print Network (OSTI)

In absence of matter Einstein gravity with a cosmological constant $\\La$ can be formulated as a scale-free theory depending only on the dimensionless coupling constant G \\Lambda where G is Newton constant. We derive the conformal field theory (CFT) and its improved stress-energy tensor that describe the dynamics of conformally flat perturbations of the metric. The CFT has the form of a constrained \\lambda \\phi^{4} field theory. In the cosmological framework the model describes the usual Friedmann-Robertson-Walker flat universe. The conformal symmetry of the gravity sector is broken by coupling with matter. The dimensional coupling constants G and \\Lambda are introduced by different terms in this coupling. If the vacuum of quantum matter fields respects the symmetry of the gravity sector, the vacuum energy has to be zero and the ``physical'' cosmological constant is generated by the coupling of gravity with matter. This could explain the tiny value of the observed energy density driving the accelerating expansion of the universe.

Mariano Cadoni

2006-06-29T23:59:59.000Z

224

New Cosmological Model and Its Implications on Observational Data Interpretation  

E-Print Network (OSTI)

The paradigm of \\Lambda CDM cosmology works impressively well and with the concept of inflation it explains the universe after the time of decoupling. However there are still a few concerns; after much effort there is no detection of dark matter and there are significant problems in the theoretical description of dark energy. We will consider a variant of the cosmological spherical shell model, within FRW formalism and will compare it with the standard \\Lambda CDM model. We will show that our new topological model satisfies cosmological principles and is consistent with all observable data, but that it may require new interpretation for some data. Considered will be constraints imposed on the model, as for instance the range for the size and allowed thickness of the shell, by the supernovae luminosity distance and CMB data. In this model propagation of the light is confined along the shell, which has as a consequence that observed CMB originated from one point or a limited space region. It allows to interpret the uniformity of the CMB without inflation scenario. In addition this removes any constraints on the uniformity of the universe at the early stage and opens a possibility that the universe was not uniform and that creation of galaxies and large structures is due to the inhomogeneities that originated in the Big Bang.

B. Vlahovic

2013-03-03T23:59:59.000Z

225

Fluid Mechanics Explains Cosmology, Dark Matter, Dark Energy, and Life  

E-Print Network (OSTI)

Observations of the interstellar medium by the Herschel, Planck etc. infrared satellites throw doubt on standard {\\Lambda}CDMHC cosmological processes to form gravitational structures. According to the Hydro-Gravitational-Dynamics (HGD) cosmology of Gibson (1996), and the quasar microlensing observations of Schild (1996), the dark matter of galaxies consists of Proto-Globular-star-Cluster (PGC) clumps of Earth-mass primordial gas planets in metastable equilibrium since PGCs began star production at 0.3 Myr by planet mergers. Dark energy and the accelerating expansion of the universe inferred from SuperNovae Ia are systematic dimming errors produced as frozen gas dark matter planets evaporate to form stars. Collisionless cold dark matter that clumps and hierarchically clusters does not exist. Clumps of PGCs began diffusion from the Milky Way Proto-Galaxy upon freezing at 14 Myr to give the Magellanic Clouds and the faint dwarf galaxies of the 10^22 m diameter baryonic dark matter Galaxy halo. The first stars persist as old globular star clusters (OGCs). Water oceans and the biological big bang occurred at 2-8 Myr. Life inevitably formed and evolved in the cosmological primordial organic soup provided by 10^80 big bang planets and their hot oceans as they gently merged to form larger binary planets and small binary stars.

Carl H. Gibson

2012-11-02T23:59:59.000Z

226

Non-minimal Higgs inflation and frame dependence in cosmology  

Science Conference Proceedings (OSTI)

We investigate a very general class of cosmological models with scalar fields non-minimally coupled to gravity. A particular representative in this class is given by the non-minimal Higgs inflation model in which the Standard Model Higgs boson and the inflaton are described by one and the same scalar particle. While the predictions of the non-minimal Higgs inflation scenario come numerically remarkably close to the recently discovered mass of the Higgs boson, there remains a conceptual problem in this model that is associated with the choice of the cosmological frame. While the classical theory is independent of this choice, we find by an explicit calculation that already the first quantum corrections induce a frame dependence. We give a geometrical explanation of this frame dependence by embedding it into a more general field theoretical context. From this analysis, some conceptional points in the long lasting cosmological debate: 'Jordan frame vs. Einstein frame' become more transparent and in principle can be resolved in a natural way.

Steinwachs, Christian F. [School of Mathematical Sciences, University of Nottingham University Park, Nottingham, NG7 2RD (United Kingdom); Kamenshchik, Alexander Yu. [Dipartimento di Fisica e Astronomia and INFN, Via Irnerio 46, 40126 Bologna, Italy and L.D. Landau Institute for Theoretical Physics of the Russian Academy of Sciences, Kosygin str. 2, 119334 Moscow (Russian Federation)

2013-02-21T23:59:59.000Z

227

The trace anomaly and dynamical vacuum energy in cosmology  

Science Conference Proceedings (OSTI)

The trace anomaly of conformal matter implies the existence of massless scalar poles in physical amplitudes involving the stress-energy tensor. These poles may be described by a local effective action with massless scalar fields, which couple to classical sources, contribute to gravitational scattering processes, and can have long range gravitational effects at macroscopic scales. In an effective field theory approach, the effective action of the anomaly is an infrared relevant term that should be added to the Einstein-Hilbert action of classical General Relativity to take account of macroscopic quantum effects. The additional scalar degrees of freedom contained in this effective action may be understood as responsible for both the Casimir effect in flat spacetime and large quantum backreaction effects at the horizon scale of cosmological spacetimes. These effects of the trace anomaly imply that the cosmological vacuum energy is dynamical, and its value depends on macroscopic boundary conditions at the cosmological horizon scale, rather than sensitivity to the extreme ultraviolet Planck scale.

Mottola, Emil [Los Alamos National Laboratory

2010-01-01T23:59:59.000Z

228

Cosmological lepton asymmetry with a nonzero mixing angle $\\theta_{13}$  

E-Print Network (OSTI)

While the baryon asymmetry of the Universe is nowadays well measured by cosmological observations, the bounds on the lepton asymmetry in the form of neutrinos are still significantly weaker. We place limits on the relic neutrino asymmetries using some of the latest cosmological data, taking into account the effect of flavor oscillations. We present our results for two different values of the neutrino mixing angle \\theta_{13}, and show that for large \\theta_{13} the limits on the total neutrino asymmetry become more stringent, diluting even large initial flavor asymmetries. In particular, we find that the present bounds are still dominated by the limits coming from Big Bang Nucleosynthesis, while the limits on the total neutrino mass from cosmological data are essentially independent of \\theta_{13}. Finally, we perform a forecast for COrE, taken as an example of a future CMB experiment, and find that it could improve the limits on the total lepton asymmetry approximately by up to a factor 5.

Castorina, Emanuele; Lattanzi, Massimiliano; Lesgourgues, Julien; Mangano, Gianpiero; Melchiorri, Alessandro; Pastor, Sergio

2012-01-01T23:59:59.000Z

229

Information content in the halo-model dark-matter power spectrum II: Multiple cosmological parameters  

E-Print Network (OSTI)

We investigate the cosmological Fisher information in the non-linear dark-matter power spectrum in the context of the halo model. We find that there is a plateau in information content on translinear scales which is generic to all cosmological parameters we tried. There is a rise in information on smaller scales, but we find that it is quite degenerate among different cosmological parameters (except, perhaps, the tilt). This suggests that it could be difficult to constrain cosmological parameters using the non-linear regime of the dark-matter power spectrum. We suggest ways to get around this problem, such as removing the largest haloes from consideration in survey analysis.

Mark C. Neyrinck; István Szapudi

2006-10-06T23:59:59.000Z

230

The First Generation of Stars in Lambda-CDM Cosmology  

DOE Green Energy (OSTI)

We have performed a large set of high-resolution cosmological simulations using smoothed particle hydrodynamics (SPH) to study the formation of the first luminous objects in the {Lambda}CDM cosmology. We follow the collapse of primordial gas clouds in eight early structures and document the scatter in the properties of the first star-forming clouds. Our first objects span formation redshifts from z {approx} 10 to z {approx} 50 and cover an order of magnitude in halo mass. We find that the physical properties of the central star-forming clouds are very similar in all of the simulated objects despite significant differences in formation redshift and environment. This suggests that the formation path of the first stars is largely independent of the collapse redshift; the physical properties of the clouds have little correlation with spin, mass, or assembly history of the host halo. The collapse of proto-stellar objects at higher redshifts progresses much more rapidly due to the higher densities, which accelerates the formation of molecular hydrogen, enhances initial cooling and shortens the dynamical timescales. The mass of the star-forming clouds cover a broad range, from a few hundred to a few thousand solar masses, and exhibit various morphologies: some have disk-like structures which are nearly rotational supported; others form flattened spheroids; still others form bars. All of them develop a single protostellar ''seed'' which does not fragment into multiple objects up to the moment that the central gas becomes optically thick to H{sub 2} cooling lines. At this time, the instantaneous mass accretion rate onto the centre varies significantly from object to object, with disk-like structures having the smallest mass accretion rates. The formation epoch and properties of the star-forming clouds are sensitive to the values of cosmological parameters.

Gao, Liang; /Durham U. /Garching, Max Planck Inst.; Abel, T.; /KIPAC, Menlo Park; Frenk, C.S.; Jenkins, A.; /Durham U.; Springel, V.; /Garching, Max Planck Inst.; Yoshida,; /Nagoya U.

2006-10-10T23:59:59.000Z

231

Equations of State in the Brans-Dicke cosmology  

E-Print Network (OSTI)

We investigate the Brans-Dicke (BD) theory with the potential as cosmological model to explain the present accelerating universe. In this work, we consider the BD field as a perfect fluid with the energy density and pressure in the Jordan frame. Introducing the power-law potential and the interaction with the cold dark matter, we obtain the phantom divide which is confirmed by the native and effective equation of state. Also we can describe the metric $f(R)$ gravity with an appropriate potential, which shows a future crossing of phantom divide in viable $f(R)$ gravity models when employing the native and effective equations of state.

Hyung Won Lee; Kyoung Yee Kim; Yun Soo Myung

2010-10-27T23:59:59.000Z

232

Rippled Cosmological Dark Matter from Damped Oscillating Newton Constant  

E-Print Network (OSTI)

Let the reciprocal Newton 'constant' be an apparently non-dynamical Brans-Dicke scalar field damped oscillating towards its General Relativistic VEV. We show, without introducing additional matter fields or dust, that the corresponding cosmological evolution averagely resembles, in the Jordan frame, the familiar dark radiation -> dark matter -> dark energy domination sequence. The fingerprints of our theory are fine ripples, hopefully testable, in the FRW scale factor; they die away at the General Relativity limit. The possibility that the Brans-Dicke scalar also serves as the inflaton is favorably examined.

Aharon Davidson

2004-09-15T23:59:59.000Z

233

Comment on the Appropriate Null Hypothesis for Cosmological Birefringence  

E-Print Network (OSTI)

A recent paper (Nodland and Ralston, PRL 78, 3043, astro-ph/9704196) claims to have detected evidence for birefringence in the propagation of radio waves across cosmological distances. In order to assess the statistical significance of their results, the authors analyze simulated data sets, finding a stronger correlation in the real data than in the simulations. Unfortunately, the procedure used for generating the simulated data sets is based on an incorrect null hypothesis. Furthermore, the correct null hypothesis would lead to a stronger correlation in the simulated data sets, weakening the case for birefringence. We conclude that the paper's analysis does not provide statistically significant evidence of birefringence.

Daniel J. Eisenstein; Emory F. Bunn

1997-04-24T23:59:59.000Z

234

Statefinder hierarchy of bimetric and galileon models for concordance cosmology  

E-Print Network (OSTI)

In this paper, we use Statefinder hierarchy method to distinguish between bimetric theory of massive gravity, galileon modified gravity and DGP models applied to late time expansion of the universe. We also carry out comparison between bimetric and DGP models using Statefinder pairs {r, s} and {r, q}. We show that statefinder diagnostic can differentiate between {\\Lambda}CDM and above mentioned cosmological models of dark energy, and finally show that Statefinder S2 is an excellent discriminant of {\\Lambda}CDM and modified gravity models.

R. Myrzakulov; M. Shahalam

2013-02-28T23:59:59.000Z

235

Tachyon cosmology, supernovae data, and the big brake singularity  

SciTech Connect

We compare the existing observational data on type Ia supernovae with the evolutions of the Universe predicted by a one-parameter family of tachyon models which we have introduced recently [Phys. Rev. D 69, 123512 (2004)]. Among the set of the trajectories of the model which are compatible with the data there is a consistent subset for which the Universe ends up in a new type of soft cosmological singularity dubbed big brake. This opens up yet another scenario for the future history of the Universe besides the one predicted by the standard {lambda}CDM model.

Keresztes, Z.; Gergely, L. A.; Gorini, V.; Moschella, U.; Kamenshchik, A. Yu. [Department of Theoretical Physics, University of Szeged, Tisza Lajos krt 84-86, Szeged 6720 (Hungary); Department of Experimental Physics, University of Szeged, Dom Ter 9, Szeged 6720 (Hungary); Department of Theoretical Physics, University of Szeged, Tisza Lajos krt 84-86, Szeged 6720 (Hungary); Department of Experimental Physics, University of Szeged, Dom Ter 9, Szeged 6720 (Hungary); Department of Applied Science, London South Bank University, 103 Borough Road, London SE1 OAA (United Kingdom); Dipartimento di Scienze Fisiche e Mathematiche, Universita dell'Insubria, Via Valleggio 11, 22100 Como (Italy); INFN, sezione di Milano, Via Celoria 16, 20133 Milano (Italy); Dipartimento di Fisica and INFN, via Irnerio 46, 40126 Bologna (Italy); L. D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, Kosygin street 2, 119334 Moscow (Russian Federation)

2009-04-15T23:59:59.000Z

236

Gamma ray burst distances and the timescape cosmology  

E-Print Network (OSTI)

Gamma ray bursts can potentially be used as distance indicators, providing the possibility of extending the Hubble diagram to redshifts ~7. Here we follow the analysis of Schaefer (2007), with the aim of distinguishing the timescape cosmological model from the \\LambdaCDM model by means of the additional leverage provided by GRBs in the range 2 < z < 7. We find that the timescape model fits the GRB sample slightly better than the \\LambdaCDM model, but that the systematic uncertainties are still too little understood to distinguish the models.

Peter R. Smale

2011-07-27T23:59:59.000Z

237

Bianchi type-II cosmological model: some remarks  

E-Print Network (OSTI)

Within the framework of Bianchi type-II (BII) cosmological model the behavior of matter distribution has been considered. It is shown that the non-zero off-diagonal component of Einstein tensor implies some severe restriction on the choice of matter distribution. In particular for a locally rotationally symmetric Bianchi type-II (LRS BII) space-time it is proved that the matter distribution should be strictly isotropic if the corresponding matter field possesses only non-zero diagonal components of the energy-momentum tensor.

Bijan Saha

2010-10-09T23:59:59.000Z

238

2HOT: an improved parallel hashed oct-tree n-body algorithm for cosmological simulation  

Science Conference Proceedings (OSTI)

We report on improvements made over the past two decades to our adaptive treecode N-body method (HOT). A mathematical and computational approach to the cosmological N-body problem is described, with performance and scalability measured up to 256k (218) ... Keywords: N-body, computational cosmology, fast multipole method

Michael S. Warren

2013-11-01T23:59:59.000Z

239

Cosmological non-Gaussian signature detection: comparing performance of different statistical tests  

Science Conference Proceedings (OSTI)

Currently, it appears that the best method for non-Gaussianity detection in the cosmic microwave background (CMB) consists in calculating the kurtosis of the wavelet coefficients. We know that wavelet-kurtosis outperforms other methods such as the bispectrum, ... Keywords: cosmological microwave background, cosmology, curvelet, multiscale method, non-Gaussianity detection, wavelet

J. Jin; J.-L. Starck; D. L. Donoho; N. Aghanim; O. Forni

2005-01-01T23:59:59.000Z

240

Solutions to Cosmological Problems with Energy Conservation and Varying c, G and Lambda  

E-Print Network (OSTI)

The flatness and cosmological constant problems are solved with varying speed of light c, gravitational coupling strength G and cosmological parameter Lambda, by explicitly assuming energy conservation of observed matter. The present solution to the flatness problem is the same as the previous solution in which energy conservation was absent.

P. Gopakumar; G. V. Vijayagovindan

2000-03-26T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
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241

A Compact High Energy Camera for the Cherenkov Telescope Array  

E-Print Network (OSTI)

The Compact High Energy Camera (CHEC) is a camera-development project involving UK, US, Japanese and Dutch institutes for the dual-mirror Small-Sized Telescopes (SST-2M) of the Cherenkov Telescope Array (CTA). Two CHEC prototypes, based on different photosensors are funded and will be assembled and tested in the UK over the next ~18 months. CHEC is designed to record flashes of Cherenkov light lasting from a few to a hundred nanoseconds, with typical RMS image width and length of ~0.2 x 1.0 degrees, and has a 9 degree field of view. The physical camera geometry is dictated by the telescope optics: a curved focal surface with radius of curvature 1m and diameter ~35cm is required. CHEC is designed to work with both the ASTRI and GATE SST-2M telescope structures and will include an internal LED flasher system for calibration. The first CHEC prototype will be based on multi-anode photomultipliers (MAPMs) and the second on silicon photomultipliers (SiPMs or MPPCs). The first prototype will soon be installed on the...

Daniel, M K; Berge, D; Buckley, J; Chadwick, P M; Cotter, G; Funk, S; Greenshaw, T; Hidaka, N; Hinton, J; Lapington, J; Markoff, S; Moore, P; Nolan, S; Ohm, S; Okumura, A; Ross, D; Sapozhnikov, L; Schmoll, J; Sutcliffe, P; Sykes, J; Tajima, H; Varner, G S; Vandenbroucke, J; Vink, J; Williams, D

2013-01-01T23:59:59.000Z

242

Design of a telescope-occulter system for THEIA  

E-Print Network (OSTI)

The Telescope for Habitable Exoplanets and Interstellar/Intergalactic Astronomy (THEIA) is a mission concept study for a flagship-class telescope-occulter system to search for terrestrial planets and perform general astrophysics with a space-based 4m telescope. A number of design options were considered for the occulter and telescope optical systems; in this paper we discuss the design of occulters and coronagraphs for THEIA and examine their merits. We present two optimized occulters: a 25.6m-radius occulter with 19m petals that achieves 10^-12 suppression from 250-1000nm with a 75mas inner working angle, and a 20.0m-radius occulter with 10m petals that achieves 10^-12 suppression from 250-700nm with a 75mas inner working angle. For more widely separated planets (IWA > 108mas), this second occulter is designed to operate at a second closer distance where it provides 10^-12 suppression from 700-1000nm. We have also explored occulter/coronagraph hybrid systems, and found that an AIC coronagraph that exploits t...

Cady, Eric; Dumont, Philip; Egerman, Robert; Kasdin, N Jeremy; Linfield, Roger; Lisman, Doug; Savransky, Dmitry; Seager, Sara; Shaklan, Stuart; Spergel, David; Tenerelli, Domenick; Vanderbei, Robert

2009-01-01T23:59:59.000Z

243

TeV Dark Matter detection by Atmospheric Cerenkov Telescopes  

E-Print Network (OSTI)

Ground based Atmospheric Cerenkov Telescopes have recently unveiled a TeV gamma-ray signal from the direction of the Galactic Centre. We examine whether these gamma-rays, observed by the VERITAS, CANGAROO-II and HESS collaborations, may arise from annihilations of dark matter particles. Emission from nearby dwarf spheroidals, such as Sagittarius, could provide a test of this scenario.

Francesc Ferrer

2005-05-19T23:59:59.000Z

244

Google Sky, WorldWide Telescope & Celestia in the  

E-Print Network (OSTI)

Google Sky, WorldWide Telescope & Celestia in the Undergraduate Non-Science Major Classroom & Lab of Public Outreach Dept.Astronomy & Astrophysics University of Chicago Sky #12;Google Sky, World interactive labs and self-directed modules that utilize new, emerging, software tools, specifically Google Sky

Collar, Juan I.

245

Indirect Search for Dark Matter with the ANTARES Neutrino Telescope  

Science Conference Proceedings (OSTI)

One of the goals of the ANTARES underwater neutrino telescope is the search for dark matter in the universe. In this paper the first results on the search for dark matter in the Sun with ANTARES in its 5 line configuration, as well as sensitivity studies with the full ANTARES detector are presented.

Loucatos, S. [IRFU-SPP, CEA-Saclay, 91191 Gif sur Yvette (France)

2010-02-10T23:59:59.000Z

246

The Timepix Telescope for High Performance Particle Tracking  

E-Print Network (OSTI)

The Timepix particle tracking telescope has been developed as part of the LHCb VELO Upgrade project, supported by the Medipix Collaboration and the AIDA framework. It is a primary piece of infrastructure for the VELO Upgrade project and is being used for the development of new sensors and front end technologies for several upcoming LHC trackers and vertexing systems. The telescope is designed around the dual capability of the Timepix ASICs to provide information about either the deposited charge or the timing information from tracks traversing the 14 x 14mm matrix of 55 x 55 um pixels. The rate of reconstructed tracks available is optimised by taking advantage of the shutter driven readout architecture of the Timepix chip, operated with existing readout systems. Results of tests conducted in the SPS North Area beam facility at CERN show that the telescope typically provides reconstructed track rates during the beam spills of between 3.5 and 7.5 kHz, depending on beam conditions. The tracks are time stamped with 1 ns resolution with an efficiency of above 98% and provide a pointing resolution at the centre of the telescope of 1.6 um . By dropping the time stamping requirement the rate can be increased to 15 kHz, at the expense of a small increase in background. The telescope infrastructure provides CO2 cooling and a flexible mechanical interface to the device under test, and has been used for a wide range of measurements during the 2011-2012 data taking campaigns.

Kazuyoshi Akiba; Per Arne Ronning; Martin van Beuzekom; Vincent van Beveren; Silvia Borghi; Henk Boterenbrood; Jan Buytaert; Paula Collins; Alvaro Dosil Suarez; Raphael Dumps; Lars Eklund; Daniel Esperante; Abraham Gallas; Hamish Gordon; Bas van der Heijden; Christoph Hombach; Daniel Hynds; Malcolm John; Alexander Leflat; Yi Ming Li; Ian Longstaff; Alexander Morton; Noritsugu Nakatsuka; Andre Nomerotski; Chris Parkes; Eliseo Perez Trigo; Richard Plackett; Matthew M. Reid; Pablo Rodriguez Perez; Heinrich Schindler; Tomasz Szumlak; Panagiotis Tsopelas; Carlos Vazquez Sierra; Jaap Velthuis; Michal Wysokinski

2013-04-18T23:59:59.000Z

247

The Taiwanese-American Occultation Survey: The Multi-Telescope Robotic Observatory  

E-Print Network (OSTI)

The Taiwanese-American Occultation Survey (TAOS) operates four telescopes to search for occultations of stars by Kuiper Belt Objects. This paper provides a detailed description of the TAOS multi-telescope system.

Lehner, M J; Wang, J -H; Marshall, S L; Schwamb, M E; Zhang, Z -W; Bianco, F B; Giammarco, J; Porrata, R; Alcock, C; Axelrod, T; Byun, Y -I; Chen, W P; Cook, K H; Davé, R; King, S -K; Lee, T; Lin, H -C; Wang, S -Y

2008-01-01T23:59:59.000Z

248

Building a better flat-field : an instrumental calibration projector for the Large Synoptic Survey Telescope  

E-Print Network (OSTI)

The Large Synoptic Survey Telescope (LSST) is a next-generation ground-based survey telescope whose science objectives demand photometric precision at the 1% level. Recent efforts towards 1% photometry have advocated in-situ ...

Vaz, Amali L

2011-01-01T23:59:59.000Z

249

Loop Quantum Cosmology in Bianchi Type I Models: Analytical Investigation  

E-Print Network (OSTI)

The comprehensive formulation for loop quantum cosmology in the spatially flat, isotropic model was recently constructed. In this paper, the methods are extended to the anisotropic Bianchi I cosmology. Both the precursor and the improved strategies are applied and the expected results are established: (i) the scalar field again serves as an internal clock and is treated as emergent time; (ii) the total Hamiltonian constraint is derived by imposing the fundamental discreteness and gives the evolution as a difference equation; and (iii) the physical Hilbert space, Dirac observables and semi-classical states are constructed rigorously. It is also shown that the state in the kinematical Hilbert space associated with the classical singularity is decoupled in the difference evolution equation, indicating that the big bounce may take place when any of the area scales undergoes the vanishing behavior. The investigation affirms the robustness of the framework used in the isotropic model by enlarging its domain of validity and provides foundations to conduct the detailed numerical analysis.

Dah-Wei Chiou

2006-09-07T23:59:59.000Z

250

Molecular hydrogen regulated star formation in cosmological SPH simulations  

E-Print Network (OSTI)

It has been shown observationally that star formation (SF) correlates tightly with the presence of molecular hydrogen (H2). Therefore it would be important to investigate its implication on galaxy formation in a cosmological context. In the present work, we track the H2 mass fraction within our cosmological smoothed particle hydrodynamics (SPH) code GADGET-3 using an equilibrium analytic model by Krumholz et al. This model allows us to regulate the star formation in our simulation by the local abundance of H2 rather than the total cold gas density, and naturally introduce the dependence of star formation on metallicity. We investigate implications of the equilibrium H2-based SF model on galaxy population properties, such as the stellar-to-halo mass ratio (SHMR), baryon fraction, cosmic star formation rate density (SFRD), galaxy specific SFR, galaxy stellar mass functions (GSMF), and Kennicutt-Schmidt (KS) relationship. The advantage of our work over the previous ones is having a large sample of simulated gala...

Thompson, Robert; Jaacks, Jason; Choi, Jun-Hwan

2013-01-01T23:59:59.000Z

251

The Monotonicity of the Gravitational Entropy Scalar within Quiescent Cosmology  

E-Print Network (OSTI)

In this paper we show that Quiescent Cosmology [1, 2, 3] is consistent with Penrose's Weyl Curvature Hypothesis and the notion of gravitational entropy [4]. Gravitational entropy, from a conceptual point of view, acts in an opposite fashion to the more familiar notion of entropy. A closed system of gravitating particles will coalesce whereas a collection of gas particles will tend to diffuse; regarding increasing entropy, these two scenarios are identical. What has been shown previously [2, 3] is that gravitational entropy at the initial singularity predicted by Quiescent Cosmology - the Isotropic Past Singularity (IPS) - tends to zero. The results from this paper show that not only is this the case but that gravitational entropy increases as this singularity evolves. In the first section of this paper we present relevant background information and motivation. In the second section of this paper we present the main results of this paper. Our third section contains a discussion of how this result will inspire future research before we make concluding remarks in our final section.

Philip Threlfall; Susan M. Scott

2012-11-26T23:59:59.000Z

252

Cosmology, Time's Arrow, and That Old Double Standard  

E-Print Network (OSTI)

It is widely accepted that temporal asymmetry is largely a cosmological problem; the task of explaining temporal asymmetry reduces in the main to that of explaining an aspect of the condition of the early universe. However, cosmologists who discuss these issues often make mistakes similar to those that plagued nineteenth century discussions of the statistical foundations of thermodynamics. In particular, they are often guilty of applying temporal "double standards" of various kinds---e.g., in failing to recognise that certain statistical arguments apply with equal force in either temporal direction. This paper aims to clarify the issue as to what would count as adequate explanation of cosmological time asymmetry. A particular concern is the question whether it is possible to explain why entropy is low near the Big Bang without showing that it must also be low near a Big Crunch, in the event that the universe recollapses. I criticise some of the objections raised to this possibility, showing that these too oft...

Price, Huw

2009-01-01T23:59:59.000Z

253

Positive and Negative Energy Symmetry and the Cosmological Constant Problem  

E-Print Network (OSTI)

The action for gravity and the standard model includes, as well as the positive energy fermion and boson fields, negative energy fields. The Hamiltonian for the action leads through a positive and negative energy symmetry of the vacuum to a cancellation of the zero-point vacuum energy and a vanishing cosmological constant in the presence of a gravitational field solving the cosmological constant problem. To guarantee the quasi-stability of the vacuum, we postulate a positive energy sector and a negative energy sector in the universe which are identical copies of the standard model. They interact only weakly through gravity. As in the case of antimatter, the negative energy matter is not found naturally on Earth or in the universe. A positive energy spectrum and a consistent unitary field theory for a pseudo-Hermitian Hamiltonian is obtained by demanding that the pseudo-Hamiltonian is ${\\cal P}{\\cal T}$ symmetric. The quadratic divergences in the two-point vacuum fluctuations and the self-energy of a scalar field are removed. The finite scalar field self-energy can avoid the Higgs hierarchy problem in the standard model.

J. W. Moffat

2006-10-13T23:59:59.000Z

254

Cosmological Models in Modified f(R) Gravity Theories  

E-Print Network (OSTI)

The actual accelerated expansion of the universe continues being a mystery in physics. Some models had been proposed for this explanations, among them the dark energy, which however has problems of experimental character as well as theoretical. Other approximations, like modified gravity theories are an interesting alternative for this problem. Motivated in this approach we study cosmological models in f(R) theories which are natural extension of General Relativity with arbitrary functions of the Ricci scalar. One chapter has dedicated to obtain the modified field equations in the metric formalism of f(R) theories, including the discussion about boundary terms in the action. Later, we apply these equations in order to describe the dynamics of the universe, using for this as space-time, the FLRW universe. We focus our study in the problem of cosmological distances in f(R) theories. From the study of the Geodesic Deviation Equation (GDE) in this modified scenario, we obtain differential equations for the angular diameter distance, and as an extension, the Dyer-Roeder like equation in f(R) gravity.

Alejandro Guarnizo

2012-11-11T23:59:59.000Z

255

Are there cosmological evolution of Gamma-Ray Bursts?  

E-Print Network (OSTI)

The variability of gamma-ray burst (GRB) is thought to be correlated with its absolute peak luminosity, and this relation had been used to derive an estimate of the redshifts of GRBs. Recently Amati et al. present the results of spectral and energetic properties of several GRBs with know redshifts. Here we analyse the properties of two group GRBs, one group with known redshift from afterglow observation, and another group with redshift derived from the luminosity- variability relation. We study the redshift dependence of various GRBs features in their cosmological rest frames, including the burst duration, the isotropic luminosity and radiated energy, and the peak energy Ep of ?F? spectra. We find that the properties of these two group GRBs are very similar, which strongly implies that the redshift derived from the luminosity-variability relation may be reliable. If this is true, then we see that the burst properties, such as their intrinsic duration, luminosity, radiated energy and peak energy Ep, are all correlated with the redshift, which means that the GRBs features are redshift dependent, i.e. there are cosmological evolution of gamma-ray bursts, and this can provide an interesting clue to the nature of GRBs. Furthermore we find that the Ep- L relation strongly supports the idea that gamma-ray burst emission comes from the internal shock. Key words: gamma rays: bursts

D. M. Wei

2008-01-01T23:59:59.000Z

256

Development of a New Laser Beacon for Time Calibration in the ANTARES Neutrino Telescope  

Science Conference Proceedings (OSTI)

The ANTARES collaboration has built a deep sea neutrino telescope in the Mediterranean Sea consisting of a matrix of pressure resistant glass spheres holding large area photomultipliers. The aim of the telescope is to observe cosmic neutrinos through ... Keywords: Deep Sea Instrumentation, Time Calibration Device, Neutrino Telescope, Laser Beacon.

Umberto Emanuele; Diego Real; Fernando Urbano; Juan de Dios Zornoza; Juan Zuniga

2011-10-01T23:59:59.000Z

257

Design of light concentrators for Cherenkov telescope observatories  

E-Print Network (OSTI)

The Cherenkov Telescope Array (CTA) will be the largest cosmic gamma ray detector ever built in the world. It will be installed at two different sites in the North and South hemispheres and should be operational for about 30 years. In order to cover the desired energy range, the CTA is composed of typically 50-100 collecting telescopes of various sizes (from 6 to 24-m diameters). Most of them are equipped with a focal plane camera consisting of 1500 to 2000 Photomultipliers (PM) equipped with light concentrating optics, whose double function is to maximize the amount of Cherenkov light detected by the photo-sensors, and to block any stray light originating from the terrestrial environment. Two different optical solutions have been designed, respectively based on a Compound Parabolic Concentrator (CPC), and on a purely dioptric concentrating lens. In this communication are described the technical specifications, optical designs and performance of the different solutions envisioned for all these light concentra...

Hénault, F; jocou, L; Khélifi, B; Manigot, P; Hormigos, S; Knodlseder, J; Olive, J F; Jean, P; Punch, M

2013-01-01T23:59:59.000Z

258

Thermal characteristics of a classical solar telescope primary mirror  

E-Print Network (OSTI)

We present a detailed thermal and structural analysis of a 2m class solar telescope mirror which is subjected to a varying heat load at an observatory site. A 3-dimensional heat transfer model of the mirror takes into account the heating caused by a smooth and gradual increase of the solar flux during the day-time observations and cooling resulting from the exponentially decaying ambient temperature at night. The thermal and structural response of two competing materials for optical telescopes, namely Silicon Carbide -best known for excellent heat conductivity and Zerodur -preferred for its extremely low coefficient of thermal expansion, is investigated in detail. The insight gained from these simulations will provide a valuable input for devising an efficient and stable thermal control system for the primary mirror.

Banyal, Ravinder K

2011-01-01T23:59:59.000Z

259

The ANTARES Neutrino Telescope: status and first results  

E-Print Network (OSTI)

Completed in May 2008, the ANTARES neutrino telescope is located in the Mediterranean Sea, 40 km off the coast of Toulon, at a depth of about 2500 m. Consisting of 12 detector lines housing nearly 900 optical modules, the ANTARES telescope is currently the largest neutrino detector in the northern hemisphere. Utilising the Mediterranean Sea as a detecting medium, the detection principle of ANTARES relies on the observation of Cherenkov photons emitted by charged relativistic leptons, produced through neutrino interactions with the surrounding water and seabed, using a 3 dimensional lattice of photomultiplier tubes. In this paper we review the current status of the ANTARES experiment, highlighting some of the results from it's first year of full operation.

Brown, Anthony M

2009-01-01T23:59:59.000Z

260

FERMI LARGE AREA TELESCOPE OBSERVATIONS OF GRB 110625A  

SciTech Connect

Gamma-ray bursts (GRBs) that emit photons at GeV energies form a small but significant population of GRBs. However, the number of GRBs whose GeV-emitting period is simultaneously observed in X-rays remains small. We report {gamma}-ray observations of GRB 110625A using Fermi's Large Area Telescope in the energy range 100 MeV-20 GeV. Gamma-ray emission at these energies was clearly detected using data taken between 180 s and 580 s after the burst, an epoch after the prompt emission phase. The GeV light curve differs from a simple power-law decay, and probably consists of two emission periods. Simultaneous Swift X-Ray Telescope observations did not show flaring behaviors as in the case of GRB 100728A. We discuss the possibility that the GeV emission is the synchrotron self-Compton radiation of underlying ultraviolet flares.

Tam, P. H. T.; Kong, A. K. H. [Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Fan Yizhong, E-mail: phtam@phys.nthu.edu.tw [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)

2012-08-01T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


261

Mid-Infrared Instrumentation for the European Extremely Large Telescope  

E-Print Network (OSTI)

MIDIR is the proposed thermal/mid-IR imager and spectrograph for the European Extremely Large Telescope (E-ELT). It will cover the wavelength range of 3 to at least 20 microns. Designed for diffraction-limited performance over the entire wavelength range, MIDIR will require an adaptive optics system; a cryogenically cooled system could offer optimal performance in the IR, and this is a critical aspect of the instrument design. We present here an overview of the project, including a discussion of MIDIR's science goals and a comparison with other infrared (IR) facilities planned in the next decade; top level requirements derived from these goals are outlined. We describe the optical and mechanical design work carried out in the context of a conceptual design study, and discuss some important issues to emerge from this work, related to the design, operation and calibration of the instrument. The impact of telescope optical design choices on the requirements for the MIDIR instrument is demonstrated.

S. Kendrew; B. Brandl; R. Lenzen; L. Venema; H. U. Käufl; G. Finger; A. Glasse; R. Stuik

2007-08-23T23:59:59.000Z

262

Observation of GRBs by the MAGIC Telescope, Status and Outlook  

E-Print Network (OSTI)

Observation of Gamma Ray Bursts (GRBs) in the Very High Energy (VHE) domain will provide important information on the physical conditions in GRB outflows. The MAGIC telescope is the best suited Imaging Atmospheric Cherenkov Telescope (IACT) for these observations. Thanks to its fast repositioning time and low energy threshold, MAGIC is able to start quickly the follow-up observation, triggered by an alert from the GRB Coordinates Network (GCN), and observe the prompt emission and early afterglow phase from GRBs. In the last two years of operation several GRB follow-up observations were performed by MAGIC, however, until now without successful detection of VHE gamma rays above threshold energies >100 GeV. In this paper we revise the expectations for the GRB observations with MAGIC, based on the experience from the last years of operation.

D. Bastieri; N. Galante; M. Garczarczyk; M. Gaug; F. Longo; S. Mizobuchi; V. Scapin

2007-09-10T23:59:59.000Z

263

Minimal Stereoscopic Analysis for Imaging Atmospheric Cherenkov Telescope Arrays  

E-Print Network (OSTI)

The trajectory of a primary gamma-ray detected with an array of at least four atmospheric Cherenkov imaging telescopes can be reconstructed from the shower image centroid positions and geometrical considerations independent of the primary energy. Using only the image centroid positions some cosmic-ray discrimination is also possible. This minimal approach opens the possibility of pushing the analysis threshold to lower values, close to the hardware threshold.

S. LeBohec; C. Duke; P. Jordan

2006-08-15T23:59:59.000Z

264

A MEASUREMENT OF SECONDARY COSMIC MICROWAVE BACKGROUND ANISOTROPIES WITH TWO YEARS OF SOUTH POLE TELESCOPE OBSERVATIONS  

SciTech Connect

We present the first three-frequency South Pole Telescope (SPT) cosmic microwave background (CMB) power spectra. The band powers presented here cover angular scales 2000 < l < 9400 in frequency bands centered at 95, 150, and 220 GHz. At these frequencies and angular scales, a combination of the primary CMB anisotropy, thermal and kinetic Sunyaev-Zel'dovich (SZ) effects, radio galaxies, and cosmic infrared background (CIB) contributes to the signal. We combine Planck/HFI and SPT data at 220 GHz to constrain the amplitude and shape of the CIB power spectrum and find strong evidence for nonlinear clustering. We explore the SZ results using a variety of cosmological models for the CMB and CIB anisotropies and find them to be robust with one exception: allowing for spatial correlations between the thermal SZ effect and CIB significantly degrades the SZ constraints. Neglecting this potential correlation, we find the thermal SZ power at 150 GHz and l = 3000 to be 3.65 {+-} 0.69 {mu}K{sup 2}, and set an upper limit on the kinetic SZ power to be less than 2.8 {mu}K{sup 2} at 95% confidence. When a correlation between the thermal SZ and CIB is allowed, we constrain a linear combination of thermal and kinetic SZ power: D{sup tSZ}{sub 3000} + 0.5D{sub 3000}{sup kSZ} = 4.60 {+-} 0.63 {mu}K{sup 2}, consistent with earlier measurements. We use the measured thermal SZ power and an analytic, thermal SZ model calibrated with simulations to determine {sigma}{sub 8} = 0.807 {+-} 0.016. Modeling uncertainties involving the astrophysics of the intracluster medium rather than the statistical uncertainty in the measured band powers are the dominant source of uncertainty on {sigma}{sub 8}. We also place an upper limit on the kinetic SZ power produced by patchy reionization; a companion paper uses these limits to constrain the reionization history of the universe.

Reichardt, C. L.; George, E. M.; Holzapfel, W. L. [Department of Physics, University of California, Berkeley, CA 94720 (United States); Shaw, L. [Department of Physics, Yale University, P.O. Box 208210, New Haven, CT 06520-8120 (United States); Zahn, O. [Berkeley Center for Cosmological Physics, Department of Physics, University of California, and Lawrence Berkeley National Labs, Berkeley, CA 94720 (United States); Aird, K. A. [University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Benson, B. A.; Bleem, L. E.; Carlstrom, J. E.; Chang, C. L.; Crawford, T. M.; Crites, A. T.; Hoover, S. [Kavli Institute for Cosmological Physics, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Cho, H. M. [NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO 80305 (United States); De Haan, T.; Dobbs, M. A.; Dudley, J.; Holder, G. P. [Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8 (Canada); Halverson, N. W. [Department of Astrophysical and Planetary Sciences and Department of Physics, University of Colorado, Boulder, CO 80309 (United States); Hou, Z., E-mail: cr@bolo.berkeley.edu [Department of Physics, University of California, One Shields Avenue, Davis, CA 95616 (United States); and others

2012-08-10T23:59:59.000Z

265

Tests & Calibration on Ultra Violet Imaging Telescope (UVIT)  

E-Print Network (OSTI)

Ultra Violet Imaging Telescope on ASTROSAT Satellite mission is a suite of Far Ultra Violet (FUV; 130 to 180 nm), Near Ultra Violet (NUV; 200 to 300 nm) and Visible band (VIS; 320 to 550nm) imagers. ASTROSAT is a first multi wavelength mission of INDIA. UVIT will image the selected regions of the sky simultaneously in three channels & observe young stars, galaxies, bright UV Sources. FOV in each of the 3 channels is about 28 arc-minute. Targeted angular resolution in the resulting UV images is better than 1.8 arc-second (better than 2.0 arc-second for the visible channel). Two identical co-aligned telescopes (T1, T2) of Ritchey-Chretien configuration (Primary mirror of 375 mm diameter) collect the celestial radiation and feed to the detector system via a selectable filter on a filter wheel mechanism; gratings are available in the filter wheels of FUV and NUV channels for slit-less low resolution spectroscopy. The detector system for each of the 3 channels is generically identical. One telescope images in ...

Kumar, Amit; Kamath, P U; Postma, Joe; Kathiravan, S; Mahesh, P K; S, Nagbhushana; Navalgund, K H; Rajkumar, N; Rao, M N; Sarma, K S; Sriram, S; Stalin, C S; Tandon, S N

2012-01-01T23:59:59.000Z

266

A Central Laser Facility for the Cherenkov Telescope Array  

E-Print Network (OSTI)

A Central Laser Facility is a system often used in astroparticle experiments based on arrays of fluorescence or Cherenkov light detectors. The instrument is based on a laser source positioned at a certain distance from the array, emitting fast light pulses in the vertical direction with the aim of calibrating the array and/or measuring the atmospheric transmission. In view of the future Cherenkov Telescope Array (CTA), a similar device could provide a calibration of the whole installation, both relative, i.e. each individual telescope with respect to the rest of the array, and absolute, with a precision better than 10%, if certain design requirements are met. Additionally, a precise monitoring of the sensitivity of each telescope can be made on time-scales of days to years. During calibration runs of the central laser facility, all detectors will be pointed towards the same portion of the laser beam at a given altitude. Simulations of the possible configurations of a Central Laser Facility for CTA (varying la...

Gaug, Markus; Cilmo, Marco; Di Pierro, Federico; Tonachini, Aurelio; Vallania, Piero

2013-01-01T23:59:59.000Z

267

Reconstruction of some cosmological models in f(R,T) gravity  

E-Print Network (OSTI)

In this paper, we reconstruct cosmological models in the framework of $f(R,T)$ gravity, where $R$ is the Ricci scalar and $T$ is the trace of the stress-energy tensor. We show that the dust fluid reproduces $\\Lambda $CDM, phantom-non-phantom era and the phantom cosmology. Further, we reconstruct different cosmological models including, Chaplygin gas, scalar field with some specific forms of $f(R,T)$. Our numerical simulation for Hubble parameter shows good agreement with the BAO observational data for low redshifts $z<2$.

Mubasher Jamil; D. Momeni; Muhammad Raza; Ratbay Myrzakulov

2011-07-28T23:59:59.000Z

268

A Note on the Local Cosmological Constant and the Dark Energy Coincidence Problem  

E-Print Network (OSTI)

It has been suggested that the Dark Energy Coincidence Problem could be interpreted as a possible link between the cosmological constant and a massive graviton. We show that by using that link and models for the graviton mass a dark energy density can be obtained that is indeed very close to measurements by WMAP. As a consequence of the models, the cosmological constant was found to depend on the density of matter. A brief outline of the cosmological consequences such as the effect on the black hole solution is given.

M. Tajmar

2006-07-20T23:59:59.000Z

269

Cosmological Simulations for Large-Scale Sky Surveys | Argonne Leadership  

NLE Websites -- All DOE Office Websites (Extended Search)

Instantaneous velocity magnitude in a flow through an open valve in a valve/piston assembly. Instantaneous velocity magnitude in a flow through an open valve in a valve/piston assembly. Instantaneous velocity magnitude in a flow through an open valve in a valve/piston assembly. Christos Altantzis, MIT, and Martin Schmitt, LAV. All the images were generated from their work at LAV. Cosmological Simulations for Large-Scale Sky Surveys PI Name: Christos Frouzakis PI Email: frouzakis@lav.mavt.ethz.ch Institution: Swiss Federal Institute of Technology Zurich Allocation Program: INCITE Allocation Hours at ALCF: 100 Million Year: 2014 Research Domain: Chemistry The combustion of coal and petroleum-based fuels supply most of the energy needed to meet the world's transportation and power generation demands. To address the anticipated petroleum shortage, along with increasing energy

270

Luminosity distance and redshift in the Szekeres inhomogeneous cosmological models  

E-Print Network (OSTI)

The Szekeres inhomogeneous models can be used to model the true lumpy universe that we observe. This family of exact solutions to Einstein's equations was originally derived with a general metric that has no symmetries. In this work, we develop and use a framework to integrate the angular diameter and luminosity distances in the general Szekeres models. We use the affine null geodesic equations in order to derive a set of first-order ordinary differential equations that can be integrated numerically to calculate the partial derivatives of the null vector components. These equations allow the integration in all generality of the distances in the Szekeres models and some examples are given. The redshift is determined from simultaneous integration of the null geodesic equations. This work does not assume spherical or axial symmetry, and the results will be useful for comparisons of the general Szekeres inhomogeneous models to current and future cosmological data.

Anthony Nwankwo; Mustapha Ishak; John Thompson

2010-05-17T23:59:59.000Z

271

Galaxy Formation and the Cosmological Angular Momentum Problem  

E-Print Network (OSTI)

The importance of angular momentum in regulating the sizes of galactic disks and by this their star formation history is highlighted. Tidal torques and accretion of satellites in principle provide enough angular momentum to form disks with sizes that are in agreement with observations. However three major problems have been identified that challenge cold dark matter theory and affect models of galaxy evolution: (1) too much angular momentum is transferred from the gas to the dark halos during infall, leading to disks with scale lengths that are too small, (2) bulgeless disks require more specific angular momentum than is generated cosmologically even if gas would not lose angular momentum during infall, (3) gravitational torques and hierarchical merging produce a specific angular momentum distribution that does not match the distribution required to form exponential disks naturally; some gas has exceptionally high angular momentum, leading to extended outer disks while another large gas fraction will contain ...

Burkert, A; Burkert, Andreas

2004-01-01T23:59:59.000Z

272

On the Semiclassical Limit of Loop Quantum Cosmology  

E-Print Network (OSTI)

We consider a k=0 Friedman-Robertson-Walker (FRW) model within loop quantum cosmology (LQC) and explore the issue of its semiclassical limit. The model is exactly solvable and allows us to construct analytical (Gaussian) coherent-state solutions for each point on the space of classical states. We propose physical criteria that select from these coherent states, those that display semiclassical behavior, and study their properties in the deep Planck regime. Furthermore, we consider generalized squeezed states and compare them to the Gaussian states. The issue of semiclassicality preservation across the bounce is studied and shown to be generic for all the states considered. Finally, we comment on some implications these results have, depending on the topology of the spatial slice. In particular we consider the issue of the recovery, within our class of states, of a scaling symmetry present in the classical description of the system when the spatial topology is non-compact.

Alejandro Corichi; Edison Montoya

2011-05-13T23:59:59.000Z

273

Cosmological Evolution With Interaction Between Dark Energy And Dark Matter  

E-Print Network (OSTI)

In this review we consider in detail different theoretical topics associated with interaction in the dark sector. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities. We consider a number of different models (including the holographic dark energy and dark energy in a fractal universe) with interacting dark energy (DE) and dark matter (DM), have done a thorough analysis of these models. The main task of this review was not only to give an idea about the modern set of different models of dark energy, but to show how much can be diverse dynamics of the universe in these models. We find that the dynamics of a Universe that contains interaction in the dark sector can differ significantly from the Standard Cosmological Model (SCM).

Bolotin, Yu L; Lemets, O A; Yerokhin, D A

2013-01-01T23:59:59.000Z

274

Higgs boson, renormalization group, and naturalness in cosmology  

E-Print Network (OSTI)

We consider the renormalization group improvement in the theory of the Standard Model (SM) Higgs boson playing the role of an inflaton with a strong non-minimal coupling to gravity. At the one-loop level with the running of constants taken into account, it leads to a range of the Higgs mass that is entirely determined by the lower WMAP bound on the cosmic microwave background (CMB) spectral index. We find that the SM phenomenology is sensitive to current cosmological data, which suggests to perform more precise CMB measurements as a SM test complementary to the LHC program. By using the concept of a field-dependent cutoff, we show the naturalness of the gradient and curvature expansion in this model within the conventional perturbation theory range of the SM. We also discuss the relation of these results to two-loop calculations and the limitations of the latter caused by parametrization and gauge dependence problems.

A. O. Barvinsky; A. Yu. Kamenshchik; C. Kiefer; A. A. Starobinsky; C. F. Steinwachs

2009-10-06T23:59:59.000Z

275

Numerical solutions to the cosmological 3-fluid problem  

E-Print Network (OSTI)

We show that, for the scalar field cosmology with exponential potential, the set of values of the coupling parameter for which the solutions undergo a transient period of acceleration is much larger than the set discussed in the literature. The gradual inclusion of ordinary and dark matters results in an everywhere, but near the origin, smoother and right shifted (along the time axis) acceleration curve. For the 3-fluid problem, the energy density need not exhibit a plateau during the acceleration period. Much excess in the dark matter and/or ordinary matter energy densities would lead the universe to undergo an eternal deceleration expansion. For the 3-fluid problem with a single exponential potential we conclude that the Big Bang Nucleosynthesis constraint is not fulfilled if the universe is to undergo a transient period of acceleration. The 3-fluid model remains a good approximation for the description of large scale structures.

Mustapha Azreg-Aïnou

2013-02-27T23:59:59.000Z

276

The signatures of new physics, astrophysics and cosmology?  

E-Print Network (OSTI)

The first three years of the LHC experiments at CERN have ended with "the nightmare scenario": all tests, confirm the Standard Model of Particles so well that theorists must search for new physics without any experimental guidance. The supersymmetric theories, a privileged candidate for new physics are nearly excluded. As a potential escape from the crisis, we propose thinking about a series of astonishing relations suggesting fundamental interconnections between the quantum world and the large scale Universe. It seems reasonable that, for instance, the equation relating a quark-antiquark pair with the fundamental physical constants and cosmological parameters must be a sign of new physics. One of the intriguing possibilities is interpreting our relations as a signature of the quantum vacuum containing the virtual gravitational dipoles.

Hajdukovic, Dragan Slavkov

2013-01-01T23:59:59.000Z

277

Efficient Bayesian inference for multimodal problems in cosmology  

E-Print Network (OSTI)

Bayesian model selection provides the cosmologist with an exacting tool to distinguish between competing models based purely on the data, via the Bayesian evidence. Previous methods to calculate this quantity either lacked general applicability or were computationally demanding. However, nested sampling (Skilling 2004), which was recently applied successfully to cosmology by Muhkerjee et al. 2006, overcomes both of these impediments. Their implementation restricts the parameter space sampled, and thus improves the efficiency, using a decreasing ellipsoidal bound in the n-dimensional parameter space centred on the maximum likelihood point. However, if the likelihood function contains any multi-modality, then the ellipse is prevented from constraining the sampling region efficiently. In this paper we introduce a method of clustered ellipsoidal nested sampling which can form multiple ellipses around each individual peak in the likelihood. In addition we have implemented a method for determining the expectation and variance of the final evidence value without the need to use sampling error from repetitions of the algorithm ; this further reduces the computational load by at least an order of magnitude. We have applied our algorithm to a pair of toy models and one cosmological example where we demonstrate that the number of likelihood evaluations required is ~ 4% of that necessary for using previous algorithms. We have produced a fortran library containing our routines which can be called from any sampling code, in addition for convenience we have incorporated it into the popular CosmoMC code as CosmoClust. Both are available for download at http://www.mrao.cam.ac.uk/software/cosmoclust .

J. R. Shaw; M. Bridges; M. P. Hobson

2007-01-30T23:59:59.000Z

278

CMB temperature anisotropy from broken spatial isotropy due to a homogeneous cosmological magnetic field  

Science Conference Proceedings (OSTI)

We derive the cosmic microwave background temperature anisotropy two-point correlation function (including off-diagonal correlations) from broken spatial isotropy due to an arbitrarily oriented homogeneous cosmological magnetic field.

Kahniashvili, Tina [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States); Department of Physics, Laurentian University, Ramsey Lake Road, Sudbury, ON P3E 2C6 (Canada); National Abastumani Astrophysical Observatory, 2A Kazbegi Ave, Tbilisi, GE-0160 (Georgia); Lavrelashvili, George [Department of Theoretical Physics, A. Razmadze Mathematical Institute, 1 M. Aleksidze, Tbilisi, GE-0193 (Georgia); Ratra, Bharat [Department of Physics, Kansas State University, 116 Cardwell Hall, Manhattan, Kansas 66506 (United States)

2008-09-15T23:59:59.000Z

279

On the Green's function and iterative solutions of Loop Quantum Cosmology  

E-Print Network (OSTI)

Here we shall find the green's function of the difference equation of loop quantum cosmology. To illustrate how to use it, we shall obtain an iterative solution for closed model and evaluate its corresponding Bohmian trajectory.

Fatimah Shojai; Ali Shojai

2006-07-09T23:59:59.000Z

280

Solar System Constraints on a Cosmologically Viable $f(R)$ Theory  

E-Print Network (OSTI)

Recently, a model $f(R)$ theory is proposed \\cite{recent} which is cosmologically viable and distinguishable from $\\Lambda$CDM. We use chameleon mechanism to investigate viability of the model in terms of Solar System experiments.

Yousef Bisabr

2009-07-22T23:59:59.000Z

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281

Observational Constraints on Cosmological Models with the Updated Long Gamma-Ray Bursts  

E-Print Network (OSTI)

In the present work, by the help of the newly released Union2 compilation which consists of 557 Type Ia supernovae (SNIa), we calibrate 109 long Gamma-Ray Bursts (GRBs) with the well-known Amati relation, using the cosmology-independent calibration method proposed by Liang {\\it et al.}. We have obtained 59 calibrated high-redshift GRBs which can be used to constrain cosmological models without the circularity problem (we call them ``Hymnium'' GRBs sample for convenience). Then, we consider the joint constraints on 7 cosmological models from the latest observational data, namely, the combination of 557 Union2 SNIa dataset, 59 calibrated Hymnium GRBs dataset (obtained in this work), the shift parameter $R$ from the WMAP 7-year data, and the distance parameter $A$ of the measurement of the baryon acoustic oscillation (BAO) peak in the distribution of SDSS luminous red galaxies. We also briefly consider the comparison of these 7 cosmological models.

Hao Wei

2010-04-28T23:59:59.000Z

282

High resolution telescope including an array of elemental telescopes aligned along a common axis and supported on a space frame with a pivot at its geometric center  

DOE Patents (OSTI)

A large effective-aperture, low-cost optical telescope with diffraction-limited resolution enables ground-based observation of near-earth space objects. The telescope has a non-redundant, thinned-aperture array in a center-mount, single-structure space frame. It employes speckle interferometric imaging to achieve diffraction-limited resolution. The signal-to-noise ratio problem is mitigated by moving the wavelength of operation to the near-IR, and the image is sensed by a Silicon CCD. The steerable, single-structure array presents a constant pupil. The center-mount, radar-like mount enables low-earth orbit space objects to be tracked as well as increases stiffness of the space frame. In the preferred embodiment, the array has elemental telescopes with subaperture of 2.1 m in a circle-of-nine configuration. The telescope array has an effective aperture of 12 m which provides a diffraction-limited resolution of 0.02 arc seconds. Pathlength matching of the telescope array is maintained by a electro-optical system employing laser metrology. Speckle imaging relaxes pathlength matching tolerance by one order of magnitude as compared to phased arrays. Many features of the telescope contribute to substantial reduction in costs. These include eliminating the conventional protective dome and reducing on-site construction activities. The cost of the telescope scales with the first power of the aperture rather than its third power as in conventional telescopes.

Norbert, Massie A. (San Ramon, CA); Yale, Oster (Danville, CA)

1992-01-01T23:59:59.000Z

283

High resolution telescope including an array of elemental telescopes aligned along a common axis and supported on a space frame with a pivot at its geometric center  

DOE Patents (OSTI)

A large effective-aperture, low-cost optical telescope with diffraction-limited resolution enables ground-based observation of near-earth space objects. The telescope has a non-redundant, thinned-aperture array in a center-mount, single-structure space frame. It employes speckle interferometric imaging to achieve diffraction-limited resolution. The signal-to-noise ratio problem is mitigated by moving the wavelength of operation to the near-IR, and the image is sensed by a Silicon CCD. The steerable, single-structure array presents a constant pupil. The center-mount, radar-like mount enables low-earth orbit space objects to be tracked as well as increases stiffness of the space frame. In the preferred embodiment, the array has elemental telescopes with subaperture of 2.1 m in a circle-of-nine configuration. The telescope array has an effective aperture of 12 m which provides a diffraction-limited resolution of 0.02 arc seconds. Pathlength matching of the telescope array is maintained by a electro-optical system employing laser metrology. Speckle imaging relaxes pathlength matching tolerance by one order of magnitude as compared to phased arrays. Many features of the telescope contribute to substantial reduction in costs. These include eliminating the conventional protective dome and reducing on-site construction activities. The cost of the telescope scales with the first power of the aperture rather than its third power as in conventional telescopes. 15 figs.

Norbert, M.A.; Yale, O.

1992-04-28T23:59:59.000Z

284

Gauss-Bonnet Braneworld Cosmology with Modified Induced Gravity on the Brane  

E-Print Network (OSTI)

We analyze the background cosmology for an extension of the DGP gravity with Gauss-Bonnet term in the bulk and $f(R)$ gravity on the brane. We investigate implications of this setup on the late-time cosmic history. Within a dynamical system approach, we study cosmological dynamics of this setup focusing on the role played by curvature effects. Finally we constraint the parameters of the model by confrontation with recent observational data.

Kourosh Nozari; Faeze Kiani; Narges Rashidi

2013-08-27T23:59:59.000Z

285

Photo of the Week: The Webb Telescope's "Golden Spider" | Department of  

Energy.gov (U.S. Department of Energy (DOE)) Indexed Site

The Webb Telescope's "Golden Spider" The Webb Telescope's "Golden Spider" Photo of the Week: The Webb Telescope's "Golden Spider" September 14, 2012 - 2:32pm Addthis The James Webb Space Telescope is a large, infrared-optimized telescope that is anticipated to launch in 2018. The spider-like sheets and tubes of wires you see here are the Optical Telescope Simulator (OSIM) for the telescope itself. OSIM will help scientists prepare the Webb telescope for flight by generating a beam of light that the telescope optics will feed into its actual flight instruments. In this photo, engineers have blanketed the OSIM with special insulating material to help control its temperature while it goes into the deep freeze testing of the Space Environment Simulator at NASA's Goddard Space Flight Center in Greenbelt, Maryland. The simulator will mimic the environment that the telescope will experience in operational orbit, more than 1 million miles from Earth. | Photo credit: Chris Gunn/NASA.

286

The SiRi Particle-Telescope System  

E-Print Network (OSTI)

A silicon particle-telescope system for light-ion nuclear reactions is described. In particular, the system is designed to be optimized for level density and gamma-ray strength function measurements with the so-called Oslo method. Eight trapezoidal modules are mounted at 5 cm distance from the target, covering 8 forward angles between theta = 40 and 54 degrees. The thin front dE detectors (130 micrometer) are segmented into eight pads, determining the reaction angle for the outgoing charged ejectile. Guard rings on the thick back E detectors (1550 micrometer) guarantee low leakage current at high depletion voltage.

M. Guttormsen; A. Bürger; T. E. Hansen; N. Lietaer

2011-04-07T23:59:59.000Z

287

STELLAR TIDAL STREAMS IN SPIRAL GALAXIES OF THE LOCAL VOLUME: A PILOT SURVEY WITH MODEST APERTURE TELESCOPES  

Science Conference Proceedings (OSTI)

Within the hierarchical framework for galaxy formation, minor merging and tidal interactions are expected to shape all large galaxies to the present day. As a consequence, most seemingly normal disk galaxies should be surrounded by spatially extended stellar 'tidal features' of low surface brightness. As part of a pilot survey for such interaction signatures, we have carried out ultra deep, wide field imaging of eight isolated spiral galaxies in the Local Volume, with data taken at small (D = 0.1-0.5 m) robotic telescopes that provide exquisite surface brightness sensitivity ({mu}{sub lim}(V) {approx} 28.5 mag arcsec{sup -2}). This initial observational effort has led to the discovery of six previously undetected extensive (to {approx}30 kpc) stellar structures in the halos surrounding these galaxies, likely debris from tidally disrupted satellites. In addition, we confirm and clarify several enormous stellar over-densities previously reported in the literature, but never before interpreted as tidal streams. Even this pilot sample of galaxies exhibits strikingly diverse morphological characteristics of these extended stellar features: great circle-like features that resemble the Sagittarius stream surrounding the Milky Way, remote shells and giant clouds of presumed tidal debris far beyond the main stellar body, as well as jet-like features emerging from galactic disks. Together with presumed remains of already disrupted companions, our observations also capture surviving satellites caught in the act of tidal disruption. A qualitative comparison with available simulations set in a {Lambda}Cold Dark Matter cosmology (that model the stellar halo as the result of satellite disruption evolution) shows that the extraordinary variety of stellar morphologies detected in this pilot survey matches that seen in those simulations. The common existence of these tidal features around 'normal' disk galaxies and the morphological match to the simulations constitutes new evidence that these theoretical models also apply to a large number of other Milky Way-mass disk galaxies in the Local Volume.

MartInez-Delgado, David; Zibetti, Stefano; Rix, Hans-Walter [Max Planck Institut fuer Astronomie, Heidelberg (Germany); Gabany, R. Jay [Black Bird Observatory, Mayhill, NM (United States); Crawford, Ken [Rancho del Sol Observatory, Modesto, CA (United States); Majewski, Steven R.; McDavid, David A. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904-4325 (United States); Fliri, Juergen; Carballo-Bello, Julio A.; Bardalez-Gagliuffi, Daniella C.; Trujillo, Ignacio [Instituto de Astrofisica de Canarias, La Laguna (Spain); Penarrubia, Jorge [Institute of Astronomy, University of Cambridge (United Kingdom); Chonis, Taylor S. [Department of Astronomy, University of Texas, Austin, TX 78712-0259 (United States); Madore, Barry [The Observatories of the Carnegie Institution for Science, 813 Santa Barbara Street, Pasadena, CA 91101 (United States); Schirmer, Mischa [Argelander Institut fuer Astronomie, Universitaet Bonn (Germany)

2010-10-15T23:59:59.000Z

288

COSMOLOGICAL MAGNETOHYDRODYNAMIC SIMULATIONS OF CLUSTER FORMATION WITH ANISOTROPIC THERMAL CONDUCTION  

SciTech Connect

The intracluster medium (ICM) has been suggested to be buoyantly unstable in the presence of magnetic field and anisotropic thermal conduction. We perform first cosmological simulations of galaxy cluster formation that simultaneously include magnetic fields, radiative cooling, and anisotropic thermal conduction. In isolated and idealized cluster models, the magnetothermal instability (MTI) tends to reorient the magnetic fields radially whenever the temperature gradient points in the direction opposite to gravitational acceleration. Using cosmological simulations of cluster formation we detect radial bias in the velocity and magnetic fields. Such radial bias is consistent with either the inhomogeneous radial gas flows due to substructures or residual MTI-driven field rearrangements that are expected even in the presence of turbulence. Although disentangling the two scenarios is challenging, we do not detect excess bias in the runs that include anisotropic thermal conduction. The anisotropy effect is potentially detectable via radio polarization measurements with LOFAR and the Square Kilometer Array and future X-ray spectroscopic studies with the International X-ray Observatory. We demonstrate that radiative cooling boosts the amplification of the magnetic field by about two orders of magnitude beyond what is expected in the non-radiative cases. This effect is caused by the compression of the gas and frozen-in magnetic field as it accumulates in the cluster center. At z = 0 the field is amplified by a factor of about 10{sup 6} compared to the uniform magnetic field that evolved due to the universal expansion alone. Interestingly, the runs that include both radiative cooling and thermal conduction exhibit stronger magnetic field amplification than purely radiative runs. In these cases, buoyant restoring forces depend on the temperature gradients rather than the steeper entropy gradients. Thus, the ICM is more easily mixed and the winding up of the frozen-in magnetic field is more efficient, resulting in stronger magnetic field amplification. We also demonstrate that thermal conduction partially reduces the gas accretion driven by overcooling despite the fact that the effective conductivity is suppressed below the Spitzer-Braginskii value.

Ruszkowski, M. [Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109 (United States); Lee, D. [Department of Astronomy, ASC/Flash Center, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637 (United States); Brueggen, M. [School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen 05233 (Germany); Parrish, I. [Astronomy Department and Theoretical Astrophysics Center, 601 Campbell Hall, University of California, Berkeley, CA 94720 (United States); Oh, S. Peng, E-mail: mateuszr@umich.edu, E-mail: dongwook@flash.uchicago.edu, E-mail: m.brueggen@jacobs-university.de, E-mail: iparrish@astro.berkeley.edu, E-mail: peng@physics.ucsb.edu [Department of Physics, University of California, Santa Barbara, CA 93106 (United States)

2011-10-20T23:59:59.000Z

289

FERMI LARGE AREA TELESCOPE OBSERVATION OF SUPERNOVA REMNANT S147  

Science Conference Proceedings (OSTI)

We present an analysis of gamma-ray data obtained with the Large Area Telescope on board the Fermi Gamma-ray Space Telescope in the region around supernova remnant (SNR) S147 (G180.0-1.7). A spatially extended gamma-ray source detected in an energy range of 0.2-10 GeV is found to coincide with SNR S147. We confirm its spatial extension at >5{sigma} confidence level. The gamma-ray flux is (3.8 {+-} 0.6) Multiplication-Sign 10{sup -8} photons cm{sup -2} s{sup -1}, corresponding to a luminosity of 1.3 Multiplication-Sign 10{sup 34} (d/1.3 kpc){sup 2} erg s{sup -1} in this energy range. The gamma-ray emission exhibits a possible spatial correlation with the prominent H{alpha} filaments of SNR S147. There is no indication that the gamma-ray emission comes from the associated pulsar PSR J0538+2817. The gamma-ray spectrum integrated over the remnant is likely dominated by the decay of neutral {pi} mesons produced through the proton-proton collisions in the filaments. The reacceleration of the pre-existing cosmic rays and subsequent adiabatic compression in the filaments is sufficient to provide the energy density required of high-energy protons.

Katsuta, J.; Uchiyama, Y.; Tanaka, T.; Tajima, H.; Bechtol, K.; Funk, S.; Lande, J. [W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States); Ballet, J. [Laboratoire AIM, CEA-IRFU/CNRS/Universite Paris Diderot, Service d'Astrophysique, CEA Saclay, 91191 Gif sur Yvette (France); Hanabata, Y. [Department of Physical Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Lemoine-Goumard, M. [Universite Bordeaux 1, CNRS/IN2p3, Centre d'Etudes Nucleaires de Bordeaux Gradignan, 33175 Gradignan (France); Takahashi, T., E-mail: katsuta@slac.stanford.edu, E-mail: uchiyama@slac.stanford.edu [Institute of Space and Astronautical Science, Japanese Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Sagamihara, Kanagawa 252-5210 (Japan)

2012-06-20T23:59:59.000Z

290

Fermi Large Area Telescope Operations: Progress Over 4 Years  

SciTech Connect

The Fermi Gamma-ray Space Telescope was launched into orbit in June 2008, and is conducting a multi-year gamma-ray all-sky survey, using the main instrument on Fermi, the Large Area Telescope (LAT). Fermi began its science mission in August 2008, and has now been operating for almost 4 years. The SLAC National Accelerator Laboratory hosts the LAT Instrument Science Operations Center (ISOC), which supports the operation of the LAT in conjunction with the Mission Operations Center (MOC) and the Fermi Science Support Center (FSSC), both at NASA's Goddard Space Flight Center. The LAT has a continuous output data rate of about 1.5 Mbits per second, and data from the LAT are stored on Fermi and transmitted to the ground through TDRS and the MOC to the ISOC about 10 times per day. Several hundred computers at SLAC are used to process LAT data to perform event reconstruction, and gamma-ray photon data are subsequently delivered to the FSSC for public release with a few hours of being detected by the LAT. We summarize the current status of the LAT, and the evolution of the data processing and monitoring performed by the ISOC during the first 4 years of the Fermi mission, together with future plans for further changes to detected event data processing and instrument operations and monitoring.

Cameron, Robert A.; /SLAC

2012-06-28T23:59:59.000Z

291

Challenges in optics for Extremely Large Telescope instrumentation  

E-Print Network (OSTI)

We describe and summarize the optical challenges for future instrumentation for Extremely Large Telescopes (ELTs). Knowing the complex instrumental requirements is crucial for the successful design of 30-60m aperture telescopes. After all, the success of ELTs will heavily rely on its instrumentation and this, in turn, will depend on the ability to produce large and ultra-precise optical components like light-weight mirrors, aspheric lenses, segmented filters, and large gratings. New materials and manufacturing processes are currently under study, both at research institutes and in industry. In the present paper, we report on its progress with particular emphasize on volume-phase-holographic gratings, photochromic materials, sintered silicon-carbide mirrors, ion-beam figuring, ultra-precision surfaces, and free-form optics. All are promising technologies opening new degrees of freedom to optical designers. New optronic-mechanical systems will enable efficient use of the very large focal planes. We also provide exploratory descriptions of "old" and "new" optical technologies together with suggestions to instrument designers to overcome some of the challenges placed by ELT instrumentation.

P. Spanò; F. M. Zerbi; C. J. Norrie; C. R. Cunningham; K. G. Strassmeier; A. Bianco; P. A. Blanche; M. Bougoin; M. Ghigo; P. Hartmann; L. Zago; E. Atad-Ettedgui; B. Delabre; H. Dekker; M. Melozzi; B. Snyders; R. Takke; D. D. Walker

2006-03-28T23:59:59.000Z

292

Six years of GRB follow up with MITSuME Okayama Telescope  

Science Conference Proceedings (OSTI)

MITSuME Okayama Telescope is an autonomous telescope with a diameter of 50 cm dedicated primarily to follow-up {gamma}-ray bursts. The telescope has successfully been in operation since 2004. We have made 131 observations of {gamma}-ray bursts and submitted 47 reports to GCN circulars. In this article, we present an overview of the instrumentation and scientific results obtained so far.

Yanagisawa, Kenshi; Kuroda, Daisuke; Shimizu, Yasuhiro; Nagayama, Shogo; Toda, Hiroyuki [Okayama Astrophysical Observatory, Kamogata, Asakuchi, Okayama 719-0232 (Japan); Yoshida, Michitoshi [Hiroshima University, Higashi-Hiroshima, Hiroshima, 739-8526 (Japan); Ohta, Kouji [Kyoto University, Sakyo-ku, Kita-shirakawa, Kyoto, 606-8502 (Japan); Kawai, Nobuyuki [Tokyo Institute of Technology, Ookayama, Meguro, Tokyo, 152-8551 (Japan)

2010-10-15T23:59:59.000Z

293

Deployable telescope having a thin-film mirror and metering structure  

Science Conference Proceedings (OSTI)

A deployable thin-film mirror telescope comprises a base structure and a metering structure. The base structure houses a thin-film mirror, which can be rolled for stowage and unrolled for deployment. The metering structure is coupled to the base structure and can be folded for stowage and unfolded for deployment. In the deployed state, the unrolled thin-film mirror forms a primary minor for the telescope and the unfolded metering structure positions a secondary minor for the telescope.

Krumel, Leslie J. (Cedar Crest, NM); Martin, Jeffrey W. (Albuquerque, NM)

2010-08-24T23:59:59.000Z

294

Integrable Scalar Cosmologies I. Foundations and links with String Theory  

E-Print Network (OSTI)

We build a number of integrable one--scalar spatially flat cosmologies, which play a natural role in inflationary scenarios, examine their behavior in several cases and draw from them some general lessons on this type of systems, whose potentials involve combinations of exponential functions, and on similar non--integrable ones. These include the need for the scalar to emerge from the initial singularity while climbing up sufficiently steep exponential potentials ("climbing phenomenon") and the inevitable collapse in a big Crunch whenever the scalar tries to settle at negative extrema of the potential. We also elaborate on the links between these types of potentials and "brane supersymmetry breaking", a mechanism that ties together string scale and scale of supersymmetry breaking in a class of orientifold models. We show that, under some assumptions that are spelled out in the text, the extended objects of these vacua can inject inflationary phases with discrete values of the spectral index that are determined by the number of unwrapped dimensions of the branes and by the inverse power with which the string coupling $g_s$ enters their world--volume actions. An NS fivebrane, which is interestingly unstable in this class of models, when wrapped on a small internal cycle would yield a spectral index that is amusingly close to the experimentally favored PLANCK value ns ~ 0.96.

P. Fré; A. Sagnotti; A. S. Sorin

2013-07-07T23:59:59.000Z

295

Eyes Wide Open - Optimising Cosmological Surveys in a Crowded Market  

E-Print Network (OSTI)

Optimising the major next-generation cosmological surveys (such as {\\em SNAP, KAOS etc...}) is a key problem given our ignorance of the physics underlying cosmic acceleration and the plethora of surveys planned. We propose a Bayesian design framework which (1) maximises the discrimination power of a survey without assuming any underlying dark energy model, (2) finds the best niche survey geometry given current data and future competing experiments, (3) maximises the cross-section for serendipitous discoveries and (4) can be adapted to answer specific questions (such as `is dark energy dynamical?'). Integrated Parameter Space Optimisation (IPSO) is a design framework that integrates projected parameter errors over an entire dark energy parameter space and then extremises a figure of merit (such as Shannon entropy gain which we show is stable to off-diagonal covariance matrix perturbations) as a function of survey parameters using analytical, grid or MCMC techniques. We discuss examples where the optimisation can be performed analytically. IPSO is thus a general, model-independent and scalable framework that allows us to appropriately use prior information to design the best possible surveys.

Bruce A. Bassett

2004-07-12T23:59:59.000Z

296

The pattern of growth in viable f(R) cosmologies  

E-Print Network (OSTI)

We study the evolution of linear perturbations in metric f(R) models of gravity and identify a potentially observable characteristic scale-dependent pattern in the behavior of cosmological structures. While at the background level viable f(R) models must closely mimic LCDM, the differences in their prediction for the growth of large scale structures can be sufficiently large to be seen with future weak lensing surveys. While working in the Jordan frame, we perform an analytical study of the growth of structures in the Einstein frame, demonstrating the equivalence of the dynamics in the two frames. We also provide a physical interpretation of the results in terms of the dynamics of an effective dark energy fluid with a non-zero shear. We find that the growth of structure in f(R) is enhanced, but that there are no small scale instabilities associated with the additional attractive "fifth force". We then briefly consider some recently proposed observational tests of modified gravity and their utility for detecting the f(R) pattern of structure growth.

Levon Pogosian; Alessandra Silvestri

2007-09-04T23:59:59.000Z

297

Chimera: A hybrid approach to numerical loop quantum cosmology  

E-Print Network (OSTI)

The existence of a quantum bounce in isotropic spacetimes is a key result in loop quantum cosmology (LQC), which has been demonstrated to arise in all the models studied so far. In most of the models, the bounce has been studied using numerical simulations involving states which are sharply peaked and which bounce at volumes much larger than the Planck volume. An important issue is to confirm the existence of the bounce for states which have a wide spread, or which bounce closer to the Planck volume. Numerical simulations with such states demand large computational domains, making them very expensive and practically infeasible with the techniques which have been implemented so far. To overcome these difficulties, we present an efficient hybrid numerical scheme using the property that at the small spacetime curvature, the quantum Hamiltonian constraint in LQC, which is a difference equation with uniform discretization in volume, can be approximated by a Wheeler-DeWitt differential equation. By carefully choosing a hybrid spatial grid allowing the use of partial differential equations at large volumes, and with a simple change of geometrical coordinate, we obtain a surprising reduction in the computational cost. This scheme enables us to explore regimes which were so far unachievable for the isotropic model in LQC. Our approach also promises to significantly reduce the computational cost for numerical simulations in anisotropic LQC using high performance computing.

Peter Diener; Brajesh Gupt; Parampreet Singh

2013-10-17T23:59:59.000Z

298

Infrared Properties of z=7 Galaxies from Cosmological Simulations  

E-Print Network (OSTI)

Three-dimensional panchromatic dust radiative transfer calculations are performed on a set of 198 galaxies of stellar masses in the range 5x10^8-3x10^10 Msun from a cosmological hydrodynamic simulation (resolved at 29pc/h) at z=7. In a companion paper (Kimm & Cen), the stellar mass and UV luminosity functions, and UV-optical and FUV-NUV colors are shown to be in good agreement with observations, if an SMC-type dust extinction curve is adopted. Here we make useful predictions, self-consistently, of the infrared properties of these z=7 simulated galaxies that can be confronted with upcoming ALMA data. Our findings are as follows. (1) The effective radius in the rest-frame MIPS 70 micron band is in the range of 80-400pc proper for z=7 galaxies with L_FIR=10^{11.3-12}Lsun. (2) The median of the peak wavelength of the far-infrared (FIR) spectral energy distribution is in the range of 45-60 micron, depending on the dust-to-metal ratio. (3) For star formation rate in the range 3-100 Msun/yr the median FIR to bol...

Cen, Renyue

2013-01-01T23:59:59.000Z

299

False vacuum as an unstable state: possible cosmological implications  

E-Print Network (OSTI)

Recent LHC results concerning the mass of the Higgs boson indicate that the vacuum in our Universe may be unstable. We analyze properties of unstable vacuum states from the point of view of the quantum theory of unstable states. From the literature it is known that some of false vacuum states may survive up to times when their survival probability has a non-exponential form. At times much latter than the transition time, when contributions to the survival probability of its exponential and non-exponential parts are comparable, the survival probability as a function of time $t$ has an inverse power-like form. We show that at this time region the instantaneous energy of the false vacuum states tends to the energy of the true vacuum state as $1/t^{2}$ for $t \\to \\infty$. Properties of the instantaneous energy at transition times are also analyzed for a given model. It is shown that at this time region large and rapid fluctuations of the instantaneous energy take place. This suggests analogous behavior of the cosmological constant at these time regions.

K. Urbanowski

2013-06-18T23:59:59.000Z

300

Galaxy Formation and the Cosmological Angular Momentum Problem  

E-Print Network (OSTI)

The importance of angular momentum in regulating the sizes of galactic disks and by this their star formation history is highlighted. Tidal torques and accretion of satellites in principle provide enough angular momentum to form disks with sizes that are in agreement with observations. However three major problems have been identified that challenge cold dark matter theory and affect models of galaxy evolution: (1) too much angular momentum is transferred from the gas to the dark halos during infall, leading to disks with scale lengths that are too small, (2) bulgeless disks require more specific angular momentum than is generated cosmologically even if gas would not lose angular momentum during infall, (3) gravitational torques and hierarchical merging produce a specific angular momentum distribution that does not match the distribution required to form exponential disks naturally; some gas has exceptionally high angular momentum, leading to extended outer disks while another large gas fraction will contain very little specific angular momentum and is expected to fall into the galactic center, forming a massive and dominant bulge component. Any self-consistent theory of galaxy formation will require to provide solutions to these questions. Selective mass loss of low-angular-momentum gas in an early phase of galaxy evolution currently seems to be the most promising scenario. Such a process would have a strong affect on the early protogalactic evolution phase, the origin and evolution of galactic morphologies and link central properties of galaxies like the origin of central massive black holes with their global structure.

Andreas Burkert; Elena D'Onghia

2004-09-22T23:59:59.000Z

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301

Cosmological Coincidence and Dark Mass Problems in Einstein Universe and Friedman Dust Universe with Einstein's Lambda Quantum Cosmology Dark Energy Schroedinger Wave Motion  

E-Print Network (OSTI)

In this paper, it is shown that the cosmological model that was introduced in a sequence of three earlier papers under the title, A Dust Universe Solution to the Dark Energy Problem can be used to analyse and solve the Cosmological Coincidence Problem. The generic coincidence problem that appears in the original Einstein universe model is shown to arise from a misunderstanding about the magnitude of dark energy density and the epoch time governing the appearance of the integer relation between dark energy and normal energy density. The solution to the generic case then clearly points to the source of the time coincidence integer problem in the Friedman dust universe model. It is then possible to eliminate this coincidence by removing a degeneracy between different measurement epoch times. In this paper's first appendix, a fundamental time dependent relation between dark mass and dark energy is derived with suggestions how this relation could explain cosmological voids and the clumping of dark mass to become visible matter. In this paper's second appendix, it is shown that that dark energy is a conserved with time substance that is everywhere and for all time permeable to the dark mass and visible mass of which the contracting or expanding universe is composed. The last two appendices involve detailed studies of cosmology, quantum dark energy related issues. There are more detailed abstracts given with all four appendices.

James G. Gilson

2007-05-20T23:59:59.000Z

302

On the detection of relativistic magnetic monopoles by deep underwater and underice neutrino telescopes  

E-Print Network (OSTI)

I present here some reflections and very speculative remarks on the detection of relativistic magnetic monopoles by currently operating deep underwater/ice neutrino telescopes.

B. K. Lubsandorzhiev

2005-06-13T23:59:59.000Z

303

Bayes in the sky: Bayesian inference and model selection in cosmology  

E-Print Network (OSTI)

The application of Bayesian methods in cosmology and astrophysics has flourished over the past decade, spurred by data sets of increasing size and complexity. In many respects, Bayesian methods have proven to be vastly superior to more traditional statistical tools, offering the advantage of higher efficiency and of a consistent conceptual basis for dealing with the problem of induction in the presence of uncertainty. This trend is likely to continue in the future, when the way we collect, manipulate and analyse observations and compare them with theoretical models will assume an even more central role in cosmology. This review is an introduction to Bayesian methods in cosmology and astrophysics and recent results in the field. I first present Bayesian probability theory and its conceptual underpinnings, Bayes' Theorem and the role of priors. I discuss the problem of parameter inference and its general solution, along with numerical techniques such as Monte Carlo Markov Chain methods. I then review the theory and application of Bayesian model comparison, discussing the notions of Bayesian evidence and effective model complexity, and how to compute and interpret those quantities. Recent developments in cosmological parameter extraction and Bayesian cosmological model building are summarized, highlighting the challenges that lie ahead.

Roberto Trotta

2008-03-28T23:59:59.000Z

304

THE CHALLENGE OF THE LARGEST STRUCTURES IN THE UNIVERSE TO COSMOLOGY  

Science Conference Proceedings (OSTI)

Large galaxy redshift surveys have long been used to constrain cosmological models and structure formation scenarios. In particular, the largest structures discovered observationally are thought to carry critical information on the amplitude of large-scale density fluctuations or homogeneity of the universe, and have often challenged the standard cosmological framework. The Sloan Great Wall (SGW) recently found in the Sloan Digital Sky Survey (SDSS) region casts doubt on the concordance cosmological model with a cosmological constant (i.e., the flat {Lambda}CDM model). Here we show that the existence of the SGW is perfectly consistent with the {Lambda}CDM model, a result that only our very large cosmological N-body simulation (the Horizon Run 2, HR2) could supply. In addition, we report on the discovery of a void complex in the SDSS much larger than the SGW, and show that such size of the largest void is also predicted in the {Lambda}CDM paradigm. Our results demonstrate that an initially homogeneous isotropic universe with primordial Gaussian random phase density fluctuations growing in accordance with the general relativity can explain the richness and size of the observed large-scale structures in the SDSS. Using the HR2 simulation we predict that a future galaxy redshift survey about four times deeper or with 3 mag fainter limit than the SDSS should reveal a largest structure of bright galaxies about twice as big as the SGW.

Park, Changbom [School of Physics, Korea Institute for Advanced Study, Heogiro 85, Seoul 130-722 (Korea, Republic of); Choi, Yun-Young; Kim, Sungsoo S.; Kim, Kap-Sung [Department of Astronomy and Space Science, Kyung Hee University, Gyeonggi 446-701 (Korea, Republic of); Kim, Juhan [Center for Advanced Computation, Korea Institute for Advanced Study, Heogiro 85, Seoul 130-722 (Korea, Republic of); Gott III, J. Richard, E-mail: yy.choi@khu.ac.kr [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544-1001 (United States)

2012-11-01T23:59:59.000Z

305

Generating Minimally Coupled Einstein-Scalar Field Solutions from Vacuum Solutions with Arbitrary Cosmological Constant  

E-Print Network (OSTI)

This paper generalizes two previously known techniques for generating minimally coupled Einstein-scalar field solutions in 4 dimensions; the Buchdahl and Fonarev transformations. By applying this solution generation technique, minimally coupled Einstein-scalar field solutions can be generated from vacuum solutions with arbitrary cosmological constant in arbitrary dimension. The only requirement to a seed solution is that it posesses a hypersurface-orthogonal Killing vector field. The generalization that allows us to use seed solutions with arbitrary cosmological constant uncovers a new class of Einstein-scalar field solutions that has previously not been studied. We apply the new solution transformation to the (A)dS4 vacuum solution. Transforming the resulting Einstein-scalar field solution to the conformal frame, a two-parameter family of spatially finite, expanding and accelerating cosmological solutions are found that are conformally isometric to the Einstein static universe RxS^3. We study null geodesics and find that for any observer, the solution has a cosmological horizon at an angular distance of pi/2 away from the observer. We find that a subset of these solutions can be naturally interpreted as expanding cosmologies in which a scalar black hole is formed at late times. The conformally coupled scalar field satisfies the weak energy condition as long as the energy density is positive, while the strong energy condition is generally violated.

Kjell Tangen

2007-05-30T23:59:59.000Z

306

The Ultraviolet Imaging Telescope: Instrument and Data Characteristics  

E-Print Network (OSTI)

The Ultraviolet Imaging Telescope (UIT) was flown as part of the Astro observatory on the Space Shuttle Columbia in December 1990 and again on the Space Shuttle Endeavor in March 1995. Ultraviolet (1200-3300?A) images of a variety of astronomical objects, with a 40 ? field of view and a resolution of about 3 ? ? , were recorded on photographic film. The data recorded during the first flight are available to the astronomical community through the National Space Science Data Center (NSSDC); the data recorded during the second flight will soon be available as well. This paper discusses in detail the design, operation, data reduction, and calibration of UIT, providing the user of the data with information for understanding and using the data. It also provides guidelines for analyzing other astronomical imagery made with image intensifiers and photographic film. – 3 –

Theodore P. Stecher; Robert H. Cornett; Michael R. Greason; Wayne B. L; Jesse K. Hill; Robert S. Hill; Ralph C. Bohlin; Peter C. Chen; Nicholas R; Michael N. Fanelli; Joan I. Hollis; Susan G. Neff; Robert W. O’connell; Joel D. Offenberg; Ronald A. Parise; Joel Wm. Parker; Morton S. Roberts; M. Smith; William H. Waller

1997-01-01T23:59:59.000Z

307

Affordable Digital Planetariums with WorldWide Telescope  

E-Print Network (OSTI)

Digital planetariums can provide a broader range of educational experiences than the more classical planetariums that use star-balls. This is because of their ability to project images, content from current research and the 3D distribution of the stars and galaxies. While there are hundreds of planetariums in the country the reason that few of these are full digital is the cost. In collaboration with Microsoft Research (MSR) we have developed a way to digitize existing planetariums for approximately \\$40,000 using software freely available. We describe here how off the shelf equipment, together with MSR's WorldWide Telescope client can provide a rich and truly interactive experience. This will enable students and the public to pan though multi-wavelength full-sky scientific data sets, explore 3d visualizations of our Solar System (including trajectories of millions of minor planets), near-by stars, and the SDSS galaxy catalog.

Rosenfield, Philip; Fay, Jonathan; Carey, Larry; Sayres, Conor; Tofflemire, Benjamin

2010-01-01T23:59:59.000Z

308

Fourier transform method for imaging atmospheric Cherenkov telescopes  

E-Print Network (OSTI)

We propose Fourier transform (FT) method for processing images of extensive air showers (EAS) detected by imaging atmospheric Cherenkov telescopes (IACT) used in the very high energy (VHE) gamma-ray astronomy. The method is based on the discrete Fourier transforms (DFT) on compact Lie groups, and the use of continuous extension of the inverse discrete transforms to approximate the discrete EAS images by continuous EAS brightness distribution functions. Here we describe the FT-method in case of SU(3) group. It allows practical realization of the DFT technique for functions sampled on hexagonal symmetry grids. The proposed method can also be implemented in case of IACT cameras with grids of rectangular symmetry by using the DFT on the SU(2)xSU(2) group. The proposed FT-method is applied to the Monte-Carlo simulated bank of TeV proton and gamma-ray EAS images for a stand-alone telescope. Comparing between the FT-method and the currently used standard method shows that the FT technique allows a better and systematic enhancement of the gamma-ray signal. The relative difference between these two methods becomes more profound especially for `photon poor' images. It suggests that the EAS detection thresholds of IACTs could be effectively reduced with the use of FT technique. This prediction is further supported by a significant noise suppression capability of the method using simple low-pass filters in the image frequency domain. The FT-method allows very deep `tail' (and `height') image cuts, differentiation of images, operations in the image frequency domain, etc., that can be used for development of new effective parameters for the EAS image processing.

A. Atoyan; J. Patera; V. Sahakian; A. Akpherjanian

2004-09-15T23:59:59.000Z

309

HUBBLE SPACE TELESCOPE OBSERVATIONS OF THE HD 202628 DEBRIS DISK  

SciTech Connect

A ring-shaped debris disk around the G2V star HD 202628 (d = 24.4 pc) was imaged in scattered light at visible wavelengths using the coronagraphic mode of the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. The ring is inclined by {approx}64 Degree-Sign from face-on, based on the apparent major/minor axis ratio, with the major axis aligned along P.A. = 130 Degree-Sign . It has inner and outer radii (>50% maximum surface brightness) of 139 AU and 193 AU in the northwest ansae and 161 AU and 223 AU in the southeast ({Delta}r/r Almost-Equal-To 0.4). The maximum visible radial extent is {approx}254 AU. With mean surface brightness of V Almost-Equal-To 24 mag arcsec{sup -2}, this is the faintest debris disk observed to date in reflected light. The center of the ring appears offset from the star by {approx}28 AU (deprojected). An ellipse fit to the inner edge has an eccentricity of 0.18 and a = 158 AU. This offset, along with the relatively sharp inner edge of the ring, suggests the influence of a planetary-mass companion. There is a strong similarity with the debris ring around Fomalhaut, though HD 202628 is a more mature star with an estimated age of about 2 Gyr. We also provide surface brightness limits for nine other stars in our study with strong Spitzer excesses around which no debris disks were detected in scattered light (HD 377, HD 7590, HD 38858, HD 45184, HD 73350, HD 135599, HD 145229, HD 187897, and HD 201219).

Krist, John E.; Bryden, Geoffrey [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Stapelfeldt, Karl R. [Laboratory for Exoplanets and Stellar Astrophysics, Code 667, NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Plavchan, Peter [NASA Exoplanet Science Institute, California Institute of Technology, 770 S Wilson Ave., Pasadena, CA 91125 (United States)

2012-08-15T23:59:59.000Z

310

HIGH-PRECISION ASTROMETRY WITH A DIFFRACTIVE PUPIL TELESCOPE  

SciTech Connect

Astrometric detection and mass determination of Earth-mass exoplanets require sub-{mu}as accuracy, which is theoretically possible with an imaging space telescope using field stars as an astrometric reference. The measurement must, however, overcome astrometric distortions, which are much larger than the photon noise limit. To address this issue, we propose to generate faint stellar diffraction spikes using a two-dimensional grid of regularly spaced small dark spots added to the surface of the primary mirror (PM). Accurate astrometric motion of the host star is obtained by comparing the position of the spikes to the background field stars. The spikes do not contribute to scattered light in the central part of the field and therefore allow unperturbed coronagraphic observation of the star's immediate surroundings. Because the diffraction spikes are created on the PM and imaged on the same focal plane detector as the background stars, astrometric distortions affect equally the diffraction spikes and the background stars and are therefore calibrated. We describe the technique, detail how the data collected by the wide-field camera are used to derive astrometric motion, and identify the main sources of astrometric error using numerical simulations and analytical derivations. We find that the 1.4 m diameter telescope, 0.3 deg{sup 2} field we adopt as a baseline design achieves 0.2 {mu}as single measurement astrometric accuracy. The diffractive pupil concept thus enables sub-{mu}as astrometry without relying on the accurate pointing, external metrology, or high-stability hardware required with previously proposed high-precision astrometry concepts.

Guyon, Olivier; Eisner, Josh A.; Angel, Roger; Woolf, Neville J. [Steward Observatory, University of Arizona, Tucson, AZ 85721 (United States); Bendek, Eduardo A.; Milster, Thomas D. [College of Optical Sciences, University of Arizona, Tucson, AZ 85721 (United States); Mark Ammons, S. [Lawrence Livermore National Laboratory, Physics Division L-210, 7000 East Ave., Livermore, CA 94550 (United States); Shao, Michael; Shaklan, Stuart; Levine, Marie; Nemati, Bijan [Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Pitman, Joe [Exploration Sciences, P.O. Box 24, Pine, CO 80470 (United States); Woodruff, Robert A. [2081 Evergreen Avenue, Boulder, CO 80304 (United States); Belikov, Ruslan, E-mail: guyon@naoj.org [NASA Ames Research Center, Moffett Field, CA 94035 (United States)

2012-06-01T23:59:59.000Z

311

Cosmic ray physics in calculations of cosmological structure formation  

E-Print Network (OSTI)

Cosmic rays (CRs) play a decisive role within our own Galaxy. They provide partial pressure support against gravity, they trace past energetic events such as supernovae, and they reveal the underlying structure of the baryonic matter distribution through their interactions. To study the impact of CRs on galaxy and cosmic structure formation and evolution, we develop an approximative framework for treating dynamical and radiative effects of CRs in cosmological simulations. Our guiding principle is to try to find a balance between capturing as many physical properties of CR populations as possible while at the same time requiring as little extra computational resources as possible. We approximate the CR spectrum of each fluid element by a single power-law, with spatially and temporally varying normalisation, low-energy cut-off, and spectral index. Principles of conservation of particle number, energy, and pressure are then used to derive evolution equations for the basic variables describing the CR spectrum, both due to adiabatic and non-adiabatic processes. The processes considered include compression and rarefaction, CR injection via shocks in supernova remnants, injection in structure formation shock waves, in-situ re-acceleration of CRs, CR spatial diffusion, CR energy losses due to Coulomb interactions, ionisation losses, Bremsstrahlung losses, and, finally, hadronic interactions with the background gas, including the associated gamma-ray and radio emission due to subsequent pion decay. We show that the formalism reproduces CR energy densities, pressure, and cooling rates with an accuracy of ~10% in steady state conditions where CR injection balances cooling. Our framework is therefore well suited to be included into numerical simulation schemes of galaxy and structure formation. (abridged)

Torsten A. Ensslin; Christoph Pfrommer; Volker Springel; Martin Jubelgas

2006-03-17T23:59:59.000Z

312

Multi-Scale Initial Conditions For Cosmological Simulations  

SciTech Connect

We discuss a new algorithm to generate multi-scale initial conditions with multiple levels of refinements for cosmological 'zoom-in' simulations. The method uses an adaptive convolution of Gaussian white noise with a real-space transfer function kernel together with an adaptive multi-grid Poisson solver to generate displacements and velocities following first- (1LPT) or second-order Lagrangian perturbation theory (2LPT). The new algorithm achieves rms relative errors of the order of 10{sup -4} for displacements and velocities in the refinement region and thus improves in terms of errors by about two orders of magnitude over previous approaches. In addition, errors are localized at coarse-fine boundaries and do not suffer from Fourier-space-induced interference ringing. An optional hybrid multi-grid and Fast Fourier Transform (FFT) based scheme is introduced which has identical Fourier-space behaviour as traditional approaches. Using a suite of re-simulations of a galaxy cluster halo our real-space-based approach is found to reproduce correlation functions, density profiles, key halo properties and subhalo abundances with per cent level accuracy. Finally, we generalize our approach for two-component baryon and dark-matter simulations and demonstrate that the power spectrum evolution is in excellent agreement with linear perturbation theory. For initial baryon density fields, it is suggested to use the local Lagrangian approximation in order to generate a density field for mesh-based codes that is consistent with the Lagrangian perturbation theory instead of the current practice of using the Eulerian linearly scaled densities.

Hahn, Oliver; /KIPAC, Menlo Park; Abel, Tom; /KIPAC, Menlo Park /ZAH, Heidelberg /HITS, Heidelberg

2011-11-04T23:59:59.000Z

313

Inflaton perturbations in brane-world cosmology with induced gravity  

E-Print Network (OSTI)

We study cosmological perturbations in the brane models with an induced Einstein-Hilbert term on a brane. We consider an inflaton confined to a de Sitter brane in a five-dimensional Minkowski spacetime. Inflaton fluctuations excite Kaluza-Klein modes of bulk metric perturbations with mass $m^2 = -2(2\\ell-1) (\\ell +1) H^2$ and $m^2 = -2\\ell(2\\ell+3) H^2$ where $\\ell$ is an integer. There are two branches ($\\pm$ branches) of solutions for the background spacetime. In the $+$ branch, which includes the self-accelerating universe, a resonance appears for a mode with $m^2 = 2 H^2$ due to a spin-0 perturbation with $m^2 = 2H^2$. The self-accelerating universe has a distinct feature because there is also a helicity-0 mode of spin-2 perturbations with $m^2 = 2H^2$. In the $-$ branch, which can be thought as the Randall-Sundrum type brane-world with the high energy quantum corrections, there is no resonance. At high energies, we analytically confirm that four-dimensional Einstein gravity is recovered, which is related to the disappearance of van Dam-Veltman-Zakharov discontinuity in de Sitter spacetime. On sufficiently small scales, we confirm that the lineariaed gravity on the brane is well described by the Brans-Dicke theory with $\\omega=3Hr_c$ in $-$ branch and $\\omega = -3H r_c$ in $+$ branch, respectively, which confirms the existence of the ghost in $+$ branch. We also study large scale perturbations. In $+$ branch, the resonance induces a non-trivial anisotropic stress on the brane via the projection of Weyl tensor in the bulk, but no instability is shown to exist on the brane.

Kazuya Koyama; Shuntaro Mizuno

2006-06-13T23:59:59.000Z

314

The Taiwanese-American Occultation Survey: The Multi-Telescope Robotic Observatory  

E-Print Network (OSTI)

The Taiwanese-American Occultation Survey (TAOS) operates four fully automatic telescopes to search for occultations of stars by Kuiper Belt Objects. It is a versatile facility that is also useful for the study of initial optical GRB afterglows. This paper provides a detailed description of the TAOS multi-telescope system, control software, and high-speed imaging.

M. J. Lehner; C. -Y. Wen; J. -H. Wang; S. L. Marshall; M. E. Schwamb; Z. -W. Zhang; F. B. Bianco; J. Giammarco; R. Porrata; C. Alcock; T. Axelrod; Y. -I. Byun; W. P. Chen; K. H. Cook; R. Dave; S. -K. King; T. Lee; H. -C. Lin; S. -Y. Wang

2008-02-04T23:59:59.000Z

315

A 610-MHz Galactic Plane Pulsar Search with the Giant Meterwave Radio Telescope  

E-Print Network (OSTI)

We report on the discovery of three new pulsars in the first blind survey of the north Galactic plane (45 < l < 135 ; |b| < 1) with the Giant Meterwave Radio telescope (GMRT) at an intermediate frequency of 610 MHz. The timing parameters, obtained in follow up observations with the Lovell Telescope at Jodrell Bank Observatory and the GMRT, are presented.

B. C. Joshi; M. A. McLaughlin; M. Kramer; A. G. Lyne; D. R. Lorimer; D. A. Ludovici; M. Davies; A. J. Faulkner

2007-10-16T23:59:59.000Z

316

The Universe Viewed in Gamma-Rays 1 Pachmarhi Array of Cerenkov Telescopes  

E-Print Network (OSTI)

The Universe Viewed in Gamma-Rays 1 Pachmarhi Array of Cerenkov Telescopes P.Majumdar, B of Cerenkov Telescopes (PACT) has been designed to search for celestial TeV -rays using the wavefront sampling Atmospheric Cerenkov technique is the only method which has been suc- cessfully used to probe the sky

Enomoto, Ryoji

317

March 18, 2010 James Webb Space Telescope Studies of Dark Energy  

E-Print Network (OSTI)

March 18, 2010 James Webb Space Telescope Studies of Dark Energy Jonathan P. Gardner (NASA. Introduction The Hubble Space Telescope (HST) has contributed significantly to studies of dark energy) was due to dark energy rather than observational or astrophysical effects such as systematic errors

Sirianni, Marco

318

First Light Adaptive Optics System for Large Binocular Telescope S. Espositoa  

E-Print Network (OSTI)

First Light Adaptive Optics System for Large Binocular Telescope S. Espositoa , A. Tozzia , D of the single conjugate Adaptive Optics system to be installed on the LBT telescope. This system will be located optics is supposed to start from the beginning. The Adaptive Optics system to be used in first light

Fini, Luca

319

Before this decade is out: a student project to place a telescope on the internet  

Science Conference Proceedings (OSTI)

This paper describes a student project to place a telescope on the internet: such a telescope can be pointed via a web interface, and images from it displayed on a user's computer. We discuss recent developments in astronomy hardware and computer software ...

Michael P. Rogers

2001-10-01T23:59:59.000Z

320

Discovery of Dark Energy Ushered in a New Era in Computational Cosmology  

NLE Websites -- All DOE Office Websites (Extended Search)

Discovery of Dark Discovery of Dark Energy Ushered in a New Era in Computational Cosmology Discovery of Dark Energy Ushered in a New Era in Computational Cosmology October 4, 2011 | Tags: Astrophysics, Awards John Hules, JAHules@lbl.gov, +1 510 486 6008 "If NERSC does not enable a major scientific discovery every few years, then we're not doing our job." That was the challenge issued by Bill McCurdy, then Lawrence Berkeley National Laboratory's Associate Laboratory Director for Computing Sciences, at the first all-hands meeting for staff of the National Energy Research Scientific Computing Center (NERSC) when the center reopened after moving to Berkeley Lab in spring of 1996. No one at that meeting could have guessed that the first major breakthrough enabled by NERSC would be a startling discovery in cosmology-that the

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


321

Evolution of primordial black holes in Jordan-Brans-Dicke cosmology  

E-Print Network (OSTI)

We consider the evolution of primordial black holes in a generalyzed Jordan-Brans-Dicke cosmological model where both the Brans-Dicke scalar field and its coupling to gravity are dynamical functions determined from the evolution equations. The evaporation rate for the black holes changes compared to that in standard cosmology. We show that accretion of radiation can proceed effectively in the radiation dominated era. The black hole lifetime shortens for low initial mass, but increases for high initial mass, and is thus considerably modified compared to the case of standard cosmology. We derive a cut-off value for the initial black hole mass, below which primordial black holes evaporate out in the radiation dominated era, and above which they survive beyond the present era.

A. S. Majumdar; D. Gangopadhyay; L. P. Singh

2007-09-20T23:59:59.000Z

322

Asymptotically safe gravity as a scalar-tensor theory and its cosmological implications  

E-Print Network (OSTI)

We study asymptotically safe gravity with Einstein-Hilbert truncation taking into account the renormalization group running of both gravitational and cosmological constants. We show the classical behavior of the theory is equivalent to a specific class of Jordan-Brans-Dicke theories with vanishing Brans-Dicke parameter, and potential determined by the renormalization group equation. The theory may be reformulated as an $f(R)$ theory. In the simplest cosmological scenario, we find large--field inflationary solutions near the Planck scale where the effective field theory description breaks down. Finally, we discuss the implications of a running gravitational constant to background dynamics via cosmological perturbation theory. We show that compatibility with General Relativity requires contributions from the running gravitational constant to the stress energy tensor to be taken into account in the perturbation analysis.

Yi-Fu Cai; Damien A. Easson

2011-07-28T23:59:59.000Z

323

Scalar-tensor cosmologies with a potential in the general relativity limit: time evolution  

E-Print Network (OSTI)

We consider Friedmann-Lema\\^{\\i}tre-Robertson-Walker flat cosmological models in the framework of general Jordan frame scalar-tensor theories of gravity with arbitrary coupling function and potential. For the era when the cosmological energy density of the scalar potential dominates over the energy density of ordinary matter, we use a nonlinear approximation of the decoupled scalar field equation for the regime close to the so-called limit of general relativity where the local weak field constraints are satisfied. We give the solutions in cosmological time with a particular attention to the classes of models asymptotically approaching general relativity. The latter can be subsumed under two types: (i) exponential convergence, and (ii) damped oscillations around general relativity. As an illustration we present an example of oscillating dark energy.

Laur Järv; Piret Kuusk; Margus Saal

2010-06-07T23:59:59.000Z

324

Cosmological constraints in the presence of ionizing and resonance radiation at recombination  

E-Print Network (OSTI)

With the recent measurement of full sky cosmic microwave background polarization from WMAP, key cosmological degeneracies have been broken, allowing tighter constraints to be placed on cosmological parameters inferred assuming a standard recombination scenario. Here we consider the effect on cosmological constraints if additional ionizing and resonance radiation sources are present at recombination. We find that the new CMB data significantly improve the constraints on the additional radiation sources, with $\\log_{10}[\\epsilon_{\\alpha}] < -0.5$ and $\\log_{10}[\\epsilon_{i}] <-2.4$ at 95% c.l. for resonance and ionizing sources respectively. Including the generalized recombination scenario, however, we find that the constraints on the scalar spectral index $n_s$ are weakened to $n_s=0.98\\pm0.03$, with the $n_s=1$ case now well inside the 95% c.l.. The relaxation of constraints on tensor modes, scale invariance, dark energy and neutrino masses are also discussed.

Rachel Bean; Alessandro Melchiorri; Joe Silk

2007-01-09T23:59:59.000Z

325

Cosmological constraints from the CMB and Ly-alpha forest revisited  

E-Print Network (OSTI)

The WMAP team has recently highlighted the usefulness of combining the Ly-alpha forest constraints with those from the cosmic microwave background. This combination is particularly powerful as a probe of the primordial shape of the power spectrum. Converting between the Ly-alpha forest observations and the linear mass power spectrum requires a careful treatment of nuisance parameters and modeling with cosmological simulations. We point out several errors and inconsistencies in the previous treatments that propagate into the estimations and associated errors of cosmological parameters, including those reported by the WMAP team. The two most important are the insufficient range of cosmological parameters explored in simulations used to date and an incorrect treatment of the mean transmitted flux constraints. We employ a likelihood calculator for the current data set based on an extensive 6-dimensional grid of simulations. We show that the current uncertainties in the mean transmission and the flux power spectru...

Seljak, U; Makarov, A; Seljak, Uros; Donald, Patrick Mc; Makarov, Alexey

2003-01-01T23:59:59.000Z

326

Limits on Cosmological Birefringence from the Ultraviolet Polarization of Distant Radio Galaxies  

E-Print Network (OSTI)

We report on an update of the test on the rotation of the plane of linear polarization for light traveling over cosmological distances, using a comparison between the measured direction of the UV polarization in 8 radio galaxies at z>2 and the direction predicted by the model of scattering of anisotropic nuclear radiation, which explains the polarization. No rotation is detected within a few degrees for each galaxy and, if the rotation does not depend on direction, then the all-sky-average rotation is constrained to be \\theta = -0.8 +/- 2.2. We discuss the relevance of this result for constraining cosmological birefringence, when this is caused by the interaction with a cosmological pseudo-scalar field or by the presence of a Cherns-Simons term.

Sperello di Serego Alighieri; Fabio Finelli; Matteo Galaverni

2010-03-25T23:59:59.000Z

327

A note on the effect of the cosmological constant on the bending of light  

E-Print Network (OSTI)

We take another look at the equations behind the description of light bending in a Universe with a cosmological constant. We show that even within the impact parameter entering into the photon's differential equation, and which is defined here with exclusive reference to the beam of light as it bends around the central mass, lies the contribution of the cosmological constant. The latter is shown to enter in a novel way into the equation. When the latter is solved our approach implies, beyond the first two orders in the mass-term and the lowest-order in the cosmological constant, a slightly different expression for the bending angle from what is previously found in the literature.

Fayçal Hammad

2013-09-01T23:59:59.000Z

328

The tension of cosmological magnetic fields as a contribution to dark energy  

E-Print Network (OSTI)

We propose that cosmological magnetic fields generated in regions of finite spatial dimensions may manifest themselves in the global dynamics of the Universe as `dark energy'. We test our model in the context of spatially flat cosmological models by assuming that the Universe contains non-relativistic matter $\\rho_m\\propto \\alpha^{-3}$, dark energy $\\rho_{Q}\\propto \\alpha^{-3(1+w)}$, and an extra fluid with $\\rho_{B} \\propto \\alpha^{n-3}$ that corresponds to the magnetic field. We place constraints on the main cosmological parameters of our model by combining the recent supernovae type Ia data and the differential ages of passively evolving galaxies. In particular, we find that the model which best reproduces the observational data when $\\Omega_m=0.26$ is one with $\\Omega_{B}\\simeq 0.03$, $n\\simeq 7.68$, $\\Omega_{Q}\\simeq 0.71$ and $w\\simeq -0.8$.

Ioannis Contopoulos; Spyros Basilakos

2007-05-14T23:59:59.000Z

329

Experience with the Hubble Space Telescope: 20 years of an archetype  

E-Print Network (OSTI)

The Hubble Space Telescope's mission is summarized, with special emphasis placed on the Space Telescope Science Institute's unique experience with Hubble's behavior as an astronomical telescope in the environment of low earth orbit for over two decades. Historical context and background are given, and the project's early scientific expectations are described. A general overview of the spacecraft is followed by a more detailed look at the optical design, both as intended and as built. Basic characteristics of the complete complement of science instruments are also summarized. Experience with the telescope on-orbit is reviewed, starting with the major initial problems, solutions, human servicing missions, and the associated expansion of the observatory's capabilities over this time. Specific attention is then given to understanding Hubble's optical quality and pointing/jitter performance, two fundamental characteristics of a telescope. Experience with-and the important mitigation of-radiation damage and contami...

Lallo, Matthew

2012-01-01T23:59:59.000Z

330

Building ISOC Status Displays for the Large AreaTelescope aboard the Gamma Ray Large Area Space Telescope (GLAST) Observatory  

DOE Green Energy (OSTI)

In September 2007 the Gamma Ray Large Area Space Telescope (GLAST) is scheduled to launch aboard a Delta II rocket in order to put two high-energy gamma-ray detectors, the Large Area Telescope (LAT) and the GLAST Burst Monitor (GBM) into low earth orbit. The Instrument Science Operations Center (ISOC) at SLAC is responsible for the LAT operations for the duration of the mission, and will therefore build an operations center including a monitoring station at SLAC to inform operations staff and visitors of the status of the LAT instrument and GLAST. This monitoring station is to include sky maps showing the location of GLAST in its orbit as well as the LAT's projected field of view on the sky containing known gamma-ray sources. The display also requires a world map showing the locations of GLAST and three Tracking and Data Relay Satellites (TDRS) relative to the ground, their trail lines, and ''footprint'' circles indicating the range of communications for each satellite. The final display will also include a space view showing the orbiting and pointing information of GLAST and the TDRS satellites. In order to build the displays the astronomy programs Xephem, DS9, SatTrack, and STK were employed to model the position of GLAST and pointing information of the LAT instrument, and the programming utilities Python and Cron were used in Unix to obtain updated information from database and load them into the programs at regular intervals. Through these methods the indicated displays were created and combined to produce a monitoring display for the LAT and GLAST.

Ketchum, Christina; /SLAC

2006-09-01T23:59:59.000Z

331

Intrinsic and Cosmological Signatures in Gamma-Ray Burst Time Profiles: Time Dilation  

E-Print Network (OSTI)

The time profiles of many gamma-ray bursts consist of distinct pulses, which offers the possibility of characterizing the temporal structure of these bursts using a relatively small set of pulse shape parameters. We have used a pulse decomposition procedure to analyze the Time-to-Spill (TTS) data for all bursts observed by BATSE up through trigger number 2000, in all energy channels for which TTS data is available. We obtain amplitude, rise and decay timescales, a pulse shape parameter, and the fluences of individual pulses in all of the bursts. We investigate the correlations between brightness measures (amplitude and fluence) and timescale measures (pulse width and separation) which may result from cosmological time dilation of bursts, or from intrinsic properties of burst sources or from selection effects. The effects of selection biases are evaluated through simulations. The correlations between these parameters among pulses within individual bursts give a measure of the intrinsic effects while the correlations among bursts could result both from intrinsic and cosmological effects. We find that timescales tend to be shorter in bursts with higher peak fluxes, as expected from cosmological time dilation effects, but also find that there are non-cosmological effects contributing to this inverse correlation. We find that timescales tend to be longer in bursts with higher total fluences, contrary to what is expected from cosmological effects. We also find that peak fluxes and total fluences of bursts are uncorrelated, indicating that they cannot both be good distance indicators for bursts. Subject headings: gamma rays: bursts—cosmology: theory

Andrew Lee; Elliott D. Bloom; Vahé Petrosian

2000-01-01T23:59:59.000Z

332

Cosmological and Wormhole Solutions in Low-Energy Effective String Theory  

E-Print Network (OSTI)

We derive and study a class of cosmological and wormhole solutions of low-energy effective string field theory. We consider a general four-dimensional string effective action where moduli of the compactified manifold and the electromagnetic field are present. The cosmological solutions of the two-dimensional effective theory obtained by dimensional reduction of the former are discussed. In particular we demonstrate that the two-dimensional theory possesses a scale-factor duality invariance. Euclidean four-dimensional instantons describing the nucleation of the baby universes are found and the probability amplitude for the nucleation process is given.

Mariano Cadoni; Marco Cavaglia

1994-06-09T23:59:59.000Z

333

Notes on the compatibility of type Ia supernovae data and varying--$G$ cosmology  

E-Print Network (OSTI)

Observational data for type Ia supernovae, shows that the expansion of the universe is accelerated. This accelerated expansion can be described by a cosmological constant or by dark energy models like quintessence. An interesting question may be raised here. Is it possible to describe the accelerated expansion of universe using varying--$G$ cosmological models? Here we shall show that the price for having accelerated expansion in slow--varying--$G$ models (in which the dynamical terms of $G$ are ignored) is to have highly non--conserved matter and also that it is in contradiction with other data.

Shojai, F

2013-01-01T23:59:59.000Z

334

Anomaly-free perturbations with inverse-volume and holonomy corrections in Loop Quantum Cosmology  

E-Print Network (OSTI)

This article addresses the issue of the closure of the algebra of constraints for generic (cosmological) perturbations when taking into account simultaneously the two main corrections of effective loop quantum cosmology, namely the holonomy and the inverse-volume terms. Previous works on either the holonomy or the inverse volume case are reviewed and generalized. In the inverse-volume case, we point out new possibilities. An anomaly-free solution including both corrections is found for perturbations, and the corresponding equations of motion are derived.

Thomas Cailleteau; Linda Linsefors; Aurelien Barrau

2013-07-19T23:59:59.000Z

335

Hints of the Existence of Axion-Like-Particles From the Gamma-Ray Spectra of Cosmological Sources  

Science Conference Proceedings (OSTI)

Axion Like Particles (ALPs) are predicted to couple with photons in the presence of magnetic fields. This effect may lead to a significant change in the observed spectra of gamma-ray sources such as AGNs. Here we carry out a detailed study that for the first time simultaneously considers in the same framework both the photon/axion mixing that takes place in the gamma-ray source and that one expected to occur in the intergalactic magnetic fields. An efficient photon/axion mixing in the source always means an attenuation in the photon flux, whereas the mixing in the intergalactic medium may result in a decrement and/or enhancement of the photon flux, depending on the distance of the source and the energy considered. Interestingly, we find that decreasing the value of the intergalactic magnetic field strength, which decreases the probability for photon/axion mixing, could result in an increase of the expected photon flux at Earth if the source is far enough. We also find a 30% attenuation in the intensity spectrum of distant sources, which occurs at an energy that only depends on the properties of the ALPs and the intensity of the intergalactic magnetic field, and thus independent of the AGN source being observed. Moreover, we show that this mechanism can easily explain recent puzzles in the spectra of distant gamma-ray sources, like the possible detection of TeV photons from 3C 66A (a source located at z=0.444) by MAGIC and VERITAS, which should not happen according to conventional models of photon propagation over cosmological distances. Another puzzle is the recent published lower limit to the EBL intensity at 3.6 {micro}m (which is almost twice larger as the previous one), which implies very hard spectra for some detected TeV gamma-ray sources located at z=0.1-0.2. The consequences that come from this work are testable with the current generation of gamma-ray instruments, namely Fermi (formerly known as GLAST) and imaging atmospheric Cherenkov telescopes like CANGAROO, HESS, MAGIC and VERITAS.

Sanchez-Conde, M.A.; /IAA, Granada /SLAC; Paneque, D.; Bloom, E.; /KIPAC, Menlo Park; Prada, F.; /IAA, Granada /UC, Santa Cruz; Dominguez, A.; /IAA, Granada /Seville U.

2009-06-23T23:59:59.000Z

336

The Integration of Telescopes, Instruments, and User Interfaces at KPNO and WIYN  

E-Print Network (OSTI)

. The telescopes at KPNO and WIYN use various methods to integrate the control of the telescopes and instruments with the user interfaces. These methods are described, showing the evolution from FORTH based serial connections to ethernet based RPC protocols and then to the WIYN message system and the GWC protocol in use at WIYN. The integration at WIYN is highlighted, including the operation of the message routers. 1. Introduction The six telescopes at Kitt Peak operated by NOAO for KPNO and WIYN use a variety of methods for control of the telescopes, sub-systems, and instruments. There is also a variety of user interfaces used with these systems. We first give an overview of these methods and then describe the integration of these systems. The KPNO telescopes discussed are: Mayall 4 meter, 2.1 meter, Coude Feed, 0.9 meter, and the Burrell-Schmidt. The WIYN telescope is a 3.5 meter telescope operated by NOAO for the WIYN Consortium (University of Wisconsin, Indiana University, Yale U...

B. Marshall; K. Gillies; J. Lewis

1996-01-01T23:59:59.000Z

337

HUBBLE SPACE TELESCOPE PHOTOMETRY OF GLOBULAR CLUSTERS IN M81  

SciTech Connect

We perform aperture photometry and profile fitting on 419 globular cluster (GC) candidates with m{sub V} {<=} 23 mag identified in Hubble Space Telescope/Advanced Camera for Surveys BVI imaging, and estimate the effective radii of the clusters. We identify 85 previously known spectroscopically confirmed clusters, and newly identify 136 objects as good cluster candidates within the 3{sigma} color and size ranges defined by the spectroscopically confirmed clusters, yielding a total of 221 probable GCs. The luminosity function peak for the 221 probable GCs with estimated total dereddening applied is V {approx} (20.26 {+-} 0.13) mag, corresponding to a distance of {approx}3.7 {+-} 0.3 Mpc. The blue and red GC candidates, and the metal-rich and metal-poor spectroscopically confirmed clusters, respectively, are similar in half-light radius. Red confirmed clusters are about 6% larger in median half-light radius than blue confirmed clusters, and red and blue good GC candidates are nearly identical in half-light radius. The total population of confirmed and 'good' candidates shows an increase in half-light radius as a function of galactocentric distance.

Nantais, Julie B. [Departamento de Astronomia, Universidad de Concepcion Av. Esteban Iturra s/n Barrio Universitario Casilla 160-C Concepcion (Chile); Huchra, John P.; Zezas, Andreas; Gazeas, Kosmas; Strader, Jay [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)

2011-12-15T23:59:59.000Z

338

Software Spectral Correlator for the 44-Element Ooty Radio Telescope  

E-Print Network (OSTI)

A Spectral Correlator is the main component of the real time signal processing for a Radio Telescope array. The correlation of signals received at each element with every other element of the array is a classic case of an application requiring a complete graph connectivity between its data sources, as well as a very large number of simple operations to carry out the correlation. Datarates can be extremely large in order to achieve high sensitivities required for the detection of weak celestial signals. Hence, correlators are prime targets for HPC implementations. In this paper, we present the design and implementation of a massively parallel software spectral Correlator for a 44 element array. The correlator handles ~735 MB/s of incoming data from the 44 spatially distributed sources, and concurrently sustains a computational load of ~100 Gflops. We first describe how we partition the large incoming data stream into grouped datasets suited for transport over high speed serial networks, as well as ideal for pr...

Prasad, Peeyush

2011-01-01T23:59:59.000Z

339

Position-sensitive detector for the 6-meter optical telescope  

E-Print Network (OSTI)

The Position-Sensitive Detector (PSD) for photometrical and spectral observation on the 6-meter optical telescope of the Special Astrophysical Observatory (Russia) is described. The PSD consists of a position-sensitive tube, amplifiers of output signals, analog-to-digital converters (ADC) and a digital logic plate, which produces a signal for ADC start and an external strob pulse for reading information by registration system. If necessary, the thermoelectric cooler can be used. The position-sensitive tube has the following main elements: a photocathode, electrodes of inverting optics, a block of microchannel plates (MCP) and a position-sensitive collector of quadrant type. The main parameters of the PSD are the diameter of the sensitive surface is 25 mm, the spatial resolution is better than 100 (\\mu)m in the centre and a little worse on the periphery; the dead time is near 0.5 (\\mu)s; the detection quantum efficiency is defined by the photocathode and it is not less than 0.1, as a rule; dark current is about hundreds of cps, or less, when cooling. PSD spectral sensitivity depends on the type of photocathode and input window material. We use a multialkali photocathode and a fiber or UV-glass, which gives the short- wave cut of 360 nm or 250 nm, respectively.

V. Debur; T. Arkhipova; G. Beskin; V. Plokhotnichenko; M. Pakhomov; M. Smirnova; A. Solin

2003-10-14T23:59:59.000Z

340

The Allen Telescope Array Search for Electrostatic Discharges on Mars  

E-Print Network (OSTI)

The Allen Telescope Array was used to monitor Mars between 9 March and 2 June 2010, over a total of approximately 30 hours, for radio emission indicative of electrostatic discharge. The search was motivated by the report from Ruf et al. (2009) of the detection of non-thermal microwave radiation from Mars characterized by peaks in the power spectrum of the kurtosis, or kurtstrum, at 10 Hz, coinciding with a large dust storm event on 8 June 2006. For these observations, we developed a wideband signal processor at the Center for Astronomy Signal Processing and Electronics Research (CASPER). This 1024-channel spectrometer calculates the accumulated power and power-squared, from which the spectral kurtosis is calculated post-observation. Variations in the kurtosis are indicative of non-Gaussianity in the signal, which can be used to detect variable cosmic signals as well as radio frequency interference (RFI). During the three month period of observations, dust activity occurred on Mars in the form of small-scale d...

Anderson, Marin M; Barott, William C; Bower, Geoffrey C; Delory, Gregory T; de Pater, Imke; Werthimer, Dan

2011-01-01T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


341

The Burst Alert Telescope (BAT) on the Swift MIDEX Mission  

E-Print Network (OSTI)

The Burst Alert Telescope (BAT) is one of 3 instruments on the Swift MIDEX spacecraft to study gamma-ray bursts (GRBs). The BAT first detects the GRB and localizes the burst direction to an accuracy of 1-4 arcmin within 20 sec after the start of the event. The GRB trigger initiates an autonomous spacecraft slew to point the two narrow field-of-view (FOV) instruments at the burst location within 20-70 sec so to make follow-up x-ray and optical observations. The BAT is a wide-FOV, coded-aperture instrument with a CdZnTe detector plane. The detector plane is composed of 32,768 pieces of CdZnTe (4x4x2mm), and the coded-aperture mask is composed of approximately 52,000 pieces of lead (5x5x1mm) with a 1-m separation between mask and detector plane. The BAT operates over the 15-150 keV energy range with approximately 7 keV resolution, a sensitivity of approximately 10E-8 erg*cm^-2*s^-1, and a 1.4 sr (half-coded) FOV. We expect to detect >100 GRBs/yr for a 2-year mission. The BAT also performs an all-sky hard x-ray survey with a sensitivity of approximately 2 mCrab (systematic limit) and it serves as a hard x-ray transient monitor.

S. D. Barthelmy; L. M. Barbier; J. R. Cummings; E. E. Fenimore; N. Gehrels; D. Hullinger; H. A. Krimm; C. B. Markwardt; D. M. Palmer; A. Parsons; G. Sato; M. Suzuki; T. Takahashi; M. Tashiro; J. Tueller

2005-07-18T23:59:59.000Z

342

Calibration systems and methods for the ANTARES neutrino telescope  

E-Print Network (OSTI)

The ANTARES neutrino telescope is currently being constructed in the Mediterranean Sea. The complete detector will consist of 12 strings, supplemented by an additional instrumentation line. Nine strings are at present deployed of which five are already connected to the shore and operating. Each string is equipped with 75 Optical Modules (OMs) housing the photomultipliers to detect the Cherenkov light induced by the charged particles produced in neutrino reactions. An accurate measurement of the Cherenkov photon arrival times as well as the positions and orientations of the OMs is required for a precise reconstruction of the direction of the detected neutrinos. For this purpose the ANTARES detector is provided with several system s to facilitate the calibration of the detector. The time calibration is performed using light pulses emitted from LED and laser devices. The positioning is done via acoustic triangulation using hydrophones. Additionally, local tilt angles and the orientations of the modules are measured with a set of tiltmeters and compasses. In this paper, it is demonstrated that the ANTARES time and alignment calibration systems operate successfully in situ. In particular, it is shown that the ANTARES read-out electronics is capable of reaching a sub-nanosecond time resolution.

Felix Fehr; for the ANTARES Collaboration

2007-11-14T23:59:59.000Z

343

Cosmic String constraints from WMAP and the South Pole Telescope  

E-Print Network (OSTI)

The predictions of the inflationary LCDM paradigm match today's high-precision measurements of the cosmic microwave background anisotropy extremely well. The same data put tight limits on other sources of anisotropy. Cosmic strings are a particularly interesting alternate source to constrain. Strings are topological defects, remnants of inflationary-era physics that persist after the big bang. They are formed in a variety of models of inflation, including string theory models such as brane inflation. We assume a "Nambu-Goto" model for strings, approximated by a collection of unconnected segments with zero width, and show that measurements of temperature anisotropy by the South Pole Telescope break a parameter degeneracy in the WMAP data, permitting us to place a strong upper limit on the possible string contribution to the CMB anisotropy: the power sourced by zero-width strings must be <1.75% (95% CL) of the total or the string tension Gmu <1.7x10^{-7}. These limits imply that the best hope for detecting strings in the CMB will come from B-mode polarization measurements at arcminute scales rather than the degree scale measurements pursued for gravitational wave detection.

Cora Dvorkin; Mark Wyman; Wayne Hu

2011-09-22T23:59:59.000Z

344

Cosmological Shock Waves in the Large Scale Structure of the Universe: Non-gravitational Effects  

E-Print Network (OSTI)

Cosmological shock waves result from supersonic flow motions induced by hierarchical clustering of nonlinear structures in the universe. These shocks govern the nature of cosmic plasma through thermalization of gas and acceleration of nonthermal, cosmic-ray (CR) particles. We study the statistics and energetics of shocks formed in cosmological simulations of a concordance $\\Lambda$CDM universe, with a special emphasis on the effects of non-gravitational processes such as radiative cooling, photoionization/heating, and galactic superwind feedbacks. Adopting an improved model for gas thermalization and CR acceleration efficiencies based on nonlinear diffusive shock acceleration calculations, we then estimate the gas thermal energy and the CR energy dissipated at shocks through the history of the universe. Since shocks can serve as sites for generation of vorticity, we also examine the vorticity that should have been generated mostly at curved shocks in cosmological simulations. We find that the dynamics and energetics of shocks are governed primarily by the gravity of matter, so other non-gravitational processes do not affect significantly the global energy dissipation and vorticity generation at cosmological shocks. Our results reinforce scenarios in which the intracluster medium and warm-hot intergalactic medium contain energetically significant populations of nonthermal particles and turbulent flow motions.

Hyesung Kang; Dongsu Ryu; Renyue Cen; J. P. Ostriker

2007-04-12T23:59:59.000Z

345

Non-linear evolution of f(R) cosmologies I: methodology  

E-Print Network (OSTI)

We introduce the method and the implementation of a cosmological simulation of a class of metric-variation f(R) models that accelerate the cosmological expansion without a cosmological constant and evade solar-system bounds of small-field deviations to general relativity. Such simulations are shown to reduce to solving a non-linear Poisson equation for the scalar degree of freedom introduced by the f(R) modifications. We detail the method to efficiently solve the non-linear Poisson equation by using a Newton-Gauss-Seidel relaxation scheme coupled with multigrid method to accelerate the convergence. The simulations are shown to satisfy tests comparing the simulated outcome to analytical solutions for simple situations, and the dynamics of the simulations are tested with orbital and Zeldovich collapse tests. Finally, we present several static and dynamical simulations using realistic cosmological parameters to highlight the differences between standard physics and f(R) physics. In general, we find that the f(R) modifications result in stronger gravitational attraction that enhances the dark matter power spectrum by ~20% for large but observationally allowed f(R) modifications. More detailed study of the non-linear f(R) effects on the power spectrum are presented in a companion paper.

Hiroaki Oyaizu

2008-07-15T23:59:59.000Z

346

Bulk viscous fluid hypersurface - homogeneous cosmological models with time varying G and ?  

Science Conference Proceedings (OSTI)

Hypersurface - homogeneous cosmological models containing a bulk viscous fluid with time varying G and ? have been presented. We have shown that the field equations are solvable for any arbitrary cosmic scale function. The viscosity coefficient ... Keywords: bulk viscosity, hypersurface - homogeneous, variable G and ?. LATEX

Shri Ram; M. K. Verma

2010-02-01T23:59:59.000Z

347

Cosmological model with viscosity media (dark fluid) described by an effective equation of state  

E-Print Network (OSTI)

A generally parameterized equation of state (EOS) is investigated in the cosmological evolution with bulk viscosity media modelled as dark fluid, which can be regarded as a unification of dark energy and dark matter. Compared with the case of the perfect fluid, this EOS has possessed four additional parameters, which can be interpreted as the case of the non-perfect fluid with time-dependent viscosity or the model with variable cosmological constant. From this general EOS, a completely integrable dynamical equation to the scale factor is obtained with its solution explicitly given out. (i) In this parameterized model of cosmology, for a special choice of the parameters we can explain the late-time accelerating expansion universe in a new view. The early inflation, the median (relatively late time) deceleration, and the recently cosmic acceleration may be unified in a single equation. (ii) A generalized relation of the Hubble parameter scaling with the redshift is obtained for some cosmology interests. (iii) By using the SNe Ia data to fit the effective viscosity model we show that the case of matter described by $p=0$ plus with effective viscosity contributions can fit the observational gold data in an acceptable level

J. Ren; Xin He Meng

2005-11-07T23:59:59.000Z

348

Dark energy, exotic matter and properties of horizons in black hole physics and cosmology  

E-Print Network (OSTI)

We summarize recent results on the properties of near-horizon metrics in different spherically symmetric space-times, including Kantowski-Sachs cosmological models whose evolution begins with a horizon (the so-called Null Big Bang) and static metrics related to black holes. We describe the types of matter compatible with cosmological and black-hole horizons. It turns out, in particular, that a black hole horizon can be in equilibrium with a fluid of disordered cosmic strings ("black holes can have curly hair"). We also discuss different kinds of horizons from the viewpoint of the behavior of tidal forces acting on an extended body and recently classified as "usual", "naked" and "truly naked" ones; in the latter case, tidal forces are infinite in a freely falling reference frame. It is shown that all truly naked horizons, as well as many of those previously characterized as naked and even usual ones, do not admit an extension and therefore must be considered as singularities. The whole analysis is performed locally (in a neighborhood of a candidate horizon) in a model-independent manner. Finally, the possible importance of some of these models in generating dynamic, perturbatively small vacuum fluctuation contributions to the cosmological constant (within a cosmological Casimir-effect approach to this problem) is discussed.

K. A. Bronnikov; E. Elizalde; O. B. Zaslavskii

2008-10-28T23:59:59.000Z

349

How robust are the constraints on cosmology and galaxy evolution from the lens-redshift test?  

E-Print Network (OSTI)

The redshift distribution of galaxy lenses in known gravitational lens systems provides a powerful test that can potentially discriminate amongst cosmological models. However, applications of this elegant test have been curtailed by two factors: our ignorance of how galaxies evolve with redshift, and the absence of methods to deal with the effect of incomplete information in lensing systems. In this paper, we investigate both issues in detail. We explore how to extract the properties of evolving galaxies, assuming that the cosmology is well determined by other techniques. We propose a new nested Monte Carlo method to quantify the effects of incomplete data. We apply the lens-redshift test to an improved sample of seventy lens systems derived from recent observations, primarily from the SDSS, SLACS and the CLASS surveys. We find that the limiting factor in applying the lens-redshift test derives from poor statistics, including incomplete information samples, and biased sampling. Many lenses that uniformly sample the underlying true image separation distribution will be needed to use this test as a complementary method to measure the value of the cosmological constant or the properties of evolving galaxies. Planned future surveys by missions like the SNAP satellite or LSST are likely to usher in a new era for strong lensing studies that utilize this test. With expected catalogues of thousands of new strong lenses, the lens-redshift test could offer a powerful tool to probe cosmology as well as galaxy evolution.

Pedro R. Capelo; Priyamvada Natarajan

2007-05-22T23:59:59.000Z

350

A New Approach to Statistics of Cosmological Gamma-Ray Bursts  

E-Print Network (OSTI)

We use a new method of analysis to determine parameters of cosmological gamma-ray bursts (GRBs), assuming that their distribution follows the star-formation history of the universe. Spectral evolution is calculated from an external shock model for fireball/blast wave evolution, and used to evaluate the measured peak flux, duration, and $\

M. Boettcher; C. D. Dermer

1998-12-02T23:59:59.000Z

351

The chemical evolution of a Milky Way-like galaxy: the importance of a cosmologically motivated infall law  

E-Print Network (OSTI)

We aim at finding a cosmologically motivated infall law to understand if the LambdaCDM cosmology can reproduce the main chemical characteristics of a Milky Way-like spiral galaxy. In this work we test several different gas infall laws, starting from that suggested in the two-infall model for the chemical evolution of the Milky Way by Chiappini et al., but focusing on laws derived from cosmological simulations which follows a concordance LambdaCDM cosmology. By means of a detailed chemical evolution model for the solar vicinity, we study the effects of the different gas infall laws on the abundance patterns and the G-dwarf metallicity distribution. The cosmological gas infall law predicts two main gas accretion episodes. By means of this cosmologically motivated infall law, we study the star formation rate, the SNIa and SNII rate, the total amount of gas and stars in the solar neighbourhood and the behaviour of several chemical abundances. We find that the results of the two-infall model are fully compatible with the evolution of the Milky Way with cosmological accretion laws. A gas assembly history derived from a DM halo, compatible with the formation of a late-type galaxy from the morphological point of view, can produce chemical properties in agreement with the available observations.

Edoardo Colavitti; Francesca Matteucci; Giuseppe Murante

2008-02-13T23:59:59.000Z

352

Green Bank Telescope Studies of Giant Pulses from Millisecond Pulsars  

E-Print Network (OSTI)

We have conducted a search for giant pulses from four millisecond pulsars using the 100m Green Bank Telescope. Coherently dedispersed time-series from PSR J0218+4232 were found to contain giant pulses of very short intrinsic duration whose energies follow power-law statistics. The giant pulses are in phase with the two minima of the radio integrated pulse profile but are phase aligned with the peaks of the X-ray profile. Historically, individual pulses more than 10-20 times the mean pulse energy have been deemed to be ``giant pulses''. As only 4 of the 155 pulses had energies greater than 10 times the mean pulse-energy, we argue the emission mechanism responsible for giant pulses should instead be defined through: (a) intrinsic timescales of microsecond or nanosecond duration; (b) power-law energy statistics; and (c) emission occurring in narrow phase-windows coincident with the phase windows of non-thermal X-ray emission. Four short-duration pulses with giant-pulse characteristics were also observed from PSR B1957+20. As the inferred magnetic fields at the light cylinders of the millisecond pulsars that emit giant pulses are all very high, this parameter has previously been considered to be an indicator of giant pulse emissivity. However, the frequency of giant pulse emission from PSR~B1957+20 is significantly lower than for other millisecond pulsars that have similar magnetic fields at their light cylinders. This suggests that the inferred magnetic field at the light cylinder is a poor indicator of the rate of emission of giant pulses.

H. S. Knight; M. Bailes; R. N. Manchester; S. M. Ord; B. A. Jacoby

2005-12-13T23:59:59.000Z

353

HUBBLE SPACE TELESCOPE IMAGING OF POST-STARBURST QUASARS  

Science Conference Proceedings (OSTI)

We present images of 29 post-starburst quasars (PSQs) from a Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) Wide Field Channel Snapshot program. These broadlined active galactic nuclei (AGNs) possess the spectral signatures of massive (M{sub burst} {approx} 10{sup 10} M{sub sun}), moderate-aged stellar populations (hundreds of Myr). Thus, their composite nature provides insight into the AGN-starburst connection. We measure quasar-to-host galaxy light contributions via semi-automated two-dimensional light profile fits of point-spread-function-subtracted images. We examine the host morphologies and model the separate bulge and disk components. The HST/ACS-F606W images reveal an equal number of spiral (13/29) and early-type (13/29) hosts, with the remaining three hosts having indeterminate classifications. AGNs hosted by early-type galaxies have on average greater luminosity than those hosted by spiral galaxies. Disturbances such as tidal tails, shells, star-forming knots, and asymmetries are seen as signposts of interaction/merger activity. Disturbances like these were found in 17 of the 29 objects and are evenly distributed among early-type and spiral galaxies. Two of these systems are clearly merging with their companions. Compared to other AGNs of similar luminosity and redshift, these PSQs have a higher fraction of early-type hosts and disturbances. Our most luminous objects with disturbed early-type host galaxies appear to be consistent with merger products. Thus, these luminous galaxies may represent a phase in an evolutionary scenario for merger-driven activity. Our less luminous objects appear to be consistent with Seyfert galaxies not requiring triggering by major mergers. Many of these Seyferts are barred spiral galaxies.

Cales, S. L.; Brotherton, M. S.; Shang Zhaohui [Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071 (United States); Bennert, Vardha Nicola [Department of Physics, University of California, Santa Barbara, CA 93106 (United States); Canalizo, G. [Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States); Stoll, R. [Department of Astronomy, Ohio State University, Columbus, OH 43210 (United States); Ganguly, R. [Department of Computer Science, Engineering, and Physics, University of Michigan-Flint, Flint, MI 48502 (United States); Vanden Berk, D. [Department of Physics, Saint Vincent College, Latrobe, PA 15650 (United States); Paul, C. [Physics Department, University of California, Davis, CA 95616 (United States); Diamond-Stanic, A., E-mail: scales@uwyo.edu, E-mail: mbrother@uwyo.edu, E-mail: shang@uwyo.edu, E-mail: bennert@physics.ucsb.edu, E-mail: gabriela.canalizo@ucr.edu, E-mail: stoll@astronomy.ohio-state.edu, E-mail: ganguly@umflint.edu, E-mail: daniel.vandenberk@email.stvincent.edu, E-mail: capaul@ucdavis.edu, E-mail: aleks@ucsd.edu [Center for Astrophysics and Space Sciences, University of California, San Diego, La Jolla, CA 92093 (United States)

2011-11-10T23:59:59.000Z

354

User Interface for the Control of the Gemini Telescopes S. S. Smith and K. Gillies  

E-Print Network (OSTI)

on the science detectors is a primary goal. Keywords: Gemini Telescope Control User Interface Tcl/Tk EPICS 1 are being built using Tcl/Tk 1 and are implemented to follow the ESO Graphical User Interface Common

355

User Interface for the Control of the Gemini Telescopes S. S. Smith and K. Gillies  

E-Print Network (OSTI)

detectors is a primary goal. Keywords: Gemini Telescope Control User Interface Tcl/Tk EPICS 1. INTRODUCTION software to cover the requirements of both. Applications are being built using Tcl/Tk1 and are implemented

356

Optical-level structural modelling of membrane mirrors for spaceborne telescopes  

E-Print Network (OSTI)

The astronomy and Earth observation communities desire ever-larger space telescopes, but launch costs limit mass and technology limits size. Current research in large aperture mirrors largely supports deployed rigid optics, ...

De Blonk, Brett Jeffrey, 1971-

2003-01-01T23:59:59.000Z

357

Thin optic surface analysis for high resolution X-ray telescopes  

E-Print Network (OSTI)

The art of glass developed throughout the years has covered artifacts ranging from crude ornaments to high precision optics used in flat panel displays, hard disk drives, and x-ray telescopes. Methods for manufacturing ...

Akilian, Mireille

2004-01-01T23:59:59.000Z

358

THE NEW CANGAROO TELESCOPE AND THE PROSPECT OF VHE GAMMA RAY OBSERVATION AT  

E-Print Network (OSTI)

), the doppler boosting of secondary gamma-rays is sufficient to produce TeV gamma-rays. Gamma-ray bursts: Fireballs expanding with relativistic speed explain gamma-ray bursts at cosmological distancesStudy of Celestial Objects with Very High Energy Gamma Rays CANGAROO III Project Description

Enomoto, Ryoji

359

Watching an uniformly moving source of light using a telescope and a frequency-meter  

E-Print Network (OSTI)

We propose a scenario that involves a stationary observer who detects a point like source of light moving with constant velocity at a constant altitude, using a telescope and a frequency-meter. We derive a formula for the angular velocity at which we should rotate the axis of the telescope and a formula that relates the proper period at which the source emits successive wave crests and the proper period at which the stationary observer receives them

Bernhard Rothenstein; Ioan Damian

2005-04-04T23:59:59.000Z

360

CCD drift-scan imaging lunar occultations: a feasible approach for sub-meter class telescopes  

E-Print Network (OSTI)

A CCD drift-scanning technique for lunar occultation (LO) observations is presented. While this approach has been addressed before by Sturmann (1994) for the case of large telescopes, the technical validity has never been discussed for sub-meter class telescopes. In contrast to Sturmann's scheme, the proposed technique places the CCD in the image plane of the telescope. This does not represent a problem in the case of small telescopes, where the practical angular resolution attainable by LO is not limited by aperture smoothing. Photon-generated charge is read out at millisecond rate on a column-per-column basis, as the diffraction pattern of the occulted star is being tracked. Two LO events (SAO 79031 and SAO 77911) were observed to demonstrate the feasibility of the method. Data analysis was carried out and no angular diameter the observed stars were resolved. We show, however, that the technique could be useful for close binary detections with small telescopes. A discussion of the limiting resolution and magnitude imposed by our instrumentation is carried out, showing that drift-scanning technique could be extended to 1-2m telescopes for stellar diameter determination purposes. Finally, we point out that the technical demands required by this technique can be easily met by most small professional observatories and advanced amateurs.

O. Fors; J. Nunez; A. Richichi

2001-08-27T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
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361

Modified f(R) gravity consistent with realistic cosmology: from matter dominated epoch to dark energy universe  

E-Print Network (OSTI)

We develop the general scheme for modified $f(R)$ gravity reconstruction from any realistic FRW cosmology. We formulate several versions of modified gravity compatible with Solar System tests where the following sequence of cosmological epochs occurs: a. matter dominated phase (with or without usual matter), transition from decceleration to acceleration, accelerating epoch consistent with recent WMAP data b. $\\Lambda$CDM cosmology without cosmological constant. As a rule, such modified gravities are expressed implicitly (in terms of special functions) with late-time asymptotics of known type (for instance, the model with negative and positive powers of curvature). In the alternative approach, it is demonstrated that even simple versions of modified gravity may lead to the unification of matter dominated and accelerated phases at the price of the introduction of compensating dark energy.

Shin'ichi Nojiri; Sergei D. Odintsov

2006-08-01T23:59:59.000Z

362

Modified f(R) gravity consistent with realistic cosmology: from matter dominated epoch to dark energy universe  

E-Print Network (OSTI)

We develop the general scheme for modified $f(R)$ gravity reconstruction from any realistic FRW cosmology. We formulate several versions of modified gravity compatible with Solar System tests where the following sequence of cosmological epochs occurs: a. matter dominated phase (with or without usual matter), transition from decceleration to acceleration, accelerating epoch consistent with recent WMAP data b. $\\Lambda$CDM cosmology without cosmological constant. As a rule, such modified gravities are expressed implicitly (in terms of special functions) with late-time asymptotics of known type (for instance, the model with negative and positive powers of curvature). In the alternative approach, it is demonstrated that even simple versions of modified gravity may lead to the unification of matter dominated and accelerated phases at the price of the introduction of compensating dark energy.

Nojiri, S; Nojiri, Shin'ichi; Odintsov, Sergei D.

2006-01-01T23:59:59.000Z

363

Large Synoptic Survey Telescope: From Science Drivers to Reference Design  

SciTech Connect

In the history of astronomy, major advances in our understanding of the Universe have come from dramatic improvements in our ability to accurately measure astronomical quantities. Aided by rapid progress in information technology, current sky surveys are changing the way we view and study the Universe. Next-generation surveys will maintain this revolutionary progress. We focus here on the most ambitious survey currently planned in the visible band, the Large Synoptic Survey Telescope (LSST). LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: constraining dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. It will be a large, wide-field ground-based system designed to obtain multiple images covering the sky that is visible from Cerro Pachon in Northern Chile. The current baseline design, with an 8.4 m (6.5 m effective) primary mirror, a 9.6 deg{sup 2} field of view, and a 3,200 Megapixel camera, will allow about 10,000 square degrees of sky to be covered using pairs of 15-second exposures in two photometric bands every three nights on average. The system is designed to yield high image quality, as well as superb astrometric and photometric accuracy. The survey area will include 30,000 deg{sup 2} with {delta} < +34.5{sup o}, and will be imaged multiple times in six bands, ugrizy, covering the wavelength range 320-1050 nm. About 90% of the observing time will be devoted to a deep-wide-fast survey mode which will observe a 20,000 deg{sup 2} region about 1000 times in the six bands during the anticipated 10 years of operation. These data will result in databases including 10 billion galaxies and a similar number of stars, and will serve the majority of science programs. The remaining 10% of the observing time will be allocated to special programs such as Very Deep and Very Fast time domain surveys. We describe how the LSST science drivers led to these choices of system parameters.

Ivezic, Z.; Axelrod, T.; Brandt, W.N.; Burke, D.L.; Claver, C.F.; Connolly, A.; Cook, K.H.; Gee, P.; Gilmore, D.K.; Jacoby, S.H.; Jones, R.L.; Kahn, S.M.; Kantor, J.P.; Krabbendam, V.; Lupton, R.H.; Monet, D.G.; Pinto, P.A.; Saha, A.; Schalk, T.L.; Schneider, D.P.; Strauss, Michael A.; /Washington U., Seattle, Astron. Dept. /LSST Corp. /Penn State U., Astron. Astrophys. /KIPAC, Menlo Park /NOAO, Tucson /LLNL, Livermore /UC, Davis /Princeton U., Astrophys. Sci. Dept. /Naval Observ., Flagstaff /Arizona U., Astron. Dept. - Steward Observ. /UC, Santa Cruz /Harvard U. /Johns Hopkins U. /Illinois U., Urbana

2011-10-14T23:59:59.000Z

364

Report of the March '2002 Atacama  

E-Print Network (OSTI)

,Valotto, R.Vrech and L.Keller with "Annie" and Rusty in Casa de Don Tomás Hotel #12;R.Vrech, M.Domínguez, C of Cerros Toco and Negro, being observed that in the case of Toco they could take the data using the utility

365

Scale Transformations, Tree-level Perturbation Theory, and the Cosmological Matter Bispectrum  

E-Print Network (OSTI)

Scale transformations have played an extremely successful role in studies of cosmological large-scale structure by relating the non-linear spectrum of cosmological density fluctuations to the linear primordial power at longer wavelengths. Here we generalize this approach to investigate the usefulness of scale transformations for nonlinear higher-order statistics, specifically the bispectrum. We find that the bispectrum predicted by perturbation theory at tree-level can be rescaled to match the results of full numerical simulations in the weakly and intermediately nonlinear regimes, especially at high redshifts, with an accuracy that is surprising given the simplicity of the procedure used. This discovery not only offers a simple practical way of calculating the matter bispectrum, but also suggests that scale transformations may yet yield even deeper insights into the physics of hierarchical clustering.

Jun Pan; Peter Coles; Istvan Szapudi

2007-07-11T23:59:59.000Z

366

Astrophysical and cosmological problems of invisible mass and dark energy in the Universe  

E-Print Network (OSTI)

The Workshop on results of the Project Kosmomikrofizyka-2 (Astroparticle Physics) of the National Academy of Sciences (NAS) of Ukraine "Astrophysical and cosmological problems of invisible mass and dark energy in the Universe" was held on November 21-22, 2012 in the Institute for Nuclear Research, Kyiv, Ukraine (http://lpd.kinr.kiev.ua/kmf12). This Project was carried out during three years (2010-2012) by scientists from various universities and institutes of the National Academy of Sciences of Ukraine; it was a logical continuation of the previous scientific program of the NAS of Ukraine "Researches of structure and composition of the Universe, hidden mass and dark energy (Kosmomikrofizyka)" in 2007-2009. These programs were devoted to theoretical and experimental investigations in astronomy, astrophysics, cosmology, physics of atomic nuclei and particle physics, which are related with the problems of dark matter and dark energy in the Universe.

P. Belli; L. A. Berdina; R. Bernabei; A. Bogdan; R. S. Boiko; A. Yu. Burgazli; F. Cappella; R. Cerulli; D. M. Chernyak; F. A. Danevich; A. d'Angelo; M. V. Eingorn; S. H. Fakhr; E. Fedorova; E. N. Galashov; A. Giuliani; B. I. Hnatyk; A. Incicchitti; G. Ivashchenko; V. V. Kobychev; O. O. Kobzar; H. Kraus; B. N. Kropivyansky; A. V. Kudinova; Yu. A. Kulinich; M. Laubenstein; V. V. Marchenko; S. Marnieros; V. B. Mikhailik; A. A. Minakov; V. M. Mokina; L. L. Nagornaya; A. S. Nikolaiko; C. Nones; B. S. Novosyadlyj; E. Olivieri; V. O. Pelykh; D. V. Poda; R. B. Podviyanuk; O. G. Polischuk; O. N. Sergijenko; V. N. Shlegel; V. M. Shulga; V. M. Sliusar; O. B. Sushchov; Y. V. Taistra; M. Tenconi; O. Torbaniuk; V. I. Tretyak; V. S. Tsvetkova; V. G. Vakulik; Ya. V. Vasiliev; A. Vasylenko; O. Vasylenko; V. I. Zhdanov; A. I. Zhuk

2013-04-16T23:59:59.000Z

367

The holographic dark energy in non-flat Brans-Dicke cosmology  

E-Print Network (OSTI)

In this paper we study cosmological application of holographic dark energy density in the Brans-Dicke framework. We employ the holographic model of dark energy to obtain the equation of state for the holographic energy density in non-flat (closed) universe enclosed by the event horizon measured from the sphere of horizon named $L$. Our calculation show, taking $\\Omega_{\\Lambda}=0.73$ for the present time, the lower bound of $w_{\\rm \\Lambda}$ is -0.9. Therefore it is impossible to have $w_{\\rm \\Lambda}$ crossing -1. This implies that one can not generate phantom-like equation of state from a holographic dark energy model in non-flat universe in the Brans-Dicke cosmology framework. In the other hand, we suggest a correspondence between the holographic dark energy scenario in flat universe and the phantom dark energy model in framework of Brans-Dicke theory with potential.

M R Setare

2006-10-17T23:59:59.000Z

368

Interacting new agegraphic dark energy in non-flat Brans-Dicke cosmology  

E-Print Network (OSTI)

We construct a cosmological model of late acceleration based on the new agegraphic dark energy model in the framework of Brans-Dicke cosmology where the new agegraphic energy density $\\rho_{D}= 3n^2 m^2_p /\\eta^{2}$ is replaced with $\\rho_{D}= {3n^2\\phi^2}/({4\\omega \\eta^2}$). We show that the combination of Brans-Dicke field and agegraphic dark energy can accommodate $w_D = -1 $ crossing for the equation of state of \\textit{noninteracting} dark energy. When an interaction between dark energy and dark matter is taken into account, the transition of $w_D $ to phantom regime can be more easily accounted for than when resort to the Einstein field equations is made. In the limiting case $\\alpha = 0$ $(\\omega\\to \\infty)$, all previous results of the new agegraphic dark energy in Einstein gravity are restored.

Ahmad Sheykhi

2009-08-05T23:59:59.000Z

369

Dependence of hadronic properties on Quark Masses and Constraints on their Cosmological Variation  

E-Print Network (OSTI)

We follow our previous paper on possible cosmological variation of weak scale (quark masses) and strong scale, inspired by data on cosmological variation of the electromagnetic fine structure constant from distant quasar (QSO) absorption spectra. In this work we identify the {\\em strange quark mass} $m_s$ as the most important quantity, and the {\\em sigma meson mass} as the ingredient of the nuclear forces most sensitive to it. As a result, we claim significantly stronger limits on ratio of weak/strong scale ($W=m_s/\\Lambda_{QCD}$) variation following from our previous discussion of primordial Big-Bang Nucleosynthesis ($|\\delta W/W|nuclear reactor ($|\\delta W/W|<1.2 \\cdot 10^{-10}$; there is also a non-zero solution $\\delta W/W=(-0.56 \\pm 0.05) \\cdot 10^{-9}$) .

V. V. Flambaum; E. V. Shuryak

2002-12-31T23:59:59.000Z

370

Tracking quintessence and k-essence in a general cosmological background  

E-Print Network (OSTI)

We derive conditions for stable tracker solutions for both quintessence and k-essence in a general cosmological background, H^2 \\propto f(\\rho). We find that tracker solutions are possible only when \\eta = d ln f /d ln \\rho is constant, aside from a few special cases, which are enumerated. Expressions for the quintessence or k-essence equation of state are derived as a function of \\eta and the equation of state of the dominant background component.

Rupam Das; Thomas W. Kephart; Robert J. Scherrer

2006-09-05T23:59:59.000Z

371

Cosmological Models of Universe with Variable Deceleration Parameter in Lyra's Manifold  

E-Print Network (OSTI)

FRW models of the universe have been studied in the cosmological theory based on Lyra's manifold. A new class of exact solutions has been obtained by considering a time dependent displacement field for variable deceleration parameter from which three models of the universe are derived (i) exponential (ii) polynomial and (iii) sinusoidal form respectively. The behaviour of these models of the universe are also discussed. Finally some possibilities of further problems and their investigations have been pointed out.

A. Pradhan; J. P. Shahi; C. B. Singh

2006-08-14T23:59:59.000Z

372

Nonlinearities in modified gravity cosmology: Signatures of modified gravity in the nonlinear matter power spectrum  

SciTech Connect

A large fraction of cosmological information on dark energy and gravity is encoded in the nonlinear regime. Precision cosmology thus requires precision modeling of nonlinearities in general dark energy and modified gravity models. We modify the Gadget-2 code and run a series of N-body simulations on modified gravity cosmology to study the nonlinearities. The modified gravity model that we investigate in the present paper is characterized by a single parameter {zeta}, which determines the enhancement of particle acceleration with respect to general relativity (GR), given the identical mass distribution ({zeta}=1 in GR). The first nonlinear statistics we investigate is the nonlinear matter power spectrum at k < or approx. 3h/Mpc, which is the relevant range for robust weak lensing power spectrum modeling at l < or approx. 2000. In this study, we focus on the relative difference in the nonlinear power spectra at corresponding redshifts where different gravity models have the same linear power spectra. This particular statistics highlights the imprint of modified gravity in the nonlinear regime and the importance of including the nonlinear regime in testing GR. By design, it is less susceptible to the sample variance and numerical artifacts. We adopt a mass assignment method based on wavelet to improve the power spectrum measurement. We run a series of tests to determine the suitable simulation specifications (particle number, box size, and initial redshift). We find that, the nonlinear power spectra can differ by {approx}30% for 10% deviation from GR (|{zeta}-1|=0.1) where the rms density fluctuations reach 10. This large difference, on one hand, shows the richness of information on gravity in the corresponding scales, and on the other hand, invalidates simple extrapolations of some existing fitting formulae to modified gravity cosmology.

Cui Weiguang; Zhang Pengjie; Yang Xiaohu [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Partner Group of MPA, Nandan Road 80, Shanghai, 200030 (China)

2010-05-15T23:59:59.000Z

373

Holographic dark energy with varying gravitational constant in Horava-Lifshitz cosmology  

E-Print Network (OSTI)

We investigate the holographic dark energy scenario with a varying gravitational constant in a flat background in the context of Ho\\v{r}ava-Lifshitz gravity. We extract the exact differential equation determining the evolution of the dark energy density parameter, which includes $G$ variation term. Also we discuss a cosmological implication of our work by evaluating the dark energy equation of state for low redshifts containing varying $G$ corrections.

M. R. Setare; Mubasher Jamil

2010-01-08T23:59:59.000Z

374

The dynamics of scalar-tensor cosmology from RS two-brane model  

E-Print Network (OSTI)

We consider a Randall-Sundrum two-brane cosmological model in the low energy gradient expansion approximation by Kanno and Soda. It is a scalar-tensor theory with a specific coupling function and a specific potential. Upon introducing the FLRW metric and perfect fluid matter on both branes in the Jordan frame, the effective dynamical equation for the the A-brane (our Universe) scale factor decouples from the scalar field and B-brane matter leaving only a non-vanishing integration constant (the dark radiation term). We find exact solutions for the A-brane scale factor for four types of matter: cosmological constant, radiation, dust, and cosmological constant plus radiation. We perform a complementary analysis of the dynamics of the scalar field (radion) using phase space methods and examine convergence towards the limit of general relativity. In particular, we find that radion stabilizes at a certain finite value for suitable negative matter densities on the B-brane. Observational constraints from Solar system experiments (PPN) and primordial nucleosynthesis (BBN) are also briefly discussed.

Laur Jarv; Piret Kuusk; Margus Saal

2006-08-24T23:59:59.000Z

375

Chaos-order transition in Bianchi type I non-Abelian Born-Infeld cosmology  

SciTech Connect

We investigate the Bianchi I cosmology with the homogeneous SU(2) Yang-Mills field governed by the non-Abelian Born-Infeld action. A similar system with the standard Einstein-Yang-Mills (EYM) action is known to exhibit chaotic behavior induced by the Yang-Mills field. When the action is replaced by the Born-Infeld-type non-Abelian action (NBI), the chaos-order transition is observed in the high-energy region. This is interpreted as a smothering effect due to (nonperturbative in {alpha}{sup '}) string corrections to the classical EYM action. We give numerical evidence for the chaos-order transition and present an analytical proof of regularity of color oscillations in the limit of strong Born-Infeld nonlinearity. We also perform a general analysis of the Bianchi I NBI cosmology and derive an exact solution in the case of only the U(1) component excited. Our new exact solution generalizes the Rosen solution of the Bianchi I Einstein-Maxwell cosmology to the U(1) Einstein-Born-Infeld theory.

Dyadichev, Vladimir V.; Gal' tsov, Dmitri V.; Moniz, Paulo Vargas [Department of Theoretical Physics, Moscow State University, 119899, Moscow (Russian Federation); Astronomy Unit, School of Mathematical Sciences, University of London, Mile End Road, London E1 4NS (United Kingdom)

2005-10-15T23:59:59.000Z

376

Extending the redshift-distance relation in Cosmological General Relativity to higher redshifts  

E-Print Network (OSTI)

The redshift-distance modulus relation, the Hubble Diagram, derived from Cosmological General Relativity has been extended to arbitrarily large redshifts. Numerical methods were employed and a density function was found that results in a valid solution of the field equations at all redshifts. The extension has been compared to 302 type Ia supernova data as well as to 69 Gamma-ray burst data. The latter however do not not truly represent a `standard candle' as the derived distance modulii are not independent of the cosmology used. Nevertheless the analysis shows a good fit can be achieved without the need to assume the existence of dark matter. The Carmelian theory is also shown to describe a universe that is always spatially flat. This results from the underlying assumption of the energy density of a cosmological constant $\\Omega_{\\Lambda} = 1$, the result of vacuum energy. The curvature of the universe is described by a \\textit{spacevelocity} metric where the energy content of the curvature at any epoch is $\\Omega_K = \\Omega_{\\Lambda} - \\Omega = 1-\\Omega$, where $\\Omega$ is the matter density of the universe. Hence the total density is always $\\Omega_K + \\Omega = 1$

John G. Hartnett

2007-05-22T23:59:59.000Z

377

CMB and Matter Power Spectra of Early f(R) Cosmology in Palatini Formalism  

E-Print Network (OSTI)

We calculate in this article the CMB and matter power spectra of a class of early $f(R)$ cosmologies, which takes the form of $f(R) = R + \\lambda_1 H_0^2\\text{exp}[R/(\\lambda_2 H_0^2)]$. Unlike the late-time $f(R)$ cosmologies such as $f(R) = R + \\alpha(-R)^\\beta$ ($\\betaR)$ Cosmology}), and this important feature leads to rather different ISW effect and CMB spectrum. The matter power spectrum of this model is, at the same time, again very sensitive to the chosen parameters, and LSS observations such as SDSS should constrain the parameter space stringently. We expect that our results are applicable at least qualitatively to other models that produce $f(R)$ modification to GR at earlier times (\\emph{e.g.}, redshifts $\\mathcal{O}(10) \\lesssim z \\lesssim \\mathcal{O}(1)$) than when dark energy begins to dominate -- such models are strongly disfavored by data on CMB and matter power spectra.

Baojiu Li; Ming-Chung Chu

2006-10-16T23:59:59.000Z

378

Bianchi Type-$V$ cosmology in $f(R,T)$ gravity with $?(T)$  

E-Print Network (OSTI)

A new class of cosmological models in $f(R, T)$ modified theories of gravity proposed by Harko et al. (2011), where the gravitational Lagrangian is given by an arbitrary function of Ricci scalar $R$ and the trace of the stress-energy tensor $T$, have been investigated for a specific choice of $f(R, T) = f_{1}(R) + f_{2}(T)$ by considering time dependent deceleration parameter. The concept of time dependent deceleration parameter (DP) with some proper assumptions yield the average scale factor $a(t) = \\sinh^{\\frac{1}{n}}(\\alpha t)$, where $n$ and $\\alpha$ are positive constants. For $0 1$, the models of universe exhibit phase transition from early decelerating phase to present accelerating phase which is in good agreement with the results from recent astrophysical observations. Our intention is to reconstruct $f(R,T)$ models inspired by this special law for the deceleration parameter in connection with the theories of modified gravity. In the present study we consider the cosmological constant $\\Lambda$ as a function of the trace of the stress energy-momentum-tensor, and dub such a model "$\\Lambda(T)$ gravity" where we have specified a certain form of $\\Lambda(T)$. Such models may display better uniformity with the cosmological observations. The statefinder diagnostic pair $\\{r,s\\}$ parameter has been embraced to characterize different phases of the universe. We also discuss the physical consequences of the derived models.

Nasr Ahmed; Anirudh Pradhan

2013-03-12T23:59:59.000Z

379

The drive system of the Major Atmospheric Gamma-ray Imaging Cherenkov Telescope  

E-Print Network (OSTI)

The MAGIC telescope is an imaging atmospheric Cherenkov telescope, designed to observe very high energy gamma-rays while achieving a low energy threshold. One of the key science goals is fast follow-up of the enigmatic and short lived gamma-ray bursts. The drive system for the telescope has to meet two basic demands: (1) During normal observations, the 72-ton telescope has to be positioned accurately, and has to track a given sky position with high precision at a typical rotational speed in the order of one revolution per day. (2) For successfully observing GRB prompt emission and afterglows, it has to be powerful enough to position to an arbitrary point on the sky within a few ten seconds and commence normal tracking immediately thereafter. To meet these requirements, the implementation and realization of the drive system relies strongly on standard industry components to ensure robustness and reliability. In this paper, we describe the mechanical setup, the drive control and the calibration of the pointing, as well as present measurements of the accuracy of the system. We show that the drive system is mechanically able to operate the motors with an accuracy even better than the feedback values from the axes. In the context of future projects, envisaging telescope arrays comprising about 100 individual instruments, the robustness and scalability of the concept is emphasized.

T. Bretz; D. Dorner; R. M. Wagner; P. Sawallisch

2008-10-27T23:59:59.000Z

380

DETECTION AND IMAGING OF THE CRAB NEBULA WITH THE NUCLEAR COMPTON TELESCOPE  

SciTech Connect

The Nuclear Compton Telescope (NCT) is a balloon-borne Compton telescope designed for the study of astrophysical sources in the soft gamma-ray regime (200 keV-20 MeV). NCT's 10 high-purity germanium crossed-strip detectors measure the deposited energies and three-dimensional positions of gamma-ray interactions in the sensitive volume, and this information is used to restrict the initial photon to a circle on the sky using the Compton scatter technique. Thus NCT is able to perform spectroscopy, imaging, and polarization analysis on soft gamma-ray sources. NCT is one of the next generation of Compton telescopes-the so-called compact Compton telescopes (CCTs)-which can achieve effective areas comparable to the Imaging Compton Telescope's with an instrument that is a fraction of the size. The Crab Nebula was the primary target for the second flight of the NCT instrument, which occurred on 2009 May 17 and 18 in Fort Sumner, New Mexico. Analysis of 29.3 ks of data from the flight reveals an image of the Crab at a significance of 4{sigma}. This is the first reported detection of an astrophysical source by a CCT.

Bandstra, M. S.; Bellm, E. C.; Boggs, S. E.; Perez-Becker, D.; Zoglauer, A. [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States); Chang, H.-K.; Chiu, J.-L.; Liang, J.-S. [Department of Physics, National Tsing Hua University, Hsinchu 30013, Taiwan (China); Chang, Y.-H.; Liu, Z.-K.; Hung, W.-C. [Department of Physics, National Central University, Taoyuan 32001, Taiwan (China); Huang, M.-H. A. [Department of Energy Engineering, National United University, Miaoli 36003, Taiwan (China); Chiang, S. J. [Department of Electrical Engineering, National United University, Miaoli 36003, Taiwan (China); Run, R.-S. [Department of Electronic Engineering, National United University, Miaoli 36003, Taiwan (China); Lin, C.-H. [Institute of Physics, Academia Sinica, Taipei 11529, Taiwan (China); Amman, M.; Luke, P. N. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Jean, P.; Von Ballmoos, P. [Centre d'Etude Spatiale des Rayonnements (CESR), 31028 Toulouse Cedex 4 (France); Wunderer, C. B., E-mail: bandstra@ssl.berkeley.edu [Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607 Hamburg (Germany)

2011-09-01T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


381

Revised version of essay for volume edited by Bill Stoeger on philosophical issues in cosmology, in Pachart Press Philosophy in Science series  

E-Print Network (OSTI)

1 Revised version of essay for volume edited by Bill Stoeger on philosophical issues in cosmology defined realms. Encompassing is intellectually respectful, and a worldwide community of creativity

California at Santa Cruz, University of

382

Perspectives of a mid-rapidity dimuon program at the RHIC: a novel and compact muon telescope detector  

E-Print Network (OSTI)

Telescope Detector L. Ruan Brookhaven National Laboratory,Connecticut 06520 Z. Xu Brookhaven National Laboratory,York 11973 K. Asselta Brookhaven National Laboratory, Upton,

Ruan, L.

2010-01-01T23:59:59.000Z

383

South Pole Telescope helps Argonne scientists study earliest ages of the  

NLE Websites -- All DOE Office Websites (Extended Search)

Related Content Related Content Employee Spotlight: Clarence Chang South Pole Telescope helps Argonne scientists study earliest ages of the universe By Louise Lerner * October 28, 2013 Tweet EmailPrint For physicist Clarence Chang at the U.S. Department of Energy's (DOE) Argonne National Laboratory, looking backward in time to the earliest ages of the universe is all in a day's work. Chang helped design and operate part of the South Pole Telescope, a project that aims a giant telescope at the night sky to track tiny bits of radiation that are still traveling across the universe from the period just after it was born. "Basically, what we're looking at is the afterglow light of the Big Bang," Chang said. In the wake of the Big Bang, all the matter in the universe was just hot,

384

Metrology for x-ray telescope mirrors in a vertical configuration  

Science Conference Proceedings (OSTI)

Mirrors used in x-ray telescope systems for observations outside of the earth`s atmosphere are usually made of several thin nested shells, each formed by a pair of paraboloidal and hyperboloidal surfaces. The thin shells are very susceptible to self-weight deflection caused by gravity and are nearly impossible to test by conventional interferometric techniques. The metrology requirements for these mirrors are extremely challenging. This paper presents a prototype of a Vertical Scanning Long Trace Profiler (VSLTP) which is optimized to measure the surface figure of x-ray telescope mirrors in a vertical orientation. The optical system of the VSLTP is described. Experimental results from measurements on an x-ray telescope mandrel and tests of the accuracy and repeatability of the prototype VSLTP are presented. The prototype instrument has achieved a height measurement accuracy of about 50 nanometers with a repeatability of better than 20 nanometers, and a slope measurement accuracy of about 1 microradian.

Li, Haizhang; Li, Xiaodan; Grindel, M.W.

1995-09-01T23:59:59.000Z

385

Neutron Star Astronomy in the era of the European Extremely Large Telescope  

Science Conference Proceedings (OSTI)

About 25 isolated neutron stars (INSs) are now detected in the optical domain, mainly thanks to the HST and to VLT-class telescopes. The European Extremely Large Telescope(E-ELT) will yield {approx}100 new identifications, many of which from the follow-up of SKA, IXO, and Fermi observations. Moreover, the E-ELT will allow to carry out, on a much larger sample, INS observations which still challenge VLT-class telescopes, enabling studies on the structure and composition of the NS interior, of its atmosphere and magnetosphere, as well as to search for debris discs. In this contribution, I outline future perspectives for NS optical astronomy with the E-ELT.

Mignani, Roberto P. [Mullard Space Science Laboratory-University College London (United Kingdom)

2011-09-21T23:59:59.000Z

386

Autonomous Observing and Control Systems for PAIRITEL, a 1.3m Infrared Imaging Telescope  

E-Print Network (OSTI)

The Peters Automated Infrared Imaging Telescope (PAIRITEL) is the first meter-class telescope operating as a fully robotic IR imaging system. Dedicated in October 2004, PAIRITEL began regular observations in mid-December 2004 as part of a 1.5 year commissioning period. The system was designed to respond without human intervention to new gamma-ray burst transients: this milestone was finally reached on November 9, 2005 but the telescope had a number of semi-automated sub-10 minute responses throughout early commissioning. When not operating in Target of Opportunity mode, PAIRITEL performs a number of queue scheduled transient monitoring campaigns. To achieve this level of automation, we have developed communicating tools to connect the various sub-systems: an intelligent queue scheduling database, run-time configurable observation sequence software, a data reduction pipeline, and a master state machine which monitors and controls all functions within and affecting the observatory.

J. S. Bloom; Dan L. Starr; Cullen H. Blake; M. F. Skrutskie; Emilio E. Falco

2005-11-30T23:59:59.000Z

387

The Trigger System of the H.E.S.S. Telescope Array  

E-Print Network (OSTI)

H.E.S.S. -- The High Energy Stereoscopic System-- is a new system of large atmospheric Cherenkov telescopes for GeV/TeV Gamma-ray astronomy. This paper describes the trigger system of H.E.S.S. with emphasis on the multi-telescope array level trigger. The system trigger requires the simultaneous detection of air-showers by several telescopes at the hardware level. This requirement allows a suppression of background events which in turn leads to a lower system energy threshold for the detection of Gamma-rays. The implementation of the H.E.S.S. trigger system is presented along with data taken to characterise its performance.

S. Funk; G. Hermann; J. Hinton; D. Berge; K. Bernloehr; W. Hofmann; P. Nayman; F. Toussenel; P. Vincent

2004-08-20T23:59:59.000Z

388

KM3NeT:a large underwater neutrino telescope in the Mediterranean Sea  

E-Print Network (OSTI)

High energy neutrinos produced in astrophysical processes will allow for a new way of studying the universe. In order to detect the expected flux of high energy neutrinos from specific astrophysical sources, neutrino telescopes of a scale of a km^3 of water will be needed. A Northern Hemisphere detector is being proposed to be sited in a deep area of the Mediterranean Sea. This detector will provide complimentary sky coverage to the IceCube detector being built at the South Pole. The three neutrino telescope projects in the Mediterranean (ANTARES, NEMO and NESTOR) are partners in an effort to design, and build such a km^3 size neutrino telescope, the KM3NeT. The EU is funding a 3-year Design Study; the status of the Design Study is presented and some technical issues are discussed.

P. A. Rapidis; for the KM3NeT consortium

2008-03-17T23:59:59.000Z

389

Frozen Telescope Looks to Ends of the Earth for Answers | Department of  

Energy.gov (U.S. Department of Energy (DOE)) Indexed Site

Frozen Telescope Looks to Ends of the Earth for Answers Frozen Telescope Looks to Ends of the Earth for Answers Frozen Telescope Looks to Ends of the Earth for Answers May 3, 2012 - 2:20pm Addthis Researchers drilled holes in the ice to a depth of almost 1.5 miles, and lowered 60 basketball-sized detectors called digital optical modules (DOMs) into each of the 86 holes. They then had to pull cables to connect the sensors to IceCube Lab’s servers in order to collect data. | Photo courtesy of the National Science Foundation Researchers drilled holes in the ice to a depth of almost 1.5 miles, and lowered 60 basketball-sized detectors called digital optical modules (DOMs) into each of the 86 holes. They then had to pull cables to connect the sensors to IceCube Lab's servers in order to collect data. | Photo

390

The High-Resolution Lightweight Telescope for the EUV (HiLiTE)  

SciTech Connect

The High-resolution Lightweight Telescope for the EUV (HiLiTE) is a Cassegrain telescope that will be made entirely of Silicon Carbide (SiC), optical substrates and metering structure alike. Using multilayer coatings, this instrument will be tuned to operate at the 465 {angstrom} Ne VII emission line, formed in solar transition region plasma at {approx}500,000 K. HiLiTE will have an aperture of 30 cm, angular resolution of {approx}0.2 arc seconds and operate at a cadence of {approx}5 seconds or less, having a mass that is about 1/4 that of one of the 20 cm aperture telescopes on the Atmospheric Imaging Assembly (AIA) instrument aboard NASA's Solar Dynamics Observatory (SDO). This new instrument technology thus serves as a path finder to a post-AIA, Explorer-class missions.

Martinez-Galarce, D S; Boerner, P; Soufli, R; De Pontieu, B; Katz, N; Title, A; Gullikson, E M; Robinson, J C; Baker, S L

2008-06-02T23:59:59.000Z

391

Status of GLAST, the Gamma-ray Large-area Space Telescope  

SciTech Connect

GLAST is a satellite-based observatory consisting of the Large-Area Telescope (LAT), a modular 4 x 4-tower pair-conversion telescope with a field-of-view greater than 2 steradians, capable of measuring gamma-ray energies in the range 20 MeV to 300 GeV, and the GLAST Burst Monitor (GBM), a set of NaI and BGO detectors covering 8 steradians and sensitive to photons with energies between 10 keV and 25 MeV, allowing for correlative observations of transient events. The observatory is currently being constructed and is scheduled to be launched in August 2007.

Rochester, L.; /SLAC

2005-12-14T23:59:59.000Z

392

Neutrino telescopes as a probe of active and sterile neutrino mixings  

E-Print Network (OSTI)

If the ultrahigh-energy (UHE) neutrino fluxes produced from a distant astrophysical source can be measured at a km^3-size neutrino telescope, they will provide a promising way to help determine the flavor mixing pattern of three active neutrinos. Considering the conventional UHE neutrino source with the flavor ratio \\phi_e : \\phi_\\mu : \\phi_\\tau = 1 : 2 : 0, I show that \\phi^D_e : \\phi^D_\\mu : \\phi^D_\\tau = (1 -2 \\Delta) : (1 +\\Delta) : (1 +\\Delta) holds at the detector of a neutrino telescope, where \\Delta characterizes the effect of \\mu-\\tau symmetry breaking (i.e., \\theta_13 \

Xing, Zhi-zhong

2007-01-01T23:59:59.000Z

393

Neutrino telescopes as a probe of active and sterile neutrino mixings  

E-Print Network (OSTI)

If the ultrahigh-energy (UHE) neutrino fluxes produced from a distant astrophysical source can be measured at a km^3-size neutrino telescope, they will provide a promising way to help determine the flavor mixing pattern of three active neutrinos. Considering the conventional UHE neutrino source with the flavor ratio \\phi_e : \\phi_\\mu : \\phi_\\tau = 1 : 2 : 0, I show that \\phi^D_e : \\phi^D_\\mu : \\phi^D_\\tau = (1 -2 \\Delta) : (1 +\\Delta) : (1 +\\Delta) holds at the detector of a neutrino telescope, where \\Delta characterizes the effect of \\mu-\\tau symmetry breaking (i.e., \\theta_13 \

Zhi-zhong Xing

2007-11-27T23:59:59.000Z

394

The Liverpool Telescope Automatic Pipeline for Real-time GRB Afterglow Detection  

E-Print Network (OSTI)

The 2-m robotic Liverpool Telescope (LT) is ideally suited to the rapid follow-up of unpredictable and transient events such as GRBs. Our GRB follow-up strategy is designed to identify optical/IR counterparts in real time; it involves the automatic triggering of initial observations, on receipt of an alert from Gamma Ray Observatories HETE-2, INTEGRAL and Swift, followed by automated data reduction, analysis, OT identification and subsequent observing mode choice. The lack of human intervention in this process requires robustness at all stages of the procedure. Here we describe the telescope, its instrumentation and GRB pipeline.

A. Gomboc; A. Monfardini; C. Guidorzi; C. G. Mundell; C. J. Mottram; S. N. Fraser; R. J. Smith; I. A. Steele; D. Carter; M. F. Bode; A. M. Newsam

2005-02-24T23:59:59.000Z

395

Towards the Chalonge 17th Paris Cosmology Colloquium 2013: highlights and conclusions of the Chalonge 16th Paris Cosmology Colloquium 2012  

E-Print Network (OSTI)

LWDM (Warm Dark Matter) is progressing impressively.The galactic scale crisis and decline of LCDM+baryons are staggering. The 16th Paris Chalonge Colloquium 2012 combined real cosmological/astrophysical data and hard theory predictive approach in the LWDM Standard Model. News and reviews from ACT,WMAP,SPT,QUIET,Planck,Herschel,JWST,UFFO,KATRIN and MARE experiments; astrophysics, particle and nuclear physics WDM searches, galactic observations, related theory and simulations, with the aim of synthesis and clarification. Here highlights by P Biermann, C Burigana, C Conselice, A Cooray, H de Vega, C Giunti & M Laveder, J Kormendi & K Freeman, E Ma, J Mather, L Page, G Smoot, N Sanchez. Summary and conclusions by de Vega, Falvella and Sanchez. Data confirm primordial CMB gaussianity. Effective (Ginsburg-Landau) Inflation theory predicts r about 0.04-0.05, negligeable running of ns, the inflation energy scale (GUT scale) and the set of CMB observables in agreement with the data. WMAP9 and Planck measurements are compatible with one or two Majorana sterile neutrinos in the eV mass scale. Cored (non cusped) DM halos and keV WDM are strongly favored by theory and observations, Wimps are strongly disfavoured. LambdaCDM with baryons do not work at small scales. Inside galaxy cores, quantum WDM effects are important. Quantum WDM calculations (Thomas-Fermi) provide galaxy masses, velocity dispersions and cored profiles and their sizes in agreement with observations. A WDM fermion of about 2 keV naturally reproduces galaxy, large scale and cosmological observations. WDM keV particles deserve dedicated astronomical and laboratory searches, theoretical work and numerical simulations. KATRIN can be adapted to look to keV scale sterile neutrinos. It will be a fantastic discovery to detect dark matter in beta decay. Photos of the Colloquium are included

H. J. de Vega; M. C. Falvella; N. G. Sanchez

2013-07-07T23:59:59.000Z

396

Search for ultra-high energy photons using Telescope Array surface detector  

SciTech Connect

We search for ultra-high energy photons by analyzing geometrical properties of shower fronts of events registered by the Telescope Array surface detector. By making use of an event-by-event statistical method, we derive an upper limit on the absolute flux of primary photons with energies above 10{sup 19} eV.

Rubtsov, G. I.; Troitsky, S. V. [Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, 117312 (Russian Federation); Ivanov, D.; Stokes, B. T. [Rutgers - State University of New Jersey, Piscataway (United States); Thomson, G. B. [University of Utah, High Energy Astrophysics Institute, Salt Lake City, Utah (United States)

2011-09-22T23:59:59.000Z

397

Search for Short Duration Bursts of TeV Gamma Rays with the Milagrito Telescope  

E-Print Network (OSTI)

OG 2.3.07 Search for Short Duration Bursts of TeV Gamma Rays with the Milagrito Telescope Gus for short duration bursts of TeV photons. Such bursts may result from "traditional" gamma-ray bursts to gamma-ray bursts, the final stages of black hole evaporation) the most compelling reason may

California at Santa Cruz, University of

398

32ND INTERNATIONAL COSMIC RAY CONFERENCE, BEIJING 2011 The HEAT Telescopes of the Pierre Auger Observatory  

E-Print Network (OSTI)

tanks on a 750 m grid close to the HEAT site the energy range of high quality hybrid air shower32ND INTERNATIONAL COSMIC RAY CONFERENCE, BEIJING 2011 The HEAT Telescopes of the Pierre Auger. A surface array of 1660 water Cherenkov detectors on a 1500 m triangular grid covers an area of 3000 km2

Hörandel, Jörg R.

399

Focal plane instrumentation for the Wide-Field X-ray Telescope  

E-Print Network (OSTI)

The three X-ray imaging focal planes of the Wide-Field X-ray Telescope (WFXT) Mission will each have a field of view up to 1 degree square, pixel pitch smaller than 1 arcsec, excellent X-ray detection efficiency and spectral ...

Bautz, Marshall W.

400

The Animated Gamma-ray Sky Revealed by the Fermi Gamma-ray Space Telescope  

SciTech Connect

The Fermi Gamma-ray Space Telescope has been observing the sky in gamma-rays since August 2008. In addition to breakthrough capabilities in energy coverage (20 MeV-300 GeV) and angular resolution, the wide field of view of the Large Area Telescope enables observations of 20% of the sky at any instant, and of the whole sky every three hours. It has revealed a very animated sky with bright gamma-ray bursts flashing and vanishing in minutes, powerful active galactic nuclei flaring over hours and days, many pulsars twinkling in the Milky Way, and X-ray binaries shimmering along their orbit. Most of these variable sources had not been seen by the Fermi predecessor, EGRET, and the wealth of new data already brings important clues to the origin of the high-energy emission and particles powered by the compact objects. The telescope also brings crisp images of the bright gamma-ray emission produced by cosmic-ray interactions in the interstellar medium, thus allowing to measure the cosmic nuclei and electron spectra across the Galaxy, to weigh interstellar clouds, in particular in the dark-gas phase. The telescope sensitivity at high energy will soon provide useful constraints on dark-matter annihilations in a variety of environments. I will review the current results and future prospects of the Fermi mission.

Grenier, Isabelle (University Paris Diderot and CEA Saclay, France)

2009-04-01T23:59:59.000Z

Note: This page contains sample records for the topic "atacama cosmology telescope" from the National Library of EnergyBeta (NLEBeta).
While these samples are representative of the content of NLEBeta,
they are not comprehensive nor are they the most current set.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


401

Solar Physics, Space Weather, and Wide-field X-ray Telescopes  

E-Print Network (OSTI)

Solar Physics, Space Weather, and Wide-field X-ray Telescopes CREOL & FPCE: The College of Optics of the Earth). The detrimental effects of solar storm induced "space weather" ranges from disruption of our. The National Oceanic & Atmospheric Administration (NOAA) and NASA are cooperating on a Solar X-ray Imager (SXI

Van Stryland, Eric

402

Detection and Imaging of the Crab Nebula with the Nuclear Compton Telescope  

E-Print Network (OSTI)

The Nuclear Compton Telescope (NCT) is a balloon-borne Compton telescope designed for the study of astrophysical sources in the soft gamma-ray regime (200 keV--20 MeV). NCT's ten high-purity germanium crossed-strip detectors measure the deposited energies and three-dimensional positions of gamma-ray interactions in the sensitive volume, and this information is used to restrict the initial photon to a circle on the sky using the Compton scatter technique. Thus NCT is able to perform spectroscopy, imaging, and polarization analysis on soft gamma-ray sources. NCT is one of the next generation of Compton telescopes --- so-called compact Compton telescopes (CCTs) --- which can achieve effective areas comparable to COMPTEL's with an instrument that is a fraction of the size. The Crab Nebula was the primary target for the second flight of the NCT instrument, which occurred on 17--18 May 2009 in Fort Sumner, New Mexico. Analysis of 29.3 ks of data from the flight reveals an image of the Crab at a significance of 4-si...

Bandstra, M S; Boggs, S E; Perez-Becker, D; Zoglauer, A; Chang, H -K; Chiu, J -L; Liang, J -S; Chang, Y -H; Liu, Z -K; Hung, W -C; Huang, M -H A; Chiang, S J; Run, R -S; Lin, C -H; Amman, M; Luke, P N; Jean, P; von Ballmoos, P; Wunderer, C B

2011-01-01T23:59:59.000Z

403

Cosmological dynamics of $f(R)$ gravity scalar degree of freedom in Einstein frame  

E-Print Network (OSTI)

$f(R)$ gravity models belong to an important class of modified gravity models where the late time cosmic accelerated expansion is considered as the manifestation of the large scale modification of the force of gravity. $f(R)$ gravity models can be expressed in terms of a scalar degree of freedom by redefinition of models variable. The conformal transformation of the action from Jordan frame to Einstein frame makes the scalar degree of freedom more explicit and can be studied conveniently. We have investigated the features of the scalar degree of freedoms and the consequent cosmological implications of the power-law ($\\xi R^n$) and the Starobinsky (disappearing cosmological constant) $f(R)$ gravity models numerically in the Einstein frame. Both the models show interesting behaviour of their scalar degree of freedom and could produce the accelerated expansion of the Universe in the Einstein frame with the negative equation of state of the scalar field. However the scalar field potential for the power-law model is the well behaved function of the field, whereas the potential becomes flat for higher value of field in the case of the Starobinsky model. Moreover, the equation of state of the scalar field for the power-law model is always negative and less than -1/3, which corresponds to the behaviour of the dark energy that produces the accelerated expansion of the Universe. This is not always the case for the Starobinsky model. At late times Starobinsky model behaves as cosmological constant $\\Lambda$ as behaves by power-law model for the values of $n\\rightarrow 2$ at all times.

Umananda Dev Goswami; Kabita Deka

2013-03-23T23:59:59.000Z

404

How unitary cosmology generalizes thermodynamics and solves the inflationary entropy problem  

E-Print Network (OSTI)

We analyze cosmology assuming unitary quantum mechanics, using a tripartite partition into system, observer and environment degrees of freedom. This generalizes the second law of thermodynamics to "The system's entropy can't decrease unless it interacts with the observer, and it can't increase unless it interacts with the environment." The former follows from the quantum Bayes Theorem we derive. We show that because of the long-range entanglement created by cosmological inflation, the cosmic entropy decreases exponentially rather than linearly with the number of bits of information observed, so that a given observer can reduce entropy by much more than the amount of information her brain can store. Indeed, we argue that as long as inflation has occurred in a non-negligible fraction of the volume, almost all sentient observers will find themselves in a post-inflationary low-entropy Hubble volume, and we humans have no reason to be surprised that we do so as well, which solves the so-called inflationary entropy problem. An arguably worse problem for unitary cosmology involves gamma-ray-burst constraints on the "Big Snap", a fourth cosmic doomsday scenario alongside the "Big Crunch", "Big Chill" and "Big Rip", where an increasingly granular nature of expanding space modifies our life-supporting laws of physics. Our tripartite framework also clarifies when it is valid to make the popular quantum gravity approximation that the Einstein tensor equals the quantum expectation value of the stress-energy tensor, and how problems with recent attempts to explain dark energy as gravitational backreaction from super-horizon scale fluctuations can be understood as a failure of this approximation.

Max Tegmark

2011-08-15T23:59:59.000Z

405

Cosmological implications of the MAXIMA-1 high-resolution cosmicmicrowave background anisotropy measurement  

SciTech Connect

We discuss the cosmological implications of the new constraints on the power spectrum of the cosmic microwave background (CMB) anisotropy derived from a new high-resolution analysis of the MAXIMA-1 measurement. The power spectrum indicates excess power at lsimilar to 860 over the average level of power at 411 less than or equal to l less than or equal to 785. This excess is statistically significant at the similar to 95 percent confidence level. Its position coincides with that of the third acoustic peak, as predicted by generic inflationary models selected to fit the first acoustic peak as observed in the data. The height of the excess power agrees with the predictions of a family of inflationary models with cosmological parameters that are fixed to fit the CMB data previously provided by BOOMERANG-LDB and MAXIMA-1 experiments. Our results therefore lend support for inflationary models and more generally for the dominance of adiabatic coherent perturbations in the structure formation of the universe. At the same time, they seem to disfavor a large variety of the nonstandard (but inflation-based) models that have been proposed to improve the quality of fits to the CMB data and the consistency with other cosmological observables. Within standard inflationary models, our results combined with the COBE/Differential Microwave Radiometer data give best-fit values and 95 percent confidence limits for the baryon density, Omega (b)h(2)similar or equal to 0.033 +/- 0.013, and the total density, Omega =0.9(-0.16)(+0.18). The primordial spectrum slope (n(s)) and the optical depth to the last scattering surface (tau (c)) are found to be degenerate and to obey the relation n(s) similar or equal to (0.99 +/- 0.14) + 0.46tau (c), for tau (c) less than or equal to 0.5 (all at 95 percent confidence levels).

Stompor, R.; Abroe, M.; Ade, P.; Balbi, A.; Barbosa, D.; Bock,J.; Borrill, J.; Boscaleri, A.; de Bernardis, P.; Ferreira, P.G.; Hanany,S.; Hristov, V.; Jaffe, A.H.; Lee, A.T.; Pascale, E.; Rabii, B.; Richards, P.L.; Smoot, G.F.; Winant, C.D.; Wu, J.H.P.

2001-05-03T23:59:59.000Z

406

Confronting the Hubble Diagram of Gamma-Ray Bursts with Cardassian Cosmology  

E-Print Network (OSTI)

We construct the Hubble diagram (HD) of Gamma-Ray Bursts (GRBs) with redshifts reaching up to $z \\sim 6$, by using five luminosity vs. luminosity indicator relations calibrated with the Cardassian cosmology. This model has a major interesting feature: despite of being matter-dominated and flat, it can explain the present accelerate expansion of the universe. This is the first study of this class of models using high redshift GRBs. We have performed a $\\chi$-square statistical analysis of the GRBs calibrated with the Cardassian model, and also combined them with both the current Cosmic Microwave Background and Baryonic Acoustic Oscillation data. Our results show consistency between the current observational data and the model predictions. In particular, the best-fit parameters obtained from the $\\chi^2$-analysis are in agreement with those obtained from the Concordance Cosmology ($\\Lambda$-CDM). We determine the redshift at which the universe would start to follow the Cardassian expansion, i. e., \\zc, and both the redshift at which the universe had started to accelerate, i. e., \\zac, and the age-redshift relation $H_0t_0$. Our results also show that the universe, from the point of view of GRBs, had undergo a transition to acceleration at a redshift $z \\approx 0.2-0.7$, which agrees with the SNIa results. Hence, after confronting the Cardassian scenario with the GRBs HD and proving its consistency with it, we conclude that GRBs should indeed be considered a complementary tool to several other astronomical observations for studies of high accuracy in cosmology.

Herman J. Mosquera Cuesta; Habib Dumet M.; Cristina Furlanetto

2007-08-10T23:59:59.000Z

407

A program for a problem free Cosmology within a framework of a rich class of scalar tensor theories  

E-Print Network (OSTI)

A search for a problem free cosmology within the framework of an effective non - minimally coupled scalar tensor theory is suggested. With appropriate choice of couplings in variants of a Lee - Wick model [as also in a model supporting Q - ball solutions], non topological solutions [NTS's], varying in size upto 10 kpc to 1 Mpc can exist. We explore the properties of a ``toy'' Milne model containing a distribution of NTS domains. The interior of these domains would be regions where effective gravitational effects would be indistinguishable from those expected in standard Einstein theory. For a large class of non - minimal coupling terms and the scalar effective potential, the effective cosmological constant identically vanishes. The model passes classical cosmological tests and we describe reasons to expect it to fare well as regards nucleosynthesis and structure formation.

Daksh Lohiya; Meetu Sethi

1998-03-14T23:59:59.000Z

408

Variability of the proton-to-electron mass ratio on cosmological scales  

E-Print Network (OSTI)

So far the only seemingly significant indication of a cosmological variation exists for the proton-to-electron mass ratio as stated by Reinhold et al. (2006). The measured indication of variation is based on the combined analysis of H2 absorption systems in the spectra of Q0405-443 and Q0347-383 at z=2.595 and z=3.025, respectively. The high resolution data of the latter is reanalyzed in this work to examine the influence of different fitting procedures and further potential nonconformities. This analysis cannot reproduce the significance achieved by the previous detection.

Martin Wendt; Dieter Reimers

2008-02-08T23:59:59.000Z

409

The energy spectrum of gravitational waves in a loop quantum cosmological model  

E-Print Network (OSTI)

We explore the consequences of loop quantum cosmology (inverse-volume corrections) in the spectrum of the gravitational waves using the method of the Bogoliubov coefficients. These corrections are taken into account at the background level of the theory as well as at the first order in the perturbations theory framework. We show that these corrections lead to an intense graviton production during the loop super-inflationary phase prior to the standard slow-roll era, which leave their imprints through new features on the energy spectrum of the gravitational waves as would be measured today, including a new maximum on the low frequency end of the spectrum.

Joao Morais; Mariam Bouhmadi-Lopez; Alfredo B. Henriques

2013-09-30T23:59:59.000Z

410

The Linet-Tian solution with a positive cosmological constant in four and higher dimensions  

E-Print Network (OSTI)

The static, apparently cylindrically symmetric vacuum solution of Linet and Tian for the case of a positive cosmological constant $\\Lambda$ is shown to have toroidal symmetry and, besides $\\Lambda$, to include three arbitrary parameters. It possesses two curvature singularities, of which one can be removed by matching it across a toroidal surface to a corresponding region of the dust-filled Einstein static universe. In four dimensions, this clarifies the geometrical properties, the coordinate ranges and the meaning of the parameters in this solution. Some other properties and limiting cases of this space-time are described. Its generalisation to any higher number of dimensions is also explicitly given.

J. B. Griffiths; J. Podolsky

2010-02-22T23:59:59.000Z

411

New Features about Chaos in Bianchi I non-Abelian Born-Infeld cosmology  

SciTech Connect

When the action is replaced by the Born-Infeld-type non-Abelian action (NBI), a chaos-order transition is observed in the high energy region for a Bianchi I cosmology with the homogeneous SU(2) Yang-Mills field. This is interpreted as a smothering effect due to (non-perturbative in {alpha}') string corrections to the classical EYM action. We give a numerical evidence for the chaos-order transition and present an analytical proof of regularity of color oscillations in the limit of strong Born-Infeld non-linearity.

Dyadichev, Vladimir V.; Gal' tsov, Dmitri V. [Theoretical Physics, Moscow State University, 119899, Moscow (Russian Federation); Moniz, Paulo Vargas [Astronomy Unit, Mathematical Sciences, University of London, Mile End Road, London E1 4NS (United Kingdom)

2006-11-03T23:59:59.000Z

412

Computation of inflationary cosmological perturbations in chaotic inflationary scenarios using the phase-integral method  

Science Conference Proceedings (OSTI)

The phase-integral approximation devised by Froeman and Froeman is used for computing cosmological perturbations in the quadratic chaotic inflationary model. The phase-integral formulas for the scalar and tensor power spectra are explicitly obtained up to fifth order of the phase-integral approximation. We show that the phase integral gives a very good approximation for the shape of the power spectra associated with scalar and tensor perturbations as well as the spectral indices. We find that the accuracy of the phase-integral approximation compares favorably with the numerical results and those obtained using the slow-roll and uniform-approximation methods.

Rojas, Clara [Departamento de Fisica, Aplicada IVIC/Merida, Merida 5107 (Venezuela, Bolivarian Republic of); Villalba, Victor M. [Centro de Fisica IVIC Apdo 21827, Caracas 1020A (Venezuela, Bolivarian Republic of)

2009-05-15T23:59:59.000Z

413

Open Strings on D-Branes and Hagedorn Regime in String Gas Cosmology  

E-Print Network (OSTI)

We consider early time cosmic evolution in string gas cosmology dominated by open strings attached to D-branes. After reviewing statistical properties of open strings in D-brane backgrounds, we use dilaton-gravity equations to determine the string frame fields. Although, there are distinctions in the Hagedorn regime thermodynamics and dilaton coupling as compared to closed strings, it seems difficult to avoid Jeans instability and assume thermal equilibrium simultaneously, which is already a known problem for closed strings. We also examine characteristics of a possible subsequent large radius regime in this setup.

Arslanargin, Ayse

2009-01-01T23:59:59.000Z

414

Accelerating Anisotropic Cosmologies in Brans-Dicke Gravity coupled to a Mass-Varying Vector Field  

E-Print Network (OSTI)

The field equations of Brans-Dicke gravity coupled to a mass-varying vector field are derived. Anisotropic cosmological solutions with a locally rotationally symmetric Bianchi type I metric and time-dependent scalar and electric vector fields are studied. A particular class of exact solutions for which all the variable parameters have a power-law time dependence is given. The universe expands with a constant expansion anisotropy within this class of solutions. We show that the accelerating expansion is driven by the scalar field and the electric vector field can be interpreted as an anisotropic dark-matter source.

Ozgur Akarsu; Tekin Dereli; Neslihan Oflaz

2013-11-11T23:59:59.000Z

415

From the Cosmological Constant: Higgs Boson, Dark Matter, and Quantum Gravity Scales  

E-Print Network (OSTI)

We suggest discovery targets for the Higgs boson, dark matter, and quantum gravity mass scales, motivated by the Dirac equation for the electron in deSitter space, and a sixth-order constraint between the electron QED parameters and the cosmological constant. We go on to show that this constraint can be viewed as a structural parameter of the electron, and leads naturally to a new cosmic horizon. A dual fourth-order constraint implies a second-order one, from which the electron neutrino mass is derived.

James R. Bogan

2009-02-16T23:59:59.000Z

416

Testing of Dark Energy and a Solution of the Cosmological Constant Problem  

E-Print Network (OSTI)

A probable solution of the cosmological constant problem was recently found. We propose that dark energy of the Universe is vacuum energy. Our Universe during its expansion is spending its vacuum energy for creation of new quantum states, but in the quantum regime phase transitions were more effective in reducing the vacuum energy than creation of new quantum states. Here we show how the 123 crisis orders of the vacuum energy are reduced by conventional physical processes in both the quantum and classical regimes of the Universe evolution. Numeral estimates of dark energy evolution are also presented.

Burdyuzha, Vladimir

2014-01-01T23:59:59.000Z

417

Testing of Dark Energy and a Solution of the Cosmological Constant Problem  

E-Print Network (OSTI)

A probable solution of the cosmological constant problem was recently found. We propose that dark energy of the Universe is vacuum energy. Our Universe during its expansion is spending its vacuum energy for creation of new quantum states, but in the quantum regime phase transitions were more effective in reducing the vacuum energy than creation of new quantum states. Here we show how the 123 crisis orders of the vacuum energy are reduced by conventional physical processes in both the quantum and classical regimes of the Universe evolution. Numeral estimates of dark energy evolution are also presented.

Vladimir Burdyuzha

2014-01-19T23:59:59.000Z

418

Reply to 'Comment on 'Quantization of Friedmann-Robertson-Walker spacetimes in the presence of a negative cosmological constant and radiation''  

SciTech Connect

The previous Comment contains a valid criticism of the numerical precision of the results reported in a recent paper of ours, as well as fresh ideas on how to characterize a quantum cosmological singularity. However, we argue that, contrary to what is suggested in the Comment, the quantum cosmological models we studied show hardly any sign of singular behavior.

Lemos, N. A.; Monerat, G. A.; Silva, E. V. Correa; Oliveira-Neto, G.; Filho, L. G. Ferreira [Instituto de Fisica, Universidade Federal Fluminense, R. Gal. Milton Tavares de Souza s/n, CEP 24210-340, Niteroi, RJ (Brazil); Departamento de Matematica e Computacao, Faculdade de Tecnologia, Universidade do Estado do Rio de Janeiro, Estrada Resende-Riachuelo s/n, CEP 27523-000, Resende, RJ (Brazil); Departamento de Mecanica e Energia, Faculdade de Tecnologia, Universidade do Estado do Rio de Janeiro, Estrada Resende-Riachuelo s/n, CEP 27523-000, Resende, RJ (Brazil)

2007-03-15T23:59:59.000Z

419

Wide Field Hard X-ray Survey Telescope: ProtoEXIST1  

E-Print Network (OSTI)

We report our progress on the development of pixellated imaging CZT detector arrays for our first-generation balloon-borne wide-field hard X-ray (20 - 600 keV) telescope, ProtoEXIST1. Our ProtoEXIST program is a pathfinder for the High Energy Telescope (HET) on the Energetic X-ray Imaging Survey telescope (EXIST), a proposed implementation of the Black Hole Finder Probe. ProtoEXIST1 consists of four independent coded-aperture telescopes with close-tiled (~0.4 mm gaps) CZT detectors that preserve their 2.5mm pixel pitch. Multiple shielding/field-of-view configurations are planned to identify optimal geometry for the HET in EXIST. The primary technical challenge in ProtoEXIST is the development of large area, close-tiled modules of imaging CZT detectors (1000 cm2 for ProtoEXIST1), with all readout and control systems for the ASIC readout vertically stacked. We describe the overall telescope configuration of ProtoEXIST1 and review the current development status of the CZT detectors, from individual detector crystal units (DCUs) to a full detector module (DM). We have built the first units of each component for the detector plane and have completed a few Rev2 DCUs (2x2 cm2), which are under a series of tests. Bare DCUs (pre-crystal bonding) show high, uniform ASIC yield (~70%) and ~30% reduction in electronics noise compared to the Rev1 equivalent. A Rev1 DCU already achieved ~1.2% FWHM at 662 keV, and preliminary analysis of the initial radiation tests on a Rev2 DCU shows ~ 4 keV FWHM at 60 keV (vs. 4.7 keV for Rev1). We therefore expect about <~1% FWHM at 662 keV with the Rev2 detectors.

J. Hong; J. E. Grindlay; N. Chammas; B. Allen; A. Copete; B. Said; M. Burke; J. Howell; T. Gauron; R. G. Baker; S. D. Barthelmy; S. Sheikh; N. Gehrels; W. R. Cook; J. A. Burnham; F. A. Harrison; J. Collins; S. Labov; A. Garson III; H. Krawczynski

2007-09-17T23:59:59.000Z

420

Constraints on Cosmological Parameters from the Analysis of the Cosmic Lens All Sky Survey Radio-Selected Gravitational Lens Statistics  

E-Print Network (OSTI)

We derive constraints on cosmological parameters and the properties of the lensing galaxies from gravitational lens statistics based on the final Cosmic Lens All Sky Survey (CLASS) data. For a flat universe with a classical cosmological constant, we find that the present matter fraction of the critical density is $\\Omega_{\\rm m}=0.31^{+0.27}_{-0.14}$ (68%) $^{+0.12}_{-0.10}$ (systematic). For a flat universe with a constant equation of state for dark energy $w = p_x({pressure})/\\rho_x({energy density})$, we find $w < -0.55^{+0.18}_{-0.11}$ (68%).

K. -H. Chae; A. D. Biggs; R. D. Blandford; I. W. A. Browne; A. G. de Bruyn; C. D. Fassnacht; P. Helbig; N. J. Jackson; L. J. King; L. V. E. Koopmans; S. Mao; D. R. Marlow; J. P. McKean; S. T. Myers; M. Norbury; T. J. Pearson; P. M. Phillips; A. C. S. Readhead; D. Rusin; C. M. Sykes; P. N. Wilkinson; E. Xanthopoulos; T. York

2002-09-28T23:59:59.000Z

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421

Cosmological constraints from the CMB and Ly-alpha forest revisited  

E-Print Network (OSTI)

The WMAP team has recently highlighted the usefulness of combining the Ly-alpha forest constraints with those from the cosmic microwave background (CMB). This combination is particularly powerful as a probe of the primordial shape of the power spectrum. Converting between the Ly-alpha forest observations and the linear mass power spectrum requires a careful treatment of nuisance parameters and modeling with cosmological simulations. We point out several issues which lead to an expansion of the errors, the two most important being the range of cosmological parameters explored in simulations and the treatment of the mean transmitted flux constraints. We employ a likelihood calculator for the current Ly-alpha data set based on an extensive 6-dimensional grid of simulations. We show that the current uncertainties in the mean transmission and the flux power spectrum define a degeneracy line in the amplitude-slope plane. The CMB degeneracy due to the primordial power spectrum shape follows a similar relation in this plane. This weakens the statistical significance of the primordial power spectrum shape constraints based on combined CMB+Ly-alpha forest analysis. Using the current data the simplest n=1 scale invariant model with dn/dln k=0 and no tensors has a Delta chi^2=4 compared to the best fitting model in which these 3 parameters are free. Current data therefore do not require relaxing these parameters to improve the fit.

Uros Seljak; Patrick McDonald; Alexey Makarov

2003-02-27T23:59:59.000Z

422

Gravitational Clustering in Redshift Space: Non-Gaussian Tail of the Cosmological Density Distribution Function  

E-Print Network (OSTI)

We study the non-Gaussian tail of the probability distribution function of density in cosmological N-Body simulations for a variety of initial conditions. We compare the behaviour of the non-Gaussian tail in the real space with that in the redshift space. The form of the PDF in redshift space is of great significance as galaxy surveys probe this and not the real space analogue predicted using theoretical models. We model the non-Gaussian tail using the halo model. In the weakly non-linear regime the moments of counts in cells in the redshift space approach the values expected from perturbation theory for moments in real space. We show that redshift space distortions in the non-linear regime dominate over signatures of initial conditions or the cosmological background. We illustrate this using Skewness and higher moments of counts in cells, as well as using the form of the non-Gaussian tail of the distribution function. We find that at scales smaller than the scale of non-linearity the differences in Skewness, etc. for different models are very small compared to the corresponding differences in real space. We show that bias also leads to smaller values of higher moments, but the redshift space distortions are typically the dominant effect.

J. S. Bagla; Suryadeep Ray

2006-04-28T23:59:59.000Z

423

A Quantum Cosmology: No Dark Matter, Dark Energy nor Accelerating Universe  

E-Print Network (OSTI)

We show that modelling the universe as a pre-geometric system with emergent quantum modes, and then constructing the classical limit, we obtain a new account of space and gravity that goes beyond Newtonian gravity even in the non-relativistic limit. This account does not require dark matter to explain the spiral galaxy rotation curves, and explains as well the observed systematics of black hole masses in spherical star systems, the bore hole $g$ anomalies, gravitational lensing and so on. As well the dynamics has a Hubble expanding universe solution that gives an excellent parameter-free account of the supernovae and gamma-ray-burst red-shift data, without dark energy or dark matter. The Friedmann-Lema\\^{i}tre-Robertson-Walker (FLRW) metric is derived from this dynamics, but is shown not satisfy the General Relativity based Friedmann equations. It is noted that General Relativity dynamics only permits an expanding flat 3-space solution if the energy density in the pressure-less dust approximation is non-zero. As a consequence dark energy and dark matter are required in this cosmological model, and as well the prediction of a future exponential accelerating Hubble expansion. The FLRW $\\Lambda$CDM model data-based parameter values, $\\Omega_\\Lambda=0.73$, $\\Omega_{DM}=0.27$, are derived within the quantum cosmology model, but are shown to be merely artifacts of using the Friedmann equations in fitting the red-shift data.

Reginald T Cahill

2007-09-18T23:59:59.000Z

424

Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Parameter Results  

E-Print Network (OSTI)

We present cosmological parameter constraints based on the final nine-year WMAP data, in conjunction with additional cosmological data sets. The WMAP data alone, and in combination, continue to be remarkably well fit by a six-parameter LCDM model. When WMAP data are combined with measurements of the high-l CMB anisotropy, the BAO scale, and the Hubble constant, the densities, Omegabh2, Omegach2, and Omega_L, are each determined to a precision of ~1.5%. The amplitude of the primordial spectrum is measured to within 3%, and there is now evidence for a tilt in the primordial spectrum at the 5sigma level, confirming the first detection of tilt based on the five-year WMAP data. At the end of the WMAP mission, the nine-year data decrease the allowable volume of the six-dimensional LCDM parameter space by a factor of 68,000 relative to pre-WMAP measurements. We investigate a number of data combinations and show that their LCDM parameter fits are consistent. New limits on deviations from the six-parameter model are p...

Hinshaw, G; Komatsu, E; Spergel, D N; Bennett, C L; Dunkley, J; Nolta, M R; Halpern, M; Hill, R S; Odegard, N; Page, L; Smith, K M; Weiland, J L; Gold, B; Jarosik, N; Kogut, A; Limon, M; Meyer, S S; Tucker, G S; Wollack, E; Wright, E L

2012-01-01T23:59:59.000Z

425

Chameleonic dilaton, nonequivalent frames, and the cosmological constant problem in quantum string theory  

Science Conference Proceedings (OSTI)

The chameleonic behavior of the string theory dilaton is suggested. Some of the possible consequences of the chameleonic string dilaton are analyzed in detail. In particular, (1) we suggest a new stringy solution to the cosmological constant problem and (2) we point out the nonequivalence of different conformal frames at the quantum level. In order to obtain these results, we start taking into account the (strong coupling) string loop expansion in the string frame (S-frame), therefore the so-called form factors are present in the effective action. The correct dark energy scale is recovered in the Einstein frame (E-frame) without unnatural fine-tunings and this result is robust against all quantum corrections, granted that we assume a proper structure of the S-frame form factors in the strong coupling regime. At this stage, the possibility still exists that a certain amount of fine-tuning may be required to satisfy some phenomenological constraints. Moreover in the E-frame, in our proposal, all the interactions are switched off on cosmological length scales (i.e., the theory is IR-free), while higher derivative gravitational terms might be present locally (on short distances) and it remains to be seen whether these facts clash with phenomenology. A detailed phenomenological analysis is definitely necessary to clarify these points.

Zanzi, Andrea [Via Pioppa 261, 44123 Pontegradella, Ferrara (Italy)

2010-08-15T23:59:59.000Z

426

A fundamental scale of mass for black holes from the cosmological constant  

E-Print Network (OSTI)

The existence of a positive cosmological constant leads naturally to two fundamental scales of length, being the De Sitter horizon and the radius of the cell associated with a holographic degree of freedom. Associated with each of those scales of length are a macroscopic gravitational mass and a microscopic quantum mechanical mass. Three of those four fundamental masses have been discussed in the literature, and this present work identifies the physical significance of the remaining mass, being the gravitational mass associated with the holographic length. That mass, which is of the order 10^{12}kg and inversely proportional to the sixth root of the cosmological constant, represents the mass of the black hole whose evaporation time is equal to the fundamental cosmic time, which is of the order the current age of the universe. It also represents the minimum mass of a black hole that is capable of accreting a particle whose Compton wavelength is equal to the fundamental holographic length, which is of the order the Compton wavelength of the nucleon.

Scott Funkhouser

2007-01-24T23:59:59.000Z

427

Frequentist estimation of cosmological parameters from theMAXIMA-1 cosmic microwave background anisotropy data  

SciTech Connect

We use a frequentist statistical approach to set confidence intervals on the values of cosmological parameters using the MAXIMA-1 and COBE measurements of the angular power spectrum of the cosmic microwave background. We define a Deltachi (2) statistic, simulate the measurements of MAXIMA-1 and COBE, determine the probability distribution of the statistic, and use it and the data to set confidence intervals on several cosmological parameters. We compare the frequentist confidence intervals with Bayesian credible regions. The frequentist and Bayesian approaches give best estimates for the parameters that agree within 15 per cent, and confidence interval widths that agree to within 30 per cent. The results also suggest that a frequentist analysis gives slightly broader confidence intervals than a Bayesian analysis. The frequentist analysis gives values of Omega = 0.89(-0.19)(+0.26), Omega(B) h(2) =0.026(-0.011)(+0.020) and n = 1.02(-0.10)(+0.31), and the Bayesian analysis gives values of Omega = 0.98(-0.19)(+0.14) Omega(B) h(2) =0.029(-0.010)(+0.015), and n = 1.18(-0.23)(+0.10), all at the 95 per cent confidence level.

Abroe, M.E.; Balbi, A.; Borrill, J.; Bunn, E.F.; Hanany, S.; Ferreira, P.G.; Jaffe, A.H.; Lee, A.T.; Olive, K.A.; Rabii, B.; Richards,P.L.; Smoot, G.F.; Stompor, R.; Winant, C.D.; Wu, J.H.P.

2001-11-07T23:59:59.000Z

428

Angular two-point correlation functions for cosmological gamma-ray burst model  

E-Print Network (OSTI)

We compute the angular two-point correlation functions of the gamma-ray bursts at cosmological distances. Since the gamma-ray burst emission mechanism is not yet established, we simply assume that the gamma-ray burst sources are associated with high-redshift galaxies in some way. Then on the basis of several simple models for the evolution of galaxy spatial correlations, we calculate the amplitude of angular two-point correlation functions on scales appropriate for the Compton Gamma Ray Observatory data. we find that in most cases the predicted correlations are difficult to detect with the current data rate and the angular resolution, but models in which the bursts preferentially occur at relatively low redshift ($z \\simlt 0.5$) predict correlation amplitudes on $\\theta \\sim 5^\\circ$ which will be marginally detectable with the Gamma Ray Observatory data in several years. If future observations detect a signal of angular correlations, it will imply useful information on the correlation of galaxies at high redshifts provided that the gamma-ray bursts are cosmological.

Shiho Kobayashi; Shin Sasaki; Yasushi Suto

1994-09-16T23:59:59.000Z

429

Cosmological Consequences of Topological Defects: Dark Energy and Varying Fundamental Constants  

E-Print Network (OSTI)

We investigated domain wall networks as a possible candidate to explain the present accelerated expansion of the universe. We discuss various requirements that any stable lattice of frustrated walls must obey and propose a class of `ideal' model (in terms of its potential to lead to network frustration). By using the results of the largest and most accurate three-dimensional field theory simulations of domain wall networks with junctions, we find compelling evidence for a gradual approach to scaling. We conjecture that, even though one can build (by hand) lattices that would be stable, no such lattices will ever come out of realistic domain wall forming cosmological phase transitions. We consider cosmic strings and magnetic monopoles in Bekenstein-type models and show that there is a class of models of this type for which the classical Nielsen-Olesen vortex and 't Hooft-Polyakov monopoles are still valid solutions. We show that Equivalence Principle constraints impose tight limits on the allowed variations of $\\alpha$ induced by string networks on cosmological scales. We show that the results obtained using the spherical infall model for an infinite wavelength inhomogeneity are inconsistent with the results of a local linearized gravity study and we argue in favor of the second approach. We also criticize the claim that the value of $\\alpha$ inside collapsed regions could be significantly different from the background one on the basis of these findings.

J. Menezes

2008-08-25T23:59:59.000Z

430

1 Thermodynamics and quantum cosmology Continuous topological evolution of topologically coherent defects  

E-Print Network (OSTI)

As a point of departure it is suggested that Quantum Cosmology is a topological concept independent from metrical constraints. Methods of continuous topological evolution and topological thermodynamics are used to construct a cosmological model of the present universe, using the techniques based upon Cartan’s theory of exterior differential systems. Thermodynamic domains, which are either Open, Closed, Isolated, or in Equilibrium, can be put into correspondence with topological systems of Pfaff topological dimension 4, 3, 2 and 1. If the environment of the universe is assumed to be a physical vacuum of Pfaff topological dimension 4, then continuous but irreversible topological evolution can cause the emergence of topologically coherent defect structures of Pfaff topological dimension less than 4. As galaxies and stars exchange radiation but not matter with the environment, they are emergent topological defects of Pfaff topological dimension 3 which are far from equilibrium. DeRham topological theory of period integrals over closed but not exact exterior differential systems leads to the emergence of quantized, deformable, but topologically coherent, singular macrostates at all scales. The method leads to the conjecture that dark matter and energy is represented by those thermodynamic topological defect structures of Pfaff dimension 2 or less. 2

R. M. Kiehn

2006-01-01T23:59:59.000Z

431

Behavior of Friedmann-Robertson-Walker Cosmological Models in Scalar-Tensor Gravity  

E-Print Network (OSTI)

We analyze solutions to Friedmann-Robertson-Walker cosmologies in Brans-Dicke theory, where a scalar field is coupled to gravity. Matter is modelled by a $\\gamma$-law perfect fluid, including false-vacuum energy as a special case. Through a change of variables, we reduce the field equations from fourth order to second order, and they become equivalent to a two-dimensional dynamical system. We then analyze the entire solution space of this dynamical system, and find that many qualitative features of these cosmologies can be gleaned, including standard non-inflationary or extended inflationary expansion, but also including bifurcations of stable or unstable expansion or contraction, noninflationary vacuum-energy dominated models, and several varieties of ``coasting," ``bouncing," ``hesitating," and ``vacillating" universes. It is shown that inflationary dogma, which states that a universe with curvature and dominated by inflationary matter will always approach a corresponding flat-space solution at late times, does not hold in general for the scalar-tensor