Powered by Deep Web Technologies
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.


1

The Atacama Cosmology Telescope Project: A Progress Report  

E-Print Network [OSTI]

The Atacama Cosmology Telescope is a project to map the microwave background radiation at arcminute angular resolution and high sensitivity in three frequency bands over substantial sky areas. Cosmological signals driving such an experiment are reviewed, and current progress in hardware construction is summarized. Complementary astronomical observations in other wavebands are also discussed.

Arthur Kosowsky; for the ACT Collaboration

2006-08-25T23:59:59.000Z

2

THE ATACAMA COSMOLOGY TELESCOPE: DATA CHARACTERIZATION AND MAPMAKING  

SciTech Connect (OSTI)

We present a description of the data reduction and mapmaking pipeline used for the 2008 observing season of the Atacama Cosmology Telescope (ACT). The data presented here at 148 GHz represent 12% of the 90 TB collected by ACT from 2007 to 2010. In 2008 we observed for 136 days, producing a total of 1423 hr of data (11 TB for the 148 GHz band only), with a daily average of 10.5 hr of observation. From these, 1085 hr were devoted to an 850 deg{sup 2} stripe (11.2 hr by 9. Degree-Sign 1) centered on a declination of -52. Degree-Sign 7, while 175 hr were devoted to a 280 deg{sup 2} stripe (4.5 hr by 4. Degree-Sign 8) centered at the celestial equator. The remaining 163 hr correspond to calibration runs. We discuss sources of statistical and systematic noise, calibration, telescope pointing, and data selection. For the 148 GHz band, out of 1260 survey hours and 1024 detectors in the array, 816 hr and 593 effective detectors remain after data selection, yielding a 38% survey efficiency. The total sensitivity in 2008, determined from the noise level between 5 Hz and 20 Hz in the time-ordered data stream (TOD), is 32 {mu}K{radical}s in cosmic microwave background units. Atmospheric brightness fluctuations constitute the main contaminant in the data and dominate the detector noise covariance at low frequencies in the TOD. The maps were made by solving the least-squares problem using the Preconditioned Conjugate Gradient method, incorporating the details of the detector and noise correlations. Simulations, as well as cross-correlations with Wilkinson Microwave Anisotropy Probe sky maps on large angular scales, reveal that our maps are unbiased at multipoles l > 300. This paper accompanies the public release of the 148 GHz southern stripe maps from 2008. The techniques described here will be applied to future maps and data releases.

Duenner, Rolando; Aguirre, Paula; Barrientos, L. Felipe [Departamento de Astronomia y Astrofisica, Facultad de Fisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile)] [Departamento de Astronomia y Astrofisica, Facultad de Fisica, Pontificia Universidad Catolica de Chile, Casilla 306, Santiago 22 (Chile); Hasselfield, Matthew; Amiri, Mandana; Battistelli, Elia S.; Burger, Bryce [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z4 (Canada)] [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z4 (Canada); Marriage, Tobias A.; Acquaviva, Viviana; Das, Sudeep [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States)] [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States); Sievers, Jon; Appel, John William [Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States)] [Joseph Henry Laboratories of Physics, Jadwin Hall, Princeton University, Princeton, NJ 08544 (United States); Addison, Graeme E.; Calabrese, Erminia [Department of Astrophysics, Oxford University, Oxford OX1 3RH (United Kingdom)] [Department of Astrophysics, Oxford University, Oxford OX1 3RH (United Kingdom); Ade, Peter A. R. [School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA (United Kingdom)] [School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA (United Kingdom); Bond, J. Richard [Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8 (Canada)] [Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8 (Canada); Brown, Ben [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 (United States)] [Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260 (United States); Chervenak, Jay [Code 553/665, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States)] [Code 553/665, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Devlin, Mark J.; Dicker, Simon R. [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States)] [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104 (United States); and others

2013-01-01T23:59:59.000Z

3

HIGH-FREQUENCY RADIO SPECTRAL ENERGY DISTRIBUTIONS AND POLARIZATION FRACTIONS OF SOURCES IN AN ATACAMA COSMOLOGY TELESCOPE SURVEY FIELD  

SciTech Connect (OSTI)

We present flux densities and polarization percentages of 159 radio galaxies based on nearly simultaneous Very Large Array observations at four frequencies, 4.86, 8.46, 22.46, and 43.34 GHz. This sample is selected from the high-frequency Australia Telescope 20 GHz (AT20G) survey and consists of all sources with flux density S{sub 20GHz} > 40 mJy in an equatorial field of the Atacama Cosmology Telescope (ACT) survey. For a subset of 25 of these sources, we used the Green Bank Telescope (GBT) to obtain 90 GHz data. The goals of this program are: (1) a characterization of the spectra, polarization, and variability of high-frequency-selected radio sources, (2) extrapolating from the few GHz regime to the {approx}150 GHz regime of the ACT survey, allowing for more accurate removal of the radio source signal in our particular field, and (3) providing a data set that will allow more accurate modeling of the high-frequency radio source contamination in current and future Sunyaev-Zeldovich and cosmic microwave background experiments. We find that, as expected, this sample consists of flatter spectrum and more compact or point-like sources than low-frequency-selected samples. In the K band, variability is typically {approx}<20%, although there are exceptions. The higher frequency data are well suited to the detection of extreme gigahertz peak spectrum sources. The inclusion of the 43 GHz data causes the relative fraction of inverted spectrum sources to go down and of peaked spectrum sources to go up when compared with the AT20G survey results. The trend largely continues with the inclusion of the 90 GHz data, although {approx}10% of the sources with GBT data show a spectral upturn from 43 GHz to 90 GHz. The measured polarization fractions are typically <5%, although in some cases they are measured to be up to {approx}20%. For sources with detected polarized flux in all four bands, about 40% of the sample, the polarization fractions typically increase with frequency. This trend is stronger for steeper spectrum sources as well as for the lower flux density sources.

Sajina, Anna [Department of Physics and Astronomy, Tufts University, Medford, MA 02155 (United States); Partridge, Bruce; Evans, Tyler; Vechik, Nicholas [Department of Physics and Astronomy, Haverford College, Haverford, PA 19041 (United States); Stefl, Shannon [Kent State University, Kent, OH 44242 (United States); Myers, Steve [National Radio Astronomy Observatory, Socorro, NM 87801 (United States); Dicker, Simon; Korngut, Phillip [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104 (United States)

2011-05-01T23:59:59.000Z

4

E-Print Network 3.0 - atacama telescope ccat Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

applicability of Electric Vehicles (EVs) is the scarce capacity of Summary: a main solar panel on the roof and a secondary, telescopic panel under the main panel. When...

5

Improved constraint on the primordial gravitational-wave density using recent cosmological data and its impact on cosmic string models  

E-Print Network [OSTI]

The production of a primordial stochastic gravitational-wave background by processes occuring in the early Universe is expected in a broad range of models. Observing this background would open a unique window onto the Universe's evolutionary history. Probes like the Cosmic Microwave Background (CMB) or the Baryon Acoustic Oscillations (BAO) can be used to set upper limits on the stochastic gravitational-wave background energy density $\\Omega_{GW}$ for frequencies above $10^{-15}$ Hz. We perform a profile likelihood analysis of the Planck CMB temperature anisotropies and gravitational lensing data combined with WMAP low-$\\ell$ polarization, BAO, South Pole Telescope and Atacama Cosmology Telescope data. We find that $\\Omega_{GW}h_{0}^{2} strings, we have derived exclusion limits in th...

Henrot-Versillé, Sophie; Leroy, Nicolas; Plaszczynski, Stéphane; Arnaud, Nicolas; Bizouard, Marie-Anne; Cavalier, Fabien; Christensen, Nelson; Couchot, François; Franco, Samuel; Hello, Patrice; Huet, Dominique; Kasprzack, Marie; Perdereau, Olivier; Spinelli, Marta; Tristram, Matthieu

2014-01-01T23:59:59.000Z

6

Cosmological data and indications for new physics  

SciTech Connect (OSTI)

Data from the Atacama Cosmology Telescope (ACT) and the South Pole Telescope (SPT), combined with the nine-year data release from the WMAP satellite, provide very precise measurements of the cosmic microwave background (CMB) angular anisotropies down to very small angular scales. Augmented with measurements from Baryonic Acoustic Oscillations surveys and determinations of the Hubble constant, we investigate whether there are indications for new physics beyond a Harrison-Zel'dovich model for primordial perturbations and the standard number of relativistic degrees of freedom at primordial recombination. All combinations of datasets point to physics beyond the minimal Harrison-Zel'dovich model in the form of either a scalar spectral index different from unity or additional relativistic degrees of freedom at recombination (e.g., additional light neutrinos). Beyond that, the extended datasets including either ACT or SPT provide very different indications: while the extended-ACT (eACT) dataset is perfectly consistent with the predictions of standard slow-roll inflation, the extended-SPT (eSPT) dataset prefers a non-power-law scalar spectral index with a very large variation with scale of the spectral index. Both eACT and eSPT favor additional light degrees of freedom on top of the Harrison-Zel'dovich model. eACT is consistent with zero neutrino masses, while eSPT favors nonzero neutrino masses at more than 95% confidence.

Benetti, Micol [Physics Department and ICRA, Università di Roma ''La Sapienza'', Ple. Aldo Moro 2, 00185, Rome (Italy); Gerbino, Martina; Melchiorri, Alessandro; Pagano, Luca [Physics Department and INFN, Università di Roma ''La Sapienza'', Ple Aldo Moro 2, 00185, Rome (Italy); Kinney, William H. [Department of Physics, University at Buffalo, the State University of New York, Buffalo, NY 14260-1500 (United States); Kolb, Edward W. [Department of Astronomy and Astrophysics, Enrico Fermi Institute, and Kavli Institute for Cosmological Physics, University of Chicago, Chicago, Illinois 60637-1433 (United States); Lattanzi, Massimiliano [Dipartimento di Fisica e Science della Terra, Università di Ferrara and INFN, sezione di Ferrara, Polo Scientifico e Tecnologico - Edificio C Via Saragat, 1, I-44122 Ferrara Italy (Italy); Riotto, Antonio, E-mail: micol.benetti@roma1.infn.it, E-mail: martina.gerbino@roma1.infn.it, E-mail: whkinney@buffalo.edu, E-mail: Rocky.Kolb@uchicago.edu, E-mail: lattanzi@fe.infn.it, E-mail: alessandro.melchiorri@roma1.infn.it, E-mail: luca.pagano@roma1.infn.it, E-mail: antonio.riotto@unige.ch [Department of Theoretical Physics and Center for Astroparticle Physics (CAP) 24 quai E. Ansermet, CH-1211 Geneva 4 (Switzerland)

2013-10-01T23:59:59.000Z

7

A search for ultra-light axions using precision cosmological data  

E-Print Network [OSTI]

Ultra-light axions (ULAs) with masses in the range 10^{-33} eV dark-matter or dark-energy density of the Universe. ULAs could suppress the growth of structure on small scales, or lead to an enhanced integrated Sachs-Wolfe effect on large-scale cosmic microwave-background (CMB) anisotropies. In this work, cosmological observables over the full ULA mass range are computed, and then used to search for evidence of ULAs using CMB data from the Wilkinson Microwave Anisotropy Probe (WMAP), Planck satellite, Atacama Cosmology Telescope, and South Pole Telescope, as well as galaxy clustering data from the WiggleZ galaxy-redshift survey. In the mass range 10^{-32} eV dark-matter relic density \\Omega_{d}) must obey the constraints \\Omega_{a}/\\Omega_{d} 10^{-24} eV, ULAs are indistinguishable from standard cold dark matter on the length scales probed, and are thus allowed by these data. For m dark energy.

Renée Hlozek; Daniel Grin; David J. E. Marsh; Pedro G. Ferreira

2014-10-10T23:59:59.000Z

8

The Cherenkov Telescope Array Large Size Telescope  

E-Print Network [OSTI]

The two arrays of the Very High Energy gamma-ray observatory Cherenkov Telescope Array (CTA) will include four Large Size Telescopes (LSTs) each with a 23 m diameter dish and 28 m focal distance. These telescopes will enable CTA to achieve a low-energy threshold of 20 GeV, which is critical for important studies in astrophysics, astroparticle physics and cosmology. This work presents the key specifications and performance of the current LST design in the light of the CTA scientific objectives.

Ambrosi, G; Baba, H; Bamba, A; Barceló, M; de Almeida, U Barres; Barrio, J A; Bigas, O Blanch; Boix, J; Brunetti, L; Carmona, E; Chabanne, E; Chikawa, M; Colin, P; Conteras, J L; Cortina, J; Dazzi, F; Deangelis, A; Deleglise, G; Delgado, C; Díaz, C; Dubois, F; Fiasson, A; Fink, D; Fouque, N; Freixas, L; Fruck, C; Gadola, A; García, R; Gascon, D; Geffroy, N; Giglietto, N; Giordano, F; Grañena, F; Gunji, S; Hagiwara, R; Hamer, N; Hanabata, Y; Hassan, T; Hatanaka, K; Haubold, T; Hayashida, M; Hermel, R; Herranz, D; Hirotani, K; Inoue, S; Inoue, Y; Ioka, K; Jablonski, C; Kagaya, M; Katagiri, H; Kishimoto, T; Kodani, K; Kohri, K; Konno, Y; Koyama, S; Kubo, H; Kushida, J; Lamanna, G; Flour, T Le; López-Moya, M; López, R; Lorenz, E; Majumdar, P; Manalaysay, A; Mariotti, M; Martínez, G; Martínez, M; Mazin, D; Miranda, J M; Mirzoyan, R; Monteiro, I; Moralejo, A; Murase, K; Nagataki, S; Nakajima, D; Nakamori, T; Nishijima, K; Noda, K; Nozato, A; Ohira, Y; Ohishi, M; Ohoka, H; Okumura, A; Orito, R; Panazol, J L; Paneque, D; Paoletti, R; Paredes, J M; Pauletta, G; Podkladkin, S; Prast, J; Rando, R; Reimann, O; Ribó, M; Rosier-Lees, S; Saito, K; Saito, T; Saito, Y; Sakaki, N; Sakonaka, R; Sanuy, A; Sasaki, H; Sawada, M; Scalzotto, V; Schultz, S; Schweizer, T; Shibata, T; Shu, S; Sieiro, J; Stamatescu, V; Steiner, S; Straumann, U; Sugawara, R; Tajima, H; Takami, H; Tanaka, S; Tanaka, M; Tejedor, L A; Terada, Y; Teshima, M; Totani, T; Ueno, H; Umehara, K; Vollhardt, A; Wagner, R; Wetteskind, H; Yamamoto, T; Yamazaki, R; Yoshida, A; Yoshida, T; Yoshikoshi, T

2013-01-01T23:59:59.000Z

9

E-Print Network 3.0 - atacama combining bioarchaeology Sample...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

evidence, along a 1200-kilometre transect (16-26S) in the Atacama Desert Source: Massachusetts at Amherst, University of - Climate System Research Center; Vuille, Mathias...

10

Improved constraint on the primordial gravitational-wave density using recent cosmological data and its impact on cosmic string models  

E-Print Network [OSTI]

The production of a primordial stochastic gravitational-wave background by processes occuring in the early Universe is expected in a broad range of models. Observing this background would open a unique window onto the Universe's evolutionary history. Probes like the Cosmic Microwave Background (CMB) or the Baryon Acoustic Oscillations (BAO) can be used to set upper limits on the stochastic gravitational-wave background energy density $\\Omega_{GW}$ for frequencies above $10^{-15}$ Hz. We perform a profile likelihood analysis of the Planck CMB temperature anisotropies and gravitational lensing data combined with WMAP low-$\\ell$ polarization, BAO, South Pole Telescope and Atacama Cosmology Telescope data. We find that $\\Omega_{GW}h_{0}^{2} strings, we have derived exclusion limits in the cosmic string parameter space. If the size of the loops is determined by gravitational back-reaction, string tension values lower than $\\sim 4 \\times 10^{-9}$ are excluded for a reconnection probability of $10^{-3}$.

Sophie Henrot-Versillé; Florent Robinet; Nicolas Leroy; Stéphane Plaszczynski; Nicolas Arnaud; Marie-Anne Bizouard; Fabien Cavalier; Nelson Christensen; François Couchot; Samuel Franco; Patrice Hello; Dominique Huet; Marie Kasprzack; Olivier Perdereau; Marta Spinelli; Matthieu Tristram

2014-08-22T23:59:59.000Z

11

Supernova Cosmology Project  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (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.

12

Laser Cosmology  

E-Print Network [OSTI]

Recent years have seen tremendous progress in our understanding of the cosmos, which in turn points to even deeper questions to be further addressed. Concurrently the laser technology has undergone dramatic revolutions, providing exciting opportunity for science applications. History has shown that the symbiosis between direct observations and laboratory investigation is instrumental in the progress of astrophysics. We believe that this remains true in cosmology. Current frontier phenomena related to particle astrophysics and cosmology typically involve one or more of the following conditions: (1) extremely high energy events; (2) very high density, high temperature processes; (3) super strong field environments. Laboratory experiments using high intensity lasers can calibrate astrophysical observations, investigate underlying dynamics of astrophysical phenomena, and probe fundamental physics in extreme limits. In this article we give an overview of the exciting prospect of laser cosmology. In particular, we showcase its unique capability of investigating frontier cosmology issues such as cosmic accelerator and quantum gravity.

Pisin Chen

2014-02-24T23:59:59.000Z

13

Endolithic cyanobacteria in soil gypsum: Occurrences in Atacama (Chile), Mojave (United States), and Al-Jafr Basin (Jordan) Deserts  

E-Print Network [OSTI]

), and Al-Jafr Basin (Jordan) Deserts Hailiang Dong,1 Jason A. Rech,1 Hongchen Jiang,1 Henry Sun,2, United States, and Al-Jafr Basin, Jordan, revealed endolithic cyanobacteria communities just below the Atacama and Mojave Desert, but insignificant in the fibrous gypsum from the Jordan Desert. Endolithic life

Ahmad, Sajjad

14

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

E-Print Network [OSTI]

cosmological parameters and dark energy through weak lensing measurements in the COSMOS survey (Massey et al 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

Sirianni, Marco

15

PLANETARY TRANSITS WITH THE ATACAMA LARGE MILLIMETER/SUBMILLIMETER ARRAY RADIO INTERFEROMETER  

SciTech Connect (OSTI)

Planetary transits are commonly observed at visible wavelengths. Here we investigate the shape of a planetary transit observed at radio wavelengths. Solar maps at 17 GHz are used as a proxy for the stellar eclipse by several sizes of planets from super-Earths to hot Jupiters. The relative depth at mid-transit is the same as observed at visible wavelengths, but the limb brightening of the stellar disk at 17 GHz is clearly seen in the shape of the transit light curve. Moreover, when the planet occults an active region the depth of the transit decreases even further, depending on the brightness of the active region relative to the surrounding disk. For intense active region, with 50 times the brightness temperature of the surrounding disk, the decrease can supercede the unperturbed transit depth depending on the size of the eclipsing planet. For a super-Earth (R{sub p} = 0.02 R{sub s} ) crossing, the decrease in intensity is 0.04%, increasing to 0.86% in the case when a strong active region is present. On the other hand, for a hot Jupiter with R{sub p} = 0.17R{sub s} , the unperturbed transit depth is 3% increasing to 4.7% when covering this strong active region. This kind of behavior can be verified with observation of planetary transits with the Atacama Large Millimeter/submillimeter Array radio interferometer.

Selhorst, C. L.; Barbosa, C. L. [IP and D, Universidade do Vale do Paraíba (UNIVAP), São José dos Campos, SP (Brazil)] [IP and D, Universidade do Vale do Paraíba (UNIVAP), São José dos Campos, SP (Brazil); Válio, Adriana, E-mail: caius@univap.br [CRAAM, Universidade Presbiteriana Mackenzie, São Paulo, SP (Brazil)] [CRAAM, Universidade Presbiteriana Mackenzie, São Paulo, SP (Brazil)

2013-11-10T23:59:59.000Z

16

Cosmological parameters are dressed  

E-Print Network [OSTI]

In the context of the averaging problem in relativistic cosmology, we provide a key to the interpretation of cosmological parameters by taking into account the actual inhomogeneous geometry of the Universe. We discuss the relation between `bare' cosmological parameters determining the cosmological model, and the parameters interpreted by observers with a ``Friedmannian bias'', which are `dressed' by the smoothed-out geometrical inhomogeneities of the surveyed spatial region.

Thomas Buchert; Mauro Carfora

2002-10-15T23:59:59.000Z

17

LXCDM cosmologies: solving the cosmological coincidence problem?  

E-Print Network [OSTI]

We explore the possibility of having a composite (self-conserved) dark energy (DE) whose dynamics is controlled by the quantum running of the cosmological parameters. We find that within this scenario it is feasible to find an explanation for the cosmological coincidence problem and at the same time a good qualitative description of the present data.

Javier Grande; Joan Sola; Hrvoje Stefancic

2006-09-25T23:59:59.000Z

18

Alignment telescope for Antares  

SciTech Connect (OSTI)

The Antares Automatic Alignment System employs a specially designed telescope for alignment of its laser beamlines. There are two telescopes in the system, and since each telescope is a primary alignment reference, stringent boresight accuracy and stability over the focus range were required. Optical and mechanical designs, which meet this requirement as well as that of image quality over a wide wavelength band, are described. Special test techniques for initial assembly and alignment of the telescope are also presented. The telescope, which has a 180-mm aperture FK51-KZF2 type glass doublet objective, requires a boresight accuracy of 2.8 ..mu..rad at two focal lengths, and object distances between 11 meters and infinity. Travel of a smaller secondary doublet provides focus from 11 m to infinity with approximately 7.8 m effective focal length. By flipping in a third doublet, the effective focal length is reduced to 2.5 m. Telescope alignment was accomplished by using a rotary air bearing to establish an axis in front of the system and placing the focus of a Laser Unequal Path Interferometer (LUPI) at the image plane.

Appert, Q.D.; Swann, T.A.; Ward, J.H.; Hardesty, C.; Wright, L.

1983-01-01T23:59:59.000Z

19

Averaging Hypotheses in Newtonian Cosmology  

E-Print Network [OSTI]

Average properties of general inhomogeneous cosmological models are discussed in the Newtonian framework. It is shown under which circumstances the average flow reduces to a member of the standard Friedmann--Lema\\^\\i tre cosmologies. Possible choices of global boundary conditions of inhomogeneous cosmologies as well as consequences for the interpretation of cosmological parameters are put into perspective.

T. Buchert

1995-12-20T23:59:59.000Z

20

Neutrino conversions in cosmological gamma-ray burst fireballs  

E-Print Network [OSTI]

We study neutrino conversions in a recently envisaged source of high-energy neutrinos (E \\geq 10^6 GeV), that is, in the vicinity of cosmological Gamma-Ray Burst fireballs (GRB). We consider the effects of flavor and spin-flavor conversions and point out that in both situations, a some what higher than estimated high energy tau neutrino flux from GRBs is expected in new km^2 surface area under water/ice neutrino telescopes.

H. Athar

2000-04-20T23:59:59.000Z

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

D-braneworld cosmology  

Science Journals Connector (OSTI)

We discuss D-braneworld cosmology; that is, the brane is described by the Born-Infeld action. Compared with the usual Randall-Sundrum braneworld cosmology where the brane action is the Nambu-Goto one, we can see some drastic changes in the very early universe: (i) the universe may experience a rapidly accelerating phase; (ii) the closed universe may avoid the initial singularity. We also briefly address the dynamics of the cosmology in the open string metric, which might be more favored than the induced metric from the viewpoint of the D-brane.

Tetsuya Shiromizu; Takashi Torii; Tomoko Uesugi

2003-06-26T23:59:59.000Z

22

Cosmology and New Physics  

E-Print Network [OSTI]

A comparison of the standard models in particle physics and in cosmology demonstrates that they are not compatible, though both are well established. Basics of modern cosmology are briefly reviewed. It is argued that the measurements of the main cosmological parameters are achieved through many independent physical phenomena and this minimizes possible interpretation errors. It is shown that astronomy demands new physics beyond the frameworks of the (minimal) standard model in particle physics. More revolutionary modifications of the basic principles of the theory are also discussed.

A. D. Dolgov

2006-06-21T23:59:59.000Z

23

Cosmological Ontology and Epistemology  

E-Print Network [OSTI]

In cosmology, we would like to explain our observations and predict future observations from theories of the entire universe. Such cosmological theories make ontological assumptions of what entities exist and what their properties and relationships are. One must also make epistemological assumptions or metatheories of how one can test cosmological theories. Here I shall propose a Bayesian analysis in which the likelihood of a complete theory is given by the normalized measure it assigns to the observation used to test the theory. In this context, a discussion is given of the trade-off between prior probabilities and likelihoods, of the measure problem of cosmology, of the death of Born's rule, of the Boltzmann brain problem, of whether there is a better principle for prior probabilities than mathematical simplicity, and of an Optimal Argument for the Existence of God.

Don N. Page

2014-12-23T23:59:59.000Z

24

Multiverses and physical cosmology  

Science Journals Connector (OSTI)

......Cosmological Data and the Values of the Fundamental Parameters, to appear. ASP Publications, San Francisco(. Sciama D. , 1993, inIs the universe unique Die Kosmologie der Gegenwart. Serie Piper. Smolin L. , 1999, The Life of the Universe. Oxford Univ......

G. F. R. Ellis; U. Kirchner; W. R. Stoeger

2004-01-21T23:59:59.000Z

25

Massive neutrinos and cosmology  

E-Print Network [OSTI]

The present experimental results on neutrino flavour oscillations provide evidence for non-zero neutrino masses, but give no hint on their absolute mass scale, which is the target of beta decay and neutrinoless double-beta decay experiments. Crucial complementary information on neutrino masses can be obtained from the analysis of data on cosmological observables, such as the anisotropies of the cosmic microwave background or the distribution of large-scale structure. In this review we describe in detail how free-streaming massive neutrinos affect the evolution of cosmological perturbations. We summarize the current bounds on the sum of neutrino masses that can be derived from various combinations of cosmological data, including the most recent analysis by the WMAP team. We also discuss how future cosmological experiments are expected to be sensitive to neutrino masses well into the sub-eV range.

Julien Lesgourgues; Sergio Pastor

2006-05-29T23:59:59.000Z

26

Upgrade of the MAGIC telescopes  

E-Print Network [OSTI]

The MAGIC telescopes are two Imaging Atmospheric Cherenkov Telescopes (IACTs) located on the Canary island of La Palma. With 17m diameter mirror dishes and ultra-fast electronics, they provide an energy threshold as low as 50 GeV for observations at low zenith angles. The first MAGIC telescope was taken in operation in 2004 whereas the second one joined in 2009. In 2011 we started a major upgrade program to improve and to unify the stereoscopic system of the two similar but at that time different telescopes. Here we report on the upgrade of the readout electronics and digital trigger of the two telescopes, the upgrade of the camera of the MAGIC I telescope as well as the commissioning of the system after this major upgrade.

Mazin, Daniel; Garczarczyk, Markus; Giavitto, Gianluca; Sitarek, Julian

2014-01-01T23:59:59.000Z

27

High Energy Neutrino Telescopes  

E-Print Network [OSTI]

This paper presents a review of the history, motivation and current status of high energy neutrino telescopes. Many years after these detectors were first conceived, the operation of kilometer-cubed scale detectors is finally on the horizon at both the South Pole and in the Mediterranean Sea. These new detectors will perhaps provide us the first view of high energy astrophysical objects with a new messenger particle and provide us with our first real glimpse of the distant universe at energies above those accessible by gamma-ray instruments. Some of the topics that can be addressed by these new instruments include the origin of cosmic rays, the nature of dark matter, and the mechanisms at work in high energy astrophysical objects such as gamma-ray bursts, active galactic nuclei, pulsar wind nebula and supernova remnants.

Hoffman, K D

2008-01-01T23:59:59.000Z

28

High Energy Neutrino Telescopes  

E-Print Network [OSTI]

This paper presents a review of the history, motivation and current status of high energy neutrino telescopes. Many years after these detectors were first conceived, the operation of kilometer-cubed scale detectors is finally on the horizon at both the South Pole and in the Mediterranean Sea. These new detectors will perhaps provide us the first view of high energy astrophysical objects with a new messenger particle and provide us with our first real glimpse of the distant universe at energies above those accessible by gamma-ray instruments. Some of the topics that can be addressed by these new instruments include the origin of cosmic rays, the nature of dark matter, and the mechanisms at work in high energy astrophysical objects such as gamma-ray bursts, active galactic nuclei, pulsar wind nebula and supernova remnants.

K. D. Hoffman

2008-12-18T23:59:59.000Z

29

Space Telescope Programs Hubble Observatory  

E-Print Network [OSTI]

Assurance/Configuration Management Mr. Christopher Scholz EAG QA Manager #12;Space Telescope Programs Hubble · COS-UCB-002 QA Implementation Plan Released December 1, 1999 · COS-UCB-003 CM Plan released DecemberSpace Telescope Programs Hubble Observatory HST-COS FUV PER 11/8/00 FUV Detector System Quality

Colorado at Boulder, University of

30

SU(2) cosmological solitons  

Science Journals Connector (OSTI)

We present a class of numerical solutions to the SU(2) nonlinear ? model coupled to the Einstein equations with a cosmological constant ?>~0 in spherical symmetry. These solutions are characterized by the presence of a regular static region which includes a center of symmetry. They are parametrized by a dimensionless “coupling constant” ?, the sign of the cosmological constant, and an integer “excitation number” n. The phenomenology we find is compared to the corresponding solutions found for the Einstein-Yang-Mills (EYM) equations with a positive ? (EYM?). If we choose ? positive and fix n, we find a family of static spacetimes with a Killing horizon for 0<~?cosmological context, we apply the concept of a trapping horizon as formulated by Hayward. For small values of ? an asymptotically de Sitter dynamic region contains the static region within a Killing horizon of cosmological type. For strong coupling the static region contains an “eternal cosmological black hole.”

C. Lechner; S. Husa; P. C. Aichelburg

2000-07-27T23:59:59.000Z

31

Nuclear physics and cosmology  

SciTech Connect (OSTI)

There are important aspects of Cosmology, the scientific study of the large scale properties of the universe as a whole, for which nuclear physics can provide insights. Here, we will focus on Standard Big-Bang Nucleosynthesis and we refer to the previous edition of the School [1] for the aspects concerning the variations of constants in nuclear cosmo-physics.

Coc, Alain [Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), CNRS/IN2P3, Université Paris Sud 11, UMR 8609, Bâtiment 104, F-91405 Orsay Campus (France)

2014-05-09T23:59:59.000Z

32

Observational Cosmology With Semi-Relativistic Stars  

E-Print Network [OSTI]

Galaxy mergers lead to the formation of massive black hole binaries which can accelerate background stars close to the speed of light. We estimate the comoving density of ejected stars with a peculiar velocity in excess of $0.1c$ or $0.5c$ to be $\\sim 10^{10}$ and $10^5$ Gpc$^{-3}$ respectively, in the present-day Universe. Semi-relativistic giant stars will be detectable with forthcoming telescopes out to a distance of a few Mpc, where their proper motion, radial velocity, and age, can be spectroscopically measured. In difference from traditional cosmological messengers, such as photons, neutrinos, or cosmic-rays, these stars shine and so their trajectories need not be directed at the observer for them to be detected. Tracing the stars to their parent galaxies as a function of speed and age will provide a novel test of the equivalence principle and the standard cosmological parameters. Semi-relativistic stars could also flag black hole binaries as gravitational wave sources for the future eLISA observatory.

Loeb, Abraham

2014-01-01T23:59:59.000Z

33

The Balloon-borne Large Aperture Submillimeter Telescope: BLAST  

Science Journals Connector (OSTI)

The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a suborbital surveying experiment designed to study the evolutionary history and processes of star formation in local galaxies (including the Milky Way) and galaxies at cosmological distances. The BLAST continuum camera, which consists of 270 detectors distributed between three arrays, observes simultaneously in broadband (30%) spectral windows at 250, 350, and 500 ?m. The optical design is based on a 2 m diameter telescope, providing a diffraction-limited resolution of 30 -->'' at 250 ?m. The gondola pointing system enables raster mapping of arbitrary geometry, with a repeatable positional accuracy of ~30 -->''; postflight pointing reconstruction to 5 -->'' rms is achieved. The onboard telescope control software permits autonomous execution of a preselected set of maps, with the option of manual override. In this paper we describe the primary characteristics and measured in-flight performance of BLAST. BLAST performed a test flight in 2003 and has since made two scientifically productive long-duration balloon flights: a 100 hr flight from ESRANGE (Kiruna), Sweden to Victoria Island, northern Canada in 2005 June; and a 250 hr, circumpolar flight from McMurdo Station, Antarctica, in 2006 December.

E. Pascale; P. A. R. Ade; J. J. Bock; E. L. Chapin; J. Chung; M. J. Devlin; S Dicker; M. Griffin; J. O. Gundersen; M. Halpern; P. C. Hargrave; D. H. Hughes; J. Klein; C. J. MacTavish; G. Marsden; P. G. Martin; T. G. Martin; P. Mauskopf; C. B. Netterfield; L. Olmi; G. Patanchon; M. Rex; D. Scott; C. Semisch; N. Thomas; M. D. P. Truch; C. Tucker; G. S. Tucker; M. P. Viero; D. V. Wiebe

2008-01-01T23:59:59.000Z

34

Biases on cosmological parameter estimators from galaxy cluster number counts  

E-Print Network [OSTI]

Sunyaev-Zel'dovich (SZ) surveys are promising probes of cosmology - in particular for Dark Energy (DE) -, given their ability to find distant clusters and provide estimates for their mass. However, current SZ catalogs contain tens to hundreds of objects and maximum likelihood estimators may present biases for such sample sizes. In this work we use the Monte Carlo approach to determine the presence of bias on cosmological parameter estimators from cluster abundance as a function of the area and depth of the survey, and the number of cosmological parameters fitted. Assuming perfect knowledge of mass and redshift some estimators have non-negligible biases. For example, the bias of $\\sigma_8$ corresponds to about $40%$ of its statistical error bar when fitted together with $\\Omega_c$ and $w_0$. Including a SZ mass-observable relation decreases the relevance of the bias, for the typical sizes of current surveys. The biases become negligible when combining the SZ data with other cosmological probes. However, we show that the biases from SZ estimators do not go away with increasing sample sizes and they may become the dominant source of error for an all sky survey at the South Pole Telescope (SPT) sensitivity. The results of this work validate the use of the current maximum likelihood methods for present SZ surveys, but highlight the need for further studies for upcoming experiments. [abridged

M. Penna-Lima; M. Makler; C. A. Wuensche

2013-12-16T23:59:59.000Z

35

Quantum cosmology: a review  

E-Print Network [OSTI]

In quantum cosmology, one applies quantum physics to the whole universe. While no unique version and no completely well-defined theory is available yet, the framework gives rise to interesting conceptual, mathematical and physical questions. This review presents quantum cosmology in a new picture that tries to incorporate the importance of inhomogeneity: De-emphasizing the traditional minisuperspace view, the dynamics is rather formulated in terms of the interplay of many interacting "microscopic" degrees of freedom that describe the space-time geometry. There is thus a close relationship with more-established systems in condensed-matter and particle physics even while the large set of space-time symmetries (general covariance) requires some adaptations and new developments. These extensions of standard methods are needed both at the fundamental level and at the stage of evaluating the theory by effective descriptions.

Bojowald, Martin

2015-01-01T23:59:59.000Z

36

Cosmology with Doppler Lensing  

E-Print Network [OSTI]

Doppler lensing is the apparent change in object size and magnitude due to peculiar velocities. Objects falling into an overdensity appear larger on its near side, and smaller on its far side, than typical objects at the same redshifts. This effect dominates over the usual gravitational lensing magnification at low redshift. Doppler lensing is a promising new probe of cosmology, and we explore in detail how to utilize the effect with forthcoming surveys. We present cosmological simulations of the Doppler and gravitational lensing effects based on the Millennium simulation. We show that Doppler lensing can be detected around stacked voids or unvirialised over-densities. New power spectra and correlation functions are proposed which are designed to be sensitive to Doppler lensing. We consider the impact of gravitational lensing and intrinsic size correlations on these quantities. We compute the correlation functions and forecast the errors for realistic forthcoming surveys, providing predictions for constraints...

Bacon, David J; Clarkson, Chris; Bolejko, Krzysztof; Maartens, Roy

2014-01-01T23:59:59.000Z

37

Cosmology with running parameters  

E-Print Network [OSTI]

The experimental evidence that the equation of state (EOS) of the dark energy (DE) could be evolving with time/redshift (including the possibility that it might behave phantom-like near our time) suggests that there might be dynamical DE fields that could explain this behavior. We propose, instead, that a variable cosmological term (including perhaps a variable Newton's gravitational coupling too) may account in a natural way for all these features.

Joan Sola

2005-12-05T23:59:59.000Z

38

Standard cosmology delayed  

SciTech Connect (OSTI)

The introduction of a delay in the Friedmann equation of cosmological evolution is shown to result in the very early universe undergoing the necessary accelerated expansion in the usual radiation (or matter) dominated phase. Occurring even without a violation of the strong energy condition, this expansion slows down naturally to go over to the decelerated phase, namely the standard Hubble expansion. This may obviate the need for a scalar field driven inflationary epoch.

Choudhury, Debajyoti [Department of Physics and Astrophysics, University of Delhi, Delhi 110007 (India); Ghoshal, Debashis [School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067 (India); Sen, Anjan Ananda, E-mail: debajyoti.choudhury@gmail.com, E-mail: dghoshal@mail.jnu.ac.in, E-mail: anjan.ctp@jmi.ac.in [Centre for Theoretical Physics, Jamia Millia Islamia, New Delhi 110025 (India)

2012-02-01T23:59:59.000Z

39

Standard Cosmology Delayed  

E-Print Network [OSTI]

The introduction of a delay in the Friedmann equation of cosmological evolution is shown to result in the very early universe undergoing the necessary accelerated expansion in the usual radiation (or matter) dominated phase. Occurring even without a violation of the strong energy condition, this expansion slows down naturally to go over to the decelerated phase, namely the standard Hubble expansion. This may obviate the need for a scalar field driven inflationary epoch.

Debajyoti Choudhury; Debashis Ghoshal; Anjan Ananda Sen

2012-02-06T23:59:59.000Z

40

Standard Cosmology Delayed  

E-Print Network [OSTI]

The introduction of a delay in the Friedmann equation of cosmological evolution is shown to result in the very early universe undergoing the necessary accelerated expansion in the usual radiation (or matter) dominated phase. Occurring even without a violation of the strong energy condition, this expansion slows down naturally to go over to the decelerated phase, namely the standard Hubble expansion. This may obviate the need for a scalar field driven inflationary epoch.

Choudhury, Debajyoti; Sen, Anjan Ananda

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.


41

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

42

Cosmology for high energy physicists  

SciTech Connect (OSTI)

The standard big bang model of cosmology is presented. Although not perfect, its many successes make it a good starting point for most discussions of cosmology. Places are indicated where well understood laboratory physics is incorporated into the big bang, leading to successful predictions. Much less established aspects of high energy physics and some of the new ideas they have introduced into the field of cosmology are discussed, such as string theory, inflation and monopoles. 49 refs., 5 figs.

Albrecht, A.

1987-11-01T23:59:59.000Z

43

Probing the nature of dark energy through galaxy redshift surveys with radio telescopes  

E-Print Network [OSTI]

Galaxy redshift surveys using optical telescopes have, in combination with other cosmological probes, enabled precision measurements of the nature of dark energy. We show that radio telescopes are rapidly becoming competitive with optical facilities in spectroscopic surveys of large numbers of galaxies. Two breakthroughs are driving this change. Firstly, individual radio telescopes are more efficient at mapping the sky thanks to the large field-of-view of new phased-array feeds. Secondly, ever more dishes can be correlated in a cost-effective manner with rapid increases in computing power. The next decade will see the coming of age of the 21cm radio wavelength as a cosmological probe as first the Pathfinders then, ultimately, the Square Kilometre Array is constructed. The latter will determine precise 3D positions for a billion galaxies, mapping the distribution of matter in the Universe over the last 12 billion years. This radio telescope will be able to constrain the equation of state of dark energy, and it...

Duffy, Alan R

2014-01-01T23:59:59.000Z

44

Wide field of view telescope  

DOE Patents [OSTI]

A wide field of view telescope having two concave and two convex reflective surfaces, each with an aspheric surface contour, has a flat focal plane array. Each of the primary, secondary, tertiary, and quaternary reflective surfaces are rotationally symmetric about the optical axis. The combination of the reflective surfaces results in a wide field of view in the range of approximately 3.8.degree. to approximately 6.5.degree.. The length of the telescope along the optical axis is approximately equal to or less than the diameter of the largest of the reflective surfaces.

Ackermann, Mark R. (Albuquerque, NM); McGraw, John T. (Placitas, NM); Zimmer, Peter C. (Albuquerque, NM)

2008-01-15T23:59:59.000Z

45

Neutrino telescopes in the World  

SciTech Connect (OSTI)

Neutrino astronomy has rapidly developed these last years, being the only way to get specific and reliable information about astrophysical objects still poorly understood.Currently two neutrino telescopes are operational in the World: BAIKAL, in the lake of the same name in Siberia, and AMANDA, in the ices of the South Pole. Two telescopes of the same type are under construction in the Mediterranean Sea: ANTARES and NESTOR. All these telescopes belong to a first generation, with an instrumented volume smaller or equal to 0.02 km3. Also in the Mediterranean Sea, the NEMO project is just in its stag phase, within the framework of a cubic kilometer size neutrino telescope study. Lastly, the ICECUBE detector, with a volume reaching about 1 km3, is under construction on the site of AMANDA experiment, while an extension of the BAIKAL detector toward km3 is under study. We will present here the characteristics of these experiments, as well as the results of their observations.

Ernenwein, J.-P. [GRPHE, Universite de Haute Alsace, 61 rue Albert Camus, 68093 Mulhouse cedex (France)

2007-01-12T23:59:59.000Z

46

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

47

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

48

Dust time in quantum cosmology  

E-Print Network [OSTI]

We give a formulation of quantum cosmology with a pressureless dust and arbitrary additional matter fields. The dust provides a natural time gauge corresponding to a cosmic time, yielding a physical time independent Hamiltonian. The approach simplifies the analysis of both Wheeler-deWitt and loop quantum cosmology models, broadening the applicability of the latter.

Husain, Viqar

2013-01-01T23:59:59.000Z

49

The Standard Cosmological Model  

E-Print Network [OSTI]

The Standard Model of Particle Physics (SMPP) is an enormously successful description of high energy physics, driving ever more precise measurements to find "physics beyond the standard model", as well as providing motivation for developing more fundamental ideas that might explain the values of its parameters. Simultaneously, a description of the entire 3-dimensional structure of the present-day Universe is being built up painstakingly. Most of the structure is stochastic in nature, being merely the result of the particular realisation of the "initial conditions" within our observable Universe patch. However, governing this structure is the Standard Model of Cosmology (SMC), which appears to require only about a dozen parameters. Cosmologists are now determining the values of these quantities with increasing precision in order to search for "physics beyond the standard model", as well as trying to develop an understanding of the more fundamental ideas which might explain the values of its parameters. Although it is natural to see analogies between the two Standard Models, some intrinsic differences also exist, which are discussed here. Nevertheless, a truly fundamental theory will have to explain both the SMPP and SMC, and this must include an appreciation of which elements are deterministic and which are accidental. Considering different levels of stochasticity within cosmology may make it easier to accept that physical parameters in general might have a non-deterministic aspect.

Douglas Scott

2005-10-26T23:59:59.000Z

50

Nuclear & Particle Physics, Astrophysics, Cosmology  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

production, nuclear weapons, and nuclear threat reduction Proton radiography, muon tomography, proton active interrogation, wide-angle, fast-response optical telescopes, and...

51

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

52

THE OPTIMAL GRAVITATIONAL LENS TELESCOPE  

SciTech Connect (OSTI)

Given an observed gravitational lens mirage produced by a foreground deflector (cf. galaxy, quasar, cluster, ...), it is possible via numerical lens inversion to retrieve the real source image, taking full advantage of the magnifying power of the cosmic lens. This has been achieved in the past for several remarkable gravitational lens systems. Instead, we propose here to invert an observed multiply imaged source directly at the telescope using an ad hoc optical instrument which is described in the present paper. Compared to the previous method, this should allow one to detect fainter source features as well as to use such an optimal gravitational lens telescope to explore even fainter objects located behind and near the lens. Laboratory and numerical experiments illustrate this new approach.

Surdej, J.; Hanot, C.; Sadibekova, T. [Department of Astrophysics, Geophysics and Oceanography (AGO), AEOS Group, Liege University, Allee du 6 Aout 17, 4000 Liege (Belgium); Delacroix, C.; Habraken, S. [Department of Physics (DEPHY), Hololab Group, Liege University, Allee du 6 Aout 17, 4000 Liege (Belgium); Coleman, P. [Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822 (United States); Dominik, M. [SUPA, University of St Andrews, School of Physics and Astronomy, North Haugh, St Andrews, KY16 9SS (United Kingdom); Le Coroller, H. [Observatoire de Haute Provence, F-04870 Saint Michel l'Observatoire (France); Mawet, D. [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Quintana, H. [Departmento de Astronomia y Astrofisica, Pontificia Universidad Catolica de Chile, Casilla 306, CL 22 Santiago (Chile); Sluse, D., E-mail: surdej@astro.ulg.ac.b [Astronomisches Rechen-Institut am Zentrum fuer Astronomie der Universitaet Heidelberg, Moenchhofstrasse 12-14, 69120 Heidelberg (Germany)

2010-05-15T23:59:59.000Z

53

Protein folding and cosmology  

E-Print Network [OSTI]

Protein denaturing induced by supercooling is interpreted as a process where some or all internal symmetries of the native protein are spontaneously broken. Hence, the free-energy potential corresponding to a folding-funnel landscape becomes temperature-dependent and describes a phase transition. The idea that deformed vortices could be produced in the transition induced by temperature quenching, from native proteins to unfolded conformations is discussed in terms of the Zurek mechanism that implements the analogy between vortices, created in the laboratory at low energy, and the cosmic strings which are thought to have been left after symmetry breaking phase transitions in the early universe. An experiment is proposed to test the above idea which generalizes the cosmological analogy to also encompass biological systems and push a step ahead the view that protein folding is a biological equivalent of the big bang.

González-Diáz, P F

1997-01-01T23:59:59.000Z

54

Protein folding and cosmology  

E-Print Network [OSTI]

Protein denaturing induced by supercooling is interpreted as a process where some or all internal symmetries of the native protein are spontaneously broken. Hence, the free-energy potential corresponding to a folding-funnel landscape becomes temperature-dependent and describes a phase transition. The idea that deformed vortices could be produced in the transition induced by temperature quenching, from native proteins to unfolded conformations is discussed in terms of the Zurek mechanism that implements the analogy between vortices, created in the laboratory at low energy, and the cosmic strings which are thought to have been left after symmetry breaking phase transitions in the early universe. An experiment is proposed to test the above idea which generalizes the cosmological analogy to also encompass biological systems and push a step ahead the view that protein folding is a biological equivalent of the big bang.

P. F. Gonzalez-Diaz; C. L. Siguenza

1997-06-04T23:59:59.000Z

55

Turnaround in Cyclic Cosmology  

SciTech Connect (OSTI)

It is speculated how dark energy in a brane world can help reconcile an infinitely cyclic cosmology with the second law of thermodynamics. A cyclic model is described, in which dark energy with w<-1 equation of state leads to a turnaround at a time, extremely shortly before the would-be big rip, at which both volume and entropy of our Universe decrease by a gigantic factor, while very many independent similarly small contracting universes are spawned. The entropy of our model decreases almost to zero at turnaround but increases for the remainder of the cycle by a vanishingly small amount during contraction, empty of matter, then by a large factor during inflationary expansion.

Baum, Lauris; Frampton, Paul H. [University of North Carolina, Chapel Hill, North Carolina 27599-3255 (United States)

2007-02-16T23:59:59.000Z

56

LHC Physics and Cosmology  

E-Print Network [OSTI]

In these Lectures I review possible constraints on particle physics models, obtained by means of combining the results of collider measurements with astrophysical data. I emphasize the theoretical-model dependence of these results. I discuss supersymmetric dark matter constraints at colliders (mainly LHC) in various theoretical contexts: the standard Cosmological-Constant-Cold-Dark-Matter (Lambda-CDM) model, (super)string-inspired ones and non-equilibrium relaxation dark energy models. I then investigate the capability of LHC measurements in asserting whether supersymmetric matter (if discovered) constitutes part, or all, of the astrophysical dark matter. I also discuss prospects for improving the constraints in future precision facilities, such as the International Linear Collider.

Nikolaos E. Mavromatos

2007-08-01T23:59:59.000Z

57

Cosmology with the SKA -- overview  

E-Print Network [OSTI]

The new frontier of cosmology will be led by three-dimensional surveys of the large-scale structure of the Universe. Based on its all-sky surveys and redshift depth, the SKA is destined to revolutionize cosmology, in combination with future optical/ infrared surveys such as Euclid and LSST. Furthermore, we will not have to wait for the full deployment of the SKA in order to see transformational science. In the first phase of deployment (SKA1), all-sky HI intensity mapping surveys and all-sky continuum surveys are forecast to be at the forefront on the major questions of cosmology. We give a broad overview of the major contributions predicted for the SKA. The SKA will not only deliver precision cosmology -- it will also probe the foundations of the standard model and open the door to new discoveries on large-scale features of the Universe.

Maartens, Roy; Jarvis, Matt; Santos, Mario G

2015-01-01T23:59:59.000Z

58

Inflationary Cosmology: Theory and Phenomenology  

E-Print Network [OSTI]

This article gives a brief overview of some of the theory behind the inflationary cosmology, and discusses prospects for constraining inflation using observations. Particular care is given to the question of falsifiability of inflation or of subsets of inflationary models.

Andrew R Liddle

2001-10-18T23:59:59.000Z

59

Thermodynamics in Loop Quantum Cosmology  

E-Print Network [OSTI]

Loop quantum cosmology (LQC) is very powerful to deal with the behavior of early universe. And the effective loop quantum cosmology gives a successful description of the universe in the semiclassical region. We consider the apparent horizon of the Friedmann-Robertson-Walker universe as a thermodynamical system and investigate the thermodynamics of LQC in the semiclassical region. The effective density and effective pressure in the modified Friedmann equation from LQC not only determine the evolution of the universe in LQC scenario but are actually also found to be the thermodynamic quantities. This result comes from the energy definition in cosmology (the Misner-Sharp gravitational energy) and is consistent with thermodynamic laws. We prove that within the framework of loop quantum cosmology, the elementary equation of equilibrium thermodynamics is still valid.

Li-Fang Li; Jian-Yang Zhu

2008-12-18T23:59:59.000Z

60

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

2006-11-03T23:59:59.000Z

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

An inhomogeneous fractal cosmological model  

E-Print Network [OSTI]

We present a cosmological model in which the metric allows for an inhomogeneous Universe with no intrinsic symmetries (Stephani models), providing the ideal features to describe a fractal distribution of matter. Constraints on the metric functions are derived using the expansion and redshift relations and allowing for scaling number counts, as expected in a fractal set. The main characteristics of such a cosmological model are discussed.

Fulvio Pompilio; Marco Montuori

2001-11-28T23:59:59.000Z

62

Noncommutivity and Scalar Field Cosmology  

E-Print Network [OSTI]

In this work we extend and apply a previous proposal to study noncommutative cosmology to the FRW cosmological background coupled to a scalar field, this is done in classical and quantum scenarios. In both cases noncommutativity is introduced in the gravitational field as well as in the scalar field through a deformation of minisuperspace and are able to find exact solutions. Finally, the effects of noncommutativity on the classical evolution are analyzed.

W. Guzmán; M. Sabido; J. Socorro

2007-12-10T23:59:59.000Z

63

Cosmology at the millennium  

Science Journals Connector (OSTI)

One hundred years ago we did not know how stars generate energy, the age of the Universe was thought to be only millions of years, and our Milky Way galaxy was the only galaxy known. Today, we know that we live in an evolving and expanding universe comprising billions of galaxies, all held together by dark matter. With the hot big-bang model we can trace the evolution of the Universe from the hot soup of quarks and leptons that existed a fraction of a second after the beginning, to the formation of galaxies a few billion years later, and finally to the Universe we see today 13 billion years after the big bang, with its clusters of galaxies, superclusters, voids, and great walls. The attractive force of gravity acting on tiny primeval inhomogeneities in the distribution of matter gave rise to all the structure seen today. A paradigm based upon deep connections between cosmology and elementary particle physics—inflation+cold dark matter—holds the promise of extending our understanding to an even more fundamental level and much earlier times, as well as shedding light on the unification of the forces and particles of Nature. As we enter the 21st century, a flood of observations is testing this paradigm.

Michael S. Turner and J. Anthony Tyson

1999-03-01T23:59:59.000Z

64

Cosmology at the millennium  

SciTech Connect (OSTI)

One hundred years ago we did not know how stars generate energy, the age of the Universe was thought to be only millions of years, and our Milky Way galaxy was the only galaxy known. Today, we know that we live in an evolving and expanding universe comprising billions of galaxies, all held together by dark matter. With the hot big-bang model we can trace the evolution of the Universe from the hot soup of quarks and leptons that existed a fraction of a second after the beginning, to the formation of galaxies a few billion years later, and finally to the Universe we see today 13 billion years after the big bang, with its clusters of galaxies, superclusters, voids, and great walls. The attractive force of gravity acting on tiny primeval inhomogeneities in the distribution of matter gave rise to all the structure seen today. A paradigm based upon deep connections between cosmology and elementary particle physics{emdash}inflation+cold dark matter{emdash}holds the promise of extending our understanding to an even more fundamental level and much earlier times, as well as shedding light on the unification of the forces and particles of Nature. As we enter the 21st century, a flood of observations is testing this paradigm. {copyright} {ital 1999} {ital The American Physical Society}

Turner, M.S. [Department of Astronomy Astrophysics and Department of Physics, Enrico Fermi Institute, The University of Chicago, Chicago, Illinois 60637-1433 (United States)] [Department of Astronomy Astrophysics and Department of Physics, Enrico Fermi Institute, The University of Chicago, Chicago, Illinois 60637-1433 (United States); [NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States); Tyson, J.A. [Bell Labs, Lucent Technologies, Murray Hill, New Jersey 07974 (United States)] [Bell Labs, Lucent Technologies, Murray Hill, New Jersey 07974 (United States)

1999-03-01T23:59:59.000Z

65

Cosmology at the Millennium  

E-Print Network [OSTI]

One hundred years ago we did not know how stars generate energy, the age of the Universe was thought to be only millions of years, and our Milky Way galaxy was the only galaxy known. Today, we know that we live in an evolving and expanding Universe comprising billions of galaxies, all held together by dark matter. With the hot big-bang model, we can trace the evolution of the Universe from the hot soup of quarks and leptons that existed a fraction of a second after the beginning to the formation of galaxies a few billion years later, and finally to the Universe we see today 13 billion years after the big bang, with its clusters of galaxies, superclusters, voids, and great walls. The attractive force of gravity acting on tiny primeval inhomogeneities in the distribution of matter gave rise to all the structure seen today. A paradigm based upon deep connections between cosmology and elementary particle physics -- inflation + cold dark matter -- holds the promise of extending our understanding to an even more fu...

Turner, M S; Turner, Michael S.

1999-01-01T23:59:59.000Z

66

Cosmology at the Millennium  

E-Print Network [OSTI]

One hundred years ago we did not know how stars generate energy, the age of the Universe was thought to be only millions of years, and our Milky Way galaxy was the only galaxy known. Today, we know that we live in an evolving and expanding Universe comprising billions of galaxies, all held together by dark matter. With the hot big-bang model, we can trace the evolution of the Universe from the hot soup of quarks and leptons that existed a fraction of a second after the beginning to the formation of galaxies a few billion years later, and finally to the Universe we see today 13 billion years after the big bang, with its clusters of galaxies, superclusters, voids, and great walls. The attractive force of gravity acting on tiny primeval inhomogeneities in the distribution of matter gave rise to all the structure seen today. A paradigm based upon deep connections between cosmology and elementary particle physics -- inflation + cold dark matter -- holds the promise of extending our understanding to an even more fundamental level and much earlier times, as well as shedding light on the unification of the forces and particles of nature. As we enter the 21st century, a flood of observations is testing this paradigm.

Michael S. Turner; J. Anthony Tyson

1999-01-11T23:59:59.000Z

67

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.'' The principal conclusion derived from this example is that nonlinearities and time-dependent couplings do {\\em not} preclude the possibility of deriving a fluctuation-dissipation theorem, and do {\\em not} change the form of the late-time steady state solution for the system, but {\\em can} significantly shorten the time scale for the approach towards the steady state.

Salman Habib; Henry E. Kandrup

1992-08-13T23:59:59.000Z

68

Lectures on Quantum Cosmology  

E-Print Network [OSTI]

The problems encountered in trying to quantize the various cosmological models, are brought forward by means of a concrete example. The Automorphism groups are revealed as the key element through which G.C.T.'s can be used for a general treatment of these problems. At the classical level, the time dependent automorphisms lead to significant simplifications of the line element for the generic spatially homogeneous geometry, without loss of generality. At the quantum level, the ''frozen'' automorphisms entail an important reduction of the configuration space --spanned by the 6 components of the scale factor matrix-- on which the Wheeler-DeWitt equation, is to be based. In this spirit the canonical quantization of the most general minisuperspace actions --i.e. with all six scale factor as well as the lapse function and the shift vector present-- describing the vacuum type II, I geometries, is considered. The reduction to the corresponding physical degrees of freedom is achieved through the usage of the linear constraints as well as the quantum version of the entire set of all classical integrals of motion.

T. Christodoulakis

2001-09-18T23:59:59.000Z

69

BNL | Large Synoptic Survey Telescope (LSST)  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (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

70

Large aperture diffractive space telescope  

DOE Patents [OSTI]

A large (10's of meters) aperture space telescope including two separate spacecraft--an optical primary objective lens 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 objective lens 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 objective lens, 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 which may be either earth bound or celestial.

Hyde, Roderick A. (Livermore, CA)

2001-01-01T23:59:59.000Z

71

Cosmology: The test of inflation  

Science Journals Connector (OSTI)

... he'll have to lift a 3,500-litre tub of liquid helium with a stratospheric balloon. A microwave telescope would peer out of the bucket towards the 'southern hole' ...

Eric Hand

2009-04-15T23:59:59.000Z

72

Synergy between the Large Synoptic Survey Telescope and the Square Kilometre Array  

E-Print Network [OSTI]

We provide an overview of the science benefits of combining information from the Square Kilometre Array (SKA) and the Large Synoptic Survey Telescope (LSST). We first summarise the capabilities and timeline of the LSST and overview its science goals. We then discuss the science questions in common between the two projects, and how they can be best addressed by combining the data from both telescopes. We describe how weak gravitational lensing and galaxy clustering studies with LSST and SKA can provide improved constraints on the causes of the cosmological acceleration. We summarise the benefits to galaxy evolution studies of combining deep optical multi-band imaging with radio observations. Finally, we discuss the excellent match between one of the most unique features of the LSST, its temporal cadence in the optical waveband, and the time resolution of the SKA.

Bacon, David; Abdalla, Filipe B; Brown, Michael; Bull, Philip; Camera, Stefano; Fender, Rob; Grainge, Keith; Ivezic, Zeljko; Jarvis, Matt; Jackson, Neal; Kirk, Donnacha; Mann, Bob; McEwen, Jason; McKean, John; Newman, Jeffrey A; Raccanelli, Alvise; Sahlen, Martin; Santos, Mario; Tyson, Anthony; Zhao, Gong-Bo

2015-01-01T23:59:59.000Z

73

Science magazine names Supernova Cosmology Project "Breakthrough of the  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (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."

74

Cosmological Tests of Coupled Galileons  

E-Print Network [OSTI]

We investigate the cosmological properties of Galileon models with positive kinetic terms. We include both conformal and disformal couplings to matter and focus on constraints on the theory that arise because of these couplings. The disformal coupling to baryonic matter is extremely constrained by astrophysical and particle physics effects. The disformal coupling to photons induces a cosmological variation of the speed of light and therefore distortions of the Cosmic Microwave Background spectrum which are known to be very small. The conformal coupling to baryons leads to a variation of particle masses since Big Bang Nucleosynthesis which is also tightly constrained. We consider the background cosmology of Galileon models coupled to Cold Dark Matter (CDM), photons and baryons and impose that the speed of light and particle masses respect the observational bounds on cosmological time scales. We find that requiring that the equation of state for the Galileon models must be close to -1 now restricts severely their parameter space and can only be achieved with a combination of the conformal and disformal couplings. This leads to large variations of particle masses and the speed of light which are not compatible with observations. As a result, we find that cosmological Galileon models are viable dark energy theories coupled to dark matter but their couplings, both disformal and conformal, to baryons and photons must be heavily suppressed making them only sensitive to CDM.

Philippe Brax; Clare Burrage; Anne-Christine Davis; Giulia Gubitosi

2014-11-27T23:59:59.000Z

75

Conformal transformations and accelerated cosmologies  

Science Journals Connector (OSTI)

A cosmological theory that predicts a late-time accelerated attractor with a constant dark matter to dark energy ratio can be said to solve the coincidence problem. Such cosmologies are naturally generated in the context of nonstandard gravity theories under conformal transformation because of the resulting couplings between scalar fields and matter. The present work examines four classes of these transformed theories and finds that only a small subset-those with a single scalar field-are capable of solving the coincidence problem.

James L. Crooks and Paul H. Frampton

2006-06-09T23:59:59.000Z

76

Noncommutative models in patch cosmology  

SciTech Connect (OSTI)

We consider several classes of noncommutative inflationary models within an extended version of patch cosmological braneworlds, starting from a maximally invariant generalization of the action for scalar and tensor perturbations to a noncommutative brane embedded in a commutative bulk. Slow-roll expressions and consistency relations for the cosmological observables are provided, both in the UV and IR region of the spectrum; the inflaton field is assumed to be either an ordinary scalar field or a Born-Infeld tachyon. The effects of noncommutativity are then analyzed in a number of ways and energy regimes.

Calcagni, Gianluca [Dipartimento di Fisica, Universita di Parma, Parco Area delle Scienze 7/A, I-43100 Parma (Italy) and INFN-Gruppo Collegato di Parma, Parco Area delle Scienze 7/A, I-43100 Parma (Italy)

2004-11-15T23:59:59.000Z

77

Redshift drift in varying speed of light cosmology  

Science Journals Connector (OSTI)

Abstract We derive a redshift drift formula within the framework of varying speed of light (VSL) theory using the specific ansatz for the variability of c ( t ) = c 0 a n ( t ) . We show that negative values of the parameter n, which correspond to diminishing value of the speed of light during the evolution of the universe, effectively rescale dust matter to become little negative pressure matter, and the cosmological constant to became phantom. Positive values of n (growing c ( t ) ) make VSL model to become more like Cold Dark Matter (CDM) model. Observationally, there is a distinction between the VSL model and the ?CDM model for the admissible values of the parameter n ? ? 10 ? 5 , though it will be rather difficult to detect by planned extremely large telescopes (EELT, TMT, GMT) within their accuracy.

Adam Balcerzak; Mariusz P. Da?browski

2014-01-01T23:59:59.000Z

78

Asymmetric cyclic evolution in polymerised cosmology  

SciTech Connect (OSTI)

The dynamical systems methods are used to study evolution of the polymerised scalar field cosmologies with the cosmological constant. We have found all evolutional paths admissible for all initial conditions on the two-dimensional phase space. We have shown that the cyclic solutions are generic. The exact solution for polymerised cosmology is also obtained. Two basic cases are investigated, the polymerised scalar field and the polymerised gravitational and scalar field part. In the former the division on the cyclic and non-cyclic behaviour is established following the sign of the cosmological constant. The value of the cosmological constant is upper bounded purely from the dynamical setting.

Hrycyna, Orest [Department of Theoretical Physics, Faculty of Philosophy, The John Paul II Catholic University of Lublin, Al. Rac?awickie 14, 20-950 Lublin (Poland); Mielczarek, Jakub; Szyd?owski, Marek, E-mail: hrycyna@kul.lublin.pl, E-mail: jakub.mielczarek@uj.edu.pl, E-mail: uoszydlo@cyf-kr.edu.pl [Astronomical Observatory, Jagiellonian University, Orla 171, 30-244 Kraków (Poland)

2009-12-01T23:59:59.000Z

79

Chi-Variable-Speed-of-Light Cosmologies  

E-Print Network [OSTI]

Variable-Speed-of-Light (VSL) cosmologies are currently attracting much interest as a possible alternative to cosmological inflation. We discuss the fundamental geometrodynamic aspects of VSL cosmologies, and provide several alternative implementations. These implementations provide a large class of VSL cosmologies that pass the zeroth-order consistency tests of being compatible with both classical Einstein gravity and low-energy particle physics. While they solve the ``kinematic'' puzzles as well as inflation does, VSL cosmologies typically do not solve the flatness problem since in their purest form no violation of the strong energy condition occurs. Nevertheless, these models are easy to unify with inflation.

Stefano Liberati; Bruce A. Bassett; Carmen Molina-Paris; Matt Visser

2000-01-27T23:59:59.000Z

80

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

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.


81

The Higgs boson and cosmology  

Science Journals Connector (OSTI)

...and beyond the discovery of the Higgs boson. organised and edited by John...Tejinder Virdee and David Charlton The Higgs boson and cosmology Mikhail Shaposhnikov...and beyond the discovery of the Higgs boson . I will discuss how the Higgs...

2015-01-01T23:59:59.000Z

82

Climbing the cosmological distance ladder  

Science Journals Connector (OSTI)

......knowledge of cosmological distance - towards redshift 1000! Humankind's efforts to measure the distances of the planets, stars...the epoch when matter and radiation finally decoupled at the end of the hot Big Bang phase. Apparently we have reached a precision......

Michael Rowan-Robinson

2008-06-01T23:59:59.000Z

83

Cosmological models with variable constants  

E-Print Network [OSTI]

The behavior of the constants, G,c,h,a,e,m and Lambda, considering them as variable, in the framework of a flat cosmological model with FRW symmetries described by a bulk viscous fluid and considering mechanisms of adiabatic matter creation are investigated. Within two models; one with radiation predominance and another of matter predominance, this behavior are studied.

J. A. Belinchon

1999-07-01T23:59:59.000Z

84

Towards Noncommutative Supersymmetric Quantum Cosmology  

SciTech Connect (OSTI)

In this work a construction of supersymmetric noncommutative cosmology is presented. We start with a ''noncommutative'' deformation of the minisuperspace variables, and by using the time reparametrization invariance of the noncommutative bosonic model we proceed to construct a super field description of the model.

Sabido, M.; Socorro, J. [Physics Department of the Division of Science and Engineering of the University of Guanajuato, Campus Leon P.O. Box E-143, 37150 Leon Gto. (Mexico); Guzman, W. [Centro Brasileiro de Pesquisas Fisicas, Rua Dr. Xavier Sigaud 150, Urca 22290-180, Rio de Janeiro, RJ (Brazil)

2010-12-07T23:59:59.000Z

85

The Space Infrared Telescope for Cosmology and Astrophysics: SPICA A joint mission between JAXA and ESA  

E-Print Network [OSTI]

Vandenbussche (KUL), Christoffel Waelkens (KUL), Peter Davis (BSS), James Di Francesco (HIA/NRC), Mark Halpern. (CESR), Ravera, L. (CESR), Ristorcelli, I. (CESR), Rodriguez, L. (SAP), Vives, S. (OAMP), Zavagno, A Ramon Pardo (CSIC), Francisca Gomez (CSIC), Nieves Castro Rodriguez (CSIC), Peter Ade (CU), Mike Barlow

Naylor, David A.

86

A Comparison of Cosmological Models Using Time Delay Lenses  

E-Print Network [OSTI]

The use of time-delay gravitational lenses to examine the cosmological expansion introduces a new standard ruler with which to test theoretical models. The sample suitable for this kind of work now includes 12 lens systems, which have thus far been used solely for optimizing the parameters of $\\Lambda$CDM. In this paper, we broaden the base of support for this new, important cosmic probe by using these observations to carry out a one-on-one comparison between {\\it competing} models. The currently available sample indicates a likelihood of $\\sim 70-80%$ that the $R_{\\rm h}=ct$ Universe is the correct cosmology versus $\\sim 20-30%$ for the standard model. This possibly interesting result reinforces the need to greatly expand the sample of time-delay lenses, e.g., with the successful implementation of the Dark Energy Survey, the VST ATLAS survey, and the Large Synoptic Survey Telescope. In anticipation of a greatly expanded catalog of time-delay lenses identified with these surveys, we have produced synthetic sa...

Wei, Jun-Jie; Melia, Fulvio

2014-01-01T23:59:59.000Z

87

James Webb Space Telescope: PM Lessons Applied - Eric Smith,...  

Energy Savers [EERE]

James Webb Space Telescope: PM Lessons Applied - Eric Smith, Deputy Program Director, NASA James Webb Space Telescope: PM Lessons Applied - Eric Smith, Deputy Program Director,...

88

Digital Frequency Domain Multiplexer for mm-Wavelength Telescopes  

SciTech Connect (OSTI)

An FPGA based digital signal processing (DSP) system for biasing and reading out multiplexed bolometric detectors for mm-wavelength telescopes is presented. This readout system is being deployed for balloon-borne and ground based cosmology experiments with the primary goal of measuring the signature of inflation with the Cosmic Microwave Background Radiation. The system consists of analog superconducting electronics running at 250 mK and 4 K, coupled to digital room temperature backend electronics described here. The digital electronics perform the real time functionality with DSP algorithms implemented in firmware. A soft embedded processor provides all of the slow housekeeping control and communications. Each board in the system synthesizes multi-frequency combs of 8 to 32 carriers in the MHz band to bias the detectors. After the carriers have been modulated with the sky-signal by the detectors, the same boards digitize the comb directly. The carriers are mixed down to base-band and low pass filtered. The signal bandwidth of 0.050Hz-100 Hz places extreme requirements on stability and requires powerful filtering techniques to recover the sky-signal from the MHz carriers.

Spieler, Helmuth G; Dobbs, Matt; Bissonnette, Eric; Spieler, Helmuth G.

2007-07-23T23:59:59.000Z

89

General surface equations for glancing incidence telescopes  

Science Journals Connector (OSTI)

A generalized set of equations are derived for two mirror glancing incidence telescopes using Fermat’s principle, a differential form of the law of reflection, the generalized sine...

Saha, Timo T

1987-01-01T23:59:59.000Z

90

Cosmology with weak lensing surveys  

Science Journals Connector (OSTI)

...and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g...Large-aperture Synoptic Survey Telescope will play a major...and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g...

2005-01-01T23:59:59.000Z

91

Absolute calibration of imaging atmospheric Cherenkov telescopes  

E-Print Network [OSTI]

A calibrated laser pulse propagating through the atmosphere produces a flash of Rayleigh scattered light with an intensity that can be calculated very accurately when atmospheric conditions are good. This is used in a technique developed for the absolute calibration of ultra high energy cosmic ray fluorescence telescopes, and it can also be applied to imaging atmospheric Cherenkov telescopes (IACTs). In this paper we present the absolute calibration system being constructed and tested for the VERITAS project.

N. Shepherd; J. H. Buckley; O. Celik; J. Holder; S. LeBohec; H. Manseri; F. Pizlo; M. Roberts

2005-07-04T23:59:59.000Z

92

Thermodynamics of decaying vacuum cosmologies  

Science Journals Connector (OSTI)

The thermodynamic behavior of decaying vacuum cosmologies is investigated within a manifestly covariant formulation. Such a process corresponds to a continuous, irreversible energy flow from the vacuum component to the created matter constituents. It is shown that if the specific entropy per particle remains constant during the process, the equilibrium relations are preserved. In particular, if the vacuum decays into photons, the energy density ? and average number density of photons n scale with the temperature as ??T4 and n?T3. The temperature law is determined and a generalized Planckian-type form of the spectrum, which is preserved in the course of the evolution, is also proposed. Some consequences of these results for decaying vacuum FRW-type cosmologies as well as for models with "adiabatic" photon creation are discussed.

J. A. S. Lima

1996-08-15T23:59:59.000Z

93

Inflationary nonsingular quantum cosmological model  

SciTech Connect (OSTI)

A stiff matter-dominated universe modeled by a free massless scalar field minimally coupled to gravity in a Friedmann-Lemaitre-Robertson-Walker (FLRW) geometry is quantized. Generalized complex-width Gaussian superpositions of the solutions of the Wheeler-DeWitt equation are constructed and the Bohm-de Broglie interpretation of quantum cosmology is applied. A planar dynamical system is found in which a diversity of quantum Bohmian trajectories are obtained and discussed. One class of solutions represents nonsingular inflationary models starting at infinity past from flat space-time with Planckian size spacelike hypersurfaces, which inflates without inflaton but due to a quantum cosmological effect, until it makes an analytical graceful exit from this inflationary epoch to a decelerated classical stiff matter expansion phase.

Falciano, Felipe T.; Pinto-Neto, Nelson; Santini, E. Sergio [Instituto de Cosmologia Relatividade e Astrofisica ICRA-CBPF, Rua Xavier Sigaud, 150, Urca, 22290-180, Rio de Janeiro (Brazil); Instituto de Cosmologia Relatividade e Astrofisica ICRA-CBPF, Rua Xavier Sigaud, 150, Urca, 22290-180, Rio de Janeiro, Brazil and ComisSao Nacional de Energia Nuclear, Rua General Severiano 90, Botafogo 22290-901, Rio de Janeiro (Brazil)

2007-10-15T23:59:59.000Z

94

Effective perfect fluids in cosmology  

SciTech Connect (OSTI)

We describe the cosmological dynamics of perfect fluids within the framework of effective field theories. The effective action is a derivative expansion whose terms are selected by the symmetry requirements on the relevant long-distance degrees of freedom, which are identified with comoving coordinates. The perfect fluid is defined by requiring invariance of the action under internal volume-preserving diffeomorphisms and general covariance. At lowest order in derivatives, the dynamics is encoded in a single function of the entropy density that characterizes the properties of the fluid, such as the equation of state and the speed of sound. This framework allows a neat simultaneous description of fluid and metric perturbations. Longitudinal fluid perturbations are closely related to the adiabatic modes, while the transverse modes mix with vector metric perturbations as a consequence of vorticity conservation. This formalism features a large flexibility which can be of practical use for higher order perturbation theory and cosmological parameter estimation.

Ballesteros, Guillermo [Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Piazza del Viminale 1, I-00184 Rome (Italy); Bellazzini, Brando, E-mail: guillermo.ballesteros@unige.ch, E-mail: brando.bellazzini@pd.infn.it [Dipartimento di Fisica, Università di Padova and INFN, Sezione di Padova, Via Marzolo 8, I-35131 Padova (Italy)

2013-04-01T23:59:59.000Z

95

Code for Largest Cosmological Simulations Ever on GPUs Is Gordon Bell  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (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

96

Complex Lagrangians and phantom cosmology  

E-Print Network [OSTI]

Motivated by the generalization of quantum theory for the case of non-Hermitian Hamiltonians with PT symmetry, we show how a classical cosmological model describes a smooth transition from ordinary dark energy to the phantom one. The model is based on a classical complex Lagrangian of a scalar field. Specific symmetry properties analogous to PT in non-Hermitian quantum mechanics lead to purely real equation of motion.

A. A. Andrianov; F. Cannata; A. Y. Kamenshchik

2006-04-28T23:59:59.000Z

97

Complex Lagrangians and phantom cosmology  

E-Print Network [OSTI]

Motivated by the generalization of quantum theory for the case of non-Hermitian Hamiltonians with PT symmetry, we show how a classical cosmological model describes a smooth transition from ordinary dark energy to the phantom one. The model is based on a classical complex Lagrangian of a scalar field. Specific symmetry properties analogous to PT in non-Hermitian quantum mechanics lead to purely real equation of motion.

Andrianov, A A; Kamenshchik, A Yu

2006-01-01T23:59:59.000Z

98

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

99

Multiverse understanding of cosmological coincidences  

SciTech Connect (OSTI)

There is a deep cosmological mystery: although dependent on very different underlying physics, the time scales of structure formation, of galaxy cooling (both radiatively and against the CMB), and of vacuum domination do not differ by many orders of magnitude, but are all comparable to the present age of the universe. By scanning four landscape parameters simultaneously, we show that this quadruple coincidence is resolved. We assume only that the statistical distribution of parameter values in the multiverse grows towards certain catastrophic boundaries we identify, across which there are drastic regime changes. We find order-of-magnitude predictions for the cosmological constant, the primordial density contrast, the temperature at matter-radiation equality, the typical galaxy mass, and the age of the universe, in terms of the fine structure constant and the electron, proton and Planck masses. Our approach permits a systematic evaluation of measure proposals; with the causal patch measure, we find no runaway of the primordial density contrast and the cosmological constant to large values.

Bousso, Raphael; Hall, Lawrence J.; Nomura, Yasunori [Center for Theoretical Physics, Department of Physics, University of California, Berkeley, California 94720-7300 (United States) and Lawrence Berkeley National Laboratory, Berkeley, California 94720-8162 (United States)

2009-09-15T23:59:59.000Z

100

Disformal transformation of cosmological perturbations  

E-Print Network [OSTI]

We investigate the gauge-invariant cosmological perturbations in the gravity and matter frames in the general scalar-tensor theory where two frames are related by the disformal transformation. The gravity and matter frames are the extensions of the Einstein and Jordan frames in the scalar-tensor theory where two frames are related by the conformal transformation, respectively. First, it is shown that the curvature perturbation in the comoving gauge to the scalar field is disformally invariant as well as conformally invariant, which gives the predictions from the cosmological model where the scalar field is responsible both for inflation and cosmological perturbations. Second, in case that the disformally coupled matter sector also contributes to curvature perturbations, we derive the evolution equations of the curvature perturbation in the uniform matter energy density gauge from the energy (non)conservation in the matter sector, which are independent of the choice of the gravity sector. While in the matter frame the curvature perturbation in the uniform matter energy density gauge is conserved on superhorizon scales for the vanishing nonadiabatic pressure, in the gravity frame it is not conserved even if the nonadiabatic pressure vanishes. The formula relating two frames gives the amplitude of the curvature perturbation in the matter frame, once it is evaluated in the gravity frame.

Masato Minamitsuji

2014-09-04T23:59:59.000Z

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.


101

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

102

Emergent cosmological constant from colliding electromagnetic waves  

E-Print Network [OSTI]

In this study we advocate the view that the cosmological constant is of electromagnetic (em) origin, which can be generated from the collision of em shock waves coupled with gravitational shock waves. The wave profiles that participate in the collision have different amplitudes. It is shown that, circular polarization with equal amplitude waves does not generate cosmological constant. We also prove that the generation of the cosmological constant is related to the linear polarization. The addition of cross polarization generates no cosmological constant. Depending on the value of the wave amplitudes, the generated cosmological constant can be positive or negative. We show additionally that, the collision of nonlinear em waves in a particular class of Born-Infeld theory also yields a cosmological constant.

M. Halilsoy; S. Habib Mazharimousavi; O. Gurtug

2014-10-15T23:59:59.000Z

103

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

2008-03-05T23:59:59.000Z

104

Accelerating cosmological expansion from shear viscosity  

E-Print Network [OSTI]

The dissipation of energy from local velocity perturbations in the cosmological fluid affects the time evolution of spatially averaged fluid dynamic fields and the cosmological solution of Einstein's field equations. We show how this backreaction effect depends on shear viscosity and other material properties of the dark sector, as well as the spectrum of perturbations. If sufficiently large, this effect could account for the acceleration of the cosmological expansion.

Floerchinger, Stefan; Wiedemann, Urs Achim

2014-01-01T23:59:59.000Z

105

Cosmological Constant and Axions in String Theory  

SciTech Connect (OSTI)

String theory axions appear to be promising candidates for explaining cosmological constant via quintessence. In this paper, we study conditions on the string compactifications under which axion quintessence can happen. For sufficiently large number of axions, cosmological constant can be accounted for as the potential energy of axions that have not yet relaxed to their minima. In compactifications that incorporate unified models of particle physics, the height of the axion potential can naturally fall close to the observed value of cosmological constant.

Svrcek, Peter; /Stanford U., Phys. Dept. /SLAC

2006-08-18T23:59:59.000Z

106

Landscape Predictions from Cosmological Vacuum Selection  

E-Print Network [OSTI]

In BP models with hundreds of fluxes, we compute the effects of cosmological dynamics on the probability distribution of landscape vacua. Starting from generic initial conditions, we find that most fluxes are dynamically driven into a different and much narrower range of values than expected from landscape statistics alone. Hence, cosmological evolution will access only a tiny fraction of the vacua with small cosmological constant. This leads to a host of sharp predictions. Unlike other approaches to eternal inflation, the holographic measure employed here does not lead to "staggering", an excessive spread of probabilities that would doom the string landscape as a solution to the cosmological constant problem.

Raphael Bousso; I-Sheng Yang

2007-05-09T23:59:59.000Z

107

Schwarzschild-Couder telescope for the Cherenkov Telescope Array: Development of the Optical System  

E-Print Network [OSTI]

The CTA (Cherenkov Telescope Array) is the next generation ground-based experiment for very high-energy (VHE) gamma-ray observations. It will integrate several tens of imaging atmospheric Cherenkov telescopes (IACTs) with different apertures into a single astronomical instrument. The US part of the CTA collaboration has proposed and is developing a novel IACT design with a Schwarzschild-Couder (SC) aplanatic two mirror optical system. In comparison with the traditional single mirror Davies-Cotton IACT the SC telescope, by design, can accommodate a wide field-of-view, with significantly improved imaging resolution. In addition, the reduced plate scale of an SC telescope makes it compatible with highly integrated cameras assembled from silicon photo multipliers. In this submission we report on the status of the development of the SC optical system, which is part of the effort to construct a full-scale prototype telescope of this type at the Fred Lawrence Whipple Observatory in southern Arizona.

Rousselle, Julien; Errando, Manel; Humensky, Brian; Mukherjee, Reshmi; Nieto, Daniel; Okumura, Akira; Vassiliev, Vladimir

2013-01-01T23:59:59.000Z

108

Simulation of the Simbol-X Telescope  

SciTech Connect (OSTI)

We have developed a simulation tool for a Wolter I telescope operating in formation flight. The aim is to understand and predict the behavior of the Simbol-X instrument. As the geometry is variable, formation flight introduces new challenges and complex implications. Our code, based on Monte Carlo ray tracing, computes the full photon trajectories up to the detector plane, along with the relative drifts of the two spacecrafts. It takes into account angle and energy dependent interactions of the photons with the mirrors and applies to any grazing incidence telescope. The resulting images of simulated sources from 0.1 keV to 100 keV allow us to optimize the configuration of the instrument and to assess the performance of the Simbol-X telescope.

Chauvin, M.; Roques, J. P. [Universite de Toulouse, UPS, CESR, 9 ave colonel Roche, F-31028 Toulouse cedex 9 (France); CNRS, UMR5187, F-31028 Toulouse (France)

2009-05-11T23:59:59.000Z

109

Telescopic nanotube device for hot nanolithography  

DOE Patents [OSTI]

A device for maintaining a constant tip-surface distance for producing nanolithography patterns on a surface using a telescopic nanotube for hot nanolithography. An outer nanotube is attached to an AFM cantilever opposite a support end. An inner nanotube is telescopically disposed within the outer nanotube. The tip of the inner nanotube is heated to a sufficiently high temperature and brought in the vicinity of the surface. Heat is transmitted to the surface for thermal imprinting. Because the inner tube moves telescopically along the outer nanotube axis, a tip-surface distance is maintained constant due to the vdW force interaction, which in turn eliminates the need of an active feedback loop.

Popescu, Adrian; Woods, Lilia M

2014-12-30T23:59:59.000Z

110

Multimessenger astronomy with the Einstein Telescope  

E-Print Network [OSTI]

Gravitational waves (GWs) are expected to play a crucial role in the development of multimessenger astrophysics. The combination of GW observations with other astrophysical triggers, such as from gamma-ray and X-ray satellites, optical/radio telescopes, and neutrino detectors allows us to decipher science that would otherwise be inaccessible. In this paper, we provide a broad review from the multimessenger perspective of the science reach offered by the third generation interferometric GW detectors and by the Einstein Telescope (ET) in particular. We focus on cosmic transients, and base our estimates on the results obtained by ET's predecessors GEO, LIGO, and Virgo.

Eric Chassande-Mottin; Martin Hendry; Patrick J. Sutton; Szabolcs Márka

2010-04-12T23:59:59.000Z

111

A Time-dependent Cosmological Constant Phenomenology  

E-Print Network [OSTI]

We construct a cosmological toy model in which a step-function ``cosmological constant'' is taken into consideration beside ordinary matter. We assume that $\\Lambda$ takes two values depending on the epoch, and matter goes from a radiation dominated era to a dust dominated era. The model is exactly solvable and it can be compared with recent observations.

Salvatore Capozziello; Ruggiero de Ritis; Alma Angela Marino

1996-05-29T23:59:59.000Z

112

Planck Scale Cosmology in Resummed Quantum Gravity  

E-Print Network [OSTI]

We show that, by using resummation techniques based on the extension of the methods of Yennie, Frautschi and Suura to Feynman's formulation of Einstein's theory, we get quantum field theoretic predictions for the UV fixed-point values of the dimensionless gravitational and cosmological constants. Connections to the phenomenological asymptotic safety analysis of Planck scale cosmology by Bonanno and Reuter are discussed.

B. F. L. Ward

2008-08-23T23:59:59.000Z

113

Planck Scale Cosmology and Resummed Quantum Gravity  

E-Print Network [OSTI]

We show that, by using amplitude-based resummation techniques for Feynman's formulation of Einstein's theory, we get quantum field theoretic 'first principles' predictions for the UV fixed-point values of the dimensionless gravitational and cosmological constants. Connections to the phenomenological asymptotic safety analysis of Planck scale cosmology by Bonanno and Reuter are discussed.

B. F. L. Ward

2009-10-13T23:59:59.000Z

114

Cosmological rolling solutions of nonlocal theories  

E-Print Network [OSTI]

We find nonperturbative solutions of a nonlocal scalar field equation, with cubic or exponential potential on a cosmological background. The former case corresponds to the lowest level effective tachyon action of cubic string field theory. While the well known Minkowski solution is wildly oscillating, due to Hubble friction its cosmological counterpart describes smooth rolling towards the local minimum of the potential.

Gianluca Calcagni; Giuseppe Nardelli

2009-04-27T23:59:59.000Z

115

4 m Davies-Cotton telescope for the Cherenkov Telescope Array  

E-Print Network [OSTI]

The Cherenkov Telescope Array (CTA) is the next generation very high energy gamma-ray observatory. It will consist of three classes of telescopes, of large, medium and small sizes. The small telescopes, of 4 m diameter, will be dedicated to the observations of the highest energy gamma-rays, above several TeV. We present the technical characteristics of a single mirror, 4 m diameter, Davies-Cotton telescope for the CTA and the performance of the sub-array consisting of the telescopes of this type. The telescope will be equipped with a fully digital camera based on custom made, hexagonal Geiger-mode avalanche photodiodes. The development of cameras based on such devices is an RnD since traditionally photomultipliers are used. The photodiodes are now being characterized at various institutions of the CTA Consortium. Glass mirrors will be used, although an alternative is being considered: composite mirrors that could be adopted if they meet the project requirements. We present a design of the telescope structure,...

Moderski, R; Barnacka, A; Basili, A; Boccone, V; Bogacz, L; Cadoux, F; Christov, A; Della Volpe, M; Dyrda, M; Frankowski, A; Grudzi?ska, M; Janiak, M; Karczewski, M; Kasperek, J; Kocha?ski, W; Korohoda, P; Kozio?, J; Lubi?ski, P; Ludwin, J; Lyard, E; Marsza?ek, A; Micha?owski, J; Montaruli, T; Nicolau-Kukli?ski, J; Niemiec, J; Ostrowski, M; P?atos, ?; Rajda, P J; Rameez, M; Romaszkan, W; Rupi?ski, M; Seweryn, K; Stodulska, M; Stodulski, M; Walter, R; Winiarski, K; Wi?niewski, ?; Zagda?ski, A; Zietara, K; Zió?kowski, P; ?ychowski, P

2013-01-01T23:59:59.000Z

116

Vacuum energy and cosmological evolution  

E-Print Network [OSTI]

An expanding universe is not expected to have a static vacuum energy density. The so-called cosmological constant $\\Lambda$ should be an approximation, certainly a good one for a fraction of a Hubble time, but it is most likely a temporary description of a true dynamical vacuum energy variable that is evolving from the inflationary epoch to the present day. We can compare the evolving vacuum energy with a Casimir device where the parallel plates slowly move apart ("expand"). The total vacuum energy density cannot be measured, only the effect associated to the presence of the plates, and then also their increasing separation with time. In the universe there is a nonvanishing spacetime curvature $R$ as compared to Minkowskian spacetime that is changing with the expansion. The vacuum energy density must change accordingly, and we naturally expect $\\delta\\Lambda\\sim R\\sim H^2$. A class of dynamical vacuum models that trace such rate of change can be constructed. They are compatible with the current cosmological data, and conveniently extended can account for the complete cosmic evolution from the inflationary epoch till the present days. These models are very close to the $\\Lambda$CDM model for the late universe, but very different from it at the early times. Traces of the inherent vacuum dynamics could be detectable in our recent past.

Joan Sola

2014-03-03T23:59:59.000Z

117

Relaxing a large cosmological constant  

E-Print Network [OSTI]

The cosmological constant (CC) problem is the biggest enigma of theoretical physics ever. In recent times, it has been rephrased as the dark energy problem in order to encompass a wider spectrum of possibilities. It is, in any case, a polyhedric puzzle with many faces, including the cosmic coincidence problem, i.e. why the density of matter is presently so close to the CC density. However, the oldest, toughest and most intriguing face of this polyhedron is the big CC problem, namely why the measured value of the CC at present is so small as compared to any typical density scale existing in high energy physics, especially taking into account the many phase transitions that our Universe has undergone since the early times, including inflation. In this letter, we propose to extend the field equations of General Relativity by including a class of invariant terms that automatically relax the value of the CC irrespective of the initial size of the vacuum energy in the early epochs. We show that, at late times, the Universe enters an eternal de Sitter stage mimicking a tiny positive cosmological constant. Thus, these models could solve the big CC problem and have also a bearing on the cosmic coincidence problem. Remarkably, they mimic the LCDM model to a large extent, but they still leave some characteristic imprints that should be testable in the next generation of experiments.

Florian Bauer; Joan Sola; Hrvoje Stefancic

2009-07-23T23:59:59.000Z

118

Optical Technology Needs for Future Space Telescopes  

E-Print Network [OSTI]

instruments & sensors. Future Space Telescopes will operate over broad spectrum: Gamma Rays, X-Rays, XUV and Sensors Direct Sensing of Particles, Fields and Waves See Scientific Instruments and Sensors (SIS Structure #12;NASA's Science Missions Directorate Themes: Earth Science Sun-Solar System Connection Solar

Van Stryland, Eric

119

Pendular seismometer for correcting telescope vibrations  

Science Journals Connector (OSTI)

......Southern Observatory, Karl Schwarzschild Strabetae, 2, D-85748 Garching...is suggested that a pendular mirror in front of the telescope is...optics system or by a secondary mirror. An alternative technique...angular motions of the primary mirror cell. One may suggest monitoring......

A. Tokovinin

2000-08-11T23:59:59.000Z

120

The High Energy Telescope on EXIST  

E-Print Network [OSTI]

The Energetic X-ray Imaging Survey Telescope (EXIST) is a proposed next generation multi-wavelength survey mission. The primary instrument is a High Energy telescope (HET) that conducts the deepest survey for Gamma-ray Bursts (GRBs), obscured-accreting and dormant Supermassive Black Holes and Transients of all varieties for immediate followup studies by the two secondary instruments: a Soft X-ray Imager (SXI) and an Optical/Infrared Telescope (IRT). EXIST will explore the early Universe using high redshift GRBs as cosmic probes and survey black holes on all scales. The HET is a coded aperture telescope employing a large array of imaging CZT detectors (4.5 m^2, 0.6 mm pixel) and a hybrid Tungsten mask. We review the current HET concept which follows an intensive design revision by the HET imaging working group and the recent engineering studies in the Instrument and Mission Design Lab at the Goddard Space Flight Center. The HET will locate GRBs and transients quickly (<10-30 sec) and accurately (< 20") f...

Hong, J; Allen, B; Barthelmy, S D; Skinner, G K; Gehrels, N

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.
We encourage you to perform a real-time search of NLEBeta
to obtain the most current and comprehensive results.


121

Regional averaging and scaling in relativistic cosmology  

E-Print Network [OSTI]

Averaged inhomogeneous cosmologies lie at the forefront of interest, since cosmological parameters like the rate of expansion or the mass density are to be considered as volume-averaged quantities and only these can be compared with observations. For this reason the relevant parameters are intrinsically scale-dependent and one wishes to control this dependence without restricting the cosmological model by unphysical assumptions. In the latter respect we contrast our way to approach the averaging problem in relativistic cosmology with shortcomings of averaged Newtonian models. Explicitly, we investigate the scale-dependence of Eulerian volume averages of scalar functions on Riemannian three-manifolds. We propose a complementary view of a Lagrangian smoothing of (tensorial) variables as opposed to their Eulerian averaging on spatial domains. This program is realized with the help of a global Ricci deformation flow for the metric. We explain rigorously the origin of the Ricci flow which, on heuristic grounds, has already been suggested as a possible candidate for smoothing the initial data set for cosmological spacetimes. The smoothing of geometry implies a renormalization of averaged spatial variables. We discuss the results in terms of effective cosmological parameters that would be assigned to the smoothed cosmological spacetime.

Thomas Buchert; Mauro Carfora

2002-10-11T23:59:59.000Z

122

E-Print Network 3.0 - apex telescope large Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Telescopes Reference Reading Summary: telescopes are good for small telescopes (<1 meter) because it's very difficult to manufacture large lenses... fast system bright...

123

Large-Aperture Segmented Mirror Telescope Design Concept  

E-Print Network [OSTI]

(ATLAS) Telescope: A Technology Roadmap for the Next Decade Principal Investigator: Dr. Marc Postman .............................................................................................13 5 Technology Roadmap................................................................109 #12;Advanced Technology Large-Aperture Space Telescope: A Technology Roadmap for the Next Decade 2

Sirianni, Marco

124

Ultraviolet divergences in cosmological correlations  

SciTech Connect (OSTI)

A method is developed for dealing with ultraviolet divergences in calculations of cosmological correlations, which does not depend on dimensional regularization. An extended version of the WKB approximation is used to analyze the divergences in these calculations, and these divergences are controlled by the introduction of Pauli-Villars regulator fields. This approach is illustrated in the theory of a scalar field with arbitrary self-interactions in a fixed flat-space Robertson-Walker metric with arbitrary scale factor a(t). Explicit formulas are given for the counterterms needed to cancel all dependence on the regulator properties, and an explicit prescription is given for calculating finite regulator-independent correlation functions. The possibility of infrared divergences in this theory is briefly considered.

Weinberg, Steven [Theory Group, Department of Physics, University of Texas Austin, Texas, 78712 (United States)

2011-03-15T23:59:59.000Z

125

Gravitational wave astronomy and cosmology  

E-Print Network [OSTI]

The first direct observation of gravitational waves' action upon matter has recently been reported by the BICEP2 experiment. Advanced ground-based gravitational-wave detectors are being installed. They will soon be commissioned, and then begin searches for high-frequency gravitational waves at a sensitivity level that is widely expected to reach events involving compact objects like stellar mass black holes and neutron stars. Pulsar timing arrays continue to improve the bounds on gravitational waves at nanohertz frequencies, and may detect a signal on roughly the same timescale as ground-based detectors. The science case for space-based interferometers targeting millihertz sources is very strong. The decade of gravitational-wave discovery is poised to begin. In this writeup of a talk given at the 2013 TAUP conference, we will briefly review the physics of gravitational waves and gravitational-wave detectors, and then discuss the promise of these measurements for making cosmological measurements in the near future.

Scott A. Hughes

2014-05-02T23:59:59.000Z

126

Island Cosmology in the Landscape  

E-Print Network [OSTI]

In the eternally inflationary background driven by the metastable vacua of the landscape, it is possible that some local quantum fluctuations with the null energy condition violation can be large enough to stride over the barriers among different vacua, so that create some islands full of radiation in new vacua, and then these emergently thermalized islands will enter into the evolution of standard big bang cosmology. In this paper, we calculate the spectrum of curvature perturbation generated during the emergence of island. We find that generally the spectrum obtained is nearly scale invariant, which can be well related to that of slow roll inflation by a simple duality. This in some sense suggests a degeneracy between their scalar spectra. In addition, we also simply estimate the non-Gaussianity of perturbation, which is naturally large, yet, can lie well in the observational bound. The results shown here indicate that the island emergently thermalized in the landscape can be consistent with our observable universe.

Yun-Song Piao

2008-06-11T23:59:59.000Z

127

Cosmological Solutions of Emergent Noncommutative Gravity  

SciTech Connect (OSTI)

Matrix models of the Yang-Mills type lead to an emergent gravity theory, which does not require fine-tuning of a cosmological constant. We find cosmological solutions of the Friedmann-Robertson-Walker type. They generically have a big bounce, and an early inflationlike phase with graceful exit. The mechanism is purely geometrical; no ad hoc scalar fields are introduced. The solutions are stabilized through vacuum fluctuations and are thus compatible with quantum mechanics. This leads to a Milne-like universe after inflation, which appears to be in remarkably good agreement with observation and may provide an alternative to standard cosmology.

Klammer, Daniela; Steinacker, Harold [Fakultaet fuer Physik, Universitaet Wien, A-1090 Wien (Austria)

2009-06-05T23:59:59.000Z

128

Telescoping MATLAB for DSP Applications PhD Thesis Defense  

E-Print Network [OSTI]

Telescoping MATLAB for DSP Applications PhD Thesis Defense Arun Chauhan Computer Science, Rice University PhD Thesis Defense July 10, 2003 #12;Two True Stories PhD Thesis Defense: Telescoping MATLABD Thesis Defense: Telescoping MATLAB for DSP Applications July 10, 2003 #12;Two True Stories · the world

Chauhan, Arun

129

TASI Lectures on the cosmological constant  

E-Print Network [OSTI]

discovery in tones of wonder and stupefaction, as a “mysterious dark energy”,dark energy. 5.3 The real second problem By sharpening the cosmological constant problem, the discovery

Bousso, Raphael

2008-01-01T23:59:59.000Z

130

Cosmology of hidden sector with Higgs portal  

E-Print Network [OSTI]

In this thesis, we are investigating cosmological implications of hidden sector models which involve scalar fields that do not interact with the Standard Model gauge interactions, but couple directly to the Higgs field. ...

Cabi, Serkan

2009-01-01T23:59:59.000Z

131

Self Creation Cosmology - An Alternative Gravitational Theory  

E-Print Network [OSTI]

The premature acceptance of the standard cosmological model, the 'LambdaCDM' paradigm, is questioned; Self Creation Cosmology is offered as an alternative and shown to be as equally concordant with observed cosmological constraints and local observations including the EEP. The Brans Dicke theory is modified to enable the creation of matter and energy out of the self contained gravitational and scalar fields constrained by the local conservation of energy so that rest masses vary whereas the observed Newtonian Gravitation 'constant' does not. There is a conformal equivalence between self-creation and General Relativity in vacuo, which results in the predictions of the two theories being equal in the standard tests. In self-creation test particles in vacuo follow the geodesics of General Relativity. Nevertheless there are three types of experiment, including the LIGO apparatus, which are able to distinguish between the two theories. Self-creation is as consistent with cosmological constraints in the distant sup...

Barber, G A

2004-01-01T23:59:59.000Z

132

Cosmology at the Beach Lecture: Anne Green  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.  

Ann Green

2010-01-08T23:59:59.000Z

133

Cosmology at the Beach Lecture: David Hughes  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

David Hughes

2010-01-08T23:59:59.000Z

134

Cosmology at the Beach Lecture: Simon White  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Simon White

2010-01-08T23:59:59.000Z

135

Cosmology on the Beach: Kendrick Smith  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

George Smoot

2010-01-08T23:59:59.000Z

136

Cosmology on the Beach - George Smoot  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

George Smoot

2010-01-08T23:59:59.000Z

137

Telescoping magnetic ball bar test gage  

DOE Patents [OSTI]

A telescoping magnetic ball bar test gage for determining the accuracy of machine tools, including robots, and those measuring machines having non-disengagable servo drives which cannot be clutched out. Two gage balls are held and separated from one another by a telescoping fixture which allows them relative radial motional freedom but not relative lateral motional freedom. The telescoping fixture comprises a parallel reed flexure unit and a rigid member. One gage ball is secured by a magnetic socket knuckle assembly which fixes its center with respect to the machine being tested. The other gage ball is secured by another magnetic socket knuckle assembly which is engaged or held by the machine in such manner that the center of that ball is directed to execute a prescribed trajectory, all points of which are equidistant from the center of the fixed gage ball. As the moving ball executes its trajectory, changes in the radial distance between the centers of the two balls caused by inaccuracies in the machine are determined or measured by a linear variable differential transformer (LVDT) assembly actuated by the parallel reed flexure unit. Measurements can be quickly and easily taken for multiple trajectories about several different fixed ball locations, thereby determining the accuracy of the machine.

Bryan, J.B.

1982-03-15T23:59:59.000Z

138

Telescoping magnetic ball bar test gage  

DOE Patents [OSTI]

A telescoping magnetic ball bar test gage for determining the accuracy of machine tools, including robots, and those measuring machines having non-disengageable servo drives which cannot be clutched out. Two gage balls (10, 12) are held and separated from one another by a telescoping fixture which allows them relative radial motional freedom but not relative lateral motional freedom. The telescoping fixture comprises a parallel reed flexure unit (14) and a rigid member (16, 18, 20, 22, 24). One gage ball (10) is secured by a magnetic socket knuckle assembly (34) which fixes its center with respect to the machine being tested. The other gage ball (12) is secured by another magnetic socket knuckle assembly (38) which is engaged or held by the machine in such manner that the center of that ball (12) is directed to execute a prescribed trajectory, all points of which are equidistant from the center of the fixed gage ball (10). As the moving ball (12) executes its trajectory, changes in the radial distance between the centers of the two balls (10, 12) caused by inaccuracies in the machine are determined or measured by a linear variable differential transformer (LVDT) assembly (50, 52, 54, 56, 58, 60) actuated by the parallel reed flexure unit (14). Measurements can be quickly and easily taken for multiple trajectories about several different fixed ball (10) locations, thereby determining the accuracy of the machine.

Bryan, James B. (Pleasanton, CA)

1984-01-01T23:59:59.000Z

139

An Inertial Reaction to Cosmological Accelerations  

E-Print Network [OSTI]

Mach's "fixed stars" are actually not fixed at all. The distant clusters of galaxies are not only receding from each observer but they are also accelerating since the rate of cosmological expansion is not constant. If the distant cosmic masses in someway constitute the frame of inertial reference then an additional force should be generated among local bodies in reaction to the apparent cosmological accelerations of the distant galaxies.

Scott Funkhouser

2005-05-17T23:59:59.000Z

140

Patch dualities and remarks on nonstandard cosmologies  

SciTech Connect (OSTI)

In this paper we establish dualities between inflationary, cyclic/ekpyrotic, and phantom cosmologies within the patch formalism approximating high-energy effects in scenarios with extra dimensions. The exact dualities relating the four-dimensional spectra are broken in favor of their braneworld counterparts; the dual solutions display new interesting features because of the modification of the effective Friedmann equation on the brane. We then address some qualitative issues about phantomlike cosmologies without phantom matter.

Calcagni, Gianluca [Dipartimento di Fisica, Universita di Parma, Parma (Italy) and INFN-Gruppo Collegato di Parma, Parco Area delle Scienze 7/A, I-43100 Parma (Italy)

2005-01-15T23:59:59.000Z

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.


141

Mass Spectrum, Actons and Cosmological Landscape  

E-Print Network [OSTI]

It is suggested that the properties of the mass spectrum of elementary particles could be related with cosmology. Solutions of the Klein-Gordon equation on the Friedmann type manifold with the finite action are constructed. These solutions (actons) have a discrete mass spectrum. We suggest that such solutions could select a universe from cosmological landscape. In particular the solutions with the finite action on de Sitter space are investigated.

V. V. Kozlov; I. V. Volovich

2006-12-13T23:59:59.000Z

142

Cosmological acceleration from a gas of strings  

Science Journals Connector (OSTI)

In string gas cosmology, the extra dimensions of the underlying theory are kept at a microscopic scale by a gas of strings. In the matter-dominated era, however, dust pressure can lead to oscillations of the extra dimensions and to acceleration in the three visible dimensions, even with a vanishing cosmological term. We review the resulting oscillating expansion history, that provides an acceptable fit to the observed accelerated expansion of the Universe.

Francesc Ferrer

2009-01-01T23:59:59.000Z

143

Cosmological acceleration from a gas of strings  

E-Print Network [OSTI]

In string gas cosmology, the extra dimensions of the underlying theory are kept at a microscopic scale by a gas of strings. In the matter-dominated era, however, dust pressure can lead to oscillations of the extra dimensions and to acceleration in the three visible dimensions, even with a vanishing cosmological term. We review the resulting oscillating expansion history, that provides an acceptable fit to the observed accelerated expansion of the Universe.

Francesc Ferrer

2009-07-08T23:59:59.000Z

144

Conformal cosmological model and SNe Ia data  

SciTech Connect (OSTI)

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

145

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

146

Development of a mid-sized Schwarzschild-Couder Telescope for the Cherenkov Telescope Array  

SciTech Connect (OSTI)

The Cherenkov Telescope Array (CTA) is a ground-based observatory for very high-energy (10 GeV to 100 TeV) gamma rays, planned for operation starting in 2018. It will be an array of dozens of optical telescopes, known as Atmospheric Cherenkov Telescopes (ACTs), of 8 m to 24 m diameter, deployed over an area of more than 1 square km, to detect flashes of Cherenkov light from showers initiated in the Earth's atmosphere by gamma rays. CTA will have improved angular resolution, a wider energy range, larger fields of view and an order of magnitude improvement in sensitivity over current ACT arrays such as H.E.S.S., MAGIC and VERITAS. Several institutions have proposed a research and development program to eventually contribute 36 medium-sized telescopes (9 m to 12 m diameter) to CTA to enhance and optimize its science performance. The program aims to construct a prototype of an innovative, Schwarzschild-Couder telescope (SCT) design that will allow much smaller and less expensive cameras and much larger fields of view than conventional Davies-Cotton designs, and will also include design and testing of camera electronics for the necessary advances in performance, reliability and cost. We report on the progress of the mid-sized SCT development program.

Cameron, Robert A.

2012-06-28T23:59:59.000Z

147

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 Repl...

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

2013-01-01T23:59:59.000Z

148

E-Print Network 3.0 - antares neutrino telescope Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

oscillation parameters. Keywords: neutrino oscillations, ANTARES, neutrino telescope 1 Introduction It is now... energy neutrino telescopes, whose energy threshold is...

149

The Atacama Surface Solar Maximum  

Science Journals Connector (OSTI)

Solar radiation reaching the earth's surface is one of the major drivers of climate dynamics. By setting the surface energy balance, downwelling solar radiation indirectly heats the atmosphere and controls the hydrological cycle. Besides its critical ...

Roberto Rondanelli; Alejandra Molina; Mark Falvey

150

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

151

Cosmological Consequences of String Axions  

SciTech Connect (OSTI)

Axion fluctuations generated during inflation lead to isocurvature and non-Gaussian temperature fluctuations in the cosmic microwave background radiation. Following a previous analysis for the model independent string axion we consider the consequences of a measurement of these fluctuations for two additional string axions. We do so independent of any cosmological assumptions except for the axions being massless during inflation. The first axion has been shown to solve the strong CP problem for most compactifications of the heterotic string while the second axion, which does not solve the strong CP problem, obeys a mass formula which is independent of the axion scale. We find that if gravitational waves interpreted as arising from inflation are observed by the PLANCK polarimetry experiment with a Hubble constant during inflation of H{sub inf} {approx}> 10{sup 13} GeV the existence of the first axion is ruled out and the second axion cannot obey the scale independent mass formula. In an appendix we quantitatively justify the often held assumption that temperature corrections to the zero temperature QCD axion mass may be ignored for temperatures T {approx}< {Lambda}{sub QCD}.

Kain, Ben

2005-12-15T23:59:59.000Z

152

Friction forces in cosmological models  

E-Print Network [OSTI]

We investigate the dynamics of test particles undergoing friction forces in a Friedmann-Robertson-Walker (FRW) spacetime. The interaction with the background fluid is modeled by introducing a Poynting-Robertson-like friction force in the equations of motion, leading to measurable (at least in principle) deviations of the particle trajectories from geodesic motion. The effect on the peculiar velocities of the particles is investigated for various equations of state of the background fluid and different standard cosmological models. The friction force is found to have major effects on particle motion in closed FRW universes, where it turns the time-asymptotic value (approaching the recollapse) of the peculiar particle velocity from ultra-relativistic (close to light speed) to a co-moving one, i.e., zero peculiar speed. On the other hand, for open or flat universes the effect of the friction is not so significant, because the time-asymptotic peculiar particle speed is largely non-relativistic also in the geodesi...

Bini, Donato; Gregoris, Daniele; Succi, Sauro

2014-01-01T23:59:59.000Z

153

Friction forces in cosmological models  

E-Print Network [OSTI]

We investigate the dynamics of test particles undergoing friction forces in a Friedmann-Robertson-Walker (FRW) spacetime. The interaction with the background fluid is modeled by introducing a Poynting-Robertson-like friction force in the equations of motion, leading to measurable (at least in principle) deviations of the particle trajectories from geodesic motion. The effect on the peculiar velocities of the particles is investigated for various equations of state of the background fluid and different standard cosmological models. The friction force is found to have major effects on particle motion in closed FRW universes, where it turns the time-asymptotic value (approaching the recollapse) of the peculiar particle velocity from ultra-relativistic (close to light speed) to a co-moving one, i.e., zero peculiar speed. On the other hand, for open or flat universes the effect of the friction is not so significant, because the time-asymptotic peculiar particle speed is largely non-relativistic also in the geodesic case.

Donato Bini; Andrea Geralico; Daniele Gregoris; Sauro Succi

2014-08-23T23:59:59.000Z

154

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

155

ANTARES deep sea neutrino telescope results  

SciTech Connect (OSTI)

The ANTARES experiment is currently the largest underwater neutrino telescope in the Northern Hemisphere. It is taking high quality data since 2007. Its main scientific goal is to search for high energy neutrinos that are expected from the acceleration of cosmic rays from astrophysical sources. This contribution reviews the status of the detector and presents several analyses carried out on atmospheric muons and neutrinos. For example it shows the results from the measurement of atmospheric muon neutrino spectrum and of atmospheric neutrino oscillation parameters as well as searches for neutrinos from steady cosmic point-like sources, for neutrinos from gamma ray bursts and for relativistic magnetic monopoles.

Mangano, Salvatore [IFIC - Instituto de Física Corpuscular, Edificio Institutos de Investigatión, 46071 Valencia (Spain); Collaboration: ANTARES Collaboration

2014-06-24T23:59:59.000Z

156

LOFAR, a new low frequency radio telescope  

E-Print Network [OSTI]

LOFAR, the Low Frequency Array, is a large radio telescope consisting of approximately 100 soccer-field sized antenna stations spread over a region of 400 km in diameter. It will operate at frequencies from ~10 to 240 MHz, with a resolution at 240 MHz of better than an arcsecond. Its superb sensitivity will allow for studies of a broad range of astrophysical topics, including reionisation, transient radio sources and cosmic rays, distant galaxies and AGNs. In this contribution a status rapport of the LOFAR project and an overview of the science case is presented.

H. J. A. Rottgering

2003-09-19T23:59:59.000Z

157

Beyond the Cosmological Standard Model  

E-Print Network [OSTI]

After a decade and a half of research motivated by the accelerating universe, theory and experiment have a reached a certain level of maturity. The development of theoretical models beyond \\Lambda, or smooth dark energy, often called modified gravity, has led to broader insights into a path forward, and a host of observational and experimental tests have been developed. In this review we present the current state of the field and describe a framework for anticipating developments in the next decade. We identify the guiding principles for rigorous and consistent modifications of the standard model, and discuss the prospects for empirical tests. We begin by reviewing attempts to consistently modify Einstein gravity in the infrared, focusing on the notion that additional degrees of freedom introduced by the modification must screen themselves from local tests of gravity. We categorize screening mechanisms into three broad classes: mechanisms which become active in regions of high Newtonian potential, those in which first derivatives become important, and those for which second derivatives are important. Examples of the first class, such as f(R) gravity, employ the familiar chameleon or symmetron mechanisms, whereas examples of the last class are galileon and massive gravity theories, employing the Vainshtein mechanism. In each case, we describe the theories as effective theories. We describe experimental tests, summarizing laboratory and solar system tests and describing in some detail astrophysical and cosmological tests. We discuss future tests which will be sensitive to different signatures of new physics in the gravitational sector. Parts that are more relevant to theorists vs. observers/experimentalists are clearly indicated, in the hope that this will serve as a useful reference for both audiences, as well as helping those interested in bridging the gap between them.

Austin Joyce; Bhuvnesh Jain; Justin Khoury; Mark Trodden

2014-12-15T23:59:59.000Z

158

A 16-m Telescope for the Advanced Technology Large Aperture Telescope (ATLAST) Mission  

E-Print Network [OSTI]

for the telescope and its instruments. Solar array panels, an antenna and a solar sail are also folded up against compartment which is attached to a spacecraft bus which provides power, attitude control and communications and is separated from the launch vehicle, its solar arrays and high gain antenna will be deployed

Sirianni, Marco

159

AGN Physics with the Cherenkov Telescope Array  

E-Print Network [OSTI]

The Cherenkov Telescope Array (CTA), currently in its Preparatory Phase, will be the first open observatory for very high energy gamma-rays from galactic and extragalactic sources. The international consortium behind CTA is preparing the construction of two large arrays of Cherenkov telescopes in the Northern and Southern Hemispheres with a performance that will be significantly improved compared to the current generation of arrays. Its increased sensitivity and energy range will give CTA access to a large population of Active Galactic Nuclei (AGN) not yet detected at very high energies and provide much more details on known TeV sources. While the low end of the CTA energy coverage will close the current gap with the Fermi-LAT band, its high energy coverage will open a new window on the sky and help us understand the intrinsic shape of the hardest blazar spectra. We outline the current status of CTA and discuss the science case for AGN physics with the observatory. Predictions for source detections based on e...

Zech, A

2012-01-01T23:59:59.000Z

160

Fermi Large Area Telescope Third Source Catalog  

E-Print Network [OSTI]

We present the third Fermi Large Area Telescope source catalog (3FGL) of sources in the 100~MeV--300~GeV range. Based on the first four years of science data from the Fermi Gamma-ray Space Telescope mission, it is the deepest yet in this energy range. Relative to the 2FGL catalog, the 3FGL catalog incorporates twice as much data as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse gamma-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources above 4 sigma significance, with source location regions, spectral properties, and monthly light curves for each. Of these, 78 are flagged as potentially being due to imperfections in the model for Galactic diffuse emission. Twenty-five sources are modeled explicitly as spatially extended, and overall 232 sources are considered as identifie...

,

2015-01-01T23:59:59.000Z

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.


161

The X-ray Telescope of CAST  

E-Print Network [OSTI]

The Cern Axion Solar Telescope (CAST) is in operation and taking data since 2003. The main objective of the CAST experiment is to search for a hypothetical pseudoscalar boson, the axion, which might be produced in the core of the sun. The basic physics process CAST is based on is the time inverted Primakoff effect, by which an axion can be converted into a detectable photon in an external electromagnetic field. The resulting X-ray photons are expected to be thermally distributed between 1 and 7 keV. The most sensitive detector system of CAST is a pn-CCD detector combined with a Wolter I type X-ray mirror system. With the X-ray telescope of CAST a background reduction of more than 2 orders off magnitude is achieved, such that for the first time the axion photon coupling constant g_agg can be probed beyond the best astrophysical constraints g_agg < 1 x 10^-10 GeV^-1.

M. Kuster; H. Bräuninger; S. Cébrian; M. Davenport; C. Elefteriadis; J. Englhauser; H. Fischer; J. Franz; P. Friedrich; R. Hartmann; F. H. Heinsius; D. H. H. Hoffmann; G. Hoffmeister; J. N. Joux; D. Kang; K. Königsmann; R. Kotthaus; T. Papaevangelou; C. Lasseur; A. Lippitsch; G. Lutz; J. Morales; A. Rodríguez; L. Strüder; J. Vogel; K. Zioutas

2007-05-10T23:59:59.000Z

162

Light right-handed neutrinos: + an incursion in cosmology  

E-Print Network [OSTI]

Light right-handed neutrinos: why not? + an incursion in cosmology R. Barbieri "Neutrinos in Venice? " The typical lifetime of a new trend in high energy physics and cosmology nowadays is about 5 to 10 years

Abbondandolo, Alberto

163

Integral Field Spectroscopy with the Gemini 8-m Telescopes  

E-Print Network [OSTI]

We give an overview of the current and future IFU capabilities on the Gemini 8-m telescopes. The telescopes are well-suited to integral field spectroscopy and both telescopes will have optical and near-infrared IFUs within the next few years. Commissioning for the GMOS IFU on Gemini North has begun recently and it is now available to the community. Future integral field instruments will take advantage of wide-field adaptive optics systems.

B. W. Miller; J. Turner; M. Takamiya; D. Simons; I. Hook

2002-03-20T23:59:59.000Z

164

The Universe Adventure - The Cosmological Principle  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (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

165

Cosmological perturbations in mimetic matter model  

E-Print Network [OSTI]

We investigate the cosmological evolution of mimetic matter model with arbitrary scalar potential. The cosmological reconstruction is explicitly done for different choices of potential. The cases that mimetic matter model shows the evolution as Cold Dark Matter(CDM), wCDM model, dark matter and dark energy with dynamical $Om(z)$ or phantom dark energy with phantom-non-phantom crossing are presented in detail. The cosmological perturbations for such evolution are studied in mimetic matter model. For instance, the evolution behavior of the matter density contrast which is different from usual one, i.e. $\\ddot \\delta + 2 H \\dot \\delta - \\kappa ^2 \\rho \\delta /2 = 0$ is investigated. The possibility of peculiar evolution of $\\delta$ in the model under consideration is shown. Special attention is paid to the behavior of matter density contrast near to future singularity where decay of perturbations may occur much earlier the singularity.

Matsumoto, Jiro; Sushkov, Sergey V

2015-01-01T23:59:59.000Z

166

Cosmological and Astrophysical Probes of Vacuum Energy  

E-Print Network [OSTI]

Vacuum energy changes during cosmological phase transitions and becomes relatively important at epochs just before phase transitions. For a viable cosmology the vacuum energy just after a phase transition must be set by the critical temperature of the next phase transition, which exposes the cosmological constant problem from a different angle. Here we propose to experimentally test the properties of vacuum energy under circumstances different from our current vacuum. One promising avenue is to consider the effect of high density phases of QCD in neutron stars. Such phases have different vacuum expectation values and a different vacuum energy from the normal phase, which can contribute an order one fraction to the mass of neutron stars. Precise observations of the mass of neutron stars can potentially yield information about the gravitational properties of vacuum energy, which can significantly affect their mass-radius relation. A more direct test of cosmic evolution of vacuum energy could be inferred from a ...

Bellazzini, Brando; Hubisz, Jay; Serra, Javi; Terning, John

2015-01-01T23:59:59.000Z

167

Local Conformal Symmetry in Physics and Cosmology  

E-Print Network [OSTI]

We show how to lift a generic non-scale invariant action in Einstein frame into a locally conformally-invariant (or Weyl-invariant) theory and present a new general form for Lagrangians consistent with Weyl symmetry. Advantages of such a conformally invariant formulation of particle physics and gravity include the possibility of constructing geodesically complete cosmologies. We present a conformal-invariant version of the standard model coupled to gravity, and show how Weyl symmetry may be used to obtain unprecedented analytic control over its cosmological solutions. Within this new framework, generic FRW cosmologies are geodesically complete through a series of big crunch - big bang transitions. We discuss a new scenario of cosmic evolution driven by the Higgs field in a \\textquotedblleft minimal\\textquotedblright% \\ conformal standard model, in which there is no new physics beyond the standard model at low energies, and the current Higgs vacuum is metastable as indicated by the latest LHC data.

Itzhak Bars; Paul Steinhardt; Neil Turok

2013-07-07T23:59:59.000Z

168

Accelerating Cosmologies with Extended Product Spaces  

E-Print Network [OSTI]

Accelerating cosmologies in extra dimensional spaces have been studied. These extra dimensional spaces are products of many spaces. The physical behaviors of accelerating cosmologies are investigated from Einstein's field equation in higher dimensional Friedmann-Robertson-Walker (FRW) universe and superstring/M theory points of view. It is found that if some assumptions of flatness are made for sector of the FRW universe, the remaining sector needs to be hyperbolic. These properties are in parallel with those found in the model of superstring/M theory. The extended product made for the superstring model did not show any more new features other than those already found. A similar accelerating phase of this product space cosmology was found with difference in numerical values of the accelerating period.

Han Siong Ch'ng

2008-10-15T23:59:59.000Z

169

Quantum Exclusion of Positive Cosmological Constant?  

E-Print Network [OSTI]

We show that a positive cosmological constant is incompatible with the quantum-corpuscular resolution of de Sitter metric in form of a coherent state. The reason is very general and is due to the quantum self-destruction of the coherent state because of the scattering of constituent graviton quanta. This process creates an irreversible quantum clock, which precludes eternal de Sitter. It also eliminates the possibility of Boltzmann brains and Poincare recurrences. This effect is expected to be part of any microscopic theory that takes into account the quantum corpuscular structure of the cosmological background. This observation puts the cosmological constant problem in a very different light, promoting it, from a naturalness problem, into a question of quantum consistency. We are learning that quantum gravity cannot tolerate exceedingly-classical sources.

Gia Dvali; Cesar Gomez

2014-12-27T23:59:59.000Z

170

Cosmological birefringence constraints from CMB and astrophysical polarization data  

E-Print Network [OSTI]

Cosmological birefringence is a rotation of the polarization plane of photons coming from sources of astrophysical and cosmological origin. The rotation can also depend on the energy of the photons and not only on the distance of the source and on the cosmological evolution of the underlying theoretical model. In this work, we constrain few selected models for cosmological birefringence, combining CMB and astrophysical data at radio, optical, X and gamma wavelengths, taking into account the specific energy and distance dependences.

Galaverni, M; Paci, F; Finelli, F

2014-01-01T23:59:59.000Z

171

The Robotic Super-LOTIS Telescope: Results & Future Plans  

E-Print Network [OSTI]

We provide an overview of the robotic Super-LOTIS (Livermore Optical Transient Imaging System) telescope and present results from gamma-ray burst (GRB) afterglow observations using Super-LOTIS and other Steward Observatory telescopes. The 0.6-m Super-LOTIS telescope is a fully robotic system dedicated to the measurement of prompt and early time optical emission from GRBs. The system began routine operations from its Steward Observatory site atop Kitt Peak in April 2000 and currently operates every clear night. The telescope is instrumented with an optical CCD camera and a four position filter wheel. It is capable of observing Swift Burst Alert Telescope (BAT) error boxes as early or earlier than the Swift UV/Optical Telescope (UVOT). Super-LOTIS complements the UVOT observations by providing early R- and I-band imaging. We also use the suite of Steward Observatory telescopes including the 1.6-m Kuiper, the 2.3-m Bok, the 6.5-m MMT, and the 8.4-m Large Binocular Telescope to perform follow-up optical and near infrared observations of GRB afterglows. These follow-up observations have traditionally required human intervention but we are currently working to automate the 1.6-m Kuiper telescope to minimize its response time.

G. G. Williams; P. A. Milne; H. S. Park; S. D. Barthelmy; D. H. Hartmann; A. Updike; K. Hurley

2008-02-29T23:59:59.000Z

172

Automation of the design of a telescopic zoom system  

Science Journals Connector (OSTI)

This paper discusses the theoretical bases of the construction and computation of the parameters of a telescopic zoom system. A mathematical model and algorithm has been developed,...

Van Luen, Nguen

2013-01-01T23:59:59.000Z

173

Magnetized String Cosmological Model in Cylindrically Symmetric Inhomogeneous Universe with Variable Cosmological-Term $?$  

E-Print Network [OSTI]

Cylindrically symmetric inhomogeneous magnetized string cosmological model is investigated with cosmological term $\\Lambda$ varying with time. To get the deterministic solution, it has been assumed that the expansion ($\\theta$) in the model is proportional to the eigenvalue $\\sigma^{1}_{1}$ of the shear tensor $\\sigma^{i}_{j}$. The value of cosmological constant for the model is found to be small and positive which is supported by the results from recent supernovae Ia observations. The physical and geometric properties of the model are also discussed in presence and absence of magnetic field.

Anirudh Pradhan

2007-08-01T23:59:59.000Z

174

Cosmology with X-ray Cluster Baryons  

SciTech Connect (OSTI)

X-ray cluster measurements interpreted with a universal baryon/gas mass fraction can theoretically serve as a cosmological distance probe. We examine issues of cosmological sensitivity for current (e.g., Chandra X-ray Observatory, XMM-Newton) and next generation (e.g., Con-X, XEUS) observations, along with systematic uncertainties and biases. To give competitive next generation constraints on dark energy, we find that systematics will need to be controlled to better than 1percent and any evolution in f_gas (and other cluster gas properties) must be calibrated so the residual uncertainty is weaker than (1+z)0.03.

Linder, Eric V.

2007-04-10T23:59:59.000Z

175

Role of ? in the Cosmological Lens Equation  

Science Journals Connector (OSTI)

The cosmological constant ? affects cosmological gravitational lensing. Effects due to ? can be studied in the framework of the Schwarzschild–de Sitter spacetime. Two novel contributions, which cannot be accounted for by a proper use of angular diameter distances, are derived. First, a term ??^?=2mb?/3 has to be added to the bending angle, where m is the lens mass and b the impact parameter. Second, ? brings about a difference in the redshifts of multiple images. Both effects are quite small for real astrophysical systems, ??^??1?arcsec and ?zs?10-7.

Mauro Sereno

2009-01-14T23:59:59.000Z

176

Future Singularities and Completeness in Cosmology  

E-Print Network [OSTI]

We review recent work on the existence and nature of cosmological singularities that can be formed during the evolution of generic as well as specific cosmological spacetimes in general relativity. We first discuss necessary and sufficient conditions for the existence of geodesically incomplete spacetimes based on a tensorial analysis of the geodesic equations. We then classify the possible singularities of isotropic globally hyperbolic universes using the Bel-Robinson slice energy that closely monitors the asymptotic properties of fields near the singularity. This classification includes all known forms of spacetime singularities in isotropic universes and also predicts new types.

Spiros Cotsakis

2006-06-04T23:59:59.000Z

177

Non-standard loop quantum cosmology  

E-Print Network [OSTI]

We present results concerning the nature of the cosmological big bounce(BB) transition within the loop geometry underlying loop quantum cosmology (LQC). Our canonical quantization method is an alternative to the standard LQC. An evolution parameter we use has clear interpretation both at classical and quantum levels. The physical volume operator has discrete spectrum which is bounded from below. The minimum gap in the spectrum defines a quantum of the volume. The spectra of operators are parametrized by a free parameter to be determined.

Wlodzimierz Piechocki

2010-01-19T23:59:59.000Z

178

Asymptotic safety and the cosmological constant  

E-Print Network [OSTI]

We study the non-perturbative renormalisation of quantum gravity in four dimensions. Taking care to disentangle physical degrees of freedom, we observe the topological nature of conformal fluctuations arising from the functional measure. The resulting beta functions possess an asymptotically safe fixed point with a global phase structure leading to classical general relativity for positive, negative or vanishing cosmological constant. If only the conformal fluctuations are quantised we find an asymptotically safe fixed point predicting a vanishing cosmological constant on all scales. At this fixed point we reproduce the critical exponent, $\

Kevin Falls

2014-08-01T23:59:59.000Z

179

Constraining supersymmetric SO(10) models through cosmology  

Science Journals Connector (OSTI)

We study the impact of the symmetry-breaking patterns from supersymmetric SO(10) down to the standard model on the standard big-bang cosmology through the formation of topological defects. None of the models is consistent with the standard cosmology without invoking any mechanism to solve the monopole problem. For this purpose, we use a hybrid false vacuum inflationary scenario. Only two symmetry-breaking patterns are consistent with these topological considerations and with the actual data on the proton lifetime. © 1995 The American Physical Society.

Rachel Jeannerot and Anne-Christine Davis

1995-12-15T23:59:59.000Z

180

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

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.


181

Cosmology and gravity in the brane world  

E-Print Network [OSTI]

, and cosmological problems such as the origin and nature of dark energy and dark matter as well as inflation are not explained. Supersymmetry (SUSY) (see [2] for a review of global and local supersymmetry) is an extension of the SM that can seemingly ameliorate some... unresolved questions such as the origin and nature of both inflation and dark energy (the cosmological constant problem), the number of generations, why would the universe use certain SUSY GUTs as opposed to others, and why is spacetime 3+1 dimensional. Over...

Dent, James Blackman

2005-11-01T23:59:59.000Z

182

Cosmology as Science?: From Inflation to Eternity  

ScienceCinema (OSTI)

The last decade or two have represented the golden age of observational cosmology, producing a revolution in our picture of the Universe on its largest scales, and perhaps also its smallest ones. I will argue that these recent development bring to the forefront some vexing questions about whether various fundamental assumptions about the universe are in fact falsifiable. I will focus on 3 issues: (1) "Proving" Inflation, (2) Dark Energy and Anthropic Arguments, and (3) Cosmology of the far future.Interview with Lawrence M. Krauss

None

2011-10-06T23:59:59.000Z

183

Development of an ASIC for Dual Mirror Telescopes of the Cherenkov Telescope Array  

E-Print Network [OSTI]

We have developed an application-specific integrated circui (ASIC) for photomultipler tube (PMT) waveform digitization which is well-suited for the Schwarzschild-Couder optical system under development for the Cherenkov Telescope Array (CTA) project. The key feature of the "TARGET" ASIC is the ability to read 16 channels in parallel at a sampling speed of 1 GSa/s or faster. In combination with a focal plane instrumented with 64-channel multi-anode PMTs (MAPMTs), TARGET digitizers will enable CTA to achieve a wider field of view than the current Cherenkov telescopes and significantly reduce the cost per channel of the camera and readout electronics. We have also developed a prototype camera module, consisting of 4 TARGET ASICs and a 64-channel MAPMT. We report results from performance testing of the camera module and of the TARGET ASIC itself.

Vandenbroucke, Justin; Funk, Stefan; Okumura, Akira; Tajima, Hiro; Varner, Gary

2011-01-01T23:59:59.000Z

184

Cosmology with SKA Radio Continuum Surveys  

E-Print Network [OSTI]

Radio continuum surveys have, in the past, been of restricted use in cosmology. Most studies have concentrated on cross-correlations with the cosmic microwave background to detect the integrated Sachs-Wolfe effect, due to the large sky areas that can be surveyed. As we move into the SKA era, radio continuum surveys will have sufficient source density and sky area to play a major role in cosmology on the largest scales. In this chapter we summarise the experiments that can be carried out with the SKA as it is built up through the coming decade. We show that the SKA can play a unique role in constraining the non-Gaussianity parameter to \\sigma(f_NL) ~ 1, and provide a unique handle on the systematics that inhibit weak lensing surveys. The SKA will also provide the necessary data to test the isotropy of the Universe at redshifts of order unity and thus evaluate the robustness of the cosmological principle.Thus, SKA continuum surveys will turn radio observations into a central probe of cosmological research in th...

Jarvis, Matt J; Blake, Chris; Brown, Michael L; Lindsay, Sam N; Raccanelli, Alvise; Santos, Mario; Schwarz, Dominik

2015-01-01T23:59:59.000Z

185

Surface Tension and the Cosmological Constant  

E-Print Network [OSTI]

The astronomically observed value of the cosmological constant is small but non-zero. This raises two questions together known as the cosmological constant problem a) why is lambda so nearly zero? b) why is lambda not EXACTLY zero? Sorkin has proposed that b) can be naturally explained as a one by square root N fluctuation by invoking discreteness of spacetime at the Planck scale due to quantum gravity. In this paper we shed light on these questions by developing an analogy between the cosmological constant and the surface tension of membranes. The ``cosmological constant problem'' has a natural analogue in the membrane context: the vanishingly small surface tension of fluid membranes provides an example where question a) above arises and is answered. We go on to find a direct analogue of Sorkin's proposal for answering question b) in the membrane context, where the discreteness of spacetime translates into the molecular structure of matter. We propose analogue experiments to probe a small and fluctuating surface tension in fluid membranes. A counterpart of dimensional reduction a la Kaluza-Klein and large extra dimensions also appears in the physics of fluid membranes.

Joseph Samuel; Supurna Sinha

2006-04-18T23:59:59.000Z

186

ccsd00000531 Early Cosmology and Fundamental Physics  

E-Print Network [OSTI]

, open problems and future perspectives in connection with dark energy and string theory are overviewed. Contents I. The history of the universe 1 II. Fundamental Physics 2 III. Essentials of Cosmology 3 IV and Outlook 13 References 14 I. THE HISTORY OF THE UNIVERSE The history of the universe is a history

187

Gamma-ray bursts and cosmology  

Science Journals Connector (OSTI)

...research-article Discussion Meeting Issue Gamma-ray bursts organized by Alan Wells, Ralph...J. Wijers and Martin Rees Gamma-ray bursts and cosmology D.Q Lamb...current status of the use of gamma-ray bursts (GRBs) as probes of the early...

2007-01-01T23:59:59.000Z

188

Observed Cosmological Redshifts Support Contracting Accelerating Universe  

E-Print Network [OSTI]

The main argument that Universe is currently expanding is observed redshift increase by distance. However, this conclusion may not be correct, because cosmological redshift depends only on the scaling factors, the change in the size of the universe during the time of light propagation and is not related to the speed of observer or speed of the object emitting the light. An observer in expanding universe will measure the same redshift as observer in contracting universe with the same scaling. This was not taken into account in analysing the SN Ia data related to the universe acceleration. Possibility that universe may contract, but that the observed light is cosmologically redshifted allows for completely different set of cosmological parameters $\\Omega_M, \\Omega_{\\Lambda}$, including the solution $\\Omega_M=1, \\Omega_{\\Lambda}=0$. The contracting and in the same time accelerating universe explains observed deceleration and acceleration in SN Ia data, but also gives significantly larger value for the age of the universe, $t_0 = 24$ Gyr. This allows to reconsider classical cosmological models with $\\Lambda =0$. The contracting stage also may explain the observed association of high redshifted quasars to low redshifted galaxies.

Branislav Vlahovic

2012-07-02T23:59:59.000Z

189

Cosmology with Coupled Gravity and Dark Energy  

E-Print Network [OSTI]

Dark energy is a fundamental constituent of our universe, its status in the cosmological field equation should be equivalent to that of gravity. Here we construct a dark energy and matter gravity coupling (DEMC) model of cosmology in a way that dark energy and gravity are introduced into the cosmological field equation in parallel with each other from the beginning. The DEMC universe possesses a composite symmetry from global Galileo invariance and local Lorentz invariance. The observed evolution of the universe expansion rate at redshift z>1 is in tension with the standard LCDM model, but can be well predicted by the DEMC model from measurements of only nearby epochs. The so far most precise measured expansion rate at high z is quite a bit slower than the expectations from LCDM, but remarkably consistent with that from DEMC. It is hoped that the DEMC scenario can also help to solve other existing challenges to cosmology: large scale anomalies in CMB maps and large structures up to about 10^3 Mpc of a quasar group. The DEMC universe is a well defined mechanical system. From measurements we can quantitatively evaluate its total rest energy, present absolute radius and expanding speed.

Ti-Pei Li

2015-01-13T23:59:59.000Z

190

Cosmologies with a time dependent vacuum  

E-Print Network [OSTI]

The idea that the cosmological term, Lambda, should be a time dependent quantity in cosmology is a most natural one. It is difficult to conceive an expanding universe with a strictly constant vacuum energy density, namely one that has remained immutable since the origin of time. A smoothly evolving vacuum energy density that inherits its time-dependence from cosmological functions, such as the Hubble rate or the scale factor, is not only a qualitatively more plausible and intuitive idea, but is also suggested by fundamental physics, in particular by quantum field theory (QFT) in curved space-time. To implement this notion, is not strictly necessary to resort to ad hoc scalar fields, as usually done in the literature (e.g. in quintessence formulations and the like). A "running" Lambda term can be expected on very similar grounds as one expects (and observes) the running of couplings and masses with a physical energy scale in QFT. Furthermore, the experimental evidence that the equation of state of the dark energy could be evolving with time/redshift (including the possibility that it might currently behave phantom-like) suggests that a time-variable Lambda term (possibly accompanied by a variable Newton's gravitational coupling G=G(t)) could account in a natural way for all these features. Remarkably enough, a class of these models (the "new cosmon") could even be the clue for solving the old cosmological constant problem, including the coincidence problem.

Joan Sola

2011-02-09T23:59:59.000Z

191

Density Perturbations for Running Cosmological Constant  

E-Print Network [OSTI]

The dynamics of density and metric perturbations is investigated for the previously developed model where the decay of the vacuum energy into matter (or vice versa) is due to the renormalization group (RG) running of the cosmological constant (CC) term. The evolution of the CC depends on the single parameter \

Julio C. Fabris; Ilya L. Shapiro; Joan Sola

2007-01-26T23:59:59.000Z

192

Cosmology at the Beach Lecture: Wayne Hu  

ScienceCinema (OSTI)

Wayne Hu lectures on Secondary Anisotropy in the CMB. The lecture is the first in a series of 3 he delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Wayne Hu

2010-01-08T23:59:59.000Z

193

Cosmology with Coupled Gravity and Dark Energy  

E-Print Network [OSTI]

Dark energy is a fundamental constituent of our universe, its status in the cosmological field equation should be equivalent to that of gravity. Here we construct a dark energy and matter gravity coupling (DEMC) model of cosmology in a way that dark energy and gravity are introduced into the cosmological field equation in parallel with each other from the beginning. The DEMC universe possesses a composite symmetry from global Galileo invariance and local Lorentz invariance. The observed evolution of the universe expansion rate at redshift z>1 is in tension with the standard LCDM model, but can be well predicted by the DEMC model from measurements of only nearby epochs. The so far most precise measured expansion rate at high z is quite a bit slower than the expectations from LCDM, but remarkably consistent with that from DEMC. It is hoped that the DEMC scenario can also help to solve other existing challenges to cosmology: large scale anomalies in CMB maps and large structures up to about 10^3 Mpc of a quasar group. The DEMC universe is a well defined mechanical system. From measurements we can quantitatively evaluate its total rest energy, present absolute radius and expanding speed.

Ti-Pei Li

2014-09-01T23:59:59.000Z

194

Scalar potentials out of canonical quantum cosmology  

E-Print Network [OSTI]

Using canonical quantization of a flat FRW cosmological model containing a real scalar field $\\phi$ endowed with a scalar potential $V(\\phi)$, we are able to obtain exact and semiclassical solutions of the so called Wheeler-DeWitt equation for a particular family of scalar potentials. Some features of the solutions and their classical limit are discussed.

W. Guzman; M. Sabido; J. Socorro; L. Arturo Urena-Lopez

2005-06-06T23:59:59.000Z

195

The Cosmological Constant and the String Landscape  

E-Print Network [OSTI]

Theories of the cosmological constant fall into two classes, those in which the vacuum energy is fixed by the fundamental theory and those in which it is adjustable in some way. For each class we discuss key challenges. The string theory landscape is an example of an adjustment mechanism. We discuss the status of this idea, and future directions.

Joseph Polchinski

2006-04-21T23:59:59.000Z

196

TECHNOLOGY DEVELOPMENT PROJECT PLAN Advanced Technology Large Aperture Space Telescope  

E-Print Network [OSTI]

(ATLAST) A Roadmap for UVIOR Technology, 2010-2020 24 April, 2009 T. Tupper Hyde, ATLAST TechnologistTECHNOLOGY DEVELOPMENT PROJECT PLAN for the Advanced Technology Large Aperture Space Telescope, and Ronald Polidan. #12;Advanced Technology Large-Aperture Space Telescope (ATLAST) 22 TABLE OF CONTENTS 1

Sirianni, Marco

197

THE CHERENKOV TELESCOPE ARRAY for the CTA Consortium  

E-Print Network [OSTI]

The Cherenkov Telescope Array (CTA) is a next-generation observatory proposed for very high-energy gamma rays imaging air Cherenkov telescopes (IACTs), cover an energy range of about four decades (from a few tens of GeV to above 100 TeV), and to enhance angular and energy resolutions. CTA will have a large discovery

Boyer, Edmond

198

Muon Telescope By Nandita Sampath and Izzy Harrison  

E-Print Network [OSTI]

Muon Telescope By Nandita Sampath and Izzy Harrison #12;Abstract We wanted to determine whether the count rate of muons per hour would be affected if we changed the angle that our muon telescope pointed to the roof of the parking garage so the muons could not be affected by surrounding

California at Santa Cruz, University of

199

Atmospheric dispersion in very large telescopes with adaptive optics  

Science Journals Connector (OSTI)

......be put facing the telescope mirrors and theplano-convex lens...the beam of light from the mirrors to the focus to a collimated...lenses, and similarly the Schwarzschild (1905a, b, c) coefficients...31 cmto telescope focus mirror I I I I I T I~ 6.540 0......

Charles G. Wynne

1997-02-11T23:59:59.000Z

200

SST-GATE: A dual mirror telescope for the Cherenkov Telescope Array  

E-Print Network [OSTI]

The Cherenkov Telescope Array (CTA) will be the world's first open observatory for very high energy gamma-rays. Around a hundred telescopes of different sizes will be used to detect the Cherenkov light that results from gamma-ray induced air showers in the atmosphere. Amongst them, a large number of Small Size Telescopes (SST), with a diameter of about 4 m, will assure an unprecedented coverage of the high energy end of the electromagnetic spectrum (above ~1TeV to beyond 100 TeV) and will open up a new window on the non-thermal sky. Several concepts for the SST design are currently being investigated with the aim of combining a large field of view (~9 degrees) with a good resolution of the shower images, as well as minimizing costs. These include a Davies-Cotton configuration with a Geiger-mode avalanche photodiode (GAPD) based camera, as pioneered by FACT, and a novel and as yet untested design based on the Schwarzschild-Couder configuration, which uses a secondary mirror to reduce the plate-scale and to all...

Zech, A; Blake, S; Boisson, C; Costille, C; De-Frondat, F; Dournaux, J -L; Dumas, D; Fasola, G; Greenshaw, T; Hervet, O; Huet, J -M; Laporte, P; Rulten, C; Savoie, D; Sayede, F; Schmoll, J

2013-01-01T23:59:59.000Z

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.


201

Design of a telescope pointing and tracking subsystem for the Big Bear Solar Observatory New Solar Telescope  

E-Print Network [OSTI]

, California, U.S.A.; bNew Jersey Institute of Technology, Newark, New Jersey, U.S.A. ABSTRACT The New SolarDesign of a telescope pointing and tracking subsystem for the Big Bear Solar Observatory New Solar Telescope J. R. Varsika and G.Yangb aBig Bear Solar Observatory, 40386 North Shore Lane, Big Bear City

202

HOBBY-EBERLY TELESCOPE The Hobby-Eberly Telescope is operated by McDonald Observatory on behalf of the  

E-Print Network [OSTI]

(VIRUS) instrument is being built to support observations for the Hobby-Eberly Telescope Dark Energy The Hobby Eberly Telescope Dark Energy Experiment (HETDEX) is a project aimed at looking for Dark Energy (5000 square degrees) blind survey for Lyman alpha emitting galaxies at redshifts z

203

Real-time condition assessment of RAPTOR telescope systems  

SciTech Connect (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

204

E-Print Network 3.0 - advanced compton telescope Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Detector Subsystem Summary: COMPTEL Compton Telescope on CGRO COS-B European Gamma-ray Astronomy Satellite DAPNIA Departement d... Telescope AGILE Astro-rivelatore Gamma a...

205

E-Print Network 3.0 - area telescope measurements Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

focused telescope: Requirement of on-off- measurements With exception of: gamma-ray bursts & solar flares short time... Compton telescopes would measure: ... Source:...

206

Cosmological perturbations in f(T) gravity  

SciTech Connect (OSTI)

We investigate the cosmological perturbations in f(T) gravity. Examining the pure gravitational perturbations in the scalar sector using a diagonal vierbein, we extract the corresponding dispersion relation, which provides a constraint on the f(T) Ansaetze that lead to a theory free of instabilities. Additionally, upon inclusion of the matter perturbations, we derive the fully perturbed equations of motion, and we study the growth of matter overdensities. We show that f(T) gravity with f(T) constant coincides with General Relativity, both at the background as well as at the first-order perturbation level. Applying our formalism to the power-law model we find that on large subhorizon scales (O(100 Mpc) or larger), the evolution of matter overdensity will differ from {Lambda}CDM cosmology. Finally, examining the linear perturbations of the vector and tensor sectors, we find that (for the standard choice of vierbein) f(T) gravity is free of massive gravitons.

Chen, Shih-Hung; Dent, James B. [Department of Physics and School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287-1404 (United States); Dutta, Sourish [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Saridakis, Emmanuel N. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China)

2011-01-15T23:59:59.000Z

207

A Cosmological Model of Thermodynamic Open Universe  

E-Print Network [OSTI]

In this paper we have given a generalisation of the earlier work by Prigogine et al. who have constructed a phenomenological model of entropy production via particle creation in the very early universe generated out of the vacuum rather than from a singularity, by including radiation also as the energy source and tried to develop an alternative cosmological model in which particle creation prevents the big bang. We developed Radiation dominated model of the universe which shows a general tendency that (i) it originates from instability of vacuum rather than from a singularity. (ii) Up to a characteristic time cosmological quantities like density, pressure, Hubble constant and expansion parameter vary rapidly with time. (iii) After the characteristic time these quantities settles down and the models are turned into de-sitter type model with uniform matter, radiation, creation densities and Hubble's constant H. The de-sitter regime survives during a decay time then connects continuously to a usual adiabatic mat...

Goswami, G K

2012-01-01T23:59:59.000Z

208

A Spinor Model for Quantum Cosmology  

E-Print Network [OSTI]

The question of the interpretation of Wheeler-DeWitt solutions in the context of cosmological models is addressed by implementing the Hamiltonian constraint as a spinor wave equation in minisuperspace. We offer a relative probability interpretation based on a non-closed vector current in this space and a prescription for a parametrisation of classical solutions in terms of classical time. Such a prescription can accommodate classically degenerate metrics describing manifolds with signature change. The relative probability density, defined in terms of a Killing vector of the Dewitt metric on minisuperspace, should permit one to identify classical loci corresponding to geometries for a classical manifold. This interpretation is illustrated in the context of a quantum cosmology model for two-dimensional dilaton gravity.

T Dereli; M Onder; R W Tucker

1994-03-02T23:59:59.000Z

209

Cosmology of a Lorentz violating Galileon theory  

E-Print Network [OSTI]

We modify the scalar Einstein-aether theory by breaking the Lorentz invariance of a gravitational theory coupled to a Galileon type scalar field. This is done by introducing a Lagrange multiplier term into the action, thus ensuring that the gradient of the scalar field is time-like, with unit norm. The resulting theory is then generally invariant at the level of action, breaking the Lorentz invariance at the level of equations of motion. The theory can also be considered as an extension to the mimetic dark matter theory, by adding some derivative self interactions to the action, which keeps the equations of motion at most second order in time derivatives. The cosmological implications of the model are discussed in detail. In particular, we show that a matter dominated (dust) universe experiences a late time acceleration. The cosmological implications of a special coupling between the scalar field and the trace of the energy-momentum tensor are also explored.

Haghani, Zahra; Sepangi, Hamid Reza; Shahidi, Shahab

2015-01-01T23:59:59.000Z

210

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

SciTech Connect (OSTI)

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

211

Gamma Ray Bursts as cosmological tools  

E-Print Network [OSTI]

The use of Gamma Ray Bursts as ``standard candles'' has been made possible by the recent discovery of a very tight correlation between their rest frame intrinsic properties. This correlation relates the GRB prompt emission peak spectral energy E_peak to the energy E_gamma corrected for the collimation angle theta_jet of these sources. The possibility to use GRBs to constrain the cosmological parameters and to study the nature of Dark Energy are very promising.

G. Ghirlanda; G. Ghisellini; L. Nava; C. Firmani

2005-12-30T23:59:59.000Z

212

Gamma Ray Bursts as Cosmological Tools  

Science Journals Connector (OSTI)

The use of Gamma Ray Bursts as “standard candles” has been made possible by the recent discovery of a very tight correlation between their rest frame intrinsic properties. This correlation relates the GRB prompt emission peak spectral energy E peak to the energy E ? corrected for the collimation angle ?jet of these sources. The possibility to use GRBs to constrain the cosmological parameters and to study the nature of Dark Energy are very promising.

G. Ghirlanda; G. Ghisellini; L. Nava; C. Firmani

2005-01-01T23:59:59.000Z

213

Cosmological Constant Problems and Renormalization Group  

E-Print Network [OSTI]

The Cosmological Constant Problem emerges when Quantum Field Theory is applied to the gravitational theory, due to the enormous magnitude of the induced energy of the vacuum. The unique known solution of this problem involves an extremely precise fine-tuning of the vacuum counterpart. We review a few of the existing approaches to this problem based on the account of the quantum (loop) effects and pay special attention to the ones involving the renormalization group.

Ilya L. Shapiro; Joan Sola

2007-01-05T23:59:59.000Z

214

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

2005-06-16T23:59:59.000Z

215

Cosmological parameter estimation: impact of CMB aberration  

SciTech Connect (OSTI)

The peculiar motion of an observer with respect to the CMB rest frame induces an apparent deflection of the observed CMB photons, i.e. aberration, and a shift in their frequency, i.e. Doppler effect. Both effects distort the temperature multipoles a{sub lm}'s via a mixing matrix at any l. The common lore when performing a CMB based cosmological parameter estimation is to consider that Doppler affects only the l = 1 multipole, and neglect any other corrections. In this paper we reconsider the validity of this assumption, showing that it is actually not robust when sky cuts are included to model CMB foreground contaminations. Assuming a simple fiducial cosmological model with five parameters, we simulated CMB temperature maps of the sky in a WMAP-like and in a Planck-like experiment and added aberration and Doppler effects to the maps. We then analyzed with a MCMC in a Bayesian framework the maps with and without aberration and Doppler effects in order to assess the ability of reconstructing the parameters of the fiducial model. We find that, depending on the specific realization of the simulated data, the parameters can be biased up to one standard deviation for WMAP and almost two standard deviations for Planck. Therefore we conclude that in general it is not a solid assumption to neglect aberration in a CMB based cosmological parameter estimation.

Catena, Riccardo [Institut für Theoretische Physik, Friedrich-Hund-Platz 1, 37077 Göttingen (Germany); Notari, Alessio, E-mail: riccardo.catena@theorie.physik.uni-goettingen.de, E-mail: notari@ffn.ub.es [Departament de Física Fondamental i Institut de Ciéncies del Cosmos, Universitat de Barcelona, Martí i Franqués 1, 08028 Barcelona (Spain)

2013-04-01T23:59:59.000Z

216

Cosmological supersymmetric model of dark energy  

Science Journals Connector (OSTI)

Recently, a supersymmetric model of dark energy coupled to cold dark matter, the supersymmetron, has been proposed. In the absence of cold dark matter, the supersymmetron field converges to a supersymmetric minimum with a vanishing cosmological constant. When cold dark matter is present, the supersymmetron evolves to a matter-dependent minimum where its energy density does not vanish and could lead to the present acceleration of the Universe. The supersymmetron generates a short-ranged fifth force which evades gravitational tests. It could lead to observable signatures on structure formation due to a very strong coupling to dark matter. We investigate the cosmological evolution of the field, focusing on the linear perturbations and the spherical collapse and find that observable modifications in structure formation can indeed exist. Unfortunately, we find that when the growth rate of perturbations is in agreement with observations, an additional cosmological constant is required to account for dark energy. In this case, effects on large-scale structures are still present at the nonlinear level which are investigated using the spherical collapse approach.

Philippe Brax; Anne-Christine Davis; Hans A. Winther

2012-04-18T23:59:59.000Z

217

Bianchi type II brane-world cosmologies (U>~0)  

Science Journals Connector (OSTI)

The asymptotic properties of the Bianchi type II cosmological model in the brane-world scenario are investigated. The matter content is assumed to be a combination of a perfect fluid and a minimally coupled scalar field that is restricted to the brane. The isotropic brane-world solution is determined to represent the initial singularity in all brane-world cosmologies. Additionally, it is shown that it is the kinetic energy of the scalar field which dominates the initial dynamics in these brane-world cosmologies. It is important to note that the dynamics of these brane-world cosmologies is not necessarily asymptotic to general relativistic cosmologies to the future in the case of a zero four-dimensional cosmological constant.

R. J. van den Hoogen and J. Ibañez

2003-04-24T23:59:59.000Z

218

Brane World Cosmologies with Varying Speed of Light  

E-Print Network [OSTI]

We study cosmologies in the Randall-Sundrum models, incorporating the possibility of time-varying speed of light and Newton's constant. The cosmologies with varying speed of light (VSL) were proposed by Moffat and by Albrecht and Magueijo as an alternative to inflation for solving the cosmological problems. We consider the case in which the speed of light varies with time after the radion or the scale of the extra dimension has been stabilized. We elaborate on the conditions under which the flatness problem and the cosmological constant problem can be resolved. We find that the RS models are more restrictive about possible desirable VSL cosmological models than the standard general relativity. Particularly, the VSL cosmologies may provide with a possible mechanism for bringing the quantum corrections to the fine-tuned brane tensions after the SUSY breaking under control.

Donam Youm

2001-01-31T23:59:59.000Z

219

Minimizing high spatial frequency residual in active space telescope mirrors  

E-Print Network [OSTI]

The trend in future space telescopes is towards large apertures and lightweight, rib-stiffened, and actively controlled deformable mirrors. These mirror architectures permit the development of segmented and deployed primary ...

Gray, Thomas, S.M. (Thomas L.) Massachusetts Institute of Technology

2008-01-01T23:59:59.000Z

220

Cross section dependence of event rates at neutrino telescopes  

E-Print Network [OSTI]

We examine the dependence of event rates at neutrino telescopes on the neutrino-nucleon cross section for neutrinos with energy above 1 PeV, and contrast the results with those for cosmic ray experiments. Scaling of the ...

Marfatia, Danny; Seckel, D.; McKay, D. W.; Hussain, S.

2006-10-20T23:59:59.000Z

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.


221

An Australian Icon - Planning and Construction of the Parkes Telescope  

E-Print Network [OSTI]

By almost any measure, the Parkes Radio Telescope is the most successful scientific instrument ever built in Australia. The telescope is unsurpassed in terms of the number of astronomers, both national and international, who have used the instrument, the number of research papers that have flowed from their research, and the sheer longevity of its operation (now over fifty years). The original planners and builders could not have envisaged that the telescope would have such an extraordinarily long and productive future. From the start, it was an international project by CSIRO that in the 1950s launched Australia into the world of `big science'. Partly funded by the US Carnegie and Rockefeller foundations, it was designed in England by Freeman Fox & Partners, and built by the German firm MAN. This article will give an overview of the origins of the idea for the telescope and the funding, planning and construction of the Parkes dish over the period 1954 to 1961.

Robertson, Peter

2012-01-01T23:59:59.000Z

222

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

223

Cosmological Evolution of Fundamental Constants: From Theory to Experiment  

E-Print Network [OSTI]

In this paper we discuss a possible cosmological time evolution of fundamental constants from the theoretical and experimental point of views. On the theoretical side, we explain that such a cosmological time evolution is actually something very natural which can be described by mechanisms similar to those used to explain cosmic inflation. We then discuss implications for grand unified theories, showing that the unification condition of the gauge coupling could evolve with cosmological time. Measurements of the electron-to-proton mass ratio can test grand unified theories using low energy data. Following the theoretical discussion, we review the current status of precision measurements of fundamental constants and their potential cosmological time dependence.

Xavier Calmet; Matthias Keller

2014-12-05T23:59:59.000Z

224

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

225

Thermodynamic Stability of a Multi-Bubble Cosmological Model  

E-Print Network [OSTI]

Multibubble solutions for a cosmological model which lead to thermal inflationary states due to a semi-classical tunneling of gravity are calculated.

G. Horwitz; O. Fonarev

1994-10-20T23:59:59.000Z

226

Phenomenology and cosmology of weakly coupled string theory  

E-Print Network [OSTI]

ph/9805320 May 1998 Phenomenology and cosmology of weaklyThe important point for phenomenology is the decomposition2]. Implications for phenomenology and open questions The

Gaillard, Mary K.

1998-01-01T23:59:59.000Z

227

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

228

The next generation Cherenkov Telescope Array observatory: CTA  

E-Print Network [OSTI]

The Cherenkov Telescope Array (CTA) is a large collaborative effort aimed at the design and operation of an observatory dedicated to the VHE gamma-ray astrophysics in the energy range 30 GeV-100 TeV, which will improve by about one order of magnitude the sensitivity with respect to the current major arrays (H.E.S.S., MAGIC, and VERITAS). In order to achieve such improved performance, for both the northern and southern CTA sites, four units of 23m diameter Large Size Telescopes (LSTs) will be deployed close to the centre of the array with telescopes separated by about 100m. A larger number (about 25 units) of 12m Medium Size Telescopes (MSTs, separated by about 150m), will cover a larger area. The southern site will also include up to 24 Schwarzschild-Couder dual-mirror medium-size Telescopes (SCTs) with the primary mirror diameter of 9.5m. Above a few TeV, the Cherenkov light intensity is such that showers can be detected even well outside the light pool by telescopes significantly smaller than the MSTs. To a...

Vercellone, Stefano

2014-01-01T23:59:59.000Z

229

3D acoustic imaging applied to the Baikal Neutrino Telescope  

E-Print Network [OSTI]

A hydro-acoustic imaging system was tested in a pilot study on distant localization of elements of the Baikal underwater neutrino telescope. For this innovative approach, based on broad band acoustic echo signals and strictly avoiding any active acoustic elements on the telescope, the imaging system was temporarily installed just below the ice surface, while the telescope stayed in its standard position at 1100 m depth. The system comprised an antenna with four acoustic projectors positioned at the corners of a 50 meter square; acoustic pulses were "linear sweep-spread signals" - multiple-modulated wide-band signals (10-22 kHz) of 51.2 s duration. Three large objects (two string buoys and the central electronics module) were localized by the 3D acoustic imaging, with a accuracy of ~0.2 m (along the beam) and ~1.0 m (transverse). We discuss signal forms and parameters necessary for improved 3D acoustic imaging of the telescope, and suggest a layout of a possible stationary bottom based 3D imaging setup. The presented technique may be of interest for neutrino telescopes of km3-scale and beyond, as a flexible temporary or as a stationary tool to localize basic telescope elements, while these are completely passive.

K. G. Kebkal; R. Bannasch; O. G. Kebkal; A. I. Panfilov; R. Wischnewski

2008-11-07T23:59:59.000Z

230

The next generation Cherenkov Telescope Array observatory: CTA  

Science Journals Connector (OSTI)

Abstract The Cherenkov Telescope Array (CTA) is a large collaborative effort aimed at the design and operation of an observatory dedicated to the very high-energy gamma-ray astrophysics in the energy range 30 GeV–100 TeV, which will improve by about one order of magnitude the sensitivity with respect to the current major arrays (H.E.S.S., MAGIC, and VERITAS). In order to achieve such improved performance, for both the northern and southern CTA sites, four units of 23 m diameter Large Size Telescopes (LSTs) will be deployed close to the centre of the array with telescopes separated by about 100 m. A larger number (about 25 units) of 12 m Medium Size Telescopes (MSTs, separated by about 150 m), will cover a larger area. The southern site will also include up to 24 Schwarzschild–Couder dual-mirror medium-size Telescopes (SCTs) with the primary mirror diameter of 9.5 m. Above a few TeV, the Cherenkov light intensity is such that showers can be detected even well outside the light pool by telescopes significantly smaller than the MSTs. To achieve the required sensitivity at high energies, a huge area on the ground needs to be covered by Small Size Telescopes (SSTs) with a field of view of about 10° and an angular resolution of about 0.2°, making the dual-mirror configuration very effective. The SST sub-array will be composed of 50–70 telescopes with a mirror area of about 5–10 m2 and about 300 m spacing, distributed across an area of about 10 km2. In this presentation we will focus on the innovative solution for the optical design of the medium and small size telescopes based on a dual-mirror configuration. This layout will allow us to reduce the dimension and the weight of the camera at the focal plane of the telescope, to adopt Silicon-based photo-multipliers as light detectors thanks to the reduced plate-scale, and to have an optimal imaging resolution on a wide field of view.

S. Vercellone

2014-01-01T23:59:59.000Z

231

Cryogenic optical performance of the ASTRO-F SiC telescope  

Science Journals Connector (OSTI)

The lightweight cryogenic telescope on board the Japanese infrared astronomical satellite, ASTRO-F, which

Kaneda, Hidehiro; Onaka, Takashi; Nakagawa, Takao; Enya, Keigo; Murakami, Hiroshi; Yamashiro, Ryoji; Ezaki, Tatsuhiko; Numao, Yasuyuki; Sugiyama, Yoshikazu

2005-01-01T23:59:59.000Z

232

E-Print Network 3.0 - accelerated cosmological lattice Sample...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

, and the accelerating expansion of the universe. VUW Matt Visser Cosmology: Dark energy, dark matter, and all that... : Accelerating expansion Matt Visser Cosmology: Dark...

233

Precision cosmology in muddy waters: cosmological constraints and N-body codes  

Science Journals Connector (OSTI)

......have performed a box-car smoothing of the correlation...constitutes a plausible alternative to various other ad hoc...matrix has been box-car smoothed by a square...addition, when exploring alternative cosmological models...parameters are: dark energy EOS parameters w 0......

Robert E. Smith; Darren S. Reed; Doug Potter; Laura Marian; Martin Crocce; Ben Moore

2014-01-01T23:59:59.000Z

234

Cosmological evolution and hierarchical galaxy formation  

E-Print Network [OSTI]

We provide a new multi-waveband compilation of the data describing the cosmological evolution of quasars, and discuss a model that attributes the evolution to variation in the rate of merging between dark halos in a hierarchical universe. We present a new Press-Schechter calculation of the expected merger rate and show that this can reproduce the principal features of the evolution. We also show that the evolution in the star-formation history of the universe is well-described by this model.

L. Miller; W. J. Percival

1998-09-24T23:59:59.000Z

235

A New Approach to Cosmological Bulk Viscosity  

E-Print Network [OSTI]

We examine the cosmological consequences of an alternative to the standard expression for bulk viscosity, one which was proposed to avoid the propagation of superluminal signals without the necessity of extending the space of variables of the theory. The Friedmann equation is derived for this case, along with an expression for the effective pressure. We find solutions for the evolution of the density of a viscous component, which differs markedly from the case of conventional Eckart theory; our model evolves toward late-time phantom-like behavior with a future singularity. Entropy production is addressed, and some similarities and differences to approaches based on the Mueller-Israel-Stewart theory are discussed.

Disconzi, Marcelo M; Scherrer, Robert J

2014-01-01T23:59:59.000Z

236

Cosmological Evolution of Pilgrim Dark Energy  

E-Print Network [OSTI]

We study pilgrim dark energy model by taking IR cut-offs as particle and event horizons as well as conformal age of the universe. We derive evolution equations for fractional energy density and equation of state parameters for pilgrim dark energy. The phantom cosmic evolution is established in these scenarios which is well supported by the cosmological parameters such as deceleration parameter, statefinder parameters and phase space of $\\omega_\\vartheta$ and $\\omega'_\\vartheta$. We conclude that the consistent value of parameter $\\mu$ is $\\mu<0$ in accordance with the current Planck and WMAP$9$ results.

Sharif, M

2015-01-01T23:59:59.000Z

237

Scalar field collapse with negative cosmological constant  

E-Print Network [OSTI]

The formation of black holes or naked singularities is studied in a model in which a homogeneous time-dependent scalar field with an exponential potential couples to four dimensional gravity with negative cosmological constant. An analytic solution is derived and its consequences are discussed. The model depends only on one free parameter, which determines the equation of state and decides the fate of the spacetime. Without fine tuning the value of this parameter the collapse ends in a generic formation of a black hole or a naked singularity. The latter case violates the cosmic censorship conjecture.

R. Baier; Hiromichi Nishimura; S. A. Stricker

2014-10-13T23:59:59.000Z

238

Scalar field collapse with negative cosmological constant  

E-Print Network [OSTI]

The formation of black holes or naked singularities is studied in a model in which a homogeneous time-dependent scalar field with an exponential potential couples to four dimensional gravity with negative cosmological constant. An analytic solution is derived and its consequences are discussed. The model depends only on one free parameter which determines the equation of state and decides the fate of the spacetime. Depending on the value of this parameter the collapse ends in a black hole or a naked singularity. The latter case violates the cosmic censorship conjecture.

Baier, R; Stricker, S A

2014-01-01T23:59:59.000Z

239

Non-Gaussian signatures of tachyacoustic cosmology  

SciTech Connect (OSTI)

I investigate non-Gaussian signatures in the context of tachyacoustic cosmology, that is, a noninflationary model with superluminal speed of sound. I calculate the full non-Gaussian amplitude A, its size f{sub NL}, and corresponding shapes for a red-tilted spectrum of primordial scalar perturbations. Specifically, for cuscuton-like models I show that f{sub NL} ? O(1), and the shape of its non-Gaussian amplitude peaks for both equilateral and local configurations, the latter being dominant. These results, albeit similar, are quantitatively distinct from the corresponding ones obtained by Magueijo et al. in the context of superluminal bimetric models.

Bessada, Dennis, E-mail: dennis.bessada@unifesp.br [UNIFESP — Universidade Federal de São Paulo, Laboratório de Física Teórica e Computação Científica, Rua São Nicolau, 210, 09913-030, Diadema, SP (Brazil)

2012-09-01T23:59:59.000Z

240

Singularities of varying light speed cosmologies  

E-Print Network [OSTI]

We study the possible singularities of isotropic cosmological models that have a varying speed of light as well as a varying gravitational constant. The field equations typically reduce to two dimensional systems which are then analyzed both by dynamical systems techniques in phase space and by applying the method of asymptotic splittings. In the general case we find initially expanding closed models which recollapse to a future singularity and open universes that are eternally expanding towards the future. The precise nature of the singularities is also discussed.

John Miritzis; Spiros Cotsakis

2006-09-21T23:59:59.000Z

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.


241

Cosmological Constant and the Speed of Light  

E-Print Network [OSTI]

By exploring the relationship between the propagation of electromagnetic waves in a gravitational field and the light propagation in a refractive medium, it is shown that, in the presence of a positive cosmological constant, the velocity of light will be smaller than its special relativity value. Then, restricting again to the domain of validity of geometrical optics, the same result is obtained in the context of wave optics. It is argued that this phenomenon and the anisotropy in the velocity of light in a gravitational field are produced by the same mechanism.

W. R. Esposito Miguel; J. G. Pereira

2000-06-28T23:59:59.000Z

242

ON PROVING FUTURE STABILITY OF COSMOLOGICAL SOLUTIONS WITH ACCELERATED EXPANSION  

E-Print Network [OSTI]

ON PROVING FUTURE STABILITY OF COSMOLOGICAL SOLUTIONS WITH ACCELERATED EXPANSION HANS RINGSTR at an accelerated rate. As a consequence, it is of interest to prove that cosmological solutions to Ein- stein's equations with accelerated expansion are future stable. That is the topic of the present contribution

Ringström, Hans

243

Cosmology as Science: From Inflation to the Future  

ScienceCinema (OSTI)

Recent developments in cosmology bring to the forefront fundamental questions about our ability to falsify various fundamental assumptions about the universe.  I will discuss three issues that reflect different aspects of these questions:  (1) "Proving" Inflation (2) Anthropic "Explanations" (3) Cosmology of the far future.

Lawrence Krauss

2010-01-08T23:59:59.000Z

244

BUILDING COSMOLOGICAL MODELS VIA NONCOMMUTATIVE GEOMETRY MATILDE MARCOLLI  

E-Print Network [OSTI]

of theoretical high energy physics models that are capable of producing a range of predictions, bothBUILDING COSMOLOGICAL MODELS VIA NONCOMMUTATIVE GEOMETRY MATILDE MARCOLLI and cosmology to formulate testable predictions that can be confronted with the data. While model building

Marcolli, Matilde

245

Advanced Dark Energy Physics Telescope (ADEPT)  

SciTech Connect (OSTI)

In 2006, we proposed to NASA a detailed concept study of ADEPT (the Advanced Dark Energy Physics Telescope), a potential space mission to reliably measure the time-evolution of dark energy by conducting the largest effective volume survey of the universe ever done. A peer-review panel of scientific, management, and technical experts reported back the highest possible 'excellent' rating for ADEPT. We have since made substantial advances in the scientific and technical maturity of the mission design. With this Department of Energy (DOE) award we were granted supplemental funding to support specific extended research items that were not included in the NASA proposal, many of which were intended to broadly advance future dark energy research, as laid out by the Dark Energy Task Force (DETF). The proposed work had three targets: (1) the adaptation of large-format infrared arrays to a 2 micron cut-off; (2) analytical research to improve the understanding of the dark energy figure-of- merit; and (3) extended studies of baryon acoustic oscillation systematic uncertainties. Since the actual award was only for {approx}10% of the proposed amount item (1) was dropped and item (2) work was severely restricted, consistent with the referee reviews of the proposal, although there was considerable contradictions between reviewer comments and several comments that displayed a lack of familiarity with the research. None the less, item (3) was the focus of the work. To characterize the nature of the dark energy, ADEPT is designed to observe baryon acoustic oscillations (BAO) in a large galaxy redshift survey and to obtain substantial numbers of high-redshift Type Ia supernovae (SNe Ia). The 2003 Wilkinson Microwave Anisotropy Probe (WMAP) made a precise determination of the BAO 'standard ruler' scale, as it was imprinted on the cosmic microwave background (CMB) at z {approx} 1090. The standard ruler was also imprinted on the pattern of galaxies, and was first detected in 2005 in Sloan Digital Sky Survey (SDSS) data. A measurement of the BAO standard ruler as a function of time (or redshift) would provide powerful and reliable observational data to shed light on dark energy. In particular, the BAO data provide the angular diameter distance to each redshift, and directly give the expansion rate, H(z), at each redshift. The SNe measurements provide luminosity distances. A space mission is required to obtain the three-dimensional position of enormous numbers of galaxies at high redshift. As recognized by the Dark Energy Task Force, BAO systematic errors are naturally low. The following are the key findings: (1) The BAO method is robust. (2) Separation of the spectral and imaging detection focal planes vastly improves spectral identifications. (3) Prisms instead of grisms provide higher throughput and cleaner spectra. Prisms are clearly superior. (4) Lower prism dispersions improve signal-to-noise but high prism dispersions improve systematic. To ensure that the experiment is not systematic limited, a high dispersion should be used. (5) Counter-dispersion of the spectra reduces systematic errors on the redshift determination and assists in the reduction of confusion. (6) Small rolls are very effective for the reduction of confusion. (7) Interlopers can be recognized by a variety of methods, which combine to produce a sufficiently 'clean' survey data set so as not to limit the dark energy results. (8) A space mission can measure the BAO signature to the cosmic variance limit, limited only by statistics and not by systematic. (9) Density field reconstruction allows for significant BAO accuracy improvements, well beyond that assumed by the Dark Energy Task Force. (10) The BAO method is statistically powerful. It is more powerful than previously estimated, and far more powerful than high redshift Type 1a supernovae, for which the ultimate distance accuracy is limited by flux calibration accuracy. (11) The BAO technique is far simpler than the weak lensing technique and likely to produce more robust dark energy solutions.

Charles L. Bennett

2009-03-26T23:59:59.000Z

246

Summary of One Year Operation of the EUDET CMOS Pixel Telescope  

E-Print Network [OSTI]

Within the EUDET consortium a high resolution pixel beam telescope is being developed. The telescope consists of up to six planes of monolithic active pixel sensors. A flexible data acquisition environment is available for the telescope and the system is equipped with all the required infrastructure. Since the first installation of a demonstrator telescope in 2007, it has been extensively tested and used by various detector R&D groups. The results of test beam measurements are described here, demonstrating the telescope performance.

Ingrid-Maria Gregor

2009-01-06T23:59:59.000Z

247

Evolution of density perturbations in decaying vacuum cosmology  

SciTech Connect (OSTI)

We study cosmological perturbations in the context of an interacting dark energy model, in which the cosmological term decays linearly with the Hubble parameter, with concomitant matter production. A previous joint analysis of the redshift-distance relation for type Ia supernovas, barionic acoustic oscillations, and the position of the first peak in the anisotropy spectrum of the cosmic microwave background has led to acceptable values for the cosmological parameters. Here we present our analysis of small perturbations, under the assumption that the cosmological term, and therefore the matter production, are strictly homogeneous. Such a homogeneous production tends to dilute the matter contrast, leading to a late-time suppression in the power spectrum. Nevertheless, an excellent agreement with the observational data can be achieved by using a higher matter density as compared to the concordance value previously obtained. This may indicate that our hypothesis of homogeneous matter production must be relaxed by allowing perturbations in the interacting cosmological term.

Borges, H. A.; Pigozzo, C. [Instituto de Fisica, Universidade Federal da Bahia, Salvador, BA (Brazil); Carneiro, S. [Instituto de Fisica, Universidade Federal da Bahia, Salvador, BA (Brazil); International Centre for Theoretical Physics, Trieste (Italy); Fabris, J. C. [Institut d'Astrophysique de Paris, Paris (France)

2008-02-15T23:59:59.000Z

248

SKA SA test telescope reveals binary star system South Africa's test telescope reveals secrets of a binary star system and proves the country is able to  

E-Print Network [OSTI]

SKA SA test telescope reveals binary star system South Africa's test telescope reveals secrets, has created huge research and job opportunities. South Africa's Karoo Array Telescope (KAT-7) has at the SKA South Africa. The 64-dish MeerKAT ­ which SKA South Africa director Bernie Fanaroff once described

Jarrett, Thomas H.

249

A Renormalization Group Approach to Relativistic Cosmology  

E-Print Network [OSTI]

We discuss the averaging hypothesis tacitly assumed in standard cosmology. Our approach is implemented in a "3+1" formalism and invokes the coarse graining arguments, provided and supported by the real-space Renormalization Group (RG) methods. Block variables are introduced and the recursion relations written down explicitly enabling us to characterize the corresponding RG flow. To leading order, the RG flow is provided by the Ricci-Hamilton equations studied in connection with the geometry of three-manifolds. The properties of the Ricci-Hamilton flow make it possible to study a critical behaviour of cosmological models. This criticality is discussed and it is argued that it may be related to the formation of sheet-like structures in the universe. We provide an explicit expression for the renormalized Hubble constant and for the scale dependence of the matter distribution. It is shown that the Hubble constant is affected by non-trivial scale dependent shear terms, while the spatial anisotropy of the metric influences significantly the scale-dependence of the matter distribution.

Mauro Carfora; Kamilla Piotrkowska

1995-02-08T23:59:59.000Z

250

Cosmological evolution of a D-brane  

Science Journals Connector (OSTI)

We study the cosmological evolution of a single BPS D-brane coupled to gravity in the absence of potential. When such a D-brane moves in the bulk with nonvanishing velocity, it tends to slow down to zero velocity via mechanisms like gravitational wave leakage to the bulk, losing its kinetic energy to fuel the expansion of the Universe on the D-brane. If the initial velocity of the D-brane is high enough, the Universe on the D-brane undergoes a dustlike stage at early times and an acceleration stage at late times, realizing the original Chaplygin gas model. When the D-brane velocity is initially zero, the D-brane will always remain fixed at some position in the bulk, with the brane tension over the Plank mass squared as a cosmological constant. It is further shown that this kind of fixed brane universe can arise as defects from tachyon inflation on a non-Bogomol’nyi-Prasad-Sommerfeld D-brane with one dimension higher.

Huiquan Li

2011-03-01T23:59:59.000Z

251

Planck 2015 results. XIII. Cosmological parameters  

E-Print Network [OSTI]

We present results based on full-mission Planck observations of temperature and polarization anisotropies of the CMB. These data are consistent with the six-parameter inflationary LCDM cosmology. From the Planck temperature and lensing data, for this cosmology we find a Hubble constant, H0= (67.8 +/- 0.9) km/s/Mpc, a matter density parameter Omega_m = 0.308 +/- 0.012 and a scalar spectral index with n_s = 0.968 +/- 0.006. (We quote 68% errors on measured parameters and 95% limits on other parameters.) Combined with Planck temperature and lensing data, Planck LFI polarization measurements lead to a reionization optical depth of tau = 0.066 +/- 0.016. Combining Planck with other astrophysical data we find N_ eff = 3.15 +/- 0.23 for the effective number of relativistic degrees of freedom and the sum of neutrino masses is constrained to Spatial curvature is found to be |Omega_K| < 0.005. For LCDM we find a limit on the tensor-to-scalar ratio of r <0.11 consistent with the B-mode constraints fr...

,

2015-01-01T23:59:59.000Z

252

Holographic Dark Energy with Cosmological Constant  

E-Print Network [OSTI]

Inspired by the multiverse scenario, we study a heterotic dark energy model in which there are two parts, the first being the cosmological constant and the second being the holographic dark energy, thus this model is named the $\\Lambda$HDE model. By studying the $\\Lambda$HDE model theoretically, we find that the parameters $c$ and $\\Omega_{hde}$ are divided into a few domains in which the fate of the universe is quite different. We investigate dynamical behaviors of this model, and especially the future evolution of the universe. We perform fitting analysis on the cosmological parameters in the $\\Lambda$HDE model by using the recent observational data. We find the model yields $\\chi^2_{\\rm min}=426.27$ when constrained by Planck+SNLS3+BAO+HST, comparable to the results of the HDE model (428.20) and the concordant $\\Lambda$CDM model (431.35). At 68.3\\% CL, we obtain $-0.07<\\Omega_{\\Lambda0}<0.68$ and correspondingly $0.04<\\Omega_{hde0}<0.79$, implying at present there is considerable degeneracy bet...

Hu, Yazhou; Li, Nan; Zhang, Zhenhui

2015-01-01T23:59:59.000Z

253

Dynamical dark energy or variable cosmological parameters?  

E-Print Network [OSTI]

One of the main aims in the next generation of precision cosmology experiments will be an accurate determination of the equation of state (EOS) for the dark energy (DE). If the latter is dynamical, the resulting barotropic index \\omega should exhibit a non-trivial evolution with the redshift. Usually this is interpreted as a sign that the mechanism responsible for the DE is related to some dynamical scalar field, and in some cases this field may behave non-canonically (phantom field). Present observations seem to favor an evolving DE with a potential phantom phase near our time. In the literature there is a plethora of dynamical models trying to describe this behavior. Here we show that the simplest option, namely a model with a variable cosmological term, \\Lambda=\\Lambda(t), leads in general to a non-trivial effective EOS, with index \\omega_e, which may naturally account for these data features. We prove that in this case there is always a ``crossing'' of the \\omega_e=-1 barrier near our time. We also show how this effect is modulated (or even completely controled) by a variable Newton's constant G=G(t).

Joan Sola; Hrvoje Stefancic

2005-12-21T23:59:59.000Z

254

Fine tracking system for balloon-borne telescopes  

E-Print Network [OSTI]

We present the results of a study along with a first prototype of a high precision system (? 1 arcsec) for pointing and tracking light (near-infrared) telescopes on board stratospheric balloons. Such a system is essentially composed by a star sensor and by a star tracker, able to recognize the field and to adequately track the telescope, respectively. We present the software aimed at processing the star sensor image and the predictive algorithm that allows the fine tracking of the source at a sub-pixel level. The laboratory tests of the system are described and its performance is analyzed. We demonstrate how such a device, when used at the focal plane of enough large telescopes (2-4m, F/10), is capable to provide (sub-)arcsec diffraction limited images in the near infrared bands.

Ricci, M; Lorenzetti, D

2011-01-01T23:59:59.000Z

255

The Atmospheric Monitoring Strategy for the Cherenkov Telescope Array  

E-Print Network [OSTI]

The Imaging Atmospheric Cherenkov Technique (IACT) is unusual in astronomy as the atmosphere actually forms an intrinsic part of the detector system, with telescopes indirectly detecting very high energy particles by the generation and transport of Cherenkov photons deep within the atmosphere. This means that accurate measurement, characterisation and monitoring of the atmosphere is at the very heart of successfully operating an IACT system. The Cherenkov Telescope Array (CTA) will be the next generation IACT observatory with an ambitious aim to improve the sensitivity of an order of magnitude over current facilities, along with corresponding improvements in angular and energy resolution and extended energy coverage, through an array of Large (23m), Medium (12m) and Small (4m) sized telescopes spread over an area of order ~km$^2$. Whole sky coverage will be achieved by operating at two sites: one in the northern hemisphere and one in the southern hemisphere. This proceedings will cover the characterisation of...

Daniel, M K

2015-01-01T23:59:59.000Z

256

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

SciTech Connect (OSTI)

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

257

Simbol-X Telescope Scientific Calibrations: Requirements and Plans  

SciTech Connect (OSTI)

The Simbol-X telescope characteristics and the mission scientific requirements impose a challenging calibration plan with a number of unprecedented issues. The 20 m focal length implies for the incoming X-ray beam a divergence comparable to the incidence angle of the mirror surface also for 100 m-long facilities. Moreover this is the first time that a direct focussing X-ray telescope will be calibrated on an energy band covering about three decades, and with a complex focal plane. These problems require a careful plan and organization of the measurements, together with an evaluation of the calibration needs in terms of both hardware and software.

Malaguti, G.; Raimondi, L.; Trifoglio, M. [INAF-IASF Bologna (Italy); Angelini, L. [NASA/Goddard Space Flight Center (United States); Moretti, A. [INAF-OABrera (Italy)

2009-05-11T23:59:59.000Z

258

Cosmological model-independent Gamma-ray bursts calibration and its cosmological constraint to dark energy  

SciTech Connect (OSTI)

As so far, the redshift of Gamma-ray bursts (GRBs) can extend to z ? 8 which makes it as a complementary probe of dark energy to supernova Ia (SN Ia). However, the calibration of GRBs is still a big challenge when they are used to constrain cosmological models. Though, the absolute magnitude of GRBs is still unknown, the slopes of GRBs correlations can be used as a useful constraint to dark energy in a completely cosmological model independent way. In this paper, we follow Wang's model-independent distance measurement method and calculate their values by using 109 GRBs events via the so-called Amati relation. Then, we use the obtained model-independent distances to constrain ?CDM model as an example.

Xu, Lixin, E-mail: lxxu@dlut.edu.cn [Institute of Theoretical Physics, School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian, 116024 (China)

2012-04-01T23:59:59.000Z

259

Cosmological Landscape From Nothing: Some Like It Hot  

E-Print Network [OSTI]

We suggest a novel picture of the quantum Universe -- its creation is described by the {\\em density matrix} defined by the Euclidean path integral. This yields an ensemble of universes -- a cosmological landscape -- in a mixed state which is shown to be dynamically more preferable than the pure quantum state of the Hartle-Hawking type. The latter is dynamically suppressed by the infinitely large positive action of its instanton, generated by the conformal anomaly of quantum fields within the cosmological bootstrap (the self-consistent back reaction of hot matter). This bootstrap suggests a solution to the problem of boundedness of the on-shell cosmological action and eliminates the infrared catastrophe of small cosmological constant in Euclidean quantum gravity. The cosmological landscape turns out to be limited to a bounded range of the cosmological constant $\\Lambda_{\\rm min}\\leq \\Lambda \\leq \\Lambda_{\\rm max}$. The domain $\\Lambdalandscape. The dependence of the cosmological constant range on particle phenomenology suggests a possible dynamical selection mechanism for the landscape of string vacua.

A. O. Barvinsky; A. Yu. Kamenshchik

2006-09-13T23:59:59.000Z

260

The Cosmology of Composite Inelastic Dark Matter  

SciTech Connect (OSTI)

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

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

Cosmological origin of anomalous radio background  

SciTech Connect (OSTI)

The ARCADE 2 collaboration has reported a significant excess in the isotropic radio background, whose homogeneity cannot be reconciled with clustered sources. This suggests a cosmological origin prior to structure formation. We investigate several potential mechanisms and show that injection of relativistic electrons through late decays of a metastable particle can give rise to the observed excess radio spectrum through synchrotron emission. However, constraints from the cosmic microwave background (CMB) anisotropy, on injection of charged particles and on the primordial magnetic field, present a challenge. The simplest scenario is with a ?>9 GeV particle decaying into e{sup +}e{sup ?} at a redshift of z ? 5, in a magnetic field of ? 5?G, which exceeds the CMB B-field constraints, unless the field was generated after decoupling. Decays into exotic millicharged particles can alleviate this tension, if they emit synchroton radiation in conjunction with a sufficiently large background magnetic field of a dark U(1)' gauge field.

Cline, James M. [Department of Physics, McGill University, 3600 Rue University, Montréal, Québec, H3A 2T8 Canada (Canada); Vincent, Aaron C., E-mail: jcline@physics.mcgill.ca, E-mail: vincent@ific.uv.es [Instituto de Física Corpuscular, Universitat de València - CSIC, 46071, Valencia (Spain)

2013-02-01T23:59:59.000Z

262

On the geometry of cosmological model building  

E-Print Network [OSTI]

This article analyzes the present anomalies of cosmology from the point of view of integrable Weyl geometry. It uses P.A.M. Dirac's proposal for a weak extension of general relativity, with some small adaptations. Simple models with interesting geometrical and physical properties, not belonging to the Friedmann-Lema\\^{\\i}tre class, are studied in this frame. Those with positive spatial curvature (Einstein-Weyl universes) go well together with observed mass density $\\Omega_m$, CMB, supernovae Ia data, and quasar frequencies. They suggest a physical role for an equilibrium state of the Maxwell field proposed by I.E. Segal in the 1980s (Segal background) and for a time invariant balancing condition of vacuum energy density. The latter leads to a surprising agreement with the BF-theoretical calculation proposed by C. Castro (2002).

Erhard Scholz

2005-11-21T23:59:59.000Z

263

Large extra dimensions and cosmological problems  

Science Journals Connector (OSTI)

We consider a variant of the brane-world model in which the universe is the direct product of a Friedmann-Robertson-Walker (FRW) space and a compact hyperbolic manifold of dimension d>~2. Cosmology in this space is particularly interesting. The dynamical evolution of the space-time leads to the injection of a large entropy into the observable (FRW) universe. The exponential dependence of surface area on distance in hyperbolic geometry makes this initial entropy very large, even if the CHM has a relatively small diameter (in fundamental units). The very large statistical averaging inherent in the collapse of the initial entropy onto the brane acts to smooth out initial inhomogeneities. This smoothing is then sufficient to account for the current homogeneity of the universe. With only mild fine-tuning, the current flatness of the universe can also then be understood. Finally, recent brane-world approaches to the hierarchy problem can be readily realized within this framework.

Glenn D. Starkman; Dejan Stojkovic; Mark Trodden

2001-04-24T23:59:59.000Z

264

Quantum Rainbow Cosmological Model With Perfect Fluid  

E-Print Network [OSTI]

Isotropic quantum cosmological perfect fluid model is studied in the formalism of Rainbow gravity. It is found that the only surviving matter degree of freedom played the role of cosmic time. With the suitable choice of the Rainbow functions it is possible to find the wave packet naturally from the superposition of the wave functions of the Schr$\\ddot{o}$dinger-Wheeler-deWitt equation. The many-worlds interpretation of quantum mechanics is applied to investigate the behavior of the scale factor and the behavior is found to depend on the operator ordering. It is shown that the model in the Rainbow framework may avoid singularity yielding a bouncing non-singular universe.

Majumder, Barun

2013-01-01T23:59:59.000Z

265

Five-Dimensional Cosmological Scaling Solution  

E-Print Network [OSTI]

A five-dimensional Ricci-flat cosmological solution is studied by assuming that the induced 4D matter contains two components: the usual fluid for dark matter as well as baryons and a scalar field with an exponential potential for dark energy. With use of the phase-plane analysis it is shown that there exist two late-time attractors one of which corresponds to a universe dominated by the scalar field alone and the other is a scaling solution in which the energy density of the scalar field remains proportional to that of the dark matter. It is furthermore shown that for this 5D scaling solution the universe expands with the same rate as in the 4D FRW models and not relies on which 4D hypersurface the universe is located in the 5D manifold.

Baorong Chang; Hongya Liu; Huanying Liu; Lixin Xu

2005-05-08T23:59:59.000Z

266

Two cosmological solutions of Regge calculus  

Science Journals Connector (OSTI)

Two cosmological solutions of Regge calculus are presented which correspond to the flat Friedmann-Robertson-Walker and the Kasner solutions of general relativity. By taking advantage of the symmetries that are present, I am able to show explicitly that a limit of Regge calculus does yield Einstein's equations for these cases. The method of averaging these equations when taking limits is important, especially for the Kasner model. I display the leading error term that arises from keeping the Regge equations in discrete form rather than using their continuum limit. In particular, this work shows that for the "Reggeized" Friedmann model the minimum volume is a velocitydominated singularity as in the continuum Friedmann model. However, unlike the latter, the Regge version has a nonzero minimum volume.

Steve M. Lewis

1982-01-15T23:59:59.000Z

267

Replication Regulates Volume Weighting in Quantum Cosmology  

E-Print Network [OSTI]

Probabilities for observations in cosmology are conditioned both on the universe's quantum state and on local data specifying the observational situation. We show the quantum state defines a measure for prediction through such conditional probabilities that is well behaved for spatially large or infinite universes when the probabilities that our data is replicated are taken into account. In histories where our data are rare volume weighting connects top-down probabilities conditioned on both the data and the quantum state to the bottom-up probabilities conditioned on the quantum state alone. We apply these principles to a calculation of the number of inflationary e-folds in a homogeneous, isotropic minisuperspace model with a single scalar field moving in a quadratic potential. We find that volume weighting is justified and the top-down probabilities favor a large number of e-folds.

James Hartle; Thomas Hertog

2009-05-24T23:59:59.000Z

268

Eternal Higgs inflation and cosmological constant problem  

E-Print Network [OSTI]

We investigate the Higgs potential beyond the Planck scale in the superstring theory, under the assumption that the supersymmetry is broken at the string scale. We identify the Higgs field as a massless state of the string, which is indicated by the fact that the bare Higgs mass can be zero around the string scale. We find that, in the large field region, the Higgs potential is connected to a runaway vacuum with vanishing energy, which corresponds to opening up an extra dimension. We verify that such universal behavior indeed follows from the toroidal compactification of the non-supersymmetric $SO(16)\\times SO(16)$ heterotic string theory. We show that this behavior fits in the picture that the Higgs field is the source of the eternal inflation. The observed small value of the cosmological constant of our universe may be understood as the degeneracy with this runaway vacuum, which has vanishing energy, as is suggested by the multiple point criticality principle.

Hamada, Yuta; Oda, Kin-ya

2015-01-01T23:59:59.000Z

269

Low energy branes, effective theory, and cosmology  

Science Journals Connector (OSTI)

The low energy regime of cosmological BPS-brane configurations with a bulk scalar field is studied. We construct a systematic method to obtain five-dimensional solutions to the full system of equations governing the geometry and dynamics of the bulk. This is done for an arbitrary bulk scalar field potential and taking into account the presence of matter on the branes. The method, valid in the low energy regime, is a linear expansion of the system about the static vacuum solution. Additionally, we develop a four-dimensional effective theory describing the evolution of the system. At the lowest order in the expansion, the effective theory is a biscalar tensor theory of gravity. One of the main features of this theory is that the scalar fields can be stabilized naturally without the introduction of additional mechanisms, allowing satisfactory agreement between the model and current observational constraints. The special case of the Randall-Sundrum model is discussed.

Gonzalo A. Palma and Anne-Christine Davis

2004-09-15T23:59:59.000Z

270

Defrosting in an emergent Galileon cosmology  

Science Journals Connector (OSTI)

We study the transition from an emergent Galileon condensate phase of the early universe to a later expanding radiation phase. This defrosting or preheating transition is a consequence of the excitation of matter fluctuations by the coherent Galileon condensate, in analogy to how preheating in inflationary cosmology occurs via the excitation of matter fluctuations through coupling of matter with the coherent inflaton condensate. We show that the minimal coupling of matter (modeled as a massless scalar field) to the Galileon field introduced by Creminelli, Nicolis, and Trincherini in order to generate a scale-invariant spectrum of matter fluctuations is sufficient to lead to efficient defrosting, provided that the effects of the nonvanishing expansion rate of the universe are taken into account. If we neglect the effects of expansion, an additional coupling of matter to the Galileon condensate is required. We study the efficiency of the defrosting mechanism in both cases.

Laurence Perreault Levasseur; Robert Brandenberger; Anne-Christine Davis

2011-11-09T23:59:59.000Z

271

Probing Quintessence Potential with Future Cosmological Surveys  

E-Print Network [OSTI]

Quintessence, a scalar field model, has been proposed to account for the acceleration of the Universe at present. We discuss how accurately quintessence models are discriminated by future cosmological surveys, which include experiments of CMB, galaxy clustering, weak lensing, and the type Ia SNe surveys, by making use of the conventional parameterized dark energy models. We can see clear differences between the thawing and the freezing quintessence models at more than $1\\sigma$ ($2\\sigma$) confidence level as long as the present equation of state for quintessence is away from $-1$ as $w_X \\gtrsim -0.95 (-0.90)$. However, it is found to be difficult to probe the effective mass squared for the potential in thawing models, whose signs are different between the quadratic and the cosine-type potentials. This fact may require us to invent a new estimator to distinguish quintessence models beyond the thawing and the freezing ones.

Takeuchi, Yoshitaka; Takahashi, Tomo; Yamaguchi, Masahide

2014-01-01T23:59:59.000Z

272

Probing Quintessence Potential with Future Cosmological Surveys  

E-Print Network [OSTI]

Quintessence, a scalar field model, has been proposed to account for the acceleration of the Universe at present. We discuss how accurately quintessence models are discriminated by future cosmological surveys, which include experiments of CMB, galaxy clustering, weak lensing, and the type Ia SNe surveys, by making use of the conventional parameterized dark energy models. We can see clear differences between the thawing and the freezing quintessence models at more than $1\\sigma$ ($2\\sigma$) confidence level as long as the present equation of state for quintessence is away from $-1$ as $w_X \\gtrsim -0.95 (-0.90)$. However, it is found to be difficult to probe the effective mass squared for the potential in thawing models, whose signs are different between the quadratic and the cosine-type potentials. This fact may require us to invent a new estimator to distinguish quintessence models beyond the thawing and the freezing ones.

Yoshitaka Takeuchi; Kiyotomo Ichiki; Tomo Takahashi; Masahide Yamaguchi

2014-01-27T23:59:59.000Z

273

Antisymmetric field in string gas cosmology  

E-Print Network [OSTI]

We study how the introduction of a 2-form field flux modify the dynamics of a T-duality invariant string gas cosmology model of Greene, Kabat and Marnerides. It induces a repulsive potential term in the effective action for the scale factor of the spacial dimensions. Without the 2-form field flux, the universe fails to expand when the pressure due to string modes vanishes. With the presence of a homogeneous 2-form field flux, it propels 3 spacial dimensions to grow into a macroscopic 4 dimensional space-time. We find that it triggers an expansion of a universe away from the oscillating phase around the self-dual radius. We also investigate the effects of a constant 2-form field. We can obtain an expanding 4 dimensional space-time by tuning it at the critical value.

Igmar C. Rosas-López; Yoshihisa Kitazawa

2010-07-09T23:59:59.000Z

274

String spectra near some null cosmological singularities  

E-Print Network [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 analyse 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 wavefunctions. We find that for low lying string modes(finite oscillation number), the classical near-singularity string mode functions are non-divergent for various families of singularities. Furthermore, for any infinitesimal regularization of the vicinity of the singularity, we find a tower of string modes of ultra-high oscillation number which propagate essentially freely in the background. The resulting picture suggests that string interactions are non-negligible near the singularity.

Kallingalthodi Madhu; K. Narayan

2009-04-29T23:59:59.000Z

275

Measuring the speed of cosmological gravitational waves  

E-Print Network [OSTI]

In general relativity gravitational waves propagate at the speed of light, however in alternative theories of gravity that might not be the case. We study the effects of a modified speed of gravity, $c_T^2$, on the B-modes of the Cosmic Microwave Background (CMB) anisotropy in polarisation. We find that a departure from the light speed value would leave a characteristic imprint on the BB spectrum part induced by tensors, manifesting as a shift in the angular scale of its peaks. We derive constraints by using the available {\\it Planck} and BICEP2 datasets showing how $c_T^2$ can be measured, albeit obtaining weak constraints due to the overall poor accuracy of the current BB power spectrum measurements. The present constraint corresponds to $c_T^2 = 1.30 \\pm 0.79$ and $c_T^2measurements, largely due to the absence of degeneracy with other cosmological parameters.

Marco Raveri; Carlo Baccigalupi; Alessandra Silvestri; Shuang-Yong Zhou

2014-05-30T23:59:59.000Z

276

Quintessence and phantom cosmology with nonminimal derivative coupling  

SciTech Connect (OSTI)

We investigate cosmological scenarios with a nonminimal derivative coupling between the scalar field and the curvature, examining both the quintessence and the phantom cases in zero and constant potentials. In general, we find that the universe transits from one de Sitter solution to another, determined by the coupling parameter. Furthermore, according to the parameter choices and without the need for matter, we can obtain a big bang, an expanding universe with no beginning, a cosmological turnaround, an eternally contracting universe, a big crunch, a big rip avoidance, and a cosmological bounce. This variety of behaviors reveals the capabilities of the present scenario.

Saridakis, Emmanuel N. [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China); Sushkov, Sergey V. [Department of General Relativity and Gravitation, Kazan State University, Kremlevskaya Street 18, Kazan 420008 (Russian Federation); Department of Mathematics, Tatar State University of Humanities and Education, Tatarstan Street 2, Kazan 420021 (Russian Federation)

2010-04-15T23:59:59.000Z

277

Open Inflation, the Four Form and the Cosmological Constant  

E-Print Network [OSTI]

Fundamental theories of quantum gravity such as supergravity include a four form field strength which contributes to the cosmological constant. The inclusion of such a field into our theory of open inflation (hep-th/9802030) allows an anthropic solution to the cosmological constant problem in which the cosmological constant gives a small but non-negligible contribution to the density of today's universe. We include a discussion of the role of the singularity in our solution and a reply to Vilenkin's recent criticism (hep-th/9803084).

Neil Turok; S. W. Hawking

1998-03-19T23:59:59.000Z

278

Non minimally coupled condensate cosmologies: a phase space analysis  

E-Print Network [OSTI]

We present an analysis of the phase space of cosmological models based on a non minimal coupling between the geometry and a fermionic condensate. We obtain that the strong constraint coming from the Dirac equations allows a detailed design of the cosmology of these models and at the same time guarantees an evolution towards a state indistinguishable from General Relativistic cosmological models. In this light, we show how the use of some specific potentials is able to reproduce naturally two de Sitter phases separated by a power law expansion which could be an interesting model for the unification of an inflationary phase and a dark energy era.

Sante Carloni; Stefano Vignolo; Roberto Cianci

2014-03-11T23:59:59.000Z

279

A Modification of the Standard Cosmological Metric  

E-Print Network [OSTI]

In this article we firstly present an explicit dynamical equation satisfying the general principle of relativity under the framework of classical mechanics. In light of this fact, the necessity of Einstein's equivalence principle for the gravity being geometrized should be reexamined. Especially, Einstein's (strong) equivalence principle claims that the inertial force is equivalent to the gravitational force. But in fact the new dynamical equation proves that the essence of the inertial force is the real force exerted on the reference object, which can actually be all kinds of forces such as the gravitational force, electromagnetic force and so on. Therefore, in this context we only retain the numerical equality between the inertial mass and gravitational mass and abandon Einstein's (strong) equivalence principle. Consequently, the candidate for the standard clock should be corrected into the mathematical clock which duplicates the real clock equipped by the observer himself. Then a new physical picture for how to convert the gravitational force into a geometric description on spacetime is presented. On the other hand, we point out that all cosmological observations are made by the observer at present on the earth, instead of any other observers including the comoving observers in the earlier unverse. On this basis, we introduce an extra factor $b(t)$ in $FRW$ cosmological metric to depict the gravitational time dilation effect since the local proper clock may run in a faster and faster rate with the expanding of the universe. In this way, we may obtain a positive value of $\\rho+3p$ and avoid the introduction of dark energy in the current universe.

ChiYi Chen

2004-11-04T23:59:59.000Z

280

Integrating Seeing Measurements into the Operations of Solar Telescopes  

E-Print Network [OSTI]

conditions for solar observations: Big Bear Solar Observatory in California, Haleakala on Maui, HawaiiIntegrating Seeing Measurements into the Operations of Solar Telescopes C. Denker and A. P. Verdoni New Jersey Institute of Technology, Center for Solar-Terrestrial Research 323 Martin Luther King Blvd

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.


281

THE JAMES WEBB SPACE TELESCOPE JONATHAN P. GARDNER1,  

E-Print Network [OSTI]

Institute of Technology (ETH-Zurich), ETH H¨onggerberg, CH-8093 Zurich, Switzerland 8Space Telescope Science¨ur Astronomie, K¨onigstuhl 17, Heidelberg D-69117, Germany 15NASA Headquarters, 300 E Street Southwest Light and Reionization theme is to identify the first luminous sources to form and to determine

Colorado at Boulder, University of

282

NMSU's 1m Altaz telescope located at the Apache Point  

E-Print Network [OSTI]

Research Projects National Solar Observa- tory's facilities in Sacra- mento Peak, New Mexico NMSU RESEARCHNMSU's 1m Altaz telescope located at the Apache Point Observatory in Sunspot, New Mexico. Dr has been awarded NSF funding to enhance the quality and quantity of New Mexico State University

Johnson, Eric E.

283

Results of a Si/CdTe Compton Telescope  

E-Print Network [OSTI]

We have been developing a semiconductor Compton telescope to explore the universe in the energy band from several tens of keV to a few MeV. We use a Si strip and CdTe pixel detector for the Compton telescope to cover an energy range from 60 keV. For energies above several hundred keV, the higher efficiency of CdTe semiconductor in comparison with Si is expected to play an important role as an absorber and a scatterer. In order to demonstrate the spectral and imaging capability of a CdTe-based Compton Telescope, we have developed a Compton telescope consisting of a stack of CdTe pixel detectors as a small scale prototype. With this prototype, we succeeded in reconstructing images and spectra by solving the Compton equation from 122 keV to 662 keV. The energy resolution (FWHM) of reconstructed spectra is 7.3 keV at 511 keV and 3.1 keV at 122 keV, respectively. The angular resolution obtained at 511 keV is measured to be 12.2 degree (FWHM).

Kousuke Oonuki; Takaaki Tanaka; Shin Watanabe; Shin'ichiro Takeda; Kazuhiro Nakazawa; Takefumi Mitani; Tadayuki Takahashi; Hiroyasu Tajima; Yasushi Fukazawa; Masaharu Nomachi

2005-09-21T23:59:59.000Z

284

Review of the Solar Array Telescopes David A. Smith  

E-Print Network [OSTI]

to believe that at lower energy, wavefront sampling could have advantages [34]. After the 1973 oil crisisReview of the Solar Array Telescopes David A. Smith Centre d'Etudes Nucl´eaires de Bordeaux sensitive to astrophysical gamma rays with energies beyond the reach of EGRET but below

Paris-Sud XI, Université de

285

Adaptive Optics Simulations for the European Extremely Large Telescope  

E-Print Network [OSTI]

Louarn, Sylvain Oberti, and A. Garcia-Rissman European Southern Observatory, Karl-Schwarzschild-StraÃ?e 2 large telescopes (ELTs) of primary mirror diameters 20-42 m are in the design stages, such as the thirty of view (FOV) with a single deformable mirror (DM). Due to the sky coverage constraints of NGS systems

Liske, Jochen

286

New challenges for adaptive optics: extremely large telescopes  

Science Journals Connector (OSTI)

......Southern Observatory, Karl Schwarzschild Str. 2, D-85748 Garching...and up to three deformable mirrors, which increase up to 8-fold...optical telescopes has primary mirrors with diameters in the 8...the diameter of the primary mirror lies in a range between 40......

M. Le Louarn; N. Hubin; M. Sarazin; A. Tokovinin

2000-09-21T23:59:59.000Z

287

Design Concepts for the Cherenkov Telescope Array CTA: An Advanced Facility for Ground-Based High-Energy Gamma-Ray Astronomy  

SciTech Connect (OSTI)

Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.

Actis, M

2012-04-17T23:59:59.000Z

288

The Photodetector Plane of the 4m Davies Cotton Small Size Telescope for the Cherenkov Telescope Array  

E-Print Network [OSTI]

Photomultipliers (PMTs) are currently adopted for the photodetector plane of Imaging Atmospheric Cherenkov Telescopes (IACTs). Even though PMT quantum efficiency has improved impressively in the recent years, one of the main limitation for their application in the gamma-astronomy field - the impossibility to operate with moon light - still remains. As a matter of fact, the light excess would lead to significant and faster camera ageing. Solid state detectors, in particular Geiger-mode avalanche photo-diodes (G-APDs) represent a valuable alternative solution to overcome this limitation as demonstrated in the field by the FACT experiment (The First G- APD Cherenkov Telescope). They can be regarded as a more promising long term approach, which can be easily adopted for the new generation of cameras and for the Cherenkov Telescope Array (CTA). We describe here the Photo-Detector Plane (PDP) of the camera for the 4 m Davies Cotton CTA Small Size Telescopes, for which large area G-APD coupled to non-imaging light c...

Boccone, V; Basili, A; Christov, A; della Volpe, M; Montaruli, T

2013-01-01T23:59:59.000Z

289

Extended Theories of Gravity and their Cosmological and Astrophysical Applications  

E-Print Network [OSTI]

We review Extended Theories of Gravity in metric and Palatini formalism pointing out their cosmological and astrophysical application. The aim is to propose an alternative approach to solve the puzzles connected to dark components.

Salvatore Capozziello; Mauro Francaviglia

2007-06-08T23:59:59.000Z

290

Modern cosmology: Interactive computer simulations that use recent observational surveys  

Science Journals Connector (OSTI)

We present a collection of new open-source computational tools for numerically modeling recent large-scale observational data sets using modern cosmology theory. These tools allow both students and researchers to constrain the parameter values in competitive cosmological models thereby discovering both the accelerated expansion of the universe and its composition (e.g. dark matter and dark energy). These programs have several features to help the non-cosmologist build an understanding of cosmological models and their relation to observational data including a built-in collection of several real observational data sets. The current list of built-in observations includes several recent supernovae Type-Ia surveys baryon acoustic oscillations the cosmic microwave background radiation gamma-ray bursts and measurements of the Hubble parameter. In this article we discuss specific results for testing cosmological models using these observational data.

2013-01-01T23:59:59.000Z

291

Observational constraints on late-time {lambda}(t) cosmology  

SciTech Connect (OSTI)

The cosmological constant {lambda}, i.e., the energy density stored in the true vacuum state of all existing fields in the Universe, is the simplest and the most natural possibility to describe the current cosmic acceleration. However, despite its observational successes, such a possibility exacerbates the well-known {lambda} problem, requiring a natural explanation for its small, but nonzero, value. In this paper we study cosmological consequences of a scenario driven by a varying cosmological term, in which the vacuum energy density decays linearly with the Hubble parameter, {lambda}{proportional_to}H. We test the viability of this scenario and study a possible way to distinguish it from the current standard cosmological model by using recent observations of type Ia supernova (Supernova Legacy Survey Collaboration), measurements of the baryonic acoustic oscillation from the Sloan Digital Sky Survey, and the position of the first peak of the cosmic microwave background angular spectrum from the three-year Wilkinson Microwave Anisotropy Probe.

Carneiro, S.; Pigozzo, C. [Instituto de Fisica, Universidade Federal da Bahia, Salvador-BA, 40210-340 (Brazil); Dantas, M. A. [Departamento de Astronomia, Observatorio Nacional, Rio de Janeiro-RJ, 20921-400 (Brazil); Alcaniz, J. S. [Departamento de Astronomia, Observatorio Nacional, Rio de Janeiro-RJ, 20921-400 (Brazil); Instituto Nacional de Pesquisas Espaciais/CRN, 59076-740, Natal-RN (Brazil)

2008-04-15T23:59:59.000Z

292

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...

Gonzalez-Mestres, Luis

2012-01-01T23:59:59.000Z

293

Cosmological Parameters From Supernovae Associated With Gamma-ray Bursts  

E-Print Network [OSTI]

We report estimates of the cosmological parameters $\\Omega_m$ and $\\Omega_{\\Lambda}$ obtained using supernovae (SNe) associated with gamma-ray bursts (GRBs) at redshifts up to 0.606. Eight high-fidelity GRB-SNe with well-sampled light curves across the peak are used. We correct their peak magnitudes for a luminosity-decline rate relation to turn them into accurate standard candles with dispersion $\\sigma = 0.18$ mag. We also estimate the peculiar velocity of the host galaxy of SN 1998bw, using constrained cosmological simulations. In a flat universe, the resulting Hubble diagram leads to best-fit cosmological parameters of $(\\Omega_m, \\Omega_{\\Lambda}) = (0.52^{+0.34}_{-0.31},0.48^{+0.31}_{-0.34})$. This exploratory study suggests that GRB-SNe can potentially be used as standardizable candles to high redshifts to measure distances in the universe and constrain cosmological parameters.

Li, Xue; Wojtak, Rados?aw

2014-01-01T23:59:59.000Z

294

Cosmology on the Beach - Carlos Frenk: Lecture 1  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Carlos Frenk

2010-01-08T23:59:59.000Z

295

Cosmology at the Beach Lecture: Chung-Pei Ma  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Chung-Pei Ma

2010-01-08T23:59:59.000Z

296

Cepheid Variables and their Application to the Cosmological Distance Scale  

E-Print Network [OSTI]

In the current era of “precision cosmology”, measuring the expansion rate of the Universe (Hubble constant, or H0) more accurately and precisely helps to better constrain the properties of dark energy. Cepheid-based distances are a critical step...

Hoffmann, Samantha L

2013-05-02T23:59:59.000Z

297

Cosmology on the Beach - Carlos Frenk, Lecture 3  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Carlos Frenk

2010-01-08T23:59:59.000Z

298

Cosmology on the Beach - Carlos Frenk, Lecture 2  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Carlos Frenk

2010-01-08T23:59:59.000Z

299

Cosmology on the Beach - Eric Linder, Lecture 2  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.  

Eric Linder

2010-01-08T23:59:59.000Z

300

Cosmology on the Beach: Eric Linder, lecture 3  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Eric Linder

2010-01-08T23:59:59.000Z

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.


301

Cosmology on the Beach - Chung-Pei Ma, Lecture 3  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Chung-Pei Ma

2010-01-08T23:59:59.000Z

302

Cosmology on the Beach - Simon White, Lecture 3  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Simon White

2010-01-08T23:59:59.000Z

303

Cosmology on the Beach - Chung-Pei Ma: Lecture 2  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009

Chung-Pei Ma

2010-01-08T23:59:59.000Z

304

Cosmology on the Beach - Eric Linder: Lecture 1  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Eric Linder

2010-01-08T23:59:59.000Z

305

Cosmology on the Beach - Wayne Hu: Lecture 2  

ScienceCinema (OSTI)

The lecture was delivered as part of the "Cosmology at the Beach" winter school organized by Berkeley Lab's George Smoot in Los Cabos, Mexico from Jan. 12-16, 2009.

Wayne Hu

2010-01-08T23:59:59.000Z

306

E-Print Network 3.0 - area telescope observations Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

<< < 1 2 3 4 5 > >> 1 NASSP OT1: Telescopes I-217 Feb 2010 1 OpticalIR Observational Astronomy Summary: NASSP OT1: Telescopes I-217 Feb 2010 1 OpticalIR Observational Astronomy...

307

E-Print Network 3.0 - area telescope view Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

<< < 1 2 3 4 5 > >> 1 NASSP OT1: Telescopes I-217 Feb 2010 1 OpticalIR Observational Astronomy Summary: NASSP OT1: Telescopes I-217 Feb 2010 1 OpticalIR Observational Astronomy...

308

E-Print Network 3.0 - area telescope bright Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

<< < 1 2 3 4 5 > >> 1 NASSP OT1: Telescopes I-217 Feb 2010 1 OpticalIR Observational Astronomy Summary: ms images of a bright star 12;NASSP OT1: Telescopes I-217 Feb 2010 13...

309

E-Print Network 3.0 - area telescope points Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

<< < 1 2 3 4 5 > >> 1 NASSP OT1: Telescopes I-217 Feb 2010 1 OpticalIR Observational Astronomy Summary: NASSP OT1: Telescopes I-217 Feb 2010 1 OpticalIR Observational Astronomy...

310

Experimental Results Obtained with the Positron-Annihilation Radiation Telescope of the Toulouse-Argonne Collaboration  

Science Journals Connector (OSTI)

We present laboratory measurements obtained with a ground-based prototype of a focusing positron-annihilation-radiation telescope developed by the Toulouse-Argonne collaboration. This balloon-borne telescope has ...

J. E. Naya; P. von Ballmoos; F. Albernhe; G. Vedrenne…

1995-01-01T23:59:59.000Z

311

Tradespace Investigation of a Telescope Architecture for Next-generation Space Astronomy and Exploration  

E-Print Network [OSTI]

Humanity’s endeavor to further its scientific understanding of the celestial heavens has led to the creation and evolution of increasingly powerful and complex space telescopes. Space telescopes provide a view of the solar ...

Cataldo, Giuseppe

2014-12-19T23:59:59.000Z

312

E-Print Network 3.0 - axion solar telescope Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

solar telescope Search Powered by Explorit Topic List Advanced Search Sample search results for: axion solar telescope Page: << < 1 2 3 4 5 > >> 1 In Search Of Axions: The CAST...

313

The Balloon-borne Large Aperture Submillimeter Telescope and Its Rebirth as a Polarimeter.  

E-Print Network [OSTI]

??The Balloon-borne Large Aperture Submillimeter Telescope (BLAST) is a 1.8 meter Cassegrain telescope that operates in three bands (250, 350, and 500 ?m), each with… (more)

Thomas, Nicholas E

2011-01-01T23:59:59.000Z

314

Design and analysis of a two-channel three-mirror x-ray telescope: errata  

Science Journals Connector (OSTI)

Alternate configurations for a two-channel three-mirror glancing incidence x-ray telescope have been designed and evaluated. A Wolter-Schwarzschild type I telescope is used as a base...

Kassim, Abd M; Shealy, David L

1984-01-01T23:59:59.000Z

315

Scalar-Tensor Gravity Cosmology: Noether symmetries and analytical solutions  

E-Print Network [OSTI]

In this paper, we present a complete Noether Symmetry analysis in the framework of scalar-tensor cosmology. Specifically, we consider a non-minimally coupled scalar field action embedded in the FLRW spacetime and provide a full set of Noether symmetries for related minisuperspaces. The presence of symmetries implies that the dynamical system becomes integrable and then we can compute cosmological analytical solutions for specific functional forms of coupling and potential functions selected by the Noether Approach.

A. Paliathanasis; M. Tsamparlis; S. Basilakos; S. Capozziello

2014-03-03T23:59:59.000Z

316

Loop quantum cosmology in 2+1 dimension  

E-Print Network [OSTI]

As a first step to generalize the structure of loop quantum cosmology to the theories with the spacetime dimension other than four, the isotropic model of loop quantum cosmology in 2+1 dimension is studied in this paper. We find that the classical big bang singularity is again replaced by a quantum bounce in the model. The similarities and differences between the 2+1 dimensional model and the 3+1 dimensional one are also discussed.

Xiangdong Zhang

2014-11-19T23:59:59.000Z

317

Power Spectra to 1% Accuracy between Dynamical Dark Energy Cosmologies  

E-Print Network [OSTI]

For dynamical dark energy cosmologies we carry out a series of N-body gravitational simulations, achieving percent level accuracy in the relative mass power spectra at any redshift. Such accuracy in the power spectrum is necessary for next generation cosmological mass probes. Our matching procedure reproduces the CMB distance to last scattering and delivers subpercent level power spectra at z=0 and z~3. We discuss the physical implications for probing dark energy with surveys of large scale structure.

Matthew J. Francis; Geraint F. Lewis; Eric V. Linder

2007-04-03T23:59:59.000Z

318

Some Aspects of String Cosmology and the LHC  

E-Print Network [OSTI]

I discuss some (unconventional) aspects of String Cosmology of relevance to supersymmetric dark matter searches at the Large Hadron Collider (LHC) at CERN. In particular, I analyse the role of time-dependent dilaton fields in relaxing some of the stringent constraints that characterise minimal supersymmetric models in standard cosmology. I also study briefly CPT-violating aspects of brane Universe models with space-time brane defects at early epochs and their potential relevance to the observed Baryon Asymmetry.

Nick E. Mavromatos

2012-09-30T23:59:59.000Z

319

Newtonian limit of fully nonlinear cosmological perturbations in Einstein's gravity  

SciTech Connect (OSTI)

We prove that in the infinite speed-of-light limit (i.e., non-relativistic and subhorizon limits), the relativistic fully nonlinear cosmological perturbation equations in two gauge conditions, the zero-shear gauge and the uniform-expansion gauge, exactly reproduce the Newtonian hydrodynamic perturbation equations in the cosmological background; as a consequence, in the same two gauge conditions, the Newtonian hydrodynamic equations are exactly recovered in the Minkowsky background.

Hwang, Jai-chan [Department of Astronomy and Atmospheric Sciences, Kyungpook National University, Daegu 702-701 (Korea, Republic of); Noh, Hyerim, E-mail: jchan@knu.ac.kr, E-mail: hr@kasi.re.kr [Korea Astronomy and Space Science Institute, Daejeon 305-348 (Korea, Republic of)

2013-04-01T23:59:59.000Z

320

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

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

SLAC All Access: Fermi Gamma-ray Space Telescope  

SciTech Connect (OSTI)

Three hundred and fifty miles overhead, the Fermi Gamma-ray Space Telescope silently glides through space. From this serene vantage point, the satellite's instruments watch the fiercest processes in the universe unfold. Pulsars spin up to 700 times a second, sweeping powerful beams of gamma-ray light through the cosmos. The hyperactive cores of distant galaxies spew bright jets of plasma. Far beyond, something mysterious explodes with unfathomable power, sending energy waves crashing through the universe. Stanford professor and KIPAC member Roger W. Romani talks about this orbiting telescope, the most advanced ever to view the sky in gamma rays, a form of light at the highest end of the energy spectrum that's created in the hottest regions of the universe.

Romani, Roger

2013-05-31T23:59:59.000Z

322

FERMI LARGE AREA TELESCOPE OBSERVATIONS OF GRB 110625A  

SciTech Connect (OSTI)

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

323

SLAC All Access: Fermi Gamma-ray Space Telescope  

ScienceCinema (OSTI)

Three hundred and fifty miles overhead, the Fermi Gamma-ray Space Telescope silently glides through space. From this serene vantage point, the satellite's instruments watch the fiercest processes in the universe unfold. Pulsars spin up to 700 times a second, sweeping powerful beams of gamma-ray light through the cosmos. The hyperactive cores of distant galaxies spew bright jets of plasma. Far beyond, something mysterious explodes with unfathomable power, sending energy waves crashing through the universe. Stanford professor and KIPAC member Roger W. Romani talks about this orbiting telescope, the most advanced ever to view the sky in gamma rays, a form of light at the highest end of the energy spectrum that's created in the hottest regions of the universe.

Romani, Roger

2014-06-24T23:59:59.000Z

324

Gamma-Ray Imaging with the Coded Mask IBIS Telescope  

E-Print Network [OSTI]

The IBIS telescope onboard INTEGRAL, the ESA gamma-ray space mission to be launched in 2002, is a soft gamma-ray (20 keV - 10 MeV) device based on a coded aperture imaging system. We describe here basic concepts of coded masks, the imaging system of the IBIS telescope, and the standard data analysis procedures to reconstruct sky images. This analysis includes, for both the low-energy detector layer (ISGRI) and the high energy layer (PICSIT), iterative procedures which decode recorded shadowgrams, search for and locate sources, clean for secondary lobes, and then rotate and compose sky images. These procedures will be implemented in the Quick Look and Standard Analysis of the INTEGRAL Science Data Center (ISDC) as IBIS Instrument Specific Software.

Goldwurm, A; Gros, A; Stephen, J; Foschini, L; Gianotti, F; Natalucci, L; De Cesare, G; Santo, M D

2000-01-01T23:59:59.000Z

325

The data acquisition system for the ANTARES neutrino telescope  

E-Print Network [OSTI]

The ANTARES neutrino telescope is being constructed in the Mediterranean Sea. It consists of a large three-dimensional array of photo-multiplier tubes. The data acquisition system of the detector takes care of the digitisation of the photo-multiplier tube signals, data transport, data filtering, and data storage. The detector is operated using a control program interfaced with all elements. The design and the implementation of the data acquisition system are described.

J. A. Aguilar; ANTARES collaboration

2006-10-02T23:59:59.000Z

326

Observational constraints to a unified cosmological model  

E-Print Network [OSTI]

We propose a phenomenological unified model for dark matter and dark energy based on an equation of state parameter $w$ that scales with the $\\arctan$ of the redshift. The free parameters of the model are three constants: $\\Omega_{b0}$, $\\alpha$ and $\\beta$. Parameter $\\alpha$ dictates the transition rate between the matter dominated era and the accelerated expansion period. The ratio $\\beta / \\alpha$ gives the redshift of the equivalence between both regimes. Cosmological parameters are fixed by observational data from Primordial Nucleosynthesis (PN), Supernovae of the type Ia (SNIa), Gamma-Ray Bursts (GRB) and Baryon Acoustic Oscillations (BAO). The calibration of the 138 GRBs events is performed using the 580 SNIa of the Union2.1 data set and a new set of 79 high-redshift GRBs is obtained. The various sets of data are used in different combinations to constraint the parameters through statistical analysis. The unified model is compared to the $\\Lambda$CDM model and their differences are emphasized.

Cuzinatto, R R; de Morais, E M

2014-01-01T23:59:59.000Z

327

Solar system tests of the cosmological constant  

E-Print Network [OSTI]

We discuss the influence of the cosmological constant $\\Lambda$ on the gravitational equations of motion of bodies with arbitrary masses and eventually solve the two-body problem. Observational constraints are derived from measurements of the periastron advance in stellar systems, in particular binary pulsars and the solar system. For the latter we consider also the change in the mean motion due to $\\Lambda$. Up to now, Earth and Mars data give the best constraint, $\\Lambda \\sim 10^{-36} \\mathrm{km}^{-2}$. If properly accounting for the gravito-magnetic effect, this upper limit on $\\Lambda$ could greatly improve in the near future thanks to new data from planned or already operating space-missions. Dark matter or modifications of the Newtonian inverse-square law in the solar system are discussed as well. Variations in the $1/r^2$ behavior are considered in the form of either a possible Yukawa-like interaction or a modification of gravity of MOND type.

Philippe Jetzer; Mauro Sereno

2007-11-23T23:59:59.000Z

328

Observational tests for ?(t)CDM cosmology  

SciTech Connect (OSTI)

We investigate the observational viability of a class of cosmological models in which the vacuum energy density decays linearly with the Hubble parameter, resulting in a production of cold dark matter particles at late times. Similarly to the flat ?CDM case, there is only one free parameter to be adjusted by the data in this class of ?(t)CDM scenarios, namely, the matter density parameter. To perform our analysis we use three of the most recent SNe Ia compilation sets (Union2, SDSS and Constitution) along with the current measurements of distance to the BAO peaks at z = 0.2 and z = 0.35 and the position of the first acoustic peak of the CMB power spectrum. We show that in terms of ?{sup 2} statistics both models provide good fits to the data and similar results. A quantitative analysis discussing the differences in parameter estimation due to SNe light-curve fitting methods (SALT2 and MLCS2k2) is studied using the current SDSS and Constitution SNe Ia compilations. A matter power spectrum analysis using the 2dFGRS is also performed, providing a very good concordance with the constraints from the SDSS and Constitution MLCS2k2 data.

Pigozzo, C.; Carneiro, S. [Instituto de Física, Universidade Federal da Bahia, 40210-340 Salvador, BA (Brazil); Dantas, M.A.; Alcaniz, J.S., E-mail: cpigozzo@ufba.br, E-mail: aldinez@on.br, E-mail: saulo.carneiro@pq.cnpq.br, E-mail: alcaniz@on.br [Observatório Nacional, 20921-400 Rio de Janeiro, RJ (Brazil)

2011-08-01T23:59:59.000Z

329

Is Cosmology Compatible with Sterile Neutrinos?  

SciTech Connect (OSTI)

By combining data from cosmic microwave background experiments (including the recent WMAP third year results), large scale structure, and Lyman-{alpha} forest observations, we constrain the hypothesis of a fourth, sterile, massive neutrino. For the 3 massless+1 massive neutrino case, we bound the mass of the sterile neutrino to m{sub s}<0.26 eV (0.44 eV) at 95% (99.9%) C.L., which excludes at high significance the sterile neutrino hypothesis as an explanation of the LSND anomaly. We generalize the analysis to account for active neutrino masses and the possibility that the sterile abundance is not thermal. In the latter case, the contraints in the (mass,density) plane are nontrivial. For a mass of >1 or <0.05 eV, the cosmological energy density in sterile neutrinos is always constrained to be {omega}{sub {nu}}<0.003 at 95% C.L., but for a mass of {approx}0.25 eV, {omega}{sub {nu}} can be as large as 0.01.

Dodelson, Scott; Melchiorri, Alessandro; Slosar, Anze [Particle Astrophysics Center, FERMILAB, Batavia, Illinois 60510-0500 (United States); Physics Department and Sezione INFN, University of Rome 'La Sapienza', Ple Aldo Moro 2, 00185 Rome (Italy); Faculty of Mathematics and Physics, University of Ljubljana, 1000 Ljubljana (Slovenia)

2006-07-28T23:59:59.000Z

330

A new golden age: testing general relativity with cosmology  

Science Journals Connector (OSTI)

...Pan-STARRS-1 and -2), the Dark Energy Survey (DES), the VLT Survey...Oscillation Spectroscopic Survey (BOSS), the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX...produce galaxy redshift surveys which can be used for...

2011-01-01T23:59:59.000Z

331

E-Print Network 3.0 - annihilation radiation telescope Sample...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Collection: Physics 3 MPI Kernphysik, Heidelberg Humboldt Univ. Berlin Summary: Gamma ray bursts Cosmology Diffuse extragalactic radiation fields via cutoff in AGN spectra and...

332

Cosmological reconstruction of $f(T,\\mathcal{T})$ Gravity  

E-Print Network [OSTI]

Motivated by the newly proposal for gravity as the effect of the torsion scalar $T$ and trace of the energy momentum tensor $\\mathcal{T}$,we investigate the cosmological reconstruction of different models of the Universe. Our aim here is to show that how this modified gravity model, $f(T,\\mathcal{T})$ is able to reproduce different epoches of the cosmological history. We explicitly show that $f(T,\\mathcal{T})$ can be reconstructed for $\\Lambda $CDM as the most popular and consistent model. Also we study the mathematical reconstruction of $f(T,\\mathcal{T})$ for a flat cosmological background filled by two fluids mixture. Such model describes phantom-non-phantom era as well as the purely phantom cosmology. We extend our investigation to more cosmological models like perfect fluid,Chaplygin gas and massless scalar field. In each case we obtain some specific forms of $f(T,\\mathcal{T})$. These families of $f(T,\\mathcal{T})$ contain arbitrary function of torsion and trace of the energy momentum.

Davood Momeni; Ratbay Myrzakulov

2014-05-29T23:59:59.000Z

333

Disentangling interacting dark energy cosmologies with the three-point correlation function  

Science Journals Connector (OSTI)

......Oscillation Spectroscopic Survey and Euclid. cosmology...cosmology: theory|dark energy|dark matter|large-scale...Oscillation Spectroscopic Survey (BOSS, Schlegel, White...2009), the WiggleZ Dark Energy Survey (Blake et-al. 2011b......

Michele Moresco; Federico Marulli; Marco Baldi; Lauro Moscardini; Andrea Cimatti

2014-10-01T23:59:59.000Z

334

Cosmological toolkit project featured on DOE energy website | Argonne  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (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

335

Dark Energy Dipole in f(R T) Cosmological Model  

E-Print Network [OSTI]

Recent astronomical observations show that the universe may be anisotropic on large scales. The Union2 SnIa data hint that the universe has a preferred direction. If such a cosmological privileged axis indeed exists, one has to consider an anisotropic expanding Universe, instead of the isotropic cosmological model. In this paper, we present a detailed analysis of the cosmic dipoles in f(R; T) Cosmological Model. the maximum anisotropic deviation direction is (l, b) = (137,23) or equivalently (l, b) = (317,-23). Our numerical results show that, using Union2 data, the anisotropic f(R, T) model provides a significantly better fit than the isotropic f(R, T), CPL, and {\\Lambda}CDM models.

Salehi, Amin

2015-01-01T23:59:59.000Z

336

Cosmo++: An Object-Oriented C++ Library for Cosmology  

E-Print Network [OSTI]

This paper introduces a new publicly available numerical library for cosmology, Cosmo++. The library has been designed using object-oriented programming techniques, and fully implemented in C++. Cosmo++ introduces a unified interface for using most of the frequently used numerical methods in cosmology. Most of the features are implemented in Cosmo++ itself, while a part of the functionality is implemented by linking to other publicly available libraries. The most important features of the library are Cosmic Microwave Background anisotropies power spectrum and transfer function calculations, likelihood calculations, parameter space sampling tools, sky map simulations, and mask apodization. Cosmo++ also includes a few mathematical tools that are frequently used in numerical research in cosmology and beyond. A few simple examples are included in Cosmo++ to help the user understand the key features. The library has been fully tested, and we describe some of the important tests in this paper. Cosmo++ is publicly available at http://cosmo.grigoraslanyan.com

Grigor Aslanyan

2013-12-17T23:59:59.000Z

337

Magnetic Bianchi I Universe in Loop Quantum Cosmology  

E-Print Network [OSTI]

We examine the dynamical consequences of homogeneous cosmological magnetic fields in the framework of loop quantum cosmology. We show that a big-bounce occurs in a collapsing magnetized Bianchi I universe, thus extending the known cases of singularity-avoidance. Previous work has shown that perfect fluid Bianchi I universes in loop quantum cosmology avoid the singularity via a bounce. The fluid has zero anisotropic stress, and the shear anisotropy in this case is conserved through the bounce. By contrast, the magnetic field has nonzero anisotropic stress, and shear anisotropy is not conserved through the bounce. After the bounce, the universe enters a classical phase. The addition of a dust fluid does not change these results qualitatively.

Roy Maartens; Kevin Vandersloot

2008-12-10T23:59:59.000Z

338

Exponential cosmological redshift in a linearly expanding universe  

E-Print Network [OSTI]

The first principles analysis of the radiation by an arbitrary source in a flat Friedmann-Robertson-Walker space-time is presented. The obtained analytical solution explicitly shows that the cosmological redshift is not of kinematic origin and that the source and the observer may be regarded as being at rest with respect to eachother at all times. At the same time the effect of the time-variation of the metric on the propagation of light appears to be underestimated in the standard cosmology. The cosmological redshift caused by the linear time-variation of the metric turns out to be an exponential rather than linear function of the well-defined spatial distance and the apparent brightness of the source contains an even stronger exponential decay factor.

Neil V. Budko

2009-07-03T23:59:59.000Z

339

The cosmic coincidence in Brans-Dicke cosmologies  

E-Print Network [OSTI]

Among the suggested solutions to the cosmological constant problem, we find the idea of a dynamic vacuum, with an energy density decaying with the universe expansion. We investigate the possibility of a variation in the gravitational constant as well, induced, at the cosmological scale, by the vacuum decay. We consider an effective Brans-Dicke theory in the spatially flat FLRW spacetime, finding late time solutions characterized by a constant ratio between the matter and vacuum energy densities. By using the observed limits for the universe age, we fix the only free parameter of our solutions, obtaining a relative matter density in the range 0.25-0.4. In particular, for Ht = 1 we obtain a relative matter density equals to 1/3. This constitutes a possible explanation for another problem related to the cosmological term, the cosmic coincidence problem.

Carneiro, S

2005-01-01T23:59:59.000Z

340

The Expansion of the Universe and the Cosmological Constant Problem  

E-Print Network [OSTI]

The discovery that the expansion of the universe is accelerating in time is a major discovery which still awaits adequate explanation. It is generally agreed that this implies a cosmic repulsion as a result of the existence of a cosmological constant . However, estimates of the cosmological constant, based on calculations of the zero-point fluctuations of quantum fields are too large by over a hundred orders of magnitude. This result is obtained by summing the zero-point energies up to a large cutoff energy, based on the Planck scale. Since there is no compelling reason for this choice, we argue that since all known quantum electrodynamic (QED) effects involves interaction with matter, a preferred choice should be based on causality and other considerations, leading to a much lower value for the cosmological constant .

O'Connell, R F

2007-01-01T23:59:59.000Z

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

Structure of Cosmological CP Violation via Neutrino Seesaw  

E-Print Network [OSTI]

The cosmological matter-antimatter asymmetry can originate from CP-violating interactions of seesaw Majorana neutrinos via leptogenesis in the thermal phase of the early universe. Having the cosmological CP-phase for leptogenesis requires at least two right-handed Majorana neutrinos. Using only the low energy neutrino observables we quantitatively reconstruct a minimal neutrino seesaw. We establish a general criterion for minimal seesaw schemes in which the cosmological CP-phase is {\\it completely} reconstructed from the low energy CP-phases measured by neutrino oscillation and neutrinoless double-beta decay experiments. We reveal and analyze two distinct classes of such minimal schemes that are shown to be highly predictive. Extension of our reconstruction formalism to a three-heavy-neutrino seesaw is discussed.

V. Barger; Duane A. Dicus; Hong-Jian He; Tianjun Li

2003-12-16T23:59:59.000Z

342

Planck Scale Cosmology and Asymptotic Safety in Resummed Quantum Gravity  

E-Print Network [OSTI]

In Weinberg's asymptotic safety approach, a finite dimensional critical surface for a UV stable fixed point generates a theory of quantum gravity with a finite number of physical parameters. We argue that, in an extension of Feynman's original formulation of the theory, we recover this fixed-point UV behavior from an exact re-arrangement of the respective perturbative series. Our results are consistent with the exact field space Wilsonian renormalization group results of Reuter {\\it et al.} and with recent Hopf- algebraic Dyson-Schwinger renormalization theory results of Kreimer. We obtain the first "first principles" predictions of the dimensionless gravitational and cosmological constants and our results support the Planck scale cosmology of Bonanno and Reuter. We conclude with an estimate for the currently observed value of the cosmological constant.

B. F. L. Ward

2010-12-13T23:59:59.000Z

343

A Nested Sampling Algorithm for Cosmological Model Selection  

E-Print Network [OSTI]

The abundance of new cosmological data becoming available means that a wider range of cosmological models are testable than ever before. However, an important distinction must be made between parameter fitting and model selection. While parameter fitting simply determines how well a model fits the data, model selection statistics, such as the Bayesian Evidence, are now necessary to choose between these different models, and in particular to assess the need for new parameters. We implement a new evidence algorithm known as nested sampling, which combines accuracy, generality of application and computational feasibility, and apply it to some cosmological datasets and models. We find that a five-parameter model with Harrison-Zel'dovich initial spectrum is currently preferred.

Pia Mukherjee; David Parkinson; Andrew R. Liddle

2006-01-11T23:59:59.000Z

344

Reconstruction of $5D$ Cosmological Models From Equation of State of Dark Energy  

E-Print Network [OSTI]

We consider a class of five-dimensional cosmological solutions which contains two arbitrary function $\\mu(t)$ and $\

Lixin Xu; Hongya Liu; Chengwu Zhang

2005-10-24T23:59:59.000Z

345

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

Broader source: Energy.gov (indexed) [DOE]

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.

346

Kaluza-Klein Type Robertson Walker Cosmological Model With Dynamical Cosmological Term $\\Lambda$  

E-Print Network [OSTI]

In this paper we have analyzed the Kaluza-Klein type Robertson Walker (RW) cosmological models by considering three different forms of variable $\\Lambda$: $\\Lambda\\sim(\\frac{\\dot{a}}{a})^2$,$\\Lambda\\sim(\\frac{\\ddot{a}} {a})$ and $\\Lambda \\sim \\rho$. It is found that, the connecting free parameters of the models with cosmic matter and vacuum energy density parameters are equivalent, in the context of higher dimensional space time. The expression for the look back time, luminosity distance and angular diameter distance are also derived. This work has thus generalized to higher dimensions the well-known results in four dimensional space time. It is found that there may be significant difference in principle at least, from the analogous situation in four dimensional space time.

Pradhan, A; Otarod, S; Patki, V

2005-01-01T23:59:59.000Z

347

The Cosmic Quartet - Cosmological Parameters of a Smoothed Inhomogeneous Spacetime  

E-Print Network [OSTI]

We discuss the relation between `bare' cosmological parameters as the true spatial average characteristics that determine the cosmological model, and the parameters interpreted by observers with a `Friedmannian bias', i.e., within a homogeneous space geometry. We may say that the latter are `dressed' by the smoothed-out geometrical inhomogeneities of the surveyed spatial region. We identify two effects that quantify the difference between `bare' and `dressed' parameters: `curvature backreaction' and `volume effect'. An estimate of the latter is given in terms of a simple geometrical example.

Thomas Buchert; Mauro Carfora

2003-12-25T23:59:59.000Z

348

Phase-space analysis of interacting phantom cosmology  

SciTech Connect (OSTI)

We perform a detailed phase-space analysis of various phantom cosmological models, where the dark energy sector interacts with the dark matter one. We examine whether there exist late-time scaling attractors, corresponding to an accelerating universe and possessing dark energy and dark matter densities of the same order. We find that all the examined models, although accepting stable late-time accelerated solutions, cannot alleviate the coincidence problem, unless one imposes a form of fine-tuning in the model parameters. It seems that interacting phantom cosmology cannot fulfill the basic requirement that led to its construction.

Chen, Xi-ming; Gong, Yungui [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China)] [College of Mathematics and Physics, Chongqing University of Posts and Telecommunications, Chongqing 400065 (China); Saridakis, Emmanuel N., E-mail: chenxm@cqupt.edu.cn, E-mail: gongyg@cqupt.edu.cn, E-mail: msaridak@phys.uoa.gr [Department of Physics, University of Athens, GR-15771 Athens (Greece)

2009-04-15T23:59:59.000Z

349

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

350

Primordial Black Hole Evolution in Tensor-Scalar Cosmology  

Science Journals Connector (OSTI)

A perturbative analysis shows that black holes do not remember the value of the scalar field ? at the time they formed if ? changes in tensor-scalar cosmology. Moreover, even when the black hole mass in the Einstein frame is approximately unaffected by the changing of ?, in the Jordan-Fierz frame the mass increases. This mass increase requires a reanalysis of the evaporation of primordial black holes in tensor-scalar cosmology. It also implies that there could have been a significant magnification of the (Jordan-Fierz frame) mass of primordial black holes.

Ted Jacobson

1999-10-04T23:59:59.000Z

351

A Modified FRW Metric to Explain the Cosmological Constant  

E-Print Network [OSTI]

One of the most outstanding problems of the standard model of cosmology today is the problem of cosmological constant/dark energy. It corresponds to about 73 per cent of the energy content of the universe gone missing. I hereby postulate a modified FRW metric for our universe, which animates a universe spinning rigidly but very slowly with an angular frequency that is equal to the Hubble constant. It is shown by a simple argument that in such a universe there will be an overlooked rotational energy whose average value is identically equal to the matter-energy content of this universe as observed by a coordinate observer.

Serkan Zorba

2012-10-02T23:59:59.000Z

352

Implementing the DC Mode in Cosmological Simulations with Supercomoving Variables  

DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

As emphasized by previous studies, proper treatment of the density fluctuation on the fundamental scale of a cosmological simulation volume - the 'DC mode' - is critical for accurate modeling of spatial correlations on scales ~> 10% of simulation box size. We provide further illustration of the effects of the DC mode on the abundance of halos in small boxes and show that it is straightforward to incorporate this mode in cosmological codes that use the 'supercomoving' variables. The equations governing evolution of dark matter and baryons recast with these variables are particularly simple and include the expansion factor, and hence the effect of the DC mode, explicitly only in the Poisson equation.

Gnedin, Nickolay Y.; Kravtsov, Andrey V.; Rudd, Douglas H.

2011-06-02T23:59:59.000Z

353

The Quantum Vacuum and the Cosmological Constant Problem  

E-Print Network [OSTI]

The cosmological constant problem arises at the intersection between general relativity and quantum field theory, and is regarded as a fundamental problem in modern physics. In this paper we describe the historical and conceptual origin of the cosmological constant problem which is intimately connected to the vacuum concept in quantum field theory. We critically discuss how the problem rests on the notion of physical real vacuum energy, and which relations between general relativity and quantum field theory are assumed in order to make the problem well-defined.

Svend Erik Rugh; Henrik Zinkernagel

2000-12-28T23:59:59.000Z

354

The Quantum Vacuum and the Cosmological Constant Problem  

E-Print Network [OSTI]

The cosmological constant problem arises at the intersection between general relativity and quantum field theory, and is regarded as a fundamental problem in modern physics. In this paper we describe the historical and conceptual origin of the cosmological constant problem which is intimately connected to the vacuum concept in quantum field theory. We critically discuss how the problem rests on the notion of physical real vacuum energy, and which relations between general relativity and quantum field theory are assumed in order to make the problem well-defined.

Rugh, S E; Rugh, Svend Erik; Zinkernagel, Henrik

2000-01-01T23:59:59.000Z

355

Duality linking standard and tachyon scalar field cosmologies  

SciTech Connect (OSTI)

In this work we investigate the duality linking standard and tachyon scalar field homogeneous and isotropic cosmologies in N+1 dimensions. We determine the transformation between standard and tachyon scalar fields and between their associated potentials, corresponding to the same background evolution. We show that, in general, the duality is broken at a perturbative level, when deviations from a homogeneous and isotropic background are taken into account. However, we find that for slow-rolling fields the duality is still preserved at a linear level. We illustrate our results with specific examples of cosmological relevance, where the correspondence between scalar and tachyon scalar field models can be calculated explicitly.

Avelino, P. P.; Bazeia, D.; Losano, L.; Oliveira, J. C. R. E.; Pavan, A. B. [Centro de Fisica do Porto, Rua do Campo Alegre 687, 4169-007 Porto, Portugal and Departamento de Fisica da Faculdade de Ciencias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Departamento de Fisica, Universidade Federal da Paraiba, 58051-970 Joao Pessoa, Paraiba (Brazil); Centro de Fisica do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal) and Departamento de Engenharia Fisica da Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto (Portugal); Instituto de Fisica, Universidade de Sao Paulo, Caixa Postal 66318, 05315-970 Sao Paulo SP (Brazil)

2010-09-15T23:59:59.000Z

356

A Simple Cosmological Model with Decreasing Light Speed  

E-Print Network [OSTI]

An alternative model describing the dynamics of a flat Universe without cosmological constant and allowing a gradual change of c with time is proposed. New relationships of redshift vs. distance and cosmic background radiation temperature are given. Values for the Universal radius, matter density, Hubble parameter, light deceleration, cosmic age and recombination time are obtained. Distant SNeIa faintness is explained within this decelerating, matter-dominated Universe without invoking dark energy. Horizon, flatness and other problems of standard Big Bang cosmology are solved without the need of inflation. The top speed of any signal, force, particle or wave at any time is limited by the expansion speed of the Universe itself.

Juan Casado Gimenez

2003-10-07T23:59:59.000Z

357

Variable-speed-of-light cosmology and second law of thermodynamics  

Science Journals Connector (OSTI)

We examine whether cosmologies with a varying speed of light (VSL) are compatible with the second law of thermodynamics. We find that the VSL cosmology with a varying fundamental constant is severely constrained by the second law of thermodynamics, whereas the bimetric cosmological models are less constrained.

Donam Youm

2002-08-12T23:59:59.000Z

358

Evolution of density perturbations in decaying vacuum cosmology: The case of nonzero perturbations in the cosmological term  

SciTech Connect (OSTI)

We extend the results of a previous paper where a model of interacting dark energy, with a cosmological term decaying linearly with the Hubble parameter, is tested against the observed mass power spectrum. In spite of the agreement with observations of type Ia supernovas, baryonic acoustic oscillations, and the cosmic microwave background, we had shown previously that no good concordance is achieved if we include the mass power spectrum. However, our analysis was based on the ad hoc assumption that the interacting cosmological term is strictly homogeneous. Now we perform a more complete analysis, by perturbing such a term. Although our conclusions are still based on a particular, scale-invariant choice of the primordial spectrum of dark energy perturbations, we show that a cosmological term decaying linearly with the Hubble parameter is indeed disfavored as compared to the standard model.

Borges, H. A. [Instituto de Fisica, Universidade Federal da Bahia, Salvador, BA (Brazil); Centro de Formacao de Professores, Universidade Federal do Reconcavo da Bahia, Amargosa, BA (Brazil); Carneiro, S. [Instituto de Fisica, Universidade Federal da Bahia, Salvador, BA (Brazil); Astronomy Unit, School of Mathematical Sciences, Queen Mary, University of London, London (United Kingdom); Fabris, J. C. [Departamento de Fisica, Universidade Federal do Espirito Santo, Vitoria, ES (Brazil); Institut d'Astrophysique de Paris, Paris (France)

2008-12-15T23:59:59.000Z

359

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

SciTech Connect (OSTI)

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

360

Effects of a time-varying color-luminosity parameter $?$ on the cosmological constraints of modified gravity models  

E-Print Network [OSTI]

It has been found that, for the Supernova Legacy Survey three-year (SNLS3) data, there is strong evidence for the redshift-evolution of color-luminosity parameter $\\beta$. In previous studies, only dark energy (DE) models are used to explore the effects of a time-varying $\\beta$ on parameter estimation. In this paper, we extend the discussions to the case of modified gravity (MG), by considering Dvali-Gabadadze-Porrati (DGP) model, power-law type $f(T)$ model and exponential type $f(T)$ model. In addition to the SNLS3 data, we also use the latest Planck distance priors data, the galaxy clustering (GC) data extracted from Sloan Digital Sky Survey (SDSS) data release 7 (DR7) and Baryon Oscillation Spectroscopic Survey (BOSS), as well as the direct measurement of Hubble constant $H_0$ from the Hubble Space Telescope (HST) observation. We find that, for both cases of using the supernova (SN) data alone and using the combination of all data, adding a parameter of $\\beta$ can reduce $\\chi^2$ by $\\sim$ 36 for all the MG models, showing that a constant $\\beta$ is ruled out at 6$\\sigma$ confidence level (CL). Moreover, we find that a time-varying $\\beta$ always yields a larger fractional matter density $\\Omega_{m0}$ and a smaller reduced Hubble constant $h$; in addition, it significantly changes the shapes of 1$\\sigma$ and 2$\\sigma$ confidence regions of various MG models, and thus corrects systematic bias for the parameter estimation. These conclusions are consistent with the results of DE models, showing that $\\beta$'s evolution is completely independent of the cosmological models in the background. Therefore, our work highlights the importance of considering the evolution of $\\beta$ in the cosmology-fits.

Shuang Wang; Yong-Zhen Wang; Xin Zhang

2014-07-28T23:59:59.000Z

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.


361

Design constraints on Cherenkov telescopes with Davies-Cotton reflectors  

E-Print Network [OSTI]

This paper discusses the construction of high-performance ground-based gamma-ray Cherenkov telescopes with a Davies-Cotton reflector. For the design of such telescopes, usually physics constrains the field-of-view, while the photo-sensor size is defined by limited options. Including the effect of light-concentrators in front of the photo sensor, it is demonstrated that these constraints are enough to mutually constrain all other design parameters. The dependability of the various design parameters naturally arises once a relationship between the value of the point-spread functions at the edge of the field-of-view and the pixel field-of-view is introduced. To be able to include this constraint into a system of equations, an analytical description for the point-spread function of a tessellated Davies-Cotton reflector is derived from Taylor developments and ray-tracing simulations. Including higher order terms renders the result precise on the percent level. Design curves are provided within the typical phase sp...

Bretz, Thomas

2013-01-01T23:59:59.000Z

362

The Trigger Algorithm for the Burst Alert Telescope on Swift  

E-Print Network [OSTI]

The Swift Burst Alert Telescope (BAT) is a huge (5200 cm2) coded aperture imager that will detect gamma-ray bursts in real time and provide a location that the Swift satellite will use to slew the optical and x-ray telescopes. The huge size of BAT is a challenge for the on-board triggering: a change as small as 1% is equivalent to a 1 sigma statistical variation in 1 second. There will be three types of triggers, two based on rates and one based on images. The first type of trigger is for short time scales (4 msec to 64 msec). These will be traditional triggers (single background) and we check about 25,000 combinations of time-energy-focal plane subregions per second. The second type of trigger will be similar to what is used on HETE: fits to multiple background regions to remove trends for time scales between 64 msec and 64 seconds. About 500 triggers will be checked per second. For these rate triggers, false triggers and variable non-GRB sources will be rejected by requiring a new source to be present in an...

Fenimore, E; Galassi, M; Gehrels, N; Palmer, D; Parsons, A; Tavenner, T; Tüller, J

2004-01-01T23:59:59.000Z

363

Cosmological evolutions of F(R) nonlinear massive gravity  

Science Journals Connector (OSTI)

Recently a new extended nonlinear massive gravity model has been proposed which includes the F(R) modifications to the de Rham–Gabadadze–Tolley model. We follow the F(R) nonlinear massive gravity and study its implications on cosmological evolutions. We derive the critical points of the cosmic system and study the corresponding kinetics by performing the phase-plane analysis.

De-Jun Wu

2014-08-25T23:59:59.000Z

364

The origin of the Hubble sequence in CDM cosmology  

Science Journals Connector (OSTI)

......Hubble sequence in lambdaCDM cosmology Andrew J. Benson 1 * Nick Devereux 2 * *E-mail: abenson@caltech.edu (AJB...time and gas content of each model galaxy). The principal merits of the Perez-Gonzalez et al. (2008) work are that the SSF......

Andrew J. Benson; Nick Devereux

2010-03-11T23:59:59.000Z

365

Bouncing Loop Quantum Cosmology from $F(T)$ gravity  

E-Print Network [OSTI]

The big bang singularity could be understood as a breakdown of Einstein's General Relativity at very high energies. Adopting this viewpoint, other theories, that implement Einstein Cosmology at high energies, might solve the problem of the primeval singularity. One of them is Loop Quantum Cosmology (LQC) with a small cosmological constant that models a universe moving along an ellipse, which prevents singularities like the big bang or the big rip, in the phase space $(H,\\rho)$, where $H$ is the Hubble parameter and $\\rho$ the energy density of the universe. Using LQC when one considers a model of universe filled by radiation and matter where, due to the cosmological constant, there are a de Sitter and an anti de Sitter solution. This means that one obtains a bouncing non-singular universe which is in the contracting phase at early times. After leaving this phase, i.e., after bouncing, it passes trough a radiation and matter dominated phase and finally at late times it expands in an accelerated way (current co...

Amorós, Jaume; Odintsov, Sergei D

2013-01-01T23:59:59.000Z

366

Dark energy and dark matter from cosmological observations  

E-Print Network [OSTI]

The present status of our knowledge about the dark matter and dark energy is reviewed. Bounds on the content of cold and hot dark matter from cosmological observations are discussed in some detail. I also review current bounds on the physical properties of dark energy, mainly its equation of state and effective speed of sound.

Steen Hannestad

2005-09-13T23:59:59.000Z

367

No Open or Flat Bouncing Cosmologies in Einstein Gravity  

E-Print Network [OSTI]

We show that bouncing open or flat Friedmann-Robertson-Walker cosmologies are inconsistent with worldsheet string theory to first approximation. Specifically, the Virasoro constraint translates to the null energy condition in spacetime at leading order in the alpha-prime expansion. Thus one must go beyond minimally-coupled Einstein gravity in order to find bounce solutions.

Parikh, Maulik K

2015-01-01T23:59:59.000Z

368

Cosmological-Parameter Determination with Microwave Background Maps  

E-Print Network [OSTI]

The angular power spectrum of the cosmic microwave background (CMB) contains information on virtually all cosmological parameters of interest, including the geometry of the Universe ($\\Omega$), the baryon density, the Hubble constant ($h$), the cosmological constant ($\\Lambda$), the number of light neutrinos, the ionization history, and the amplitudes and spectral indices of the primordial scalar and tensor perturbation spectra. We review the imprint of each parameter on the CMB. Assuming only that the primordial perturbations were adiabatic, we use a covariance-matrix approach to estimate the precision with which these parameters can be determined by a CMB temperature map as a function of the fraction of sky mapped, the level of pixel noise, and the angular resolution. For example, with no prior information about any of the cosmological parameters, a full-sky CMB map with $0.5^\\circ$ angular resolution and a noise level of 15 $\\mu$K per pixel can determine $\\Omega$, $h$, and $\\Lambda$ with standard errors of $\\pm0.1$ or better, and provide determinations of other parameters which are inaccessible with traditional observations. Smaller beam sizes or prior information on some of the other parameters from other observations improves the sensitivity. The dependence on the the underlying cosmological model is discussed.

Gerard Jungman; Marc Kamionkowski; Arthur Kosowsky; David N. Spergel

1996-05-23T23:59:59.000Z

369

Measurement of the cosmological constant P. Antilogus a  

E-Print Network [OSTI]

. The usage of SN Ia to probe the vacuum energy and more generally to study the dark energy seems quite, let us expect a break through in the understanding of the dark energy, energy at the source of the observed acceleration of the universe expansion. 2. From the cosmological constant to the dark energy

Paris-Sud XI, Université de

370

Holography, Cosmology, and the Second Law of Thermodynamics  

Science Journals Connector (OSTI)

We propose that the holographic principle be replaced by the generalized second law of thermodynamics when applied to time-dependent backgrounds. For isotropic open and flat universes with a fixed equation of state, this agrees with the cosmological holographic principle proposed by Fischler and Susskind (hep-th/9806039). However, in more general situations, it does not.

Richard Easther and David Lowe

1999-06-21T23:59:59.000Z

371

The Age-Redshift Relation for Standard Cosmology  

E-Print Network [OSTI]

We present compact, analytic expressions for the age-redshift relation $\\tau(z)$ for standard Friedmann-Lema\\^ \\itre-Robertson-Walker (FLRW) cosmology. The new expressions are given in terms of incomplete Legendre elliptic integrals and evaluate much faster than by direct numerical integration.

R. C. Thomas; R. Kantowski

2000-08-10T23:59:59.000Z

372

CAPUT DARK ENERGY TOPICS, 2013 1. The Cosmological Constant  

E-Print Network [OSTI]

waves rule Physics Today, april 2008, 44 - Colless M. The WiggleZ Dark Energy Survey KIAS workshop 2008 Redshift Surveys ApJ 633, 575 - Seo H-J, Eisenstein D.J., 2005 Probing Dark Energy with Baryonic AcousticCAPUT DARK ENERGY TOPICS, 2013 1 #12;1. The Cosmological Constant - The acceleration

Weijgaert, Rien van de

373

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 energy came in 1990 in a galaxy survey study led by G. Efsthathiou of Cambridge. The analysis

Udgaonkar, Jayant B.

374

Quantum cosmologies with varying speed of light and the $?$ problem  

E-Print Network [OSTI]

In quantum cosmology the closed universe can spontaneously nucleate out of the state with no classical space and time. For the universe filled with a vacuum of constant energy density the semiclassical tunneling nucleation probability can be estimated as $\\emph{P}\\sim\\exp(-\\alpha^2/\\Lambda)$ where $\\alpha$=const and $\\Lambda$ is the cosmological constant, so once it nucleates, the universe immediately starts the de Sitter inflationary expansion. The probability $\\emph{P} $ will be large for values of $\\Lambda$ that are large enough, whereas $\\Lambda$ of our Universe is definitely small. Of course, for the early universe filled with radiation or another ''matter'' the mentioned probability is large nevertheless ($\\emph{P}\\sim 1$) but in this case we have no inflation which is a standard solution for the flatness and horizon problems. In the other hand, the alternative solution of these problems can be obtained in framework of cosmologies with varying speed of light $c(t)$ (VSL). We show that, as a matter of principle, such quantum VSL cosmologies exist that $\\emph{P}\\sim 1$, $\\rho_{_\\Lambda}/\\rho_c\\sim 0.7$ ($\\Lambda$-problem) and both horizon and flatness problems are solvable without inflation.

A. V. Yurov; V. A. Yurov

2005-02-06T23:59:59.000Z

375

Force-optimized alignment for optical control of the Advanced Technology Solar Telescope  

Science Journals Connector (OSTI)

We present formalism and analysis of three active alignment reconstruction techniques applied to the Advanced Technology Solar Telescope. The three reconstructors generate optical...

Upton, Robert; Cho, Myung; Rimmele, Thomas

2010-01-01T23:59:59.000Z

376

First Fruits of the Spitzer Space Telescope: Galactic and Solar System Studies  

E-Print Network [OSTI]

This article provides a brief overview of the Spitzer Space Telescope and discusses its initial scientific results on galactic and solar system science.

M. Werner; G. Fazio; G. Rieke; T. Roellig; D. Watson

2006-06-22T23:59:59.000Z

377

Aplanatic two mirror telescope from near-normal to grazing incidence  

Science Journals Connector (OSTI)

Surface equations for strictly aplanatic two-mirror telescopes of any configuration are given. They were used in a comparative performance analysis of the general Cassegrainian...

Korsch, Dietrich

1980-01-01T23:59:59.000Z

378

E-Print Network 3.0 - avec les telescopes Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

2010 Summary: arcsec ou plus. Possible avec optique adaptative, ou telescopes hors atmosphere. 3- v V + 5 log10... etecter a cause de la turbulence atmospherique,...

379

E-Print Network 3.0 - avec le telescope Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

12;Allen Telescope Array ATA Team Source: New Jersey Institute of Technology, Center for Solar-Terrestrial Research Collection: Physics 5 Remerciements Yannick Mellier m'a...

380

A Thousand Problems in Cosmology: Interaction in the Dark Sector  

E-Print Network [OSTI]

This is one chapter of the collection of problems in cosmology, in which we assemble the problems that concern one of the most distinctive features of modern cosmology---the interaction in the Dark Sector. The evolution of any broadly applied model is accompanied by multiple generalizations that aim to resolve conceptual difficulties and to explain the ever-growing pool of observational data. In the case of Standard Cosmological Model one of the most promising directions of generalization is replacement of the cosmological constant with a more complicated, dynamic, form of dark energy and incorporation of interaction between the dark components---dark energy (DE) and dark matter (DM). Typically, DE models are based on scalar fields minimally coupled to gravity, and do not implement explicit coupling of the field to the background DM. However, there is no fundamental reason for this assumption in the absence of an underlying symmetry which would suppress the coupling. Given that we do not know the true nature of either DE or DM, we cannot exclude the possibility that there is some kind of coupling between them. Whereas interactions between DE and normal matter particles are heavily constrained by observations (e.g. in the solar system and gravitational experiments on Earth), this is not the case for DM particles. In other words, it is possible for the dark components to interact with each other while not being coupled to standard model particles. Therefore, the possibility of DE-DM interaction should be investigated with utmost gravity. This version contains only formulations of 117 problems. The full collection, with solutions included, is available in the form of a wiki-based resource at universeinproblems.com. The cosmological community is welcome to contribute to its development.

Yu. L. Bolotin; V. A. Cherkaskiy; O. A. Lemets; I. V. Tanatarov; D. A. Yerokhin

2013-12-18T23:59:59.000Z

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.


381

LXCDM: a cosmon model solution to the cosmological coincidence problem?  

E-Print Network [OSTI]

We consider the possibility that the total dark energy (DE) of the Universe is made out of two dynamical components of different nature: a variable cosmological term, Lambda, and a dynamical ``cosmon'', X, possibly interacting with Lambda but not with matter -- which remains conserved. We call this scenario the LXCDM model. One possibility for X would be a scalar field, but it is not the only one. The overall equation of state (EOS) of the LXCDM model can effectively appear as quintessence or phantom energy depending on the mixture of the two components. Both the dynamics of Lambda and of X could be linked to high energy effects near the Planck scale. In the case of Lambda it may be related to the running of this parameter under quantum effects, whereas X might be identified with some fundamental field (say, a dilaton) left over as a low-energy ``relic'' by e.g. string theory. We find that the dynamics of the LXCDM model can trigger a future stopping of the Universe expansion and can keep the ratio rho_D/rho_m (DE density to matter-radiation density) bounded and of order 1. Therefore, the model could explain the so-called ``cosmological coincidence problem''. This is in part related to the possibility that the present value of the cosmological term can be Lambda0 because of the peculiar behavior of X as ``Phantom Matter''. We describe various cosmological scenarios made possible by the composite and dynamical nature of LXCDM, and discuss in detail their impact on the cosmological coincidence problem.

Javier Grande; Joan Sola; Hrvoje Stefancic

2006-08-06T23:59:59.000Z

382

The Balloon-borne Large Aperture Sub-millimetre Telescope  

E-Print Network [OSTI]

The Balloon-borne Large-Aperture Sub-millimetre Telescope (BLAST) will operate on a Long Duration Balloon platform with large format bolometer arrays at 250, 350 and 500 microns, initially using a 2m mirror, with plans to increase to 2.5m. BLAST is a collaboration between scientists in the USA, Canada, UK, Italy and Mexico. Funding has been approved and it is now in its building phase. The test flight is scheduled for 2002, with the first long duration flight the following year. The scientific goals are to learn about the nature of distant extragalactic star forming galaxies and cold pre-stellar sources by making deep maps both at high and low galactic latitudes. BLAST will be useful for planning Herschel key projects which use SPIRE.

Douglas Scott; the BLAST Team

2001-04-03T23:59:59.000Z

383

The Greenland Telescope (GLT): Antenna status and future plans  

E-Print Network [OSTI]

The ALMA North America Prototype Antenna was awarded to the Smithsonian Astrophysical Observatory (SAO) in 2011. SAO and the Academia Sinica Institute of Astronomy & Astrophysics (ASIAA), SAO's main partner for this project, are working jointly to relocate the antenna to Greenland to carry out millimeter and submillimeter VLBI observations. This paper presents the work carried out on upgrading the antenna to enable operation in the Arctic climate by the GLT Team to make this challenging project possible, with an emphasis on the unexpected telescope components that had to be either redesigned or changed. Five-years of inactivity, with the antenna laying idle in the desert of New Mexico, coupled with the extreme weather conditions of the selected site in Greenland have it necessary to significantly refurbish the antenna. We found that many components did need to be replaced, such as the antenna support cone, the azimuth bearing, the carbon fiber quadrupod, the hexapod, the HVAC, the tiltmeters, the antenna ...

Raffin, Philippe; Asada, Keichi; Blundell, Raymond; Burgos, Roberto; Chang, Chih-Cheng; Chen, Ming-Tang; Christensen, Robert; Grimes, Paul K; Han, C C; Ho, Paul T P; Huang, Yau-De; Inoue, Makoto; Koch, Patrick M; Kubo, Derek; Leiker, Steve; Liu, Ching-Tang; Martin-Cocher, Pierre; Matsushita, Satoki; Nakamura, Masanori; Nishioka, Hiroaki; Nystrom, George; Paine, Scott N; Patel, Nimesh A; Pradel, Nicolas; Pu, Hung-Yi; Shen, H -Y; Snow, William; Sridharan, T K; Srinivasan, Ranjani; Tong, Edward; Wang, Jackie

2014-01-01T23:59:59.000Z

384

BOOMERANG: A Balloon-borne Millimeter-Wave Telescope  

Science Journals Connector (OSTI)

We describe BOOMERANG, a balloon-borne microwave telescope designed to map the cosmic microwave background at a resolution of 10' from the Long Duration Balloon (LDB) platform. The millimeter-wave receiver employs new technology in bolometers, readout electronics, cold reimaging optics, millimeter-wave filters, and cryogenics to obtain high sensitivity to cosmic microwave background anisotropy. Sixteen detectors observe in four spectral bands centered at 90, 150, 240, and 410 GHz. The wide frequency coverage, the long-duration flight, the optical design, and the observing strategy provide strong rejection of systematic effects. We report the flight performance of the instrument during a 10.5 day stratospheric balloon flight launched from McMurdo Station, Antarctica, that mapped ~2000 square degrees of the sky.

B. P. Crill; P. A. R. Ade; D. R. Artusa; R. S. Bhatia; J. J. Bock; A. Boscaleri; P. Cardoni; S. E. Church; K. Coble; P. de Bernardis; G. de Troia; P. Farese; K. M. Ganga; M. Giacometti; C. V. Haynes; E. Hivon; V. V. Hristov; A. Iacoangeli; W. C. Jones; A. E. Lange; L. Martinis; S. Masi; P. V. Mason; P. D. Mauskopf; L. Miglio; T. Montroy; C. B. Netterfield; C. G. Paine; E. Pascale; F. Piacentini; G. Polenta; F. Pongetti; G. Romeo; J. E. Ruhl; F. Scaramuzzi; D. Sforna; A. D. Turner

2003-01-01T23:59:59.000Z

385

Exact Optics A unification of optical telescope design  

E-Print Network [OSTI]

A perfect focus telescope is one in which all rays parallel to the axis meet at a point and give equal magnification there. It is shown that these two conditions define the shapes of both primary and secondary mirrors. Apart from scale, the solution depends upon two parameters, $s$, which gives the mirror separation in terms of the effective focal length, and $K$, which gives the relative position of the final focus in that unit. The two conditions ensure that the optical systems have neither spherical aberration nor coma, no matter how fast the $f$ ratio. All known coma--free systems emerge as approximate special cases. In his classical paper, K. Schwarzschild studied all two mirror systems whose profiles were conic sections. We make no such a priori shape conditions but demand a perfect focus and solve for the mirrors' shapes.

Lynden-Bell, Donald

2002-01-01T23:59:59.000Z

386

Figures of merit for testing standard models: application to dark energy experiments in cosmology  

Science Journals Connector (OSTI)

......Kilo-Degree Survey (KIDS), Panoramic Survey Telescope Rapid Response System (Pan-STARRS),1 Dark Energy Survey (DES),2 Large Synoptic Survey Telescope (LSST),3 Joint Dark Energy Mission (JDEM)4 and Euclid.5......

A. Amara; T. D. Kitching

2011-05-21T23:59:59.000Z

387

The Fermi Large Area gamma ray Telescope and the current searches for dark matter in space  

E-Print Network [OSTI]

production [6],[7] [9]. The temptation to claim the discovery of dark matter is strongThe Fermi Large Area gamma ray Telescope and the current searches for dark matter in space Aldo Gamma-ray Space Telescope, has detected the largest amount of gamma rays, in the 20MeV 300GeV energy

Morselli, Aldo

388

The Cosmic Web Imager : An integral field spectrograph for the Hale Telescope at Palomar Observatory. Instrument  

E-Print Network [OSTI]

The Cosmic Web Imager : An integral field spectrograph for the Hale Telescope at Palomar for the Hale 200" telescope at the Palomar Observatory. CWI has been built specifically for the observation), and oxygen (OVI 1036°A) to detect and map diffuse gas around and between galaxies and quasars at redshifts 2

Martin, Chris

389

Proceedings of ICRC 2001: 741 c Copernicus Gesellschaft 2001 Calibration of the Auger Fluorescence Telescopes  

E-Print Network [OSTI]

Norte 304, (5613) Malarg¨ue, Argentina Abstract. Thirty fluorescence telescopes in four stations development (Xmax) and determi- nation of the absolute energy of EHE events. A telescope camera contains 440 in Argentina are discussed. 1 Introduction The southern hemisphere experiment of the Pierre Auger Ob- servatory

390

Design study of 8 meter monolithic mirror UV/optical space telescope H. Philip Stahl  

E-Print Network [OSTI]

Design study of 8 meter monolithic mirror UV/optical space telescope H. Philip Stahl NASA Marshall Space Flight Center, Huntsville, AL 35812 ABSTRACT The planned Ares V launch vehicle with its 10 meter to 8 meter class monolithic primary mirror telescope to Sun-Earth L2 using an Ares V. Specific

Sirianni, Marco

391

Active Optics Performance Study of the Primary Mirror of the Gemini Telescopes Project  

E-Print Network [OSTI]

Active Optics Performance Study of the Primary Mirror of the Gemini Telescopes Project Myung K. Cho Optical Sciences Center in the University of Arizona Tucson, AZ 85721 and Gemini Telescopes Project P. O. Box 26732 Tucson, AZ 85726­6732 Gemini Preprint #9 #12; Active optics performance study of the primary

392

Cornelis Zwaan, open principle, and the future of high-resolution solar telescopes  

E-Print Network [OSTI]

Cornelis Zwaan, open principle, and the future of high-resolution solar telescopes Robert H erected up till 30 m height with sensors at several heights for the measurement of temperature; (iii) the design consequences for the new generation of high-resolution solar telescopes. Keywords

Rutten, Rob

393

Type Ia Supernova Discoveries at z>1 From the Hubble Space Telescope: Evidence for Past Deceleration and Constraints on Dark Energy Evolution  

E-Print Network [OSTI]

We have discovered 16 Type Ia supernovae (SNe Ia) with the Hubble Space Telescope (HST) and have used them to provide the first conclusive evidence for cosmic deceleration that preceded the current epoch of cosmic acceleration. These objects, discovered during the course of the GOODS ACS Treasury program, include 6 of the 7 highest-redshift SNe Ia known, all at z>1.25, and populate the Hubble diagram in unexplored territory. The luminosity distances to these and 170 previous SNe Ia are provided. A purely kinematic interpretation of the SN Ia sample provides evidence at the > 99% confidence level for a transition from deceleration to acceleration or similarly, strong evidence for a cosmic jerk. Using a simple model of the expansion history, the transition between the two epochs is constrained to be at z=0.46 +/- 0.13. The data are consistent with the cosmic concordance model of Omega_M ~ 0.3, Omega_Lambda~0.7 (chi^2_dof=1.06), and are inconsistent with a simple model of evolution or dust as an alternative to dark energy. For a flat Universe with a cosmological constant. When combined with external flat-Universe constraints we find w=-1.02 + 0.13 - 0.19 (and $dark energy, P = w\\rho c^2. Joint constraints on both the recent equation of state of dark energy, $w_0$, and its time evolution, dw/dz, are a factor of ~8 more precise than its first estimate and twice as precise as those without the SNe Ia discovered with HST. Our constraints are consistent with the static nature of and value of w expected for a cosmological constant (i.e., w_0 = -1.0, dw/dz = 0), and are inconsistent with very rapid evolution of dark energy. We address consequences of evolving dark energy for the fate of the Universe.

Adam G. Riess; Louis-Gregory Strolger; John Tonry; Stefano Casertano; Henry C. Ferguson; Bahram Mobasher; Peter Challis; Alexei V. Filippenko; Saurabh Jha; Weidong Li; Ryan Chornock; Robert P. Kirshner; Bruno Leibundgut; Mark Dickinson; Mario Livio; Mauro Giavalisco; Charles C. Steidel; Narciso Benitez; Zlatan Tsvetanov

2004-02-23T23:59:59.000Z

394

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

SciTech Connect (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

395

Dark radiation from particle decay: cosmological constraints and opportunities  

SciTech Connect (OSTI)

We study particle decay as the origin of dark radiation. After elaborating general properties and useful parametrisations we provide model-independent and easy-to-use constraints from nucleosynthesis, the cosmic microwave background and structure formation. Bounds on branching ratios and mass hierarchies depend in a unique way on the time of decay. We demonstrate their power to exclude well-motivated scenarios taking the example of the lightest ordinary sparticle decaying into the gravitino. We point out signatures and opportunities in cosmological observations and structure formation. For example, if there are two dark decay modes, dark radiation and the observed dark matter with adjustable free-streaming can originate from the same decaying particle, solving small-scale problems of structure formation. Hot dark matter mimicking a neutrino mass scale as deduced from cosmological observations can arise and possibly be distinguished after a discovery. Our results can be used as a guideline for model building.

Hasenkamp, Jasper; Kersten, Jörn, E-mail: Jasper.Hasenkamp@desy.de, E-mail: Joern.Kersten@desy.de [II. Institute for Theoretical Physics, University of Hamburg, 22761 Hamburg (Germany)

2013-08-01T23:59:59.000Z

396

Revisiting Noether gauge symmetry approach in quintom cosmology  

E-Print Network [OSTI]

The Noether gauge symmetry approach is revisited to study various quintom scenarios (those that arise by the presence of two dynamical scalar fields) to comprehend the role of dark energy in our universe. For such models, we obtain smooth parameterizations of the equation of state of dark energy across the boundary of cosmological constant $w_{\\Lambda}=-1$. This study gives rise to two new cases of the potential $V(\\phi, \\sigma)$, due to a quintom field in which nonlinear coupling of the scalar fields arise. Besides we report that a few cases of Noether gauge symmetries and their invariants in [Adnan Aslam, et. al., Astrophys Space Sci (2013), 348:533-540] are incorrect. Consequently, the given cosmological model in their paper is not a feasible quintom model.

Ali, Sajid

2015-01-01T23:59:59.000Z

397

Testing the cosmological constant as a candidate for dark energy  

SciTech Connect (OSTI)

It may be difficult to single out the best model of dark energy on the basis of the existing and planned cosmological observations, because many different models can lead to similar observational consequences. However, each particular model can be studied and either found consistent with observations or ruled out. In this paper, we concentrate on the possibility to test and rule out the simplest and by far the most popular of the models of dark energy, the theory described by general relativity with positive vacuum energy (the cosmological constant). We evaluate the conditions under which this model could be ruled out by the future observations made by the Supernova/Acceleration Probe SNAP (both for supernovae and weak lensing) and by the Planck Surveyor cosmic microwave background satellite.

Kratochvil, Jan; Linde, Andrei; Linder, Eric V.; Shmakova, Marina

2003-12-03T23:59:59.000Z

398

Concluding Remarks at the 12th Potsdam Cosmology Workshop  

E-Print Network [OSTI]

Research in cosmology traditionally divided into two separate lines. On the one hand was the search for initial conditions: the cosmological parameters H, Omega, Omega_b, and Lambda, and the power spectrum P(k). On the other hand was the study of the formation and evolution of structures, from globular-cluster sized objects to large-scale structures. These lines of investigation are now becoming increasingly intertwined, and this tendency manifested itself in this conference. Following is my personal perspective on where we stand today. I also discuss some technological developments that I think will affect the field. My concluding remarks are very informal. They are not a review paper, and I omit references altogether rather than give a partial list.

A. Yahil

1998-03-05T23:59:59.000Z

399

On gravitational waves in spacetimes with a nonvanishing cosmological constant  

SciTech Connect (OSTI)

We study the effect of a cosmological constant {lambda} on the propagation and detection of gravitational waves. To this purpose we investigate the linearized Einstein's equations with terms up to linear order in {lambda} in a de Sitter and an anti-de Sitter background spacetime. In this framework the cosmological term does not induce changes in the polarization states of the waves, whereas the amplitude gets modified with terms depending on {lambda}. Moreover, if a source emits a periodic waveform, its periodicity as measured by a distant observer gets modified. These effects are, however, extremely tiny and thus well below the detectability by some 20 orders of magnitude within present gravitational wave detectors such as LIGO or future planned ones such as LISA.

Naef, Joachim; Jetzer, Philippe; Sereno, Mauro [Institut fuer Theoretische Physik, Universitaet Zuerich, Winterthurerstrasse 190, CH-8057 Zuerich (Switzerland)

2009-01-15T23:59:59.000Z

400

Dark radiation from particle decay: cosmological constraints and opportunities  

E-Print Network [OSTI]

We study particle decay as the origin of dark radiation. After elaborating general properties and useful parametrisations we provide model-independent and easy-to-use constraints from nucleosynthesis, the cosmic microwave background and structure formation. Bounds on branching ratios and mass hierarchies depend in a unique way on the time of decay. We demonstrate their power to exclude well-motivated scenarios taking the example of the lightest ordinary sparticle decaying into the gravitino. We point out signatures and opportunities in cosmological observations and structure formation. For example, if there are two dark decay modes, dark radiation and the observed dark matter with adjustable free-streaming can originate from the same decaying particle, solving small-scale problems of structure formation. Hot dark matter mimicking a neutrino mass scale as deduced from cosmological observations can arise and possibly be distinguished after a discovery. Our results can be used as a guideline for model building.

Jasper Hasenkamp; Jörn Kersten

2014-02-13T23:59:59.000Z

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

Cosmic expansion and structure formation in running vacuum cosmologies  

E-Print Network [OSTI]

We investigate the dynamics of the FLRW flat cosmological models in which the vacuum energy varies with redshift. A particularly well motivated model of this type is the so-called quantum field vacuum, in which both kind of terms $H^{2}$ and constant appear in the effective dark energy density affecting the evolution of the main cosmological functions at the background and perturbation levels. Specifically, it turns out that the functional form of the quantum vacuum endows the vacuum energy of a mild dynamical evolution which could be observed nowadays and appears as dynamical dark energy. Interestingly, the low-energy behaviour is very close to the usual $\\Lambda$CDM model, but it is by no means identical. Finally, within the framework of the quantum field vacuum we generalize the large scale structure properties, namely growth of matter perturbations, cluster number counts and spherical collapse model.

Basilakos, Spyros

2015-01-01T23:59:59.000Z

402

Cosmological and astrophysical constraints on superconducting cosmic strings  

SciTech Connect (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 ?-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.

Miyamoto, Koichi [Institute for Cosmic Ray Research, University of Tokyo, Kashiwa 277-8582 (Japan); Nakayama, Kazunori, E-mail: miyamone@icrr.u-tokyo.ac.jp, E-mail: kazunori@hep-th.phys.s.u-tokyo.ac.jp [Department of Physics, University of Tokyo, Bunkyo-ku, Tokyo 113-0033 (Japan)

2013-07-01T23:59:59.000Z

403

Cosmology from HI galaxy surveys with the SKA  

E-Print Network [OSTI]

The Square Kilometer Array (SKA) has the potential to produce galaxy redshift surveys which will be competitive with other state of the art cosmological experiments in the next decade. In this chapter we summarise what capabilities the first and the second phases of the SKA will be able to achieve in its current state of design. We summarise the different cosmological experiments which are outlined in further detail in other chapters of this Science Book. The SKA will be able to produce competitive Baryonic Oscillation (BAOs) measurements in both its phases. The first phase of the SKA will provide similar measurements as optical and IR experiments with completely different systematic effects whereas the second phase being transformational in terms of its statistical power. The SKA will produce very accurate Redshift Space Distortions (RSD) measurements, being superior to other experiments at lower redshifts, due to the large number of galaxies. Cross correlations of the galaxy redshift data from the SKA with ...

Abdalla, Filipe B; Camera, Stefano; Benoit-Lévy, Aurélien; Joachimi, Benjamin; Kirk, Donnacha; Klöckner, Hans-Rainer; Maartens, Roy; Raccanelli, Alvise; Santos, Mario G; Zhao, Gong-Bo

2015-01-01T23:59:59.000Z

404

First cosmological constraints on the Superfluid Chaplygin gas model  

E-Print Network [OSTI]

In this work we set observational constraints of the Superfluid Chaplygin gas model, which gives a unified description of the dark sector of the Universe as a Bose-Einstein condensate (BEC) that behaves as dark energy (DE) while it is in the ground state and as dark matter (DM) when it is in the excited state. We first show and perform the various steps leading to a form of the equations suitable for the observational tests to be carried out. Then, by using a Markov Chain Monte Carlo (MCMC) code, we constrain the model with a sample of cosmology-independent long gamma-ray bursts (LGRBs) calibrated using their Type I Fundamental Plane, as well as the Union2.1 set and observational Hubble parameter data. In this analysis, using our cosmological constraints, we sketch the effective equation of state parameter and deceleration parameter, and we also obtain the redshift of the transition from deceleration to acceleration: $z_t$.

Lazkoz, Ruth; Salzano, Vincenzo

2012-01-01T23:59:59.000Z

405

First cosmological constraints on the Superfluid Chaplygin gas model  

E-Print Network [OSTI]

In this work we set observational constraints of the Superfluid Chaplygin gas model, which gives a unified description of the dark sector of the Universe as a Bose-Einstein condensate (BEC) that behaves as dark energy (DE) while it is in the ground state and as dark matter (DM) when it is in the excited state. We first show and perform the various steps leading to a form of the equations suitable for the observational tests to be carried out. Then, by using a Markov Chain Monte Carlo (MCMC) code, we constrain the model with a sample of cosmology-independent long gamma-ray bursts (LGRBs) calibrated using their Type I Fundamental Plane, as well as the Union2.1 set and observational Hubble parameter data. In this analysis, using our cosmological constraints, we sketch the effective equation of state parameter and deceleration parameter, and we also obtain the redshift of the transition from deceleration to acceleration: $z_t$.

Ruth Lazkoz; Ariadna Montiel; Vincenzo Salzano

2012-11-15T23:59:59.000Z

406

Bounce Models in Brane Cosmology and a Stability Condition  

E-Print Network [OSTI]

Five-dimensional cosmological models with two 3-branes and with a buck cosmological constant are studied. It is found that for all the three cases ($\\Lambda =0$, $\\Lambda >0$, and $\\Lambda 0$ case the brane solutions could give an oscillating universe model in which the universe oscillates with each cosmic cycle begins from a ``big bounce'' and ends to a ``big crunch'', with a distinctive characteristic that in each subsequent cycle the universe expands to a larger size and then contracts to a smaller (but non-zero) size. By studying the gravitational force acted on a test particle in the bulk, a stability condition is derived and then is used to analyze those brane models. It predicts that if dark energy takes over ordinary matter, particles on the brane may become unstable in the sense that they may escape from our 4D-world and dissolve in the bulk due to the repulsive force of dark energy.

Liu, H

2003-01-01T23:59:59.000Z

407

D-branes in Standard Model building, Gravity and Cosmology  

E-Print Network [OSTI]

D-branes are by now an integral part of our toolbox towards understanding nature. In this review we will describe recent progress in their use to realize fundamental interactions. The realization of the Standard Model and relevant physics and problems will be detailed. New ideas on realizing 4-dimensional gravity use the brane idea in an important way. Such approaches will be reviewed and compared to the standard paradigm of compactification. Branes can play a pivotal role both in early- and late-universe cosmology mainly via the brane-universe paradigm. Brane realizations of various cosmological ideas (early inflation, sources for dark matter and dark energy, massive gravity etc) will be also reviewed.

Elias Kiritsis

2004-05-14T23:59:59.000Z

408

Consistent metric combinations in cosmology of massive bigravity  

E-Print Network [OSTI]

Massive bigravity models are interesting alternatives to standard cosmology. In most cases however these models have been studied for a simplified scenario in which both metrics take homogeneous and isotropic forms (Friedmann-Lema\\^{i}tre-Robertson-Walker; FLRW) with the same spatial curvatures. The interest to consider more general geometries arises in particular in view of the difficulty so far encountered in building stable cosmological solutions with homogeneous and isotropic metrics. Here we consider a number of cases in which the two metrics take more general forms, namely FLRW with different spatial curvatures, Lema\\^{i}tre, Lema\\^{i}tre-Tolman-Bondi (LTB), and Bianchi I, as well as cases where only one metric is linearly perturbed. We discuss possible consistent combinations and find that only some special cases of FLRW-Lema\\^{i}tre, LTB-LTB and FLRW-Bianchi I combinations give consistent, non-trivial solutions.

Henrik Nersisyan; Yashar Akrami; Luca Amendola

2015-02-13T23:59:59.000Z

409

Colliding Impulsive Gravitational Waves and a Cosmological Constant  

E-Print Network [OSTI]

We present a space--time model of the collision of two homogeneous, plane impulsive gravitational waves (each having a delta function profile) propagating in a vacuum before collision and for which the post collision space--time has constant curvature. The profiles of the incoming waves are $k\\,\\delta(u)$ and $l\\,\\delta(v)$ where $k, l$ are real constants and $u=0, v=0$ are intersecting null hypersurfaces. The cosmological constant $\\Lambda$ in the post collision region of the space--time is given by $\\Lambda=-6\\,k\\,l$. In this sense this model collision provides a mechanism for generating a cosmological constant and therefore may be relevant to the theoretical description of dark energy.

Barrabès, C

2015-01-01T23:59:59.000Z

410

Chiral vortons and cosmological constraints on particle physics  

Science Journals Connector (OSTI)

We investigate the cosmological consequences of particle physics theories that admit stable loops of current-carrying string—vortons. In particular, we consider chiral theories where a single fermion zero mode is excited in the string core, such as those arising in supersymmetric theories with a D term. The resulting vortons formed in such theories are expected to be more stable than their nonchiral cousins. General symmetry breaking schemes are considered in which strings formed at one symmetry breaking scale become current carrying at a subsequent phase transition. The vorton abundance is estimated and constraints placed on the underlying particle physics theories from cosmological observations. Our constraints on the chiral theory are considerably more stringent than the previous estimates for more general theories.

Brandon Carter and Anne-Christine Davis

2000-05-02T23:59:59.000Z

411

On a super-selection rule in quantum cosmology  

E-Print Network [OSTI]

The discarding of negative frequency solutions in a quantum field theory brings about the absence of antiparticles which, after all, means the violation of 4-inversion symmetry $(x \\rightarrow -x, t \\rightarrow-t)$ which is a (improper) Lorentz transformation. Suppose you have a theory of quantum gravity which lacks the negative frequency solutions (like usually people have in quantum cosmology, invoking a super-selection rule). Taking some limit in this theory in order to obtain the weak (or null) gravitational regime, the result is a theory that does not respect that symmetry and does not have place for antiparticles. That is, a theory of fields is not obtained, as it should be. For the case of a quantum cosmology model we show that if we ignore the negative frequency solutions, the rich processes of creation/annihilation of universes at the Planck scale, are lost.

E. Sergio Santini

2014-12-26T23:59:59.000Z

412

Cosmology on the Largest Scales with the SKA  

E-Print Network [OSTI]

The study of the Universe on ultra-large scales is one of the major science cases for the Square Kilometre Array (SKA). The SKA will be able to probe a vast volume of the cosmos, thus representing a unique instrument, amongst next-generation cosmological experiments, for scrutinising the Universe's properties on the largest cosmic scales. Probing cosmic structures on extremely large scales will have many advantages. For instance, the growth of perturbations is well understood for those modes, since it falls fully within the linear regime. Also, such scales are unaffected by the poorly understood feedback of baryonic physics. On ultra-large cosmic scales, two key effects become significant: primordial non-Gaussianity and relativistic corrections to cosmological observables. Moreover, if late-time acceleration is driven not by dark energy but by modifications to general relativity, then such modifications should become apparent near and above the horizon scale. As a result, the SKA is forecast to deliver transf...

Camera, S; Bull, P; Bertacca, D; Chen, X; Ferreira, P G; Kunz, M; Maartens, R; Mao, Y; Santos, M G; Shapiro, P R; Viel, M; Xu, Y

2015-01-01T23:59:59.000Z

413

Late-time cosmology with 21cm intensity mapping experiments  

E-Print Network [OSTI]

We present a framework for forecasting cosmological constraints from future neutral hydrogen intensity mapping experiments at low to intermediate redshifts. In the process, we establish a simple way of comparing such surveys with optical galaxy redshift surveys. We explore a wide range of experimental configurations and assess how well a number of cosmological observables (the expansion rate, growth rate, and angular diameter distance) and parameters (the densities of dark energy and dark matter, spatial curvature, the dark energy equation of state, etc.) will be measured by an extensive roster of upcoming experiments. A number of potential contaminants and systematic effects are also studied in detail. The overall picture is encouraging - Phase I of the SKA should be able to constrain the dark energy equation of state about as well as a DETF Stage IV galaxy redshift survey like Euclid or LSST, in roughly the same timeframe.

Bull, Philip; Patel, Prina; Santos, Mario G

2014-01-01T23:59:59.000Z

414

Reconstructing Dark Energy : A Comparison of Cosmological Parameters  

E-Print Network [OSTI]

A large number of cosmological parameters have been suggested for obtaining information on the nature of dark energy. In this work, we study the efficacy of these different parameters in discriminating theoretical models of dark energy, using both currently available supernova (SNe) data, and simulations of future observations. We find that the current data does not put strong constraints on the nature of dark energy, irrespective of the cosmological parameter used. For future data, we find that the although deceleration parameter can accurately reconstruct some dark energy models, it is unable to discriminate between different models of dark energy, therefore limiting its usefulness. Physical parameters such as the equation of state of dark energy, or the dark energy density do a good job of both reconstruction and discrimination if the matter density is known to high accuracy. However, uncertainty in matter density reduces the efficacy of these parameters. A recently proposed parameter, Om(z), constructed f...

Pan, Alexander V

2010-01-01T23:59:59.000Z

415

Anthropic versus cosmological solutions to the coincidence problem  

SciTech Connect (OSTI)

In this paper, we investigate possible solutions to the coincidence problem in flat phantom dark-energy models with a constant dark-energy equation of state and quintessence models with a linear scalar field potential. These models are representative of a broader class of cosmological scenarios in which the universe has a finite lifetime. We show that, in the absence of anthropic constraints, including a prior probability for the models inversely proportional to the total lifetime of the universe excludes models very close to the {Lambda} cold dark matter model. This relates a cosmological solution to the coincidence problem with a dynamical dark-energy component having an equation-of-state parameter not too close to -1 at the present time. We further show that anthropic constraints, if they are sufficiently stringent, may solve the coincidence problem without the need for dynamical dark energy.

Barreira, A.; Avelino, P. P. [Centro de Fisica do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal); Departamento de Fisica da Faculdade de Ciencias da Universidade do Porto, Rua do Campo Alegre 687, 4169-007 Porto (Portugal)

2011-05-15T23:59:59.000Z

416

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

417

Exponential cosmological redshift in a linearly expanding universe  

E-Print Network [OSTI]

Analytical solution of the Maxwell equations in a flat expanding Friedmann-Robertson-Walker space-time is presented. The solution is valid for arbitrary sources and for expansion rates described by positive functions of time. The near-, intermediate-, and far-field terms are explicitly identified. It is shown that the cosmological redshift introduced by a linearly expanding space-time is an exponential function of the distance factor.

Budko, Neil V

2009-01-01T23:59:59.000Z

418

A Comparison of Cosmological Models Using Strong Gravitational Lensing Galaxies  

E-Print Network [OSTI]

Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems, and carry out a one-on-one comparison between the standard model, LCDM, and the R_h=ct Universe. We find that both models account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule out either model at a ~99.7% confidence level. We find that if the real cosmology is LCDM, a sample of ~200 strong gravitational lenses would be sufficient to rule out R_h=ct at this level of accuracy, while ~300 strong gravitational lenses would be required to rule out LCDM if the real Universe were instead R_h=ct. The difference in required sample size reflects the greater number of free parameters available to fit the data with LCDM. We point out that, should the R_h=ct Universe eventually emerge as the correct cosmology, its lack of any free parameters for this kind of work will provide a remarkably powerful probe of the mass structure in lensing galaxies, and a means of better understanding the origin of the bulge-halo conspiracy.

Fulvio Melia; Jun-Jie Wei; Xue-Feng Wu

2014-10-03T23:59:59.000Z

419

Cosmology using the Parkes Multibeam Southern-Sky HI Survey  

E-Print Network [OSTI]

I discuss the implications of the Parkes HI Multibeam Southern Sky Survey for cosmology. It will determine the local mass function of HI clouds, detecting several hundred per decade of mass. Each of these will come with a redshift and, for the more massive clouds, an estimate of the velocity width. This will provide an ideal database for peculiar motion studies and for measurements of biasing of galaxies relative to the underlying matter distribution.

P. A. Thomas

1996-07-02T23:59:59.000Z

420

Conformal Supersymmetry Breaking and Dynamical Tuningof the Cosmological Constant  

SciTech Connect (OSTI)

We propose 'conformal supersymmetry breaking' models, which tightly relate the conformal breaking scale (i.e. R-symmetry breaking scale) and the supersymmetry breaking scale. The both scales are originated from the constant term in the superpotential through the common source of the R-symmetry breaking. We show that dynamical tuning between those mass scales significantly reduces the degree of fine-tuning necessary for generating the almost vanishing cosmological constant.

Ibe, M.; /SLAC; Nakayama, Y.; /UC, Berkeley; Yanagida, T.T.; /Tokyo U.

2008-03-07T23:59:59.000Z

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.


421

Quantum cosmology with varying speed of light and Bohmian trajectories  

E-Print Network [OSTI]

The classical trajectories for FLRW universe with varying speed of light are obtained for the cases in which the cosmological constant depends or not depend on the velocity of light. The theory is then quantized and the corresponding WDW equation is solved. It is shown that the method of causal interpretation of Bohm can be applied successfully to the theory. Finally the Bohmian trajectories are obtained and compared with the classical ones.

F. Shojai; S. Molladavoudi

2007-08-04T23:59:59.000Z

422

Test for the zero mean hypothesis in cosmology  

Science Journals Connector (OSTI)

One working hypothesis on which analyses of cosmological data are based is the zero ensemble mean hypothesis, which is related to the statistical homogeneity of cosmological perturbations. This hypothesis, however, should be tested by observational data in the current era of precision cosmology. Herein, we test the hypothesis by analyzing recent, foreground-reduced cosmic microwave background (CMB) maps, combining the spherical harmonic coefficients of the masked CMB temperature anisotropies in such a way that the combined variables can be treated as statistically independent samples. We find evidence against the zero mean hypothesis in two particular ranges of multipoles, with significance levels of 2.5? and 3.1? in the multipole ranges of ??61–86 and 213–256, respectively, for both the Planck and Wilkinson Microwave Anisotropy Probe maps. The latter signal is consistent with our previous result found by using brute-force Monte Carlo simulations. However, within the method employed in this paper we conclude that the zero mean hypothesis is consistent with the current CMB data on the basis of Stouffer’s weighted Z statistics, which takes multiple testing into account.

Kiyotomo Ichiki

2014-12-17T23:59:59.000Z

423

On the possible running of the cosmological "constant"  

E-Print Network [OSTI]

Despite the many outstanding cosmological observations leading to a strong evidence for a nonvanishing cosmological constant (CC) term in the gravitational field equations, the theoretical status of this quantity seems to be lagging well behind the observational successes. It thus seems timely to revisit some fundamental aspects of the CC term in Quantum Field Theory (QFT). We emphasize that, in curved space-time, nothing a priori prevents this term from potentially having a mild running behavior associated to quantum effects. Remarkably, this could be the very origin of the dynamical nature of the Dark Energy, in contrast to many other popular options considered in the literature. In discussing this possibility, we also address some recent criticisms concerning the possibility of such running. Our conclusion is that, while there is no comprehensive proof of the CC running, there is no proof of the non-running either. The problem can be solved only through a deeper understanding of the vacuum contributions of massive quantum fields on a curved spacetime background. We suggest that such investigations are at the heart of one of the most important endeavors of fundamental theoretical cosmology in the years to come.

Ilya L. Shapiro; Joan Sola

2009-10-26T23:59:59.000Z

424

The Hubble constant and dark energy from cosmological distance measures  

E-Print Network [OSTI]

We study how the determination of the Hubble constant from cosmological distance measures is affected by models of dark energy and vice versa. For this purpose, constraints on the Hubble constant and dark energy are investigated using the cosmological observations of cosmic microwave background, baryon acoustic oscillations and type Ia suprenovae. When one investigates dark energy, the Hubble constant is often a nuisance parameter, thus it is usually marginalized over. On the other hand, when one focuses on the Hubble constant, simple dark energy models such as a cosmological constant and a constant equation of state are usually assumed. Since we do not know the nature of dark energy yet, it is interesting to investigate the Hubble constant assuming some types of dark energy and see to what extent the constraint on the Hubble constant is affected by the assumption concerning dark energy. We show that the constraint on the Hubble constant is not affected much by the assumption for dark energy. We furthermore show that this holds true even if we remove the assumption that the universe is flat. We also discuss how the prior on the Hubble constant affects the constraints on dark energy and/or the curvature of the universe.

Kazuhide Ichikawa; Tomo Takahashi

2007-10-22T23:59:59.000Z

425

Cosmological implications of baryon acoustic oscillation (BAO) measurements  

E-Print Network [OSTI]

We derive constraints on cosmological parameters and tests of dark energy models from the combination of baryon acoustic oscillation (BAO) measurements with cosmic microwave background (CMB) and Type Ia supernova (SN) data. We take advantage of high-precision BAO measurements from galaxy clustering and the Ly-alpha forest (LyaF) in the BOSS survey of SDSS-III. BAO data alone yield a high confidence detection of dark energy, and in combination with the CMB angular acoustic scale they further imply a nearly flat universe. Combining BAO and SN data into an "inverse distance ladder" yields a 1.7% measurement of $H_0=67.3 \\pm1.1$ km/s/Mpc. This measurement assumes standard pre-recombination physics but is insensitive to assumptions about dark energy or space curvature, so agreement with CMB-based estimates that assume a flat LCDM cosmology is an important corroboration of this minimal cosmological model. For open LCDM, our BAO+SN+CMB combination yields $\\Omega_m=0.301 \\pm 0.008$ and curvature $\\Omega_k=-0.003 \\pm ...

Aubourg, Éric; Bautista, Julian E; Beutler, Florian; Bhardwaj, Vaishali; Bizyaev, Dmitry; Blanton, Michael; Blomqvist, Michael; Bolton, Adam S; Bovy, Jo; Brewington, Howard; Brinkmann, J; Brownstein, Joel R; Burden, Angela; Busca, Nicolás G; Carithers, William; Chuang, Chia-Hsun; Comparat, Johan; Cuesta, Antonio J; Dawson, Kyle S; Delubac, Timothée; Eisenstein, Daniel J; Font-Ribera, Andreu; Ge, Jian; Goff, J -M Le; Gontcho, Satya Gontcho A; Gott, J Richard; Gunn, James E; Guo, Hong; Guy, Julien; Hamilton, Jean-Christophe; Ho, Shirley; Honscheid, Klaus; Howlett, Cullan; Kirkby, David; Kitaura, Francisco S; Kneib, Jean-Paul; Lee, Khee-Gan; Long, Dan; Lupton, Robert H; Magaña, Mariana Vargas; Malanushenko, Viktor; Malanushenko, Elena; Manera, Marc; Maraston, Claudia; Margala, Daniel; McBride, Cameron K; Miralda-Escudé, Jordi; Myers, Adam D; Nichol, Robert C; Noterdaeme, Pasquier; Nuza, Sebastián E; Olmstead, Matthew D; Oravetz, Daniel; Pâris, Isabelle; Padmanabhan, Nikhil; Palanque-Delabrouille, Nathalie; Pan, Kaike; Pellejero-Ibanez, Marcos; Percival, Will J; Petitjean, Patrick; Pieri, Matthew M; Prada, Francisco; Reid, Beth; Roe, Natalie A; Ross, Ashley J; Ross, Nicholas P; Rossi, Graziano; Rubiño-Martín, Jose Alberto; Sánchez, Ariel G; Samushia, Lado; Santos, Ricardo Tanausú Génova; Scóccola, Claudia G; Schlegel, David J; Schneider, Donald P; Seo, Hee-Jong; Sheldon, Erin; Simmons, Audrey; Skibba, Ramin A; Slosar, Anže; Strauss, Michael A; Thomas, Daniel; Tinker, Jeremy L; Tojeiro, Rita; Vazquez, Jose Alberto; Viel, Matteo; Wake, David A; Weaver, Benjamin A; Weinberg, David H; Wood-Vasey, W M; Yèche, Christophe; Zehavi, Idit; Zhao, Gong-Bo

2014-01-01T23:59:59.000Z

426

Paradoxes of cosmological physics in the beginning of the 21-st century  

E-Print Network [OSTI]

In the history of cosmology physical paradoxes played important role for development of contemporary world models. Within the modern standard cosmological model there are both observational and conceptual cosmological paradoxes which stimulate to search their solution. Confrontation of theoretical predictions of the standard cosmological model with the latest astrophysical observational data is considered. A review of conceptual problems of the Friedmann space expending models, which are in the bases of modern cosmological model, is discussed. The main paradoxes, which are discussed in modern literature, are the Newtonian character of the exact Friedmann equation, the violation of the energy conservation within any comoving local volume, violation of the limiting recession velocity of galaxies for the observed high redshift objects. Possible observational tests of the nature of the cosmological redshift are discussed

Yurij Baryshev

2015-01-04T23:59:59.000Z

427

Paradoxes of cosmological physics in the beginning of the 21-st century  

E-Print Network [OSTI]

In the history of cosmology physical paradoxes played important role for development of contemporary world models. Within the modern standard cosmological model there are both observational and conceptual cosmological paradoxes which stimulate to search their solution. Confrontation of theoretical predictions of the standard cosmological model with the latest astrophysical observational data is considered. A review of conceptual problems of the Friedmann space expending models, which are in the bases of modern cosmological model, is discussed. The main paradoxes, which are discussed in modern literature, are the Newtonian character of the exact Friedmann equation, the violation of the energy conservation within any comoving local volume, violation of the limiting recession velocity of galaxies for the observed high redshift objects. Possible observational tests of the nature of the cosmological redshift are discussed

Baryshev, Yurij

2015-01-01T23:59:59.000Z

428

DynamiX, numerical tool for design of next-generation x-ray telescopes  

SciTech Connect (OSTI)

We present a new code aimed at the simulation of grazing-incidence x-ray telescopes subject to deformations and demonstrate its ability with two test cases: the Simbol-X and the International X-ray Observatory (IXO) missions. The code, based on Monte Carlo ray tracing, computes the full photon trajectories up to the detector plane, accounting for the x-ray interactions and for the telescope motion and deformation. The simulation produces images and spectra for any telescope configuration using Wolter I mirrors and semiconductor detectors. This numerical tool allows us to study the telescope performance in terms of angular resolution, effective area, and detector efficiency, accounting for the telescope behavior. We have implemented an image reconstruction method based on the measurement of the detector drifts by an optical sensor metrology. Using an accurate metrology, this method allows us to recover the loss of angular resolution induced by the telescope instability. In the framework of the Simbol-X mission, this code was used to study the impacts of the parameters on the telescope performance. In this paper we present detailed performance analysis of Simbol-X, taking into account the satellite motions and the image reconstruction. To illustrate the versatility of the code, we present an additional performance analysis with a particular configuration of IXO.

Chauvin, Maxime; Roques, Jean-Pierre

2010-07-20T23:59:59.000Z

429

Bekenstein Bound of Information Number N and its Relation to Cosmological Parameters in a Universe with and without Cosmological Constant  

E-Print Network [OSTI]

Bekenstein has obtained is an upper limit on the entropy S, and from that, an information number bound N is deduced. In other words, this is the information contained within a given finite region of space that includes a finite amount of energy. Similarly, this can be thought as the maximum amount of information required to perfectly describe a given physical system down to its quantum level. If the energy and the region of space are finite then the number of information N required in describing the physical system is also finite. In this short letter two information number bounds are derived and compared for two types of universe. First, a universe without a cosmological constant lamda and second a universe with a cosmological constant lamda are investigated. This is achieved with the derivation of two different relations that connect the Hubble constant and cosmological constants to the number of information N. We find that the number of information N involved in a the two universes are identical or N1=N2, and that the total mass of the universe scales as the square root of the information number N, containing an information number N of the order of 10E+122. Finally, we expressed Calogero quantization action as a function of the number of information N. We also have found that in self gravitating systems the number of information N in nats is the ratio of the total kinetic to total thermal energy of the system.

Ioannis Haranas; Ioannis Gkigkitzis

2014-06-09T23:59:59.000Z

430

E-Print Network 3.0 - ancient revisits cosmology Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

New Cosmology to revise and explain erroneous concepts such as Cold Dark Matter, Dark Energy, Dark Source: Gibson, Carl H. - Scripps Institution of Oceanography, Center for...

431

Testing foundations of modern cosmology with SKA all-sky surveys  

E-Print Network [OSTI]

Continuum and HI surveys with the Square Kilometre Array (SKA) will allow us to probe some of the most fundamental assumptions of modern cosmology, including the Cosmological Principle. SKA all-sky surveys will map an enormous slice of space-time and reveal cosmology at superhorizon scales and redshifts of order unity. We illustrate the potential of these surveys and discuss the prospects to measure the cosmic radio dipole at high fidelity. We outline several potentially transformational tests of cosmology to be carried out by means of SKA all-sky surveys.

Schwarz, Dominik J; Chen, Song; Clarkson, Chris; Huterer, Dragan; Kunz, Martin; Maartens, Roy; Raccanelli, Alvise; Rubart, Matthias; Starck, Jean-Luc

2015-01-01T23:59:59.000Z

432

E-Print Network 3.0 - axion cosmology revisited Sample Search...  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

Loeb Lecture April 23, 2009 Peering Beyond the Horizon with Axions Summary: Axion phenomenology Axion dark matter Inflationary cosmology Thursday, April 23, 2009 12;David B... ,...

433

The ASTRI Project: a mini-array of dual-mirror small Cherenkov telescopes for CTA  

E-Print Network [OSTI]

ASTRI is a flagship project of the Italian Ministry of Education, University and Research, which aims to develop an end-to-end prototype of the CTA small-size telescope. The proposed design is characterized by a dual-mirror Schwarzschild-Couder configuration and a camera based on Silicon photo-multipliers, two challenging but innovative technological solutions which will be adopted for the first time on a Cherenkov telescope. Here we describe the current status of the project, the expected performance and the possibility to realize a mini-array composed by a few small-size telescopes, which shall be placed at the final CTA Southern Site.

La Palombara, N; Antonelli, L A; Bastieri, D; Bellassai, G; Belluso, M; Bigongiari, C; Billotta, S; Biondo, B; Bonanno, G; Bonnoli, G; Bruno, P; Bulgarelli, A; Canestrari, R; Capalbi, M; Caraveo, P; Carosi, A; Cascone, E; Catalano, O; Cereda, M; Conconi, P; Conforti, V; Cusumano, G; De Caprio, V; De Luca, A; Di Paola, A; Di Pierro, F; Fantinel, D; Fiorini, M; Fugazza, D; Gardiol, D; Ghigo, M; Gianotti, F; Giarrusso, S; Giro, E; Grillo, A; Impiombato, D; Incorvaia, S; La Barbera, A; La Parola, V; La Rosa, G; Lessio, L; Leto, G; Lombardi, S; Lucarelli, F; Maccarone, M C; Malaguti, G; Malaspina, G; Mangano, V; Marano, D; Martinetti, E; Millul, R; Mineo, T; Mistó, A; Morello, C; Morlino, G; Panzera, M R; Pareschi, G; Rodeghiero, G; Romano, P; Russo, F; Sacco, B; Sartore, N; Schwarz, J; Segreto, A; Sironi, G; Sottile, G; Stamerra, A; Strazzeri, E; Stringhetti, L; Tagliaferri, G; Testa, V; Timpanaro, M C; Toso, G; Tosti, G; Trifoglio, M; Vallania, P; Vercellone, S; Zitelli, V

2013-01-01T23:59:59.000Z

434

Metal multilayer mirrors for EUV wide field telescopes  

SciTech Connect (OSTI)

Metal multilayer mirrors have been designed for the ALEXIS satellite, which is to carry six wide field telescopes to perform an all-sky survey in three or four narrow wavelength bands in the EUV. Comprised of alternating layers of molybdenum and silicon, the mirrors are optimized to provide maximum reflectivity at angles from 11.5 to 17/degree/ off normal incidence and at wavelengths of 133, 171, or 186A. Simultaneously, the mirrors use a ''wavetrap'' described below to suppress reflectivity at 304A, where the extremely strong geocoronal line of He II causes severe background problems. Low reflectivity at 304A is achieved by superposing two layer pairs that provide destructive interference with an effective 2d spacing of 152A. The Mo layers in this wavetrap must be very thin, about 10A each, in order to allow the shorter wavelengths desired for peak reflectivity to penetrate without significant attenuation. Because refraction changes the effective angle of passage through the wavetrap, a joint optimization between layer thicknesses in the deep layers and the wavetrap layers must be performed for each target peak wavelength. For the 186A mirror, the optimum design from substrate upward is 40 layer pairs, each 74A Si and 31A Mo, followed by 2 layer pairs, each 55A Si and 10A Mo. Calculations predict this design will have a peak reflectivity at 186A of 35 percent and a 304A reflectivity less than 10/sup /minus/5/, if available optical constants are correct and the multilayer can be fabricated without difficulty. We will present details of the calculations and laboratory measurements of the reflectivity performance attained with prototype mirrors. 6 refs., 2 figs.

Smith, B.W.; Bloch, J.J.; Roussel-Dupre,D.

1989-01-01T23:59:59.000Z

435

DynamiX, numerical tool for design of next-generation x-ray telescopes  

Science Journals Connector (OSTI)

We present a new code aimed at the simulation of grazing-incidence x-ray telescopes subject to deformations and demonstrate its ability with two test cases: the Simbol-X and the...

Chauvin, Maxime; Roques, Jean-Pierre

2010-01-01T23:59:59.000Z

436

Advanced Technology Solar Telescope 4.2 m Off-axis Primary Mirror Fabrication  

Science Journals Connector (OSTI)

Advanced optical surfacing technologies are applied for the Advanced Technology Solar Telescope 4.2 m off-axis primary mirror fabrication. A newly developed Stressed lap and IR...

Kim, Dae Wook; Oh, Chang Jin; Su, Peng; Burge, James H

437

NASA'S NEXT GENERATION SPACE TELESCOPE: VISITING A TIME WHEN GALAXIES WERE YOUNG  

Science Journals Connector (OSTI)

NASA's next great endeavor, a space telescope to study the origin of galaxies, is in its formulative phase. Seery and Smith update readers on the paradigms, processes, and optical...

Seery, Bernard D; Smith, Eric P

1998-01-01T23:59:59.000Z

438

Advanced Technology Large-Aperture Space Telescope (ATLAST): A Technology Roadmap for the Next Decade  

E-Print Network [OSTI]

The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a set of mission concepts for the next generation of UVOIR space observatory with a primary aperture diameter in the 8-m to 16-m range that will allow us to perform some of the most challenging observations to answer some of our most compelling questions, including "Is there life elsewhere in the Galaxy?" We have identified two different telescope architectures, but with similar optical designs, that span the range in viable technologies. The architectures are a telescope with a monolithic primary mirror and two variations of a telescope with a large segmented primary mirror. This approach provides us with several pathways to realizing the mission, which will be narrowed to one as our technology development progresses. The concepts invoke heritage from HST and JWST design, but also take significant departures from these designs to minimize complexity, mass, or both. Our report provides details on the mission concepts, shows the extraordinary s...

Postman, Marc

2009-01-01T23:59:59.000Z

439

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

440

E-Print Network 3.0 - african large telescope Sample Search Results  

Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

The Anglo-Australian Telescope 12;15 12;16 The 2dF 6 element... Midi Observatory (French Pyrenees) 12;42 The Overwhelmingly Large ... Source: Parker, Quentin A. -...

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.


441

A wide field X-ray telescope for astronomical survey purposes: from theory to practice  

Science Journals Connector (OSTI)

......act directly on the mirror design. The Wolter-Schwarzschild telescope eliminates...Wolter I and Wolter-Schwarzschild single mirror shells. Figure 3 Differences...analysis for a Wolter-Schwarzschild mirror shell and for our optimized......

Paolo Conconi; Sergio Campana; Gianpiero Tagliaferri; Giovanni Pareschi; Oberto Citterio; Vincenzo Cotroneo; Laura Proserpio; Marta Civitani

2010-06-21T23:59:59.000Z

442

Photosensor Characterization for the Cherenkov Telescope Array: Silicon Photomultiplier versus Multi-Anode Photomultiplier Tube  

E-Print Network [OSTI]

Photomultiplier tube technology has been the photodetector of choice for the technique of imaging atmospheric Cherenkov telescopes since its birth more than 50 years ago. Recently, new types of photosensors are being contemplated for the next generation Cherenkov Telescope Array. It is envisioned that the array will be partly composed of telescopes using a Schwarzschild-Couder two mirror design never built before which has significantly improved optics. The camera of this novel optical design has a small plate scale which enables the use of compact photosensors. We present an extensive and detailed study of the two most promising devices being considered for this telescope design: the silicon photomultiplier and the multi-anode photomultiplier tube. We evaluated their most critical performance characteristics for imaging gamma-ray showers, and we present our results in a cohesive manner to clearly evaluate the advantages and disadvantages that both types of device have to offer in the context of GeV-TeV gamma...

Bouvier, Aurelien; Johnson, Caitlin; Kuznetsov, Andrey; Williams, David; Otte, Nepomuk; Strausbaugh, Robert; Hidaka, Naoya; Tajima, Hiroyasu; Hinton, Jim; White, Richard; Errando, Manel; Mukherjee, Reshmi

2013-01-01T23:59:59.000Z

443

Three-Mirror Anastigmat Telescope with an Unvignetted Flat Focal Plane  

Science Journals Connector (OSTI)

......anastigmat with a two-mirror system except for some special cases (Schwarzschild 1905; Burch 1947). 3. Three-Mirror System In our three-mirror...Academic Press). Schwarzschild K. 1905, Investigations...Optics II, Theory of Mirror Telescopes, English......

Kyoji Nariai; Masanori Iye

2005-04-25T23:59:59.000Z

444

Digital signal processing hardware for a fast fourier transform radio telescope  

E-Print Network [OSTI]

21-cm tomography is a devoloping technique for measuring the Epoch of Reionization in the universe's history. The nature of the signal measured in 21-cm tomography is such that a new kind of radio telescope is needed: one ...

Losh, Jonathan L

2012-01-01T23:59:59.000Z

445

Cosmological implications of baryon acoustic oscillation (BAO) measurements  

E-Print Network [OSTI]

We derive constraints on cosmological parameters and tests of dark energy models from the combination of baryon acoustic oscillation (BAO) measurements with cosmic microwave background (CMB) and Type Ia supernova (SN) data. We take advantage of high-precision BAO measurements from galaxy clustering and the Ly-alpha forest (LyaF) in the BOSS survey of SDSS-III. BAO data alone yield a high confidence detection of dark energy, and in combination with the CMB angular acoustic scale they further imply a nearly flat universe. Combining BAO and SN data into an "inverse distance ladder" yields a 1.7% measurement of $H_0=67.3 \\pm1.1$ km/s/Mpc. This measurement assumes standard pre-recombination physics but is insensitive to assumptions about dark energy or space curvature, so agreement with CMB-based estimates that assume a flat LCDM cosmology is an important corroboration of this minimal cosmological model. For open LCDM, our BAO+SN+CMB combination yields $\\Omega_m=0.301 \\pm 0.008$ and curvature $\\Omega_k=-0.003 \\pm 0.003$. When we allow more general forms of evolving dark energy, the BAO+SN+CMB parameter constraints remain consistent with flat LCDM. While the overall $\\chi^2$ of model fits is satisfactory, the LyaF BAO measurements are in moderate (2-2.5 sigma) tension with model predictions. Models with early dark energy that tracks the dominant energy component at high redshifts remain consistent with our constraints, but models where dark matter decays into radiation are sharply limited. Expansion history alone yields an upper limit of 0.56 eV on the summed mass of neutrino species, improving to 0.26 eV if we include Planck CMB lensing. Standard dark energy models constrained by our data predict a level of matter clustering that is high compared to most, but not all, observational estimates. (Abridged)

Éric Aubourg; Stephen Bailey; Julian E. Bautista; Florian Beutler; Vaishali Bhardwaj; Dmitry Bizyaev; Michael Blanton; Michael Blomqvist; Adam S. Bolton; Jo Bovy; Howard Brewington; J. Brinkmann; Joel R. Brownstein; Angela Burden; Nicolás G. Busca; William Carithers; Chia-Hsun Chuang; Johan Comparat; Antonio J. Cuesta; Kyle S. Dawson; Timothée Delubac; Daniel J. Eisenstein; Andreu Font-Ribera; Jian Ge; J. -M. Le Goff; Satya Gontcho A Gontcho; J. Richard Gott III; James E. Gunn; Hong Guo; Julien Guy; Jean-Christophe Hamilton; Shirley Ho; Klaus Honscheid; Cullan Howlett; David Kirkby; Francisco S. Kitaura; Jean-Paul Kneib; Khee-Gan Lee; Dan Long; Robert H. Lupton; Mariana Vargas Magaña; Viktor Malanushenko; Elena Malanushenko; Marc Manera; Claudia Maraston; Daniel Margala; Cameron K. McBride; Jordi Miralda-Escudé; Adam D. Myers; Robert C. Nichol; Pasquier Noterdaeme; Sebastián E. Nuza; Matthew D. Olmstead; Daniel Oravetz; Isabelle Pâris; Nikhil Padmanabhan; Nathalie Palanque-Delabrouille; Kaike Pan; Marcos Pellejero-Ibanez; Will J. Percival; Patrick Petitjean; Matthew M. Pieri; Francisco Prada; Beth Reid; Natalie A. Roe; Ashley J. Ross; Nicholas P. Ross; Graziano Rossi; Jose Alberto Rubiño-Martín; Ariel G. Sánchez; Lado Samushia; Ricardo Tanausú Génova Santos; Claudia G. Scóccola; David J. Schlegel; Donald P. Schneider; Hee-Jong Seo; Erin Sheldon; Audrey Simmons; Ramin A. Skibba; Anže Slosar; Michael A. Strauss; Daniel Thomas; Jeremy L. Tinker; Rita Tojeiro; Jose Alberto Vazquez; Matteo Viel; David A. Wake; Benjamin A. Weaver; David H. Weinberg; W. M. Wood-Vasey; Christophe Yèche; Idit Zehavi; Gong-Bo Zhao

2014-11-18T23:59:59.000Z

446

Cosmological implications of baryon acoustic oscillation (BAO) measurements  

E-Print Network [OSTI]

We derive constraints on cosmological parameters and tests of dark energy models from the combination of baryon acoustic oscillation (BAO) measurements with cosmic microwave background (CMB) and Type Ia supernova (SN) data. We take advantage of high-precision BAO measurements from galaxy clustering and the Ly-alpha forest (LyaF) in the BOSS survey of SDSS-III. BAO data alone yield a high confidence detection of dark energy, and in combination with the CMB angular acoustic scale they further imply a nearly flat universe. Combining BAO and SN data into an "inverse distance ladder" yields a 1.7% measurement of $H_0=67.3 \\pm1.1$ km/s/Mpc. This measurement assumes standard pre-recombination physics but is insensitive to assumptions about dark energy or space curvature, so agreement with CMB-based estimates that assume a flat LCDM cosmology is an important corroboration of this minimal cosmological model. For open LCDM, our BAO+SN+CMB combination yields $\\Omega_m=0.301 \\pm 0.008$ and curvature $\\Omega_k=-0.003 \\pm 0.003$. When we allow more general forms of evolving dark energy, the BAO+SN+CMB parameter constraints remain consistent with flat LCDM. While the overall $\\chi^2$ of model fits is satisfactory, the LyaF BAO measurements are in moderate (2-2.5 sigma) tension with model predictions. Models with early dark energy that tracks the dominant energy component at high redshifts remain consistent with our constraints, but models where dark matter decays into radiation are sharply limited. Expansion history alone yields an upper limit of 0.56 eV on the summed mass of neutrino species, improving to 0.26 eV if we include Planck CMB lensing. Standard dark energy models constrained by our data predict a level of matter clustering that is high compared to most, but not all, observational estimates. (Abridged)

Éric Aubourg; Stephen Bailey; Julian E. Bautista; Florian Beutler; Vaishali Bhardwaj; Dmitry Bizyaev; Michael Blanton; Michael Blomqvist; Adam S. Bolton; Jo Bovy; Howard Brewington; J. Brinkmann; Joel R. Brownstein; Angela Burden; Nicolás G. Busca; William Carithers; Chia-Hsun Chuang; Johan Comparat; Antonio J. Cuesta; Kyle S. Dawson; Timothée Delubac; Daniel J. Eisenstein; Andreu Font-Ribera; Jian Ge; J. -M. Le Goff; Satya Gontcho A Gontcho; J. Richard Gott III; James E. Gunn; Hong Guo; Julien Guy; Jean-Christophe Hamilton; Shirley Ho; Klaus Honscheid; Cullan Howlett; David Kirkby; Francisco S. Kitaura; Jean-Paul Kneib; Khee-Gan Lee; Dan Long; Robert H. Lupton; Mariana Vargas Magaña; Viktor Malanushenko; Elena Malanushenko; Marc Manera; Claudia Maraston; Daniel Margala; Cameron K. McBride; Jordi Miralda-Escudé; Adam D. Myers; Robert C. Nichol; Pasquier Noterdaeme; Sebastián E. Nuza; Matthew D. Olmstead; Daniel Oravetz; Isabelle Pâris; Nikhil Padmanabhan; Nathalie Palanque-Delabrouille; Kaike Pan; Marcos Pellejero-Ibanez; Will J. Percival; Patrick Petitjean; Matthew M. Pieri; Francisco Prada; Beth Reid; Natalie A. Roe; Ashley J. Ross; Nicholas P. Ross; Graziano Rossi; Jose Alberto Rubiño-Martín; Ariel G. Sánchez; Lado Samushia; Ricardo Tanausú Génova Santos; Claudia G. Scóccola; David J. Schlegel; Donald P. Schneider; Hee-Jong Seo; Erin Sheldon; Audrey Simmons; Ramin A. Skibba; Anže Slosar; Michael A. Strauss; Daniel Thomas; Jeremy L. Tinker; Rita Tojeiro; Jose Alberto Vazquez; Matteo Viel; David A. Wake; Benjamin A. Weaver; David H. Weinberg; W. M. Wood-Vasey; Christophe Yèche; Idit Zehavi; Gong-Bo Zhao

2014-11-04T23:59:59.000Z

447

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

448

Calibration of Cangaroo II Telescope Using a Fast Blue LED Light Flasher  

E-Print Network [OSTI]

Calibration of Cangaroo II Telescope Using a Fast Blue LED Light Flasher John R. Patterson, David L;=460 nm) LED type Nichia (NSPB 510S), which has a temperature stable light output and a risetime of #24; 1.physics.adelaide.edu.au/astrophysics/cangaroo.html #12; FIGURE 1. The LED asher/telescope with the Ramsden eyepiece #12;tted and a previous LED holder

Enomoto, Ryoji

449

Watcher: A Telescope for Rapid Gamma-Ray Burst Follow-Up Observations  

SciTech Connect (OSTI)

The Watcher telescope is planned to begin operation in Spring 2004 in South Africa.The system has been designed to respond primarily to very precise (arcminute) gamma-ray burst locations distributed via the internet by the GCN. Watcher will be fully automatic and the planned response time for GRBs is {approx} 30 seconds or better. In addition, the telescope will be used for blazar monitoring and the photometric detection of extra-solar planets when GRBs are not being observed.

French, J.; Hanlon, L.; McBreen, B.; McBreen, S.; Moran, L. [Department of Experimental Physics, University College Dublin, Dublin 4 (Ireland); Smith, N.; Giltinan, A. [Department of Applied Physics and Instrumentation, Cork Institute of Technology, Bishopstown, Co. Cork (Ireland); Meintjes, P.; Hoffman, M. [Physics Department, University of the Free State, Bloemfontein (South Africa)

2004-09-28T23:59:59.000Z

450

The Poisson equation at second order in relativistic cosmology  

SciTech Connect (OSTI)

We calculate the relativistic constraint equation which relates the curvature perturbation to the matter density contrast at second order in cosmological perturbation theory. This relativistic ''second order Poisson equation'' is presented in a gauge where the hydrodynamical inhomogeneities coincide with their Newtonian counterparts exactly for a perfect fluid with constant equation of state. We use this constraint to introduce primordial non-Gaussianity in the density contrast in the framework of General Relativity. We then derive expressions that can be used as the initial conditions of N-body codes for structure formation which probe the observable signature of primordial non-Gaussianity in the statistics of the evolved matter density field.

Hidalgo, J.C. [Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, PO1 3FX (United Kingdom); Christopherson, Adam J. [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Malik, Karim A., E-mail: juan.hidalgo@port.ac.uk, E-mail: Adam.Christopherson@nottingham.ac.uk, E-mail: k.malik@qmul.ac.uk [Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS (United Kingdom)

2013-08-01T23:59:59.000Z

451

False vacuum decay in Jordan-Brans-Dicke cosmologies  

SciTech Connect (OSTI)

We examine the bubble nucleation rate in a first-order phase transition taking place in a background Jordan-Brans-Dicke cosmology. We compute the leading order terms in the nucleation rate when the Jordan-Brans-Dicke field is large (i.e., late times) by means of a Weyl rescaling of the fields in the theory. We find that despite the fact that the Jordan-Brans-Dicke field (hence the effective gravitational constant) has a time dependence in the false vacuum, at late times the nucleation rate is time independent. 21 refs.

Holman, R.; Wang, Yun (Carnegie-Mellon Univ., Pittsburgh, PA (USA). Dept. of Physics); Kolb, E.W.; Vadas, S.L. (Fermi National Accelerator Lab., Batavia, IL (USA) Chicago Univ., IL (USA)); Weinberg, E.J. (Columbia Univ., New York, NY (USA). Dept. of Physics)

1989-12-01T23:59:59.000Z

452

On the time arrows, and randomness in cosmological signals  

E-Print Network [OSTI]

Arrows of time - thermodynamical, cosmological, electromagnetic, quantum mechanical, psychological - are basic properties of Nature. For a quantum system-bath closed system the de-correlated initial conditions and no-memory (Markovian) dynamics are outlined as necessary conditions for the appearance of the thermodynamical arrow. The emergence of the arrow for the system evolving according to non-unitary dynamics due to the presence of the bath, then, is a result of limited observability, and we conjecture the arrow in the observable Universe as determined by the dark sector acting as a bath. The voids in the large scale matter distribution induce hyperbolicity of the null geodesics, with possible observational consequences.

V. G. Gurzadyan; S. Sargsyan; G. Yegorian

2013-02-21T23:59:59.000Z

453

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

2011-08-22T23:59:59.000Z

454

Testing the consistency between cosmological measurements of distance and age  

E-Print Network [OSTI]

We present a model independent method to test the consistency between cosmological measurements of distance and age, assuming the distance duality relation. We use type Ia supernovae, baryon acoustic oscillations, and observational Hubble data, to reconstruct the luminosity distance D_L(z), the angle averaged distance D_V(z) and the Hubble rate H(z), using Gaussian processes regression technique. We obtain estimate of the distance duality relation in the redshift range 0.1

Nair, Remya; Jain, Deepak

2015-01-01T23:59:59.000Z

455

Can mirror matter solve the the cosmological lithium problem?  

SciTech Connect (OSTI)

The abundance of lithium-7 confronts cosmology with a long lasting inconsistency between the predictions of standard Big Bang Nucleosynthesis with the baryonic density determined from the Cosmic Microwave Background observations on the one hand, and the spectroscopic determination of the lithium-7 abundance on the other hand. We investigated the influence of the existence of a mirror world, focusing on models in which mirror neutrons can oscillate into ordinary neutrons. Such a mechanism allows for an effective late time neutron injection, which induces an increase of the destruction of beryllium-7and thus a lower final lithium-7 abundance.

Coc, Alain [Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), CNRS/IN2P3, Université Paris Sud 11, UMR 8609, Bâtiment 104, 91405 Orsay Campus (France); Uzan, Jean-Philippe; Vangioni, Elisabeth [Institut d'Astrophysique de Paris, UMR-7095 du CNRS, Université Pierre et Marie Curie, 98 bis bd Arago, 75014 Paris, France and Sorbonne Universités, Institut Lagrange de Paris, 98 bis bd Arago, 75014 Paris (France)

2014-05-02T23:59:59.000Z

456

The Cosmological Constant Problem and Re-interpretation of Time  

E-Print Network [OSTI]

We abandon the interpretation that time is a global parameter in quantum mechanics, replace it by a quantum dynamical variable playing the role of time. This operational re-interpretation of time provides a solution to the cosmological constant problem. The expectation value of the zero-point energy under the new time variable vanishes. The fluctuation of the vacuum energy as the leading contribution to the gravitational effect gives a correct order to the observed "dark energy". The "dark energy" as a mirage is always seen comparable with the matter energy density by an observer using the internal clock time. Conceptual consequences of the re-interpretation of time are also discussed.

M. J. Luo

2013-12-10T23:59:59.000Z

457

Loop Quantum Gravity and Cosmology: A dynamical introduction  

E-Print Network [OSTI]

Loop quantum gravity and cosmology are reviewed with an emphasis on evaluating the dynamics, rather than constructing it. The three crucial parts of such an analysis are (i) deriving effective equations, (ii) controlling the theory's microscopic degrees of freedom that lead to its spatial discreteness and refinement, and (iii) ensuring consistency and anomaly-freedom. All three issues are crucial for making the theory testable by conceptual and observational means, and they remain challenging. Throughout this review, the Hamiltonian nature of the theory will play a large role for properties of space-time structure within the framework discussed.

Bojowald, Martin

2011-01-01T23:59:59.000Z

458

The spherical collapse model in time varying vacuum cosmologies  

E-Print Network [OSTI]

We investigate the virialization of cosmic structures in the framework of flat FLRW cosmological models, in which the vacuum energy density evolves with time. In particular, our analysis focuses on the study of spherical matter perturbations, as they decouple from the background expansion, "turn around" and finally collapse. We generalize the spherical collapse model in the case when the vacuum energy is a running function of the Hubble rate, $\\Lambda=\\Lambda(H)$. A particularly well motivated model of this type is the so-called quantum field vacuum, in which $\\Lambda(H)$ is a quadratic function, $\\Lambda(H)=n_0+n_2\\,H^2$, with $n_0\

S. Basilakos; M. Plionis; J. Sola

2010-09-22T23:59:59.000Z

459

Holography, Cosmology and the Second Law of Thermodynamics  

E-Print Network [OSTI]

We propose that in time dependent backgrounds the holographic principle should be replaced by the generalized second law of thermodynamics. For isotropic open and flat universes with a fixed equation of state, the generalized second law agrees with the cosmological holographic principle proposed by Fischler and Susskind. However, in more complicated spacetimes the two proposals disagree. A modified form of the holographic bound that applies to a post-inflationary universe follows from the generalized second law. However, in a spatially closed universe, or inside a black hole event horizon, there is no simple relationship that connects the area of a region to the maximum entropy it can contain.

Richard Easther; David A. Lowe

1999-02-11T23:59:59.000Z

460

Stochastic background of gravitational waves from cosmological sources  

E-Print Network [OSTI]

Gravitational waves (GW) can constitute a unique probe of the primordial universe. In many cases, the characteristic frequency of the emitted GW is directly related to the energy scale at which the GW source is operating in the early universe. Consequently, different GW detectors can probe different energy scales in the evolution of the universe. After a general introduction on the properties of a GW stochastic background of primordial origin, some examples of cosmological sources are presented, which may lead to observable GW signals.

Caprini, Chiara

2015-01-01T23:59:59.000Z

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.


461

Fitting oscillating string gas cosmology to supernova data  

E-Print Network [OSTI]

In string gas cosmology, extra dimensions are stabilised by a gas of strings. In the matter-dominated era, competition between matter pushing the extra dimensions to expand and the string gas pulling them back can lead to oscillations of the extra dimensions and acceleration in the visible dimensions. We fit this model to supernova data, taking into account the Big Bang Nucleosynthesis constraint on the energy density of the string gas. The fit to the Union set of supernova data is acceptable, but the fit to the ESSENCE data is poor.

Francesc Ferrer; Tuomas Multamaki; Syksy Rasanen

2008-12-22T23:59:59.000Z

462

Fitting oscillating string gas cosmology to supernova data  

Science Journals Connector (OSTI)

In string gas cosmology, extra dimensions are stabilised by a gas of strings. In the matter-dominated era, competition between matter pushing the extra dimensions to expand and the string gas pulling them back can lead to oscillations of the extra dimensions and acceleration in the visible dimensions. We fit this model to supernova data, taking into account the Big Bang Nucleosynthesis constraint on the energy density of the string gas. The fit to the Union set of supernova data is acceptable, but the fit to the ESSENCE data is poor.

Francesc Ferrer; Tuomas Multamäki; Syksy Räsänen

2009-01-01T23:59:59.000Z

463

Quantum cosmology with varying speed of light: canonical approach  

E-Print Network [OSTI]

We investigate $(n+1)$--dimensional cosmology with varying speed of light. After solving corresponding Wheeler-DeWitt equation, we obtain exact solutions in both classical and quantum levels for ($c $--$\\Lambda$)--dominated Universe. We then construct the ``canonical'' wave packets which exhibit a good classical and quantum correspondence. We show that arbitrary but appropriate initial conditions lead to the same classical description. We also study the situation from de-Broglie Bohm interpretation of quantum mechanics and show that the corresponding Bohmian trajectories are in good agreement with the classical counterparts.

P. Pedram; S. Jalalzadeh

2007-12-16T23:59:59.000Z

464

Proto-Model of an Infrared Wide-Field Off-Axis Telescope  

E-Print Network [OSTI]

We develop a proto-model of an off-axis reflective telescope for infrared wide-field observations based on the design of Schwarzschild-Chang type telescope. With only two mirrors, this design achieves an entrance pupil diameter of 50 mm and an effective focal length of 100 mm. We can apply this design to a mid-infrared telescope with a field of view of 8 deg X 8 deg. In spite of the substantial advantages of off-axis telescopes in the infrared compared to refractive or on-axis reflective telescopes, it is known to be difficult to align the mirrors in off-axis systems because of their asymmetric structures. Off-axis mirrors of our telescope are manufactured at the Korea Basic Science Institute (KBSI). We analyze the fabricated mirror surfaces by fitting polynomial functions to the measured data. We accomplish alignment of this two-mirror off-axis system using a ray tracing method. A simple imaging test is performed to compare a pinhole image with a simulated prediction.

Kim, Sanghyuk; Chang, Seunghyuk; Kim, Geon Hee; Yang, Sun Choel; Kim, Myung Sang; Lee, Sungho; Lee, Hanshin; 10.5303/JKAS.2010.43.5.169

2010-01-01T23:59:59.000Z

465

Composite dark energy: cosmon models with running cosmological term and gravitational coupling  

E-Print Network [OSTI]

In the recent literature on dark energy (DE) model building we have learnt that cosmologies with variable cosmological parameters can mimic more traditional DE pictures exclusively based on scalar fields (e.g. quintessence and phantom). In a previous work we have illustrated this situation within the context of a renormalization group running cosmological term, Lambda. Here we analyze the possibility that both the cosmological term and the gravitational coupling, G, are running parameters within a more general framework (a variant of the so-called ``LXCDM models'') in which the DE fluid can be a mixture of a running Lambda and another dynamical entity X (the ``cosmon'') which may behave quintessence-like or phantom-like. We compute the effective EOS parameter, w, of this composite fluid and show that the LXCDM can mimic to a large extent the standard LCDM model while retaining features hinting at its potential composite nature (such as the smooth crossing of the cosmological constant boundary w=-1). We further argue that the LXCDM models can cure the cosmological coincidence problem. All in all we suggest that future experimental studies on precision cosmology should take seriously the possibility that the DE fluid can be a composite medium whose dynamical features are partially caused and renormalized by the quantum running of the cosmological parameters.

Javier Grande; Joan Sola; Hrvoje Stefancic

2006-12-16T23:59:59.000Z

466

Cosmological solutions of the Einstein-Friedmann equations Summary of Friedmann's equations  

E-Print Network [OSTI]

, with the cosmic ideal fluid energy-momentum tensor Tµ = ( + p) (t) uµ u - p(t) gµ . c 2009, F. Jegerlehner R Lect to the energy density (t) (t) + ; = , c 2009, F. Jegerlehner R Lect. 7 R 439 #12;COSMOLOGY claimed to represent the vacuum energy density. c 2009, F. Jegerlehner R Lect. 7 R 440 #12;COSMOLOGY claimed

Peters, Achim

467

Long Gamma-Ray Bursts Calibrated by Pade Method and Constraints on Cosmological Models  

E-Print Network [OSTI]

Gamma-ray bursts (GRBs) are among the most powerful sources in the universe. In the recent years, GRBs have been proposed as a complementary probe to type Ia supernovae (SNIa). However, as is well known, there is a circularity problem in the use of GRBs to study cosmology. In this work, based on the Pad\\'e approximant, we propose a new cosmology-independent method to calibrate GRBs. We consider a sample consisting 138 long GRBs and obtain 79 calibrated long GRBs at high redshift $z>1.4$ (named Mayflower sample) which can be used to constrain cosmological models without the circularity problem. Then, we consider the constraints on several cosmological models with these 79 calibrated GRBs and other observational data. We show that GRBs are competent to be a complementary probe to the other well-established cosmological observations.

Jing Liu; Hao Wei

2014-10-15T23:59:59.000Z

468

Long Gamma-Ray Bursts Calibrated by Pade Method and Constraints on Cosmological Models  

E-Print Network [OSTI]

Gamma-ray bursts (GRBs) are among the most powerful sources in the universe. In the recent years, GRBs have been proposed as a complementary probe to type Ia supernovae (SNIa). However, as is well known, there is a circularity problem in the use of GRBs to study cosmology. In this work, based on the Pad\\'e approximant, we propose a new cosmology-independent method to calibrate GRBs. We consider a sample consisting 138 long GRBs and obtain 79 calibrated long GRBs at high redshift $z>1.4$ (named Mayflower sample) which can be used to constrain cosmological models without the circularity problem. Then, we consider the constraints on several cosmological models with these 79 calibrated GRBs and other observational data. We show that GRBs are competent to be a complementary probe to the other well-established cosmological observations.

Liu, Jing

2014-01-01T23:59:59.000Z

469

The semiclassical tunneling probability in quantum cosmologies with varying speed of light  

E-Print Network [OSTI]

In quantum cosmology the closed universe can spontaneously nucleate out of the state with no classical space and time. The semiclassical tunneling nucleation probability can be estimated as $\\emph{P}\\sim\\exp(-\\alpha^2/\\Lambda)$ where $\\alpha$=const and $\\Lambda$ is the cosmological constant. In classical cosmology with varying speed of light c(t) (VSL) it is possible to solve the horizon problem, the flatness problem and the $\\Lambda$-problem if c=sa^n with s=const and n0. Thus, the semiclassical tunneling nucleation probability in VSL quantum cosmology is very different from this one in quantum cosmology with c=const. In particular, this one is strongly suppressed for large values of $\\Lambda$.

A. V. Yurov; V. A. Yurov

2004-10-23T23:59:59.000Z

470

Design of a 7m Davies-Cotton Cherenkov telescope mount for the high energy section of the Cherenkov Telescope Array  

E-Print Network [OSTI]

The Cherenkov Telescope Array is the next generation ground-based observatory for the study of very-high-energy gamma-rays. It will provide an order of magnitude more sensitivity and greater angular resolution than present systems as well as an increased energy range (20 GeV to 300 TeV). For the high energy portion of this range, a relatively large area has to be covered by the array. For this, the construction of ~7 m diameter Cherenkov telescopes is an option under study. We have proposed an innovative design of a Davies-Cotton mount for such a telescope, within Cherenkov Telescope Array specifications, and evaluated its mechanical and optical performance. The mount is a reticulated-type structure with steel tubes and tensioned wires, designed in three main parts to be assembled on site. In this work we show the structural characteristics of the mount and the optical aberrations at the focal plane for three options of mirror facet size caused by mount deformations due to wind and gravity.

Rovero, A C; Vallejo, G; Supanitsky, A D; Actis, M; Botani, A; Ochoa, I; Hughes, G

2013-01-01T23:59:59.000Z

471

Large Synoptic Survey Telescope: From Science Drivers to Reference Design  

SciTech Connect (OSTI)

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

472

What is there in the black box of dark energy: variable cosmological parameters or multiple (interacting) components?  

E-Print Network [OSTI]

The coincidence problems and other dynamical features of dark energy are studied in cosmological models with variable cosmological parameters and in models with the composite dark energy. It is found that many of the problems usually considered to be cosmological coincidences can be explained or significantly alleviated in the aforementioned models.

Javier Grande; Joan Sola; Hrvoje Stefancic

2007-01-08T23:59:59.000Z

473

Theory of cosmological perturbations in an anisotropic universe  

E-Print Network [OSTI]

This article describes the theory of cosmological perturbations around a homogeneous and anisotropic universe of the Bianchi I type. Starting from a general parameterisation of the perturbed spacetime a la Bardeen, a complete set of gauge invariant variables is constructed. Three physical degrees of freedom are identified and it is shown that, in the case where matter is described by a scalar field, they generalize the Mukhanov-Sasaki variables. In order to show that they are canonical variables, the action for the cosmological perturbations at second order is derived. Two major physical imprints of the primordial anisotropy are identified: (1) a scalar-tensor ``see-saw'' mechanism arising from the fact that scalar, vector and tensor modes do not decouple and (2) an explicit dependence of the statistical properties of the density perturbations and gravity waves on the wave-vector instead of its norm. This analysis extends, but also sheds some light on, the quantization procedure that was developed under the assumption of a Friedmann-Lemaitre background spacetime, and allows to investigate the robustness of the predictions of the standard inflationary scenario with respect to the hypothesis on the symmetries of the background spacetime. These effects of a primordial anisotropy may be related to some anomalies of the cosmic microwave background anisotropies on large angular scales.

Thiago S. Pereira; Cyril Pitrou; Jean-Philippe Uzan

2007-07-05T23:59:59.000Z

474

Some Implications of the Cosmological Constant to Fundamental Physics  

E-Print Network [OSTI]

In the presence of a cosmological constant, ordinary Poincare' special relativity is no longer valid and must be replaced by a de Sitter special relativity, in which Minkowski space is replaced by a de Sitter spacetime. In consequence, the ordinary notions of energy and momentum change, and will satisfy a different kinematic relation. Such a theory is a different kind of a doubly special relativity. Since the only difference between the Poincare' and the de Sitter groups is the replacement of translations by certain linear combinations of translations and proper conformal transformations, the net result of this change is ultimately the breakdown of ordinary translational invariance. From the experimental point of view, therefore, a de Sitter special relativity might be probed by looking for possible violations of translational invariance. If we assume the existence of a connection between the energy scale of an experiment and the local value of the cosmological constant, there would be changes in the kinematics of massive particles which could hopefully be detected in high-energy experiments. Furthermore, due to the presence of a horizon, the usual causal structure of spacetime would be significantly modified at the Planck scale.

R. Aldrovandi; J. P. Beltran Almeida; J. G. Pereira

2007-02-12T23:59:59.000Z

475

Plasma Astrophysics - Cosmology and the Growth of Cosmic Structure  

SciTech Connect (OSTI)

I will present some of the ways that x-ray spectroscopy can be utilized to determine cosmological parameters focusing on 5 methods: the gas fraction in clusters, the use of the Sunyaev-Zeldovich effect, the detection of resonance scattering in clusters, the use of resonance absorption and emission in background sources and the growth of structure. All of these techniques except the S-Z effect rely heavily on high resolution x-ray spectroscopy and require the next generation of x-ray spectroscopic missions such as Constellation-X. The promise of these techniques is great and they have the potential for precision cosmology with errors similar to those of other precision techniques such as type Ia supernova. If time permits I will also talk about how we can learn about how active galaxies strongly influence the growth of cosmic structure and how broad band high resolution x-ray spectra are necessary to measure the effects of AGN and how much energy they input into the universe and the role of new atomic physics calculations in interpreting these results. A related discussion can be found in a previously published manuscript.

Mushotzky, Richard [National Aeronautics and Space Administration, Goddard Space Flight Center, Greenbelt, Maryland, 20771 (United States)

2007-08-02T23:59:59.000Z

476

Plasma Astrophysics — Cosmology and the Growth of Cosmic Structure  

Science Journals Connector (OSTI)

I will present some of the ways that x?ray spectroscopy can be utilized to determine cosmological parameters focusing on 5 methods : the gas fraction in clusters the use of the Sunyaev?Zeldovich effect the detection of resonance scattering in clusters the use of resonance absorption and emission in background sources and the growth of structure. All of these techniques except the S?Z effect rely heavily on high resolution x?ray spectroscopy and require the next generation of x?ray spectroscopic missions such as Constellation?X. The promise of these techniques is great and they have the potential for precision cosmology with errors similar to those of other precision techniques such as type Ia supernova. If time permits I will also talk about how we can learn about how active galaxies strongly influence the growth of cosmic structure and how broad band high resolution x?ray spectra are necessary to measure the effects of AGN and how much energy they input into the universe and the role of new atomic physics calculations in interpreting these results. A related discussion can be found in a previously published manuscript.

Richard Mushotzky

2007-01-01T23:59:59.000Z

477

Future cosmological sensitivity for hot dark matter axions  

E-Print Network [OSTI]

We study the potential of a future, large-volume photometric survey to constrain the axion mass $m_a$ in the hot dark matter limit. Future surveys such as Euclid will have significantly more constraining power than current observations for hot dark matter. Nonetheless, the lowest accessible axion masses are limited by the fact that axions lighter than $\\sim 0.15$ eV decouple before the QCD epoch, assumed here to occur at a temperature $T_{\\rm QCD} \\sim 170$ MeV; this leaves an axion population of such low density that its late-time cosmological impact is negligible. For larger axion masses, $m_a \\gtrsim 0.15$ eV, where axions remain in equilibrium until after the QCD phase transition, we find that a Euclid-like survey combined with Planck CMB data can detect $m_a$ at very high significance. Our conclusions are robust against assumptions about prior knowledge of the neutrino mass. Given that the proposed IAXO solar axion search is sensitive to $m_a\\lesssim 0.2$ eV, the axion mass range probed by cosmology is n...

Archidiacono, Maria; Hamann, Jan; Hannestad, Steen; Raffelt, Georg; Wong, Yvonne Y Y

2015-01-01T23:59:59.000Z

478

Scaling cosmologies, geodesic motion and pseudo-susy  

E-Print Network [OSTI]

One-parameter solutions in supergravity carried by scalars and a metric trace out curves on the scalar manifold. In ungauged supergravity these curves describe a geodesic motion. It is known that a geodesic motion sometimes occurs in the presence of a scalar potential and for time-dependent solutions this can happen for scaling cosmologies. This note contains a further study of such solutions in the context of pseudo-supersymmetry for multi-field systems whose first-order equations we derive using a Bogomol'nyi-like method. In particular we show that scaling solutions that are pseudo-BPS must describe geodesic curves. Furthermore, we clarify how to solve the geodesic equations of motion when the scalar manifold is a maximally non-compact coset such as occurs in maximal supergravity. This relies upon a parametrization of the coset in the Borel gauge. We then illustrate this with the cosmological solutions of higher-dimensional gravity compactified on a $n$-torus.

Wissam Chemissany; André ploegh; Thomas Van Riet

2007-08-17T23:59:59.000Z

479

Quantum Scalar-metric Cosmology with Chaplygin gas  

E-Print Network [OSTI]

A spatially flat Friedmann-Robertson-Walker(FRW) cosmological model with generalized Chaplygin gas is studied in the context of scalar-metric formulation of cosmology. Schutz's mechanism for the perfect fluid is applied with generalized Chaplygin gas and the classical and quantum dynamics for this model is studied. It is found that the only surviving matter degree of freedom played the role of cosmic time. For the quantum mechanical description it is possible to find the wave packet which resulted from the linear superposition of the wave functions of the Schr\\"{o}dinger-Wheeler-DeWitt(SWD) equation, which is a consequence of the above formalism. The wave packets show two distinct dominant peaks and propagate in the direction of increasing scale factor. It may happen that our present universe originated from one of those peaks. The many-world and ontological interpretation of quantum mechanics is applied to investigate about the behaviour of the scale factor and the scalar field(considered for this model). In...

Majumder, Barun

2011-01-01T23:59:59.000Z

480

The AGN Hubble Diagram and Its Implications for Cosmology  

E-Print Network [OSTI]

We use a recently proposed luminosity distance measure for relatively nearby active galactic nuclei (AGNs) to test the predicted expansion of the Universe in the R_h=ct and LCDM cosmologies. This comparative study is particularly relevant to the question of whether or not the Universe underwent a transition from decelerated to accelerated expansion, which is believed to have occurred---on the basis of Type Ia SN studies---within the redshift range (0 < z < 1.3) that will eventually be sampled by these objects. We find that the AGN Hubble Diagram constructed from currently available sources does not support the existence of such a transition. While the scatter in the AGN data is still too large for any firm conclusions to be drawn, the results reported here nonetheless confirm and strengthen similar results of comparative analyses using other types of source, such as cosmic chronometers and gamma ray bursts. We show that the Akaike, Kullback, and Bayes Information Criteria all consistently yield a likelihood of ~74-93% that R_h=ct is closer to the "true" cosmology than LCDM is.

Fulvio Melia

2014-09-27T23:59:59.000Z

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.


481

A Comparison of Cosmological Models Using Strong Gravitational Lensing Galaxies  

E-Print Network [OSTI]

Strongly gravitationally lensed quasar-galaxy systems allow us to compare competing cosmologies as long as one can be reasonably sure of the mass distribution within the intervening lens. In this paper, we assemble a catalog of 69 such systems, and carry out a one-on-one comparison between the standard model, LCDM, and the R_h=ct Universe. We find that both models account for the lens observations quite well, though the precision of these measurements does not appear to be good enough to favor one model over the other. Part of the reason is the so-called bulge-halo conspiracy that, on average, results in a baryonic velocity dispersion within a fraction of the optical effective radius virtually identical to that expected for the whole luminous-dark matter distribution. Given the limitations of doing precision cosmological testing using the current sample, we also carry out Monte Carlo simulations based on the current lens measurements to estimate how large the source catalog would have to be in order to rule o...

Melia, Fulvio; Wu, Xue-Feng

2014-01-01T23:59:59.000Z

482

Phenomenology of "dark matter"- from the Everett's quantum cosmology  

E-Print Network [OSTI]

It is widely accepted that the Everett's (or "many-worlds") interpretation of quantum mechanics is the only one which is appropriate for quantum cosmology because no environment may exist for Universe as a whole. We discuss, in the framework of the Everett's interpretation, the (quasi-) classical stage of evolution of the Universe when there coexist "classically incompatible" configurations of matter, or classical alternative realities ("alternatives" for short). In the framework of the Everett's interpretation the semiclassical gravity (where the gravitational field is classical and the non-gravitational fields are quantum) is more natural than theories including quantizing gravitational field. It is shown that the semiclassical (at least on the astrophysical and cosmological scales) Everett-type gravity leads to the observational effect known as the effect of dark matter. Instead of assuming special forms of matter (weakly interacting with the known matter), the role of the dark matter is played in this case by the matter of the usual kind which however belongs to those alternative realities (Everett's worlds) which remain {\\guillemotleft}invisible{\\guillemotright}, i.e. not perceived with the help of non-gravitational fields.

M. B. Mensky

2011-05-21T23:59:59.000Z

483

Manifestly Covariant Gauge-invariant Cosmological Perturbation Theory  

E-Print Network [OSTI]

It is shown that a first-order cosmological perturbation theory for the open, flat and closed Friedmann-Lema\\^itre-Robertson-Walker universes admits one, and only one, gauge-invariant variable which describes the perturbation to the energy density and which becomes equal to the usual Newtonian energy density in the non-relativistic limit. The same holds true for the perturbation to the particle number density. Using these two new variables, a new manifestly gauge-invariant cosmological perturbation theory has been developed. Density perturbations evolve diabatically. Perturbations in the total energy density are gravitationally coupled to perturbations in the particle number density, irrespective of the nature of the particles. There is, in first-order, no back-reaction of perturbations to the global expansion of the universe. Small-scale perturbations in the radiation-dominated era oscillate with an increasing amplitude, whereas in older, less precise treatments, oscillating perturbations are found with a decreasing amplitude. This is a completely new and, obviously, important result, since it makes it possible to explain and understand the formation of massive stars after decoupling of matter and radiation.

P. G. Miedema; W. A. van Leeuwen

2014-10-01T23:59:59.000Z

484

Towards Viable Cosmological Models of Disformal Theories of Gravity  

E-Print Network [OSTI]

The late-time cosmological dynamics of disformal gravity are investigated using dynamical systems methods. It is shown that in the general case there are no stable attractors that screen fifth-forces locally and simultaneously describe a dark energy dominated universe. Viable scenarios have late-time properties that are independent of the disformal parameters and are identical to the equivalent conformal quintessence model. Our analysis reveals that configurations where the Jordan frame metric becomes singular are only reached in the infinite future, thus explaining the natural pathology resistance observed numerically by several previous works. The viability of models where this can happen is discussed in terms of both the cosmological dynamics and local phenomena. We identify a special parameter tuning such that there is a new fixed point that can match the presently observed dark energy density and equation of state. This model is unviable when the scalar couples to the visible sector but may provide a good candidate model for theories where only dark matter is disformally coupled.

Jeremy Sakstein

2014-12-17T23:59:59.000Z

485

Generalized Chaplygin gas model: Cosmological consequences and statefinder diagnosis  

E-Print Network [OSTI]

The generalized Chaplygin gas (GCG) model in spatially flat universe is investigated. The cosmological consequences led by GCG model including the evolution of EoS parameter, deceleration parameter and dimensionless Hubble parameter are calculated. We show that the GCG model behaves as a general quintessence model. The GCG model can also represent the pressureless CDM model at the early time and cosmological constant model at the late time. The dependency of transition from decelerated expansion to accelerated expansion on the parameters of model is investigated. The statefinder parameters $r$ and $s$ in this model are derived and the evolutionary trajectories in $s-r$ plane are plotted. Finally, based on current observational data, we plot the evolutionary trajectories in $s-r$ and $q-r$ planes for best fit values of the parameters of GCG model. It has been shown that although, there are similarities between GCG model and other forms of chaplygin gas in statefinder plane, but the distance of this model from the $\\Lambda$CDM fixed point in $s-r$ diagram is shorter compare with standard chaplygin gas model.

M. Malekjani; A. Khodam-Mohammadi; N. Nazari-Pooya

2011-03-09T23:59:59.000Z

486

Imprints of cosmic strings on the cosmological gravitational wave background  

SciTech Connect (OSTI)

The equation which governs the temporal evolution of a gravitational wave (GW) in curved space-time can be treated as the Schroedinger equation for a particle moving in the presence of an effective potential. When GWs propagate in an expanding universe with constant effective potential, there is a critical value (k{sub c}) of the comoving wave number which discriminates the metric perturbations into oscillating (k>k{sub c}) and nonoscillating (kcosmological model which is driven by a two-component fluid, consisting of radiation (dominant) and cosmic strings (subdominant). It is known that the cosmological evolution gradually results in the scaling of a cosmic-string network and, therefore, after some time ({delta}{tau}) the Universe becomes radiation dominated. The evolution of the nonoscillatory GW modes during {delta}{tau} (while they were outside the horizon), results in the distortion of the GW power spectrum from what it is anticipated in a pure radiation model, at present-time frequencies in the range 10{sup -16} Hz

Kleidis, K [Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece); Department of Civil Engineering, Technological Education Institute of Serres, 62124 Serres (Greece); Papadopoulos, D B; Vlahos, L [Department of Physics, Aristotle University of Thessaloniki, 54124 Thessaloniki (Greece); Verdaguer, E [Departament de Fisica Fonamental and Institut de Ciences del Cosmos, Universitat de Barcelona, Avinguda Diagonal 647, E-08028 Barcelona (Spain)

2008-07-15T23:59:59.000Z

487

Cosmologies with varying speed of light: A historical perspective  

Science Journals Connector (OSTI)

The possibility that natural laws and constants may not be true constants, but vary over cosmic periods of time, has recently attracted much attention. In this paper, I provide some historical background to the issue and consider, in the form of a historical review, some of the more spectacular developments within recent years. The focus of the paper is on the hypothesis of a varying speed of light, which appeared shortly after the announcement of the expanding universe. After a brief account of the history of this hypothesis, I consider in more details the varying c theories that have appeared during the last decade and were originally introduced as an alternative to the inflationary model. These so-called varying speed of light (VSL) theories have been surprisingly popular and created a flood of physics and cosmology papers. However, they have also been severely criticized from conceptual points of view and their status is as yet uncertain. Although a research programme in development, a historical perspective on VSL cosmology may not be out of place.

Helge S. Kragh

2006-01-01T23:59:59.000Z

488

Variable Speed of Light Cosmology, Primordial Fluctuations and Gravitational Waves  

E-Print Network [OSTI]

A variable speed of light (VSL) cosmology is developed with a spontaneous breaking of Lorentz invariance in the early universe. A non-minimal electromagnetic coupling to curvature and the resulting quantum electrodynamic vacuum polarization dispersive medium can produce $c\\gg c_0$ in the early universe, where $c_0$ is the measured speed of light today. Higher derivative curvature contributions to the effective gravita