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Title: Searches for Astrophysical and Cosmological Axions

Abstract

The axion remains, after nearly 30 years, the most compelling and elegant solution to the strong-CP problem, i.e. why this symmetry is protected in QCD in spite of CP violation elsewhere. The axion is expected to be extremely light, and possess extraordinarily feeble couplings to matter and radiation. Because of its small couplings, the axion has defied experimental confirmation and is unlikely to be discovered in conventional laboratory experiments (i.e. production-detection). Nevertheless, a sufficiently light axion would have been produced abundantly in the Big Bang and is an excellent candidate for the dark matter of the Universe. Through the axion's two-photon coupling, implying axion-photon mixing in an external electromagnetic field, galactic halo axions may be feasibly detected by their resonant conversion to RF photons in a microwave cavity permeated by magnetic field with current technology. Over the past decade experiments have already set interesting limits in mass and coupling; upgrades in progress to photon detection schemes at or below the standard quantum limit will soon enable definitive searches. Similarly, axions produced in the solar burning core might be detectable by their conversion to x-rays in a magnetic helioscope. Indeed current published limits already equal the best bounds on axion-photon couplingmore » inferred from the concordance of stellar evolution models and observations, from horizontal branch stars. Significant improvements in both the mass range and sensitivity of the axion helioscope technique will be forthcoming in the next few years. This report will first summarize the theoretical background of the axion, and laboratory, astrophysical and cosmological limits on its mass and couplings. Cavity microwave searches for cosmic axions will then be reviewed, focusing on the current large-scale experiments (ADMX in the US; CARRACK in Japan), and their enabling technologies (HFET and SQUID amplifiers; Rydberg-atom single-quantum detection). Last, the searches for solar axions will be discussed, with particular attention to the CAST experiment at CERN. The conclusion provides a basis for cautious optimism that a definitive verdict on the axion, or at least its role as a dark matter component, could be expected within a decade.« less

Authors:
; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
903437
Report Number(s):
UCRL-JRNL-221319
TRN: US0703270
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Journal Name:
Annual Review of Nuclear and Particle Science, vol. 56, N/A, June 5, 2006, pp. 293-326
Additional Journal Information:
Journal Volume: 56
Country of Publication:
United States
Language:
English
Subject:
99 GENERAL AND MISCELLANEOUS//MATHEMATICS, COMPUTING, AND INFORMATION SCIENCE; AMPLIFIERS; AXIONS; CERN; DETECTION; ELECTROMAGNETIC FIELDS; FOCUSING; MAGNETIC FIELDS; NONLUMINOUS MATTER; PHOTONS; QUANTUM CHROMODYNAMICS; SENSITIVITY; STARS; SYMMETRY; UNIVERSE

Citation Formats

Asztalos, S J, Rosenberg, L J, van Bibber, K, Sikivie, P, and Zioutas, K. Searches for Astrophysical and Cosmological Axions. United States: N. p., 2006. Web. doi:10.1146/annurev.nucl.56.080805.140513.
Asztalos, S J, Rosenberg, L J, van Bibber, K, Sikivie, P, & Zioutas, K. Searches for Astrophysical and Cosmological Axions. United States. doi:10.1146/annurev.nucl.56.080805.140513.
Asztalos, S J, Rosenberg, L J, van Bibber, K, Sikivie, P, and Zioutas, K. Wed . "Searches for Astrophysical and Cosmological Axions". United States. doi:10.1146/annurev.nucl.56.080805.140513. https://www.osti.gov/servlets/purl/903437.
@article{osti_903437,
title = {Searches for Astrophysical and Cosmological Axions},
author = {Asztalos, S J and Rosenberg, L J and van Bibber, K and Sikivie, P and Zioutas, K},
abstractNote = {The axion remains, after nearly 30 years, the most compelling and elegant solution to the strong-CP problem, i.e. why this symmetry is protected in QCD in spite of CP violation elsewhere. The axion is expected to be extremely light, and possess extraordinarily feeble couplings to matter and radiation. Because of its small couplings, the axion has defied experimental confirmation and is unlikely to be discovered in conventional laboratory experiments (i.e. production-detection). Nevertheless, a sufficiently light axion would have been produced abundantly in the Big Bang and is an excellent candidate for the dark matter of the Universe. Through the axion's two-photon coupling, implying axion-photon mixing in an external electromagnetic field, galactic halo axions may be feasibly detected by their resonant conversion to RF photons in a microwave cavity permeated by magnetic field with current technology. Over the past decade experiments have already set interesting limits in mass and coupling; upgrades in progress to photon detection schemes at or below the standard quantum limit will soon enable definitive searches. Similarly, axions produced in the solar burning core might be detectable by their conversion to x-rays in a magnetic helioscope. Indeed current published limits already equal the best bounds on axion-photon coupling inferred from the concordance of stellar evolution models and observations, from horizontal branch stars. Significant improvements in both the mass range and sensitivity of the axion helioscope technique will be forthcoming in the next few years. This report will first summarize the theoretical background of the axion, and laboratory, astrophysical and cosmological limits on its mass and couplings. Cavity microwave searches for cosmic axions will then be reviewed, focusing on the current large-scale experiments (ADMX in the US; CARRACK in Japan), and their enabling technologies (HFET and SQUID amplifiers; Rydberg-atom single-quantum detection). Last, the searches for solar axions will be discussed, with particular attention to the CAST experiment at CERN. The conclusion provides a basis for cautious optimism that a definitive verdict on the axion, or at least its role as a dark matter component, could be expected within a decade.},
doi = {10.1146/annurev.nucl.56.080805.140513},
journal = {Annual Review of Nuclear and Particle Science, vol. 56, N/A, June 5, 2006, pp. 293-326},
number = ,
volume = 56,
place = {United States},
year = {2006},
month = {5}
}