P. Sikivie

A Cosmological Bound on the Invisible Axion

Abstract The production of axions in the early universe is studied. Axion models which break the U(1)PQ symmetry above 1012 GeV are found to produce an unacceptably large axion energy density.

SQUID-Based Microwave Cavity Search for Dark-Matter Axions

Axions in the microeV mass range are a plausible cold dark-matter candidate and may be detected by their conversion into microwave photons in a resonant cavity immersed in a static magnetic field. We report the first result from such an axion search using a superconducting first-stage amplifier (SQUID) replacing a conventional GaAs field-effect transistor amplifier. This experiment excludes KSVZ dark-matter axions with masses between 3.3 microeV and 3.53 microeV and sets the stage for a definitive axion search utilizing near quantum-limited SQUID amplifiers.

Bose-Einstein Condensation of Dark Matter Axions

We show that cold dark matter axions thermalize and form a Bose-Einstein condensate (BEC). We obtain the axion state in a homogeneous and isotropic universe, and derive the equations governing small axion perturbations. Because they form a BEC, axions differ from ordinary cold dark matter in the nonlinear regime of structure formation and upon entering the horizon. Axion BEC provides a mechanism for the production of net overall rotation in dark matter halos, and for the alignment of cosmic microwave anisotropy multipoles.

High resolution search for dark-matter axions

We have performed a high resolution search for galactic halo axions in cold flows using a microwave cavity detector. The analysis procedure and other details of this search are described. No axion signal was found in the mass range 1.98-2.17 micro-eV. We place upper limits on the density of axions in local discrete flows based on this result.

An Improved RF Cavity Search for Halo Axions

The axion is a hypothetical elementary particle and cold dark matter candidate. In this RF cavity experiment, halo axions entering a resonant cavity immersed in a static magnetic field convert into microwave photons, with the resulting photons detected by a low-noise receiver. The ADMX Collaboration presents new limits on the axion-to-photon coupling and local axion dark matter halo mass density from a RF cavity axion search in the axion mass range 1.9-2.3 {micro}eV, broadening the search range to 1.9-3.3 {micro}eV. In addition, we report first results from an improved analysis technique.

Results from a High-Sensitivity Search for Cosmic Axions

We report the first results of a high-sensitivity

The Secondary infall model of galactic halo formation and the spectrum of cold dark matter particles on earth

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On the Evolution of Global Strings in the Early Universe

search for light halo axions through their conversion to microwave photons. At the 90% confidence level, we exclude a Kim-Shifman-Vainshtein-Zakharov axion of mass

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Proposal for Axion Dark Matter Detection Using an LC Circuit

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