title: Experimental searches for galactic halo axions.
abstract: A very light axion would be copiously produced during the Big Bang as a zero-temperature Bose gas, and it would possess vanishingly small couplings to matter and radiation. It thus represents an ideal cold dark matter candidate. Galactic halo axions may be detected by their resonant conversion to microwave photons in a high-Q cavity permeated by a strong magnetic field. A large-scale search for the axion is ongoing in the US with sufficient sensitivity to see axions of plausible model couplings. Dramatic breakthroughs in the development of near-quantum limited superconducting quantum interference device amplifiers promise to improve the sensitivity of the experiment by a factor of 30 in the near future. In Japan, a group has been developing a Rydberg atom single-quantum detector as an alternative to linear amplifiers for a microwave-cavity axion experiment. Should the axion be discovered, the predicted fine structure in the axion signal would be rich in information about the history of galactic formation.
authors.affiliation: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94550, USA.
authors.forename: Karl A
authors.initials: KA
authors.lastname: van Bibber
authors.forename: S Darin
authors.initials: SD
authors.lastname: Kinion