Search for dark matter axions with ADMX and theoretical inquiries beyond the standard model

The axion affects two important issues in particle physics and astrophysics: the origin of CP symmetry in the strong interactions and the composition of the dark matter of the universe. Axions are especially significant as dark matter if their mass is of order 2-40 microeV. They would then make up the dark-matter halos of galaxies. These halo axions may be detected by their conversion into photons in a tunable high-Q microwave cavity permeated by a strong external magnetic field. The corresponding photon frequencies are in the microwave part of the electromagnetic spectrum: 0.5-10 GHz. Using near-quantum-limited SQUID amplifiers operated at ultralow temperatures (below 0.1 K), Generation-2 ADMX has demonstrated the sensitivity to detect even the most weakly-coupled QCD axions. The Florida ADMX group will continue its participation in support of the experiment's dilution refrigerator, in analysis of ADMX data for narrow spectral features arising from the expected flows of axions in the Galaxy, and in work on cavities to extend the experiment's higher-mass sensitivity. In addition, we will operate a pilot experiment that uses an LC resonant circuit to search for very light axions, with masses around 0.08-0.2 microeV.