Results of a laboratory search for cosmic axions and other weakly coupled light particles

A microwave cavity experiment designed to search for the signal from cosmic axions converting in an external magnetic field covered the mass range (4.5-16.3)×{}10^-6 eV, corresponding to the frequency range from 1.09 to 3.93 GHz. Upper limits on the coupling and abundance of nonrelativistic galactic axions have been measured; these limits yield a coupling which is 1-2 orders of magnitude higher than that predicted by the Dine-Fischler-Srednicki model. Also presented are limits on axions with a continuum spectrum, limits on the presence of a wide axion line at the frequency of the 21-cm hydrogen emission line, and limits on the production of pseudoscalar particles by photons in the cavity interacting with the magnetic field.