Limits on the abundance and coupling of cosmic axions at 4.5<ma<5.0 μeV

Abstract

We report preliminary results from a search for galactic axions in the frequency range 1.09${f}_{a}$1.22 GHz. For an axion linewidth ${\ensuremath{\Gamma}}_{a}$\ensuremath{\le}200 Hz we obtain the experimental limit (${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}$/${m}_{a}$${)}^{2}$${\ensuremath{\rho}}_{a}$1.4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}41}$. The theoretical prediction is (${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}$/${m}_{a}$${)}^{2}$${\ensuremath{\rho}}_{a}$=3.9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}44}$ with ${\ensuremath{\rho}}_{a}$=300 MeV/${\mathrm{cm}}^{3}$. We have also searched for the presence of a continuous spectrum of light pseudoscalar particles; if we assume that the above ${\ensuremath{\rho}}_{a}$ is contained between the upper and lower frequencies of our search, then we find that ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}$2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}30}$ ${\mathrm{MeV}}^{1/2}$ ${\mathrm{cm}}^{3/2}$\ensuremath{\simeq}${10}^{\mathrm{\ensuremath{-}}11}$ ${\mathrm{GeV}}^{\mathrm{\ensuremath{-}}1}$.