Modulation sensitive search for nonvirialized dark-matter axions

Abstract

Nonvirialized dark-matter axions may be present in the Milky Way halo in the form of low-velocity-dispersion flows. The Axion Dark-Matter eXperiment performed a search for the conversion of these axions into microwave photons using a resonant cavity immersed in a strong, static magnetic field. The spread of photon energy in these measurements was measured at spectral resolutions of the order of 1 Hz and below. If the energy variation were this small, the frequency modulation of any real axion signal due to the orbital and rotational motion of Earth would become non-negligible. Conservative estimates of the expected signal modulation were made and used as a guide for the search procedure. The photon frequencies covered by this search are 812--852 and 858--892 MHz, which correspond to an axion mass of 3.36--3.52 and $3.55--3.69\text{ }\text{ }\ensuremath{\mu}\mathrm{eV}$. No axion signal was found, and limits were placed on the maximum local density of nonvirialized axions of these masses.