A model of lasing axion clusters

If axions make up the majority of the dark matter, then most are nonthermal and likely to be clustered in gravitational potential wells. For a range of cluster mass M, cluster radius R, and axion mass ma, photons from spontaneous axion decay can trigger exponential growth of photon number via stimulated decay. We derive (i) constraints on these parameters for lasing to occur, and (ii) the lasing rate equations for a general axion distribution. A simple axion cluster model with a flat momentum distribution is studied in analytical and numerical detail