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 o f cluster mass M, cluster radius R, and axion mass m(a), photons from spont aneous axion decay can trigger exponential growth of photon number via stim ulated decay. We derive (i) constraints on these parameters for lasing to o ccur, and (ii) the lasing rate equations for a general axion distribution. A simple axion cluster model with a flat momentum distribution is studied i n analytical and numerical detail.