STIMULATED RADIATION FROM AXION CLUSTER EVOLUTION

If axions exist and make up part or all of the cosmological dark matte r, then some are likely to be clustered in gravitational potential wel ls. The properties of these axion clusters will depend on their veloci ty and density profiles as well as on the mass of the axions. We deriv e the stimulated and spontaneous decay rate equations for general axio n distribution functions. Under certain conditions lasing action can c ommence, and we give approximate bounds for lasing in pure (i.e., unco ntaminated by normal matter) axion clusters. A simple spherical consta nt-density axion cluster model is studied in detail. For a range of cl uster mass M and radius R, and axion mass m(a)lpha, photons from spont aneous axion decay can trigger exponential growth of photon number via stimulated decay. Approximate bounds for lasing are obtained for this model, and numerical results are presented. We show that it is possib le that lasing axion clusters played a role in forming the large-scale structure of the universe. Our results can be easily applied to any p seudo Goldstone boson coupled to photons through the anomaly.