Thermalization of Axions and Axion like Particles

Cold dark matter candidate axions form a degenerate Bose gas with large correlation length. As a result they thermalize via gravitational self interactions and form a Bose-Einstein condensate (BEC). I will show that thermalization by gravitational self interactions and the subsequent formation of BEC occurs not only for axions but for a broad class of bosons which are created by the vacumm re-alignment mechanism. Thus, besides axions, axion like particles forming a BEC also acquire net overall rotation and form caustic rings in galactic halos.