  Cold dark matter axions form a Bose-Einstein condensate if the axions
thermalize. Recently, it was found that they do thermalize when the photon
temperature reaches T ~ 100 eV(f/10^12GeV)^1/2 and that they continue to do so
thereafter. We discuss the differences between axion BEC and CDM in the linear
regime and the non-linear regime of evolution of density perturbations. We find
that axion BEC provides a mechanism for the production of net overall rotation
in dark matter halos, and for the alignment of cosmic microwave anisotropy
multi-poles.
