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
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.