Key points are not available for this paper at this time.
If axions exist, they contribute significantly to the present energy density. These axions have been collisionless and nonrelativistic since their appearance at 1 GeV. Hence axion density perturbations survive on essentially all scales, and once the axions are dominant, grow and in turn create and amplify baryon fluctuations. Axions can cluster into galactic halos even though the axion mass 10^-2 eV. If galactic halo matter is mainly axions, the Peccei-Quinn order parameter 10^10 GeV.
Ipser et al. (Mon,) studied this question.