1208.0301 (M. O. C. Pires et al.)

Galactic cold dark matter as a Bose-Einstein condensate of axion-like particles with spin    [PDF]

M. O. C. Pires, J. C. C. de Souza

We propose here the dark matter content of galaxies as a cold bosonic fluid composed of spin-1 axion-like particles thermalized in the Bose-Einstein condensation state and bounded by their self-gravitational potential. We analyze two zero-momentum configurations: the polar phases in which spin alignment of two neighbouring particles is anti-parallel and the ferromagnetic phases in which every particle spin is aligned in the same direction. Using the mean field approximation we derive the Gross-Pitaevskii equations for both cases, and, supposing the dark matter to be a polytropic fluid, we describe the particles density profile as Thomas-Fermi distributions characterized by the halo radii and in terms of the scattering lengths and mass of each particle. By comparing this model with data obtained from 59 spiral galaxies, we constrain the scattering lengths for both phases and the axion-like particle mass.

View original: http://arxiv.org/abs/1208.0301