BOSE-CONDENSED DARK MATTER HALOS WITH NON-DEGENERATE COMPONENT
Abdullin I.G., Popov V.A.
A galactic halo of dark matter is considered as a weakly interacting dilute Bose gas. The halo involves a core, in which some bosons form Bose-Einstein condensate, while the others remain in the non-degenerate state. The non-degenerate component is described as a gas of elementary excitations in the Hartree–Fock–Bogolyubov approximation taking into account the overall quasiparticle energy spectrum. A cloud of non-condensed bosons surrounds the core. Numerical solutions to the equations describing a dark matter density distribution show that the halo radius grows significantly when the condensate particle number fraction decreases. At the same time the radius of the condensate core remains almost the same. If the halo has comparable-sized condensate core, the non-degenerate component gives only insignificant contributions to the dark matter density profile and rotation curves when confronted with the pure condensate models. This conclusion is caused by constraints on the scattering cross section to the mass of dark matter particles ratio obtained from the Bullet Cluster measurements. It is shown that bosons with masses \( m \sim 100 \) eV do not violate these constraints if they form relatively small condensate “drops” (with a radius of about 100 astronomical units) inside a halo consisting of non-condensed particles.