Ultra light bosonic dark matter and cosmic microwave background

Abstract

In this paper, we consider the hypothesis in which a species of ultra light bosonic dark matter (ULBDM) with mass mB ∼ 10-22 eV could be the dominant dark matter (DM) in the universe. As a first approach we work in the context of kinetic theory, where ULBDM is described by the phase space distribution function whose dynamics is dictated by the Boltzmann-Einstein equations. We investigate the effects that this kind of DM imprints in the acoustic peaks of the cosmic microwave background. We find that the effect of the Bose-Einstein statistics is small, albeit perceptible, and is equivalent to an increase of nonrelativistic matter. It is stressed that in this approach, the mass-to-temperature ratio necessary for ULBDM to be a plausible DM candidate is about five orders of magnitude. We show that reionization is also necessary and we address a range of consistent values for this model. We find that the temperature of ULBDM is below the critical value implying that Bose-Einstein condensation is inherent to the ULBDM paradigm. © 2010. The American Astronomical Society. All rights reserved.