Ultra light bosonic dark matter and cosmic microwave background

TL;DR

This paper explores ultra light bosonic dark matter's effects on cosmic microwave background anisotropies, highlighting its potential as a dominant dark matter candidate with Bose-Einstein condensation features.

Contribution

It models ULBDM using kinetic theory and investigates its subtle effects on CMB acoustic peaks, proposing it as a plausible dark matter candidate with specific thermal properties.

Findings

Bose-Einstein statistics cause small but perceptible effects on CMB peaks.

ULBDM's mass-to-temperature ratio is about five orders of magnitude.

ULBDM temperature is below the critical value, indicating inherent Bose-Einstein condensation.

Abstract

In this paper, we consider the hypothesis in which a species of ultra light bosonic dark matter (ULBDM) with mass $m_{B}\sim 10^{-22}$ 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 dark matter 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 non-relativistic 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, impliying that Bose-Einstein condensation is inherent to the ULBDM paradigm.