Primordial abundances of subdominant dark matter

Abstract

The PIDM model consists in two types of dark matter, one component of which accounts for a small portion of the total amount of dark matter and is self-interacting. The aim is to establish the characteristics of this subdominant dark-matter part. We first present the dark matter concept by reviewing the historical evidence of dark matter as well as the different sorts of dark matter. Then we introduce the concordance model in cosmology and evoke its small-scales defects. Dark-matter models are then mentioned to solve these problems, one of which being the PIDM model. Next, starting from the Boltzmann equation, we derive a formula allowing to compute the relic density of a species and we test it for the WIMP model. Then we derive a precise expression for the thermally averaged annihilation cross section. In doing so, we determine the characteristics of the subdominant dark-matter particles by constraining the thermally averaged annihilation cross section so that its abundance remains small compared to the total dark-matter abundance as stated by the PIDM model.