The Role of Self Interactions in the Cosmological Evolution of Warm Dark Matter.

In this work we present a summary of recent studies on the effects of elastic self interactions in the evolution of Warm Dark Matter models (WDM), focusing on structure formation and the evolution of cosmological perturbations. We pay special attention to a particular class of sterile neutrino WDM known as $\nu$MSM and provide examples for the case of vector field self interactions. We calculate the effects of assuming self interacting dark matter in X-Ray astrophysical observations, in the formation of fermionic DM halos in (quasi) equilibrium states and in the evolution of DM perturbations in the early universe, assuming particle masses between $\mathcal{O}(1-100)$ keV. In the latter topic, we perform simulations using a modification to the public Boltzmann solver CLASS and compare our results with observations. We find self interactions to be an interesting addition to WDM models, which can alleviate tensions both present in standard CDM cosmology and regarding WDM itself, as well as provide an interesting avenue for DM halo formation.