Self Interactions in Warm Dark Matter: A View from Cosmological Perturbation Theory

Abstract

We provide a short overview into Self Interacting Warm Dark Matter (SI-WDM) models from the context of Cosmological Perturbation Theory (CPT). The aim is to generalize conventional Cold DM models, by proposing a more general framework both from theoretical as well as from numerical fronts, on the effects of SI-WDM on the linear power spectrum and its consequent imprints on non-linear structure formation. After describing the theoretical background, we present useful analytic expressions for the collision terms in the Boltzmann Hierarchies, and provide some numerical results within the Relaxation Time Approximation (RTA). We consider massive DM particles that decouple from the hot plasma while relativistic. We introduce elastic DM–DM interactions under an ansatz for the scattering amplitude that accounts for massive mediators on an effective way. Paying special attention to the self interaction decoupling mechanisms, we analyze scenarios where the particle undergoes self decoupling while relativistic as well as while non relativistic.