Self-interacting dark matter in cosmology: accurate numerical implementation and observational constraints

Abstract

This paper presents a systematic and accurate treatment of the evolution of cosmological perturbations in self-interacting dark matter models, for particles which decoupled from the primordial plasma while relativistic. We provide a numerical implementation of the Boltzmann hierarchies developed in a previous paper [JCAP, 09 (2020) 041] in a publicly available Boltzmann code and show how it can be applied to realistic DM candidates such as sterile neutrinos either under resonant or non-resonant production mechanisms, and for different field mediators. At difference with traditional fluid approximations — also known as a c eff-c vis parametrizations — our approach follows the evolution of phase-space perturbations under elastic DM interactions for a wide range of interaction models, including the effects of late kinetic decoupling. Finally, we analyze the imprints left by different self interacting models on linear structure formation, which can be constrained using Lyman-α forest and satellite counts. We find new lower bounds on the particle mass that are less restrictive than previous constraints.

Dark matter self-interactions in the matter power spectrum

“…This requires a modification of the publicly available code to include self-interactions, allowing DM to interpolate between perfect fluid and free streaming behavior. Related work can be found in [14][15][16]. While our analysis differs in several aspects our findings are consistent with the results presented in [14].…”

“…We have derived exact matching conditions for fermions and bosons produced relativistically (extending the work of refs. [14,15]). Interactions also affect the actual structure of the Boltzmann equations for DM perturbations, that we have here re-obtained in the so-called relaxation time approximation: a hierarchical structure of moments of the Boltzmann equations with interactions.…”

“…In this section we discuss how our approach relates to and differs from refs. [14,15], where cosmological evolution of self-interacting WDM was recently studied.…”

“…In [15] several matching conditions for the non-relativistic distribution were considered. We believe that the correct choice is the iso-entropic condition one but we do not agree with the numerical value quoted in that paper, which in our notation would correspond to α = 0.5.…”

“…A possible procedure to set limits, as outlined in [46] and adopted for example in [14,15,23], is the following:…”