Self-interacting dark matter and cosmology of a light scalar mediator

TL;DR

This paper explores a fermionic dark matter model with a scalar mediator, analyzing its cosmological and experimental constraints, and proposes a sterile neutrino extension to relax these constraints.

Contribution

It introduces a sterile neutrino extension to a scalar-mediated dark matter model, alleviating strong cosmological constraints on self-interacting dark matter.

Findings

Self-interaction constraints are significantly relaxed with sterile neutrino inclusion.

Allowed sterile neutrino mass range is between 10 MeV and 1 GeV.

The model remains consistent with dark matter abundance and collider limits.

Abstract

We consider a fermionic dark matter candidate interacting via a scalar mediator coupled with the Standard Model through a Higgs portal. We consider general setting including both scalar and pseudoscalar interactions between the scalar and fermion, and illustrate the relevant features for dark matter abundance, direct search limits and collider constraints. The case where dark matter has a self-interaction strength $\left\langle \sigma_V \right\rangle/m_\psi \sim 0.1-1 \,\mathrm{cm}^2/\mathrm{g}$ is strongly constrained, in particular by the Big Bang Nucleosynthesis. We show that these constraints can be alleviated by introducing a new light sterile neutrino $N$. The allowed region for the extended model consists of a triangle at $10 (\sin \theta)^{-2/5} \,{\rm MeV} \lesssim m_N \lesssim 1\,{\rm GeV}$.