Dark Matter Relic Abundance and Light Sterile Neutrinos

TL;DR

This paper investigates how sterile neutrinos with masses below 100 GeV affect dark matter relic abundance, especially when they decouple early, requiring adjustments in coupling strengths for accurate relic density predictions.

Contribution

It introduces a model where sterile neutrinos decouple early, altering the standard relic abundance calculations and highlighting the impact of small Yukawa couplings.

Findings

Sterile neutrinos can decouple before dark matter freeze-out.

Small Yukawa couplings increase dark matter relic abundance.

Larger dark matter-sterile neutrino couplings are needed for correct relic density.

Abstract

In this paper, we calculate the relic abundance of the dark matter particles when they can annihilate into sterile neutrinos with the mass $\lesssim 100 \text{ GeV}$ in a simple model. Unlike the usual standard calculations, the sterile neutrino may fall out of the thermal equilibrium with the thermal bath before the dark matter freezes out. In such a case, if the Yukawa coupling $y_N$ between the Higgs and the sterile neutrino is small, this process gives rise to a larger $\Omega_{\text{DM}} h^2$ so we need a larger coupling between the dark matter and the sterile neutrino for a correct relic abundance.