Freeze-in and freeze-out of sterile neutrino dark matter

TL;DR

This paper introduces a novel production mechanism for keV-scale sterile neutrino dark matter involving scalar decay and annihilation, exploring thermalisation and cosmological implications.

Contribution

It proposes a new scalar-mediated production scenario for sterile neutrino dark matter, analyzing thermalisation conditions and cosmological observables.

Findings

Identifies parameter space for dark sector thermalisation.

Describes a combined freeze-in and freeze-out production process.

Discusses implications for cosmological observables.

Abstract

A sterile neutrino with a keV-scale mass is a compelling dark matter candidate. We propose a new production mechanism involving the decay and annihilation of a complex scalar singlet with a Higgs portal coupling which develops a vacuum expectation value. The interactions of the resulting pseudo Nambu-Goldstone boson may thermalise the dark sector. We determine the region of parameter space where dark sector thermalisation is reached and discuss the most relevant cosmological observables. The scenario can be considered as the combination of a freeze-in of the dark sector followed by relativistic freeze-out.