A new mechanism of sterile neutrino dark matter production

TL;DR

This paper proposes a novel sterile neutrino dark matter production mechanism via 4-to-2 freeze-out in the dark sector, with implications for small-scale structure and potential observable decay signals.

Contribution

It introduces a new dark matter production scenario involving sterile neutrino self-interactions and models the mechanism with a scalar portal for a complete thermal history.

Findings

Relic abundance matches observations for sterile neutrino masses 500 keV to 20 GeV.

Self-interactions influence small-scale structure formation.

Potential observable signals from dark matter decay.

Abstract

We consider a scenario where the dark matter candidate is a sterile neutrino with sizable self-interactions, described by a dimension-six operator, and with negligible interactions with the Standard Model. The relic abundance is set by the freeze-out of 4-to-2 annihilations in the dark sector plasma and reproduces the observed dark matter abundance when the sterile neutrino mass is in the range $\sim 500\,{\rm keV} - 20\,\,{\rm GeV}$. The feeble interactions with the Standard Model may lead to observable signals from dark matter decay. Furthermore, the self-interactions can affect the formation of small scale structures. We also implement this mechanism in a concrete model where the sterile neutrino self-interaction is due to the exchange of a singlet scalar, and we discuss the relevance of the scalar portal interactions for constructing a complete thermal history of the dark sector.