A new life for sterile neutrino dark matter after the pandemic

TL;DR

This paper introduces a new mechanism for sterile neutrino dark matter production in the early Universe, involving scattering processes that lead to exponential growth in sterile neutrino abundance, expanding the viable parameter space.

Contribution

It presents a novel production mechanism for sterile neutrino dark matter via scattering, which enhances their abundance and broadens the parameter space for dark matter models.

Findings

Exponential growth in sterile neutrino abundance through scattering processes.

Significant new parameter space where sterile neutrinos can account for all dark matter.

Motivates improved X-ray and structure formation constraints.

Abstract

We propose a novel mechanism to generate sterile neutrinos $\nu_s$ in the early Universe, by converting ordinary neutrinos $\nu_\alpha$ in scattering processes $\nu_s\nu_\alpha\to\nu_s\nu_s$. After initial production by oscillations, this leads to an exponential growth in the $\nu_s$ abundance. We show that such a production regime naturally occurs for self-interacting $\nu_s$, and that this opens up significant new parameter space where $\nu_s$ make up all of the observed dark matter. Our results provide strong motivation to further push the sensitivity of X-ray line searches, and to improve on constraints from structure formation.