A new life for sterile neutrino dark matter after the pandemic

Abstract

We propose a novel mechanism to generate sterile neutrinos $ν_s$ in the early Universe, by converting ordinary neutrinos $ν_α$ in scattering processes $ν_sν_α\toν_sν_s$. After initial production by oscillations, this leads to an exponential growth in the $ν_s$ abundance. We show that such a production regime naturally occurs for self-interacting $ν_s$, and that this opens up significant new parameter space where $ν_s$ 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.