Minimal sterile neutrino dark matter

Abstract

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