Minimal sterile neutrino dark matter

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