Minimal Sterile Neutrino Dark Matter from exponential growth [BEL-center:pheno]

by Marco Hufnagel (ULB)

Tuesday 21 Feb 2023, 13:00 → 14:00 Europe/Brussels

We propose a novel mechanism for the production of dark matter (DM) from a thermal bath, based on the idea that DM particles χ can transform heat bath particles ψ: χψ→χχ. For a small initial abundance of χ this leads to an exponential growth of the DM number density, in close analogy to other familiar exponential growth processes in nature. We demonstrate that this mechanism complements freeze-in and freeze-out production in a generic way, opening new parameter space to explain the observed DM abundance, and we discuss observational prospects for such scenarios.

Additionally, the above mechanism can also be used to establish a new way to generate sterile neutrinos νs​ in the early Universe, by converting ordinary neutrinos να in scattering processes νs να → νs νs. 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.

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