Seminarium "High Energy, Cosmology and Astro-particle Physics (HECA)"

In the first part of the talk, we propose a novel mechanism 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. In the second part of the talk, we consider a scenario, in which the dark matter is alone in a hidden sector and consists of a real scalar particle in its spontaneously broken phase at a temperature which differs from the one of the visible sector, T' ≠ T. This is a particular case of a cannibal dark matter scenario, in which the relic abundance is sensitive to 3 → 2 and 4 → 2 processes. We study numerically and analytically the dark matter abundance both in the broken and the symmetric phases, while also reporting our results in the domain of thermal dark matter candidates.