Abstract.
In the first part of this talk, we focus on the process of Big Bang Nucleosynthesis (BBN) and on how it can be affected in the presence of different dark-sector states. In particular, we study generic constraints from BBN for MeV-scale particles decaying into electromagnetic radiation, which are neither fully relativistic nor non-relativistic during all times relevant for BBN. In addition, we also derive constraints for heavy particles decaying into neutrinos, which can distort cosmological observables via the emission of secondary particles undergoing electromagnetic interactions. For particles whose lifetime is shorter than the age of the Universe, this leads to original and stringent bounds on the particle's lifetime as a function of its abundance and mass.
In the second part of this talk, we discuss 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. 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.
(The slides will be available here)