Please contact erule@berkeley.edu for zoom links.

In this talk we consider both the possibility of dark matter being either a strongly or a weakly interacting thermal relic. For strongly interacting massive particles (SIMPs) we study the influence of bound states X on their cosmology, finding a “catalysis” of mass-depleting processes in the hidden sector, adding a qualitative change to SIMP freeze-out once X exist, hence broadening the options for SIMP dark matter. In turn, for weakly interacting massive particles (WIMPs) we study the low mass frontier of thermal relics where freeze-out happens during the cosmological non-trivial epochs of neutrino decoupling and primordial nucleosynthesis. Here we present a first self-consistent calculation of the cosmological Neff parameter that is expected to be measured with much improved accuracy in upcoming CMB experiments.