Speaker: Maíra Dutra
The nature of dark matter (DM), which is more likely to be made out of particles, is one of the biggest mysteries in the interface between particle physics and cosmology. The current status of searches for DM particles point out to a complex dark sector and indicates that DM and SM particles interact very weakly. If their interactions are too weak, the dark and visible sectors were never in thermal equilibrium in the early universe, as needed in the standard production mechanism, the thermal freeze-out. In this talk, based on the work I have done in my Ph.D, I consider the feebly interacting massive particles (FIMPs), which are DM candidates produced from the SM thermal bath in out-of-equilibrium processes (freeze-in). Heavy fields (10^{10}-10^{16} GeV) are needed in many fundamental extensions of the SM in the cosmological context, as for instance GUT, seesaw and inflation, and their exchange between the visible and dark sectors is therefore an appealing underlying reason for the feeble interactions. Such a connection, which makes the freeze-in at the earliest stages of the radiation era a reasonable possibility, is what I have called the "FIMP wonder". I discuss different realizations of the "FIMP wonder", with models involving moduli, fermions, gauge bosons and spin-2 fields as heavy mediators. Finally, I will show that if the heavy mediators were produced on-shell whithin a period of entropy production in the early universe, as in the post-inflationary reheating, the relic density of dark matter may be enhanced by many orders of magnitude relative to the standard isentropic expansion of the universe.