Hot Leptogenesis from Thermal Dark Matter

Abstract

In this work, we investigate a scenario in which heavy Majorana Right-Handed Neutrinos (RHNs) are in thermal equilibrium with a dark sector with temperature higher than the Standard Model (SM) thermal bath. Specifically, we consider the scenario in which thermal Dark Matter (DM) abundance is fixed from the freeze-out of DM annihilations into RHNs. Due to the inert nature of the RHNs, we show that it is possible for the two sectors to remain thermally decoupled by having more than two generations of the RHNs. The hotter temperature implies higher abundances of DM and RHNs with the following consequences. For leptogenesis, an enhancement in efficiency up to a factor of 51.6 can be obtained, though a resonant enhancement of CP violation is still required due to an upper mass bound of about 4 TeV for the RHNs. For the DM, an enhanced annihilation cross section up to a factor of 51.6 is required to obtain the correct DM abundance. This scenario can be probed via indirect detection of DM annihilating into RHNs, which then decay into $h\,\nu$, $Z\,\nu$ and $W^{\pm} \ell^{\mp}$ with an enhanced annihilation cross section above the typical thermal value.