Hot Leptogenesis from Thermal Dark Matter

TL;DR

This paper explores a thermal dark matter scenario with heavy Majorana neutrinos, showing how a hotter dark sector can enhance leptogenesis efficiency and dark matter annihilation, with potential for indirect detection.

Contribution

It introduces a model where multiple RHN generations keep dark and visible sectors thermally decoupled, leading to enhanced leptogenesis and dark matter annihilation signals.

Findings

Leptogenesis efficiency can be increased by up to 51.6 times.

Dark matter annihilation cross section can be similarly enhanced.

Scenario predicts detectable signals in indirect dark matter searches.

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.