Speaker
Description
Without tuning of parameters, the typical mass scale of the lightest right-handed neutrino (RHN), in the thermal leptogenesis paradigm, is about 10^{11} GeV. As opposed to the mild departure from equilibrium offered by the slow expansion, a first-order phase transition (FOPT) offers a drastic scenario of out-of-equilibrium dynamics. In this work we explore the possibility of embedding thermal leptogenesis within a FOPT such that RHNs remain massless until the FOPT arises. Their sudden and violent mass gain allows the neutrinos to become thermally decoupled, and the lepton asymmetry generated from their decay can be free from the strong wash-out processes that conventional leptogenesis scenarios suffer from, although new and important washout channels are now predicted. This allows for a decrease in the RHN's mass scale, which we quantify, as well complementary gravitional wave signals.
