Various Realizations of Leptogenesis and Neutrino Mass Constraints

Following the recent convincing evidence for neutrino oscillations, leptogenesis has become a well motivated possible explanation of the origin of the baryon asymmetry of the universe. In these proceedings, after a short introduction on the three basic ingredients of leptogenesis, we will extend the discussion of Ref. along two main directions. First, in the framework of the usual seesaw model with three right-handed neutrinos (“type-I” seesaw model), we will study the neutrino mass constraints, in particular the neutrino mass upper bound, which exist in order that leptogenesis can successfully explain the baryon asymmetry of the universe. We will show how this neutrino mass upper bound can be relaxed by no longer assuming that the right-handed neutrinos have a hierarchical mass spectrum. Secondly, other models of leptogenesis which might also be attractive for various reasons will be introduced: “type-II” seesaw model with a scalar Higgs triplet, “type-III” seesaw model with fermion triplets, and combinations of them such as the “type-I” plus “type-II” model which is motivated by left-right or SO(10) models. The corresponding neutrino mass bounds will be discussed for all these models. Finally, we will also briefly consider the case of radiative neutrino mass models.