Variations on leptogenesis

We study variations of the standard leptogenesis scenario that can arise if an additional mass scale related to the breaking of some new symmetry (as for example a flavor or the B-L symmetry) is present below the mass MN1 of the lightest right-handed Majorana neutrino. Our scheme is inspired by U(1) models of flavor à la Froggatt-Nielsen, and involves new vectorlike heavy fields F. We show that depending on the specific hierarchy between MN1 and the mass scale of the fields F, qualitatively different realizations of leptogenesis can emerge. We compute the CP asymmetries in N1 decays in all the relevant cases, and we conclude that in most situations leptogenesis could be viable at scales much lower than in the standard scenario.