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 $M_{N_1}$ 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 $M_{N_1}$ and the mass scale of the fields $F$, qualitatively different realizations of leptogenesis can emerge. We compute the CP asymmetries in $N_1$ 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.