We prove that taking correctly into account the lepton flavour dependence of the $CP$ asymmetries and washout processes, it is possible to obtain successful thermal leptogenesis from the decays of the second right-handed neutrino. The asymmetries in the muon and tau-flavour channels are then not erased by the inverse decays of the lightest right-handed neutrino $N_1$. In this way, we reopen the possibility of “thermal leptogenesis” in models with a strong hierarchy in the right-handed Majorana masses that is typically the case in models with up-quark neutrino-Yukawa unification.

• Received 23 January 2006

DOI:https://doi.org/10.1103/PhysRevD.73.073006