Leptogenesis with heavy Majorana neutrinos reexamined - art. no. 043509

The mass term for Majorana neutrinos explicitly violates lepton number. Sev eral authors have used this fact to create a lepton asymmetry in the univer se by considering CP violating effects in the one loop self-energy correcti on for decaying heavy Majorana neutrinos. We compare and comment on the dif ferent approaches used to calculate the lepton asymmetry including those us ing an effective Hamiltonian and resummed propagators. We also recalculate the asymmetry in the small mass difference limit.