CP violation in the mass matrix of heavy neutrinos
  We discuss the question of CP-violation in the effective Hamiltonian approach in models of leptogenesis through heavy right handed neutrino decays. We first formulate the problem in four component notation and then point out that before the heavy neutrinos have decayed away, the universe becomes CP-asymmetric in the heavy neutrinos. However, the lepton asymmetry generated after they completely decay are independent of this asymmetry. 
Utpal Sarkar and R. Vaidya