Leptogenesis and the Violation of Lepton Number and CP at Low Energies

In the context of the minimal supersymmetric seesaw model, we study the implications of the current neutrino data for thermal leptogenesis, ββ0ν decay, and leptonic flavourand CP-violating low-energy observables. We express the heavy singlet-neutrino Dirac Yukawa couplings (Yν)ij and Majorana masses MNi in terms of the light-neutrino observables and an auxiliary hermitian matrix H , which enables us to scan systematically over the allowed parameter space. If the lightest heavy neutrino N1 decays induce the baryon asymmetry, there are correlations between the MN1 , the lightest active neutrino mass and the primordial lepton asymmetry ǫ1 on the one hand, and the ββ0ν decay parameter mee on the other hand. However, leptogenesis is insensitive to the neutrino oscillation phase. We find lower bounds MN1 >∼ 10 GeV for the normal light-neutrino mass hierarchy, and MN1 >∼ 10 GeV for the inverted mass hierarchy, respectively, indicating a potentially serious conflict with the gravitino problem. Depending on MN1 , we find upper (upper and lower bounds) on the lightest active neutrino mass for the normal (inverted) mass hierarchy, and a lower bound on mee even for the normal mass ordering. The low-energy lepton-flavourand CP-violating observables induced by renormalization are almost independent of leptogenesis. The electron electric dipole moment may be close to the present bound, reaching de ∼ 10 e cm in our numerical examples, while dμ may reach dμ ∼ 10 e cm. CERN–TH/2002-133 June 2002