Another Look at Minimal Lepton Flavour Violation, l_i -> l_j gamma, Leptogenesis, and the Ratio M_nu/ Lambda_LFV

Abstract

We analyze lepton flavour violation (LFV), as well as generation of the observed baryon-antibaryon asymmetry of the Universe (BAU) within a generalized minimal lepton flavour violation (MLFV) framework where we allow for CP violation both at low and high energies. The generation of BAU is obtained through radiative resonant leptogenesis (RRL), where starting with three exactly degenerate right-handed neutrinos at Lambda_GUT, we demonstrate explicitly within the SM and the MSSM that the splittings between their masses at the see-saw scale M_nu, generated by renormalization group effects, are sufficient for a successful leptogenesis for M_nu even as low as 10^6 GeV. The inclusion of flavour effects plays an important role in this result and can lead to the observed BAU even in the absence of CP violation beyond the PMNS phases. The absence of a stringent lower bound on M_nu in this type of leptogenesis allows to easily satisfy present and near future upper bounds on mu -> e gamma and other charged lepton flavour violating (LFV) processes even for Lambda_LFV = O(1 TeV). We find, that the MLFV framework in the presence of heavy right-handed neutrinos and leptogenesis is not as predictive as MFV in the quark sector and point out that without a specific MLFV model, there is a rich spectrum of possibilities for charged LFV processes and for their correlation with low energy neutrino physics and the LHC physics, even if the constraint from the observed BAU is taken into account. While certain qualitative features of our analysis confirm findings of Cirigliano et al., at the quantitative level we find phenomenologically important differences. We explain the origin of these differences.