hep-ph/0301xxx Quasi-Degenerate Neutrino Mass Spectrum, µ → e + γ Decay and Leptogenesis

In a large class of SUSY GUT models with seesaw mechanism of neutrino mass generation, lepton flavor violating (LFV) decays µ → e + γ, τ → µ + γ, etc., are predicted with rates that are within the reach of present and planned experiments. A crucial element in these predictions is the matrix of neutrino Yukawa couplings Y ν which can be expressed in terms of the light and RH heavy neutrino masses, the neutrino mixing PMNS matrix U , and an orthogonal matrix R. Leptogenesis can take place only if R is complex. Considering the case of quasi-degenerate neutrinos and assuming that R is complex, we derive simple analytical expressions for the µ → e + γ, τ → µ+γ and τ → e+γ decay rates. Taking into account the leptogenesis constraints on the relevant parameters we show that the predicted rates of the LFV decays µ → e + γ, and τ → e+γ are generically enhanced by a factor of ∼ 10 3 to ∼ 10 6 with respect to the rates calculated for real R, while the τ → µ + γ decay rate is enhanced approximately by two orders of magnitude.