Quasi-degenerate neutrino mass spectrum, μ→e+γ decay and leptogenesis

In a large class of SUSY GUT models with see-saw 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 Yν 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 ∼103 to ∼106 with respect to the rates calculated for real R, while the τ→μ+γ decay rate is enhanced approximately by two orders of magnitude.