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

Abstract 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 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 ∼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.