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 mu --> e + gamma, tau --> mu + gamma, 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-nu 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 mu --> e + gamma, tau --> mu + gamma and tau --> e + gamma decay rates. Taking into account the leptogenesis constraints on the relevant parameters we show that the predicted rates of the LEV decays mu --> e + gamma, and tau --> e + gamma are Generically enhanced by a factor of similar to10(3) to similar to10(6) with respect to the rates calculated for real R, while the tau --> mu + gamma decay rate is enhanced approximately by two orders of magnitude. (C) 2003 Elsevier B.V. All rights reserved.