Majorana CP-Violating Phases, RG Running of Neutrino Mixing Parameters and Charged Lepton Flavour Violating Decays

Abstract

We consider the MSSM with see-saw mechanism of neutrino mass generation and soft SUSY breaking with flavour-universal boundary conditions at the GUT scale, in which the lepton flavour violating (LFV) decays \mu\to e + \gamma, \tau\to \mu + \gamma, etc.,are predicted with rates that can be within the reach of present and planned experiments. These predictions depend critically on the matrix of neutrino Yukawa couplings \bf{Y_{\nu}} which can be expressed in terms of the light and heavy right-handed (RH) neutrino masses, neutrino mixing matrix U_{PMNS}, and an orthogonal matrix \bf{R}. We investigate the effects of Majorana CP-violation phases in U_{PMNS}, and of the RG running of light neutrino masses and mixing angles from M_Z to the RH Majorana neutrino mass scale M_R, on the predictions for the rates of LFV decays \mu\to e + \gamma, \tau \to \mu + \gamma and \tau\to e + \gamma. Results for neutrino mass spectrum with normal hierarchy, values of the lightest \nu-mass in the range 0 \leq m_1 \leq 0.30 eV, and quasi-degenerate heavy RH Majorana neutrinos in the cases of \bf{R} = \bf{1} and complex matrix \bf{R} are presented. We find that the effects of the Majorana CP-violation phases and of the RG evolution of neutrino mixing parameters can change by few orders of magnitude the predicted rates of the LFV decays \mu \to e + \gamma and \tau \to e + \gamma. The impact of these effects on the \tau \to \mu + \gamma decay rate is typically smaller and only possible for m_1 > 0.10 eV. If the RG running effects are negligible, in a large region of soft SUSY breaking parameter space the ratio of the branching ratios of the \mu \to e + \gamma and \tau \to e + \gamma (\tau \to \mu + \gamma) decays is entirely determined in the case of \bf{R} \cong \bf{1} by the values of the neutrino mixing parameters at M_Z.