The See - Saw Mechanism , Neutrino Yukawa Couplings ,

The LFV charged lepton decays µ → e+γ, τ → e+γ and τ → µ+γ and thermal leptogenesis are analysed in the MSSM with seesaw mechanism of neutrino mass generation and soft SUSY breaking with universal boundary conditions. The case of hierarchical heavy Majorana neutrino mass spectrum, M 1 ≪ M 2 ≪ M 3 , is investigated. Leptogenesis requires M 1 > ∼ 10 9 GeV. Considering the natural range of values of the heaviest right-handed Majorana neutrino mass, M 3 > ∼ 5 × 10 13 GeV, and assuming that the soft SUSY breaking universal gaugino and/or scalar masses have values in the range of few × 100 GeV, we derive the combined constraints, which the existing stringent upper limit on the µ → e + γ decay rate and the requirement of successful thermal leptogenesis impose on the neutrino Yukawa couplings, heavy Majorana neutrino masses and SUSY parameters. Results for the three possible types of light neutrino mass spectrum – normal and inverted hierarchical and quasi-degenerate – are obtained.