The see-saw mechanism: neutrino mixing, leptogenesis and lepton flavor violation

Abstract. The see-saw mechanism to generate small neutrino masses is reviewed. After summarizing our current knowledge about the low energy neutrino mass matrix we consider reconstructing the see-saw mechanism. Low energy neutrino physics is not sufficient to reconstruct see-saw, a feature which we refer to as “see-saw degeneracy”. Indirect tests of see-saw are leptogenesis and lepton flavor violation in supersymmetric scenarios, which together with neutrino mass and mixing define the framework of see-saw phenomenology. Several examples are given, both phenomenological and GUT-related. Variants of the see-saw mechanism like the type II or triplet see-saw are also discussed. In particular, we compare many general aspects regarding the dependence of LFV on low energy neutrino parameters in the extreme cases of a dominating conventional see-saw term or a dominating triplet term. For instance, the absence of μ → eγ or τ → eγ in the pure triplet case means that CP is conserved in neutrino oscillations. Scanning models, we also find that among the decays μ → eγ, τ → eγ and τ → μγ the latter one has the largest branching ratio in (i) SO(10) type I see-saw models and in (ii) scenarios in which the triplet term dominates in the neutrino mass matrix.