New parametrization of the seesaw mechanism and applications in supersymmetric models

Abstract

We present a new parametrization of the minimal seesaw model, expressing the heavy-singlet neutrino Dirac Yukawa couplings ${(Y}_{\ensuremath{\nu}}{)}_{\mathrm{ij}}$ and Majorana masses ${M}_{{N}_{i}}$ in terms of effective light-neutrino observables and an auxiliary Hermitian matrix H. In the minimal supersymmetric version of the seesaw model, the latter can be related directly to other low-energy observables, including processes that violate charged lepton flavor and $\mathrm{CP}.$ This parametrization enables one to respect the stringent constraints on muon-number violation while studying the possible ranges for other observables by scanning over the allowed parameter space of the model. Conversely, if any of the lepton-flavor-violating process is observed, this measurement can be used directly to constrain ${(Y}_{\ensuremath{\nu}}{)}_{\mathrm{ij}}$ and ${M}_{{N}_{i}}.$ As applications, we study flavor-violating $\ensuremath{\tau}$ decays and the electric dipole moments of leptons in the minimal supersymmetric seesaw model.