Quasidegenerate neutrinos and leptogenesis fromLμ−Lτ

Abstract

We provide a framework for quasidegenerate neutrinos consistent with a successful leptogenesis, based on the ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ flavor symmetry and its breaking pattern. In this scheme, a fine-tuning is needed to arrange the small solar neutrino mass splitting. Once it is ensured, the atmospheric neutrino mass splitting and the deviation from the maximal atmospheric mixing angle $\ensuremath{\Delta}{\ensuremath{\theta}}_{23}$ are driven by the same symmetry breaking parameter $\ensuremath{\lambda}\ensuremath{\sim}0.1$, and the reactor angle ${\ensuremath{\theta}}_{13}$ is predicted to be slightly smaller than $\ensuremath{\lambda}$ while the Dirac $CP$ phase is generically of order one. Given that the pseudo-Dirac nature of right-handed neutrinos is protected from the flavor symmetry breaking, a small mass splitting can be generated radiatively. For moderate values of $\mathrm{tan}\ensuremath{\beta}\ensuremath{\sim}10$, this allows for low-scale supersymmetric leptogenesis, overcoming a strong washout effect of the quasidegenerate light neutrinos and evading the gravitino overproduction.