$μ-τ$ Symmetry and Radiatively Generated Leptogenesis

Abstract

We consider a $μ-τ$ symmetry in neutrino sectors realized at GUT scale in the context of a seesaw model. In our scenario, the exact $μ-τ$ symmetry realized in the basis where the charged lepton and heavy Majorana neutrino mass matrices are diagonal leads to vanishing lepton asymmetries. We find that, in the minimal supersymmetric extension of the seesaw model with large $\tanβ$, the renormalization group (RG) evolution from GUT scale to seesaw scale can induce a successful leptogenesis even without introducing any symmetry breaking terms by hand, whereas such RG effects lead to tiny deviations of $θ_{23}$ and $θ_{13}$ from $π/4$ and zero, respectively. It is shown that the right amount of the baryon asymmetry $η_B$ can be achieved via so-called resonant leptogenesis, which can be realized at rather low seesaw scale with large $\tanβ$ in our scenario so that the well-known gravitino problem is safely avoided.