S3 symmetry and tri-bimaximal mixing

The near maximal value for the atmospheric neutrino mixing angle together with the fact that the solar mixing angle satisfies the relation sin2θ⊙≃13 is the basis for the so-called tri-bimaximal mixing when θ13=0. In this Letter, we explore the possibility that tri-bimaximal mixing is an indication of a softly broken higher leptonic symmetry S3, the permutation of three lepton families that embeds the μ-τ exchange symmetry of leptons.