$S_3$ 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 ${\sin }^2{\theta }_{\odot }\simeq 1\mathrm{/}3$ is the basis for the so called tri-bimaximal mixing (tbm) when ${\theta }_{13}=0$. In this note, we explore the possibility that tri-bimaximal mixing is an indication of a softly broken higher leptonic symmetry $S_3$, the permutation of three lepton families that embeds the $\mu -\tau$ exchange symmetry of leptons.