Neutrino mass textures and partial μ-τ Symmetry

We discuss the viability of the μ-τ interchange symmetry imposed on the neutrino mass matrix in the flavor space. Whereas the exact symmetry is shown to lead to textures of a completely degenerate spectrum, which is incompatible with the neutrino oscillation data, introducing small perturbations into the preceding textures, inserted in a minimal way, leads, however, to four deformed textures representing an approximate μ-τ symmetry. We motivate the form of these "minimal" textures, which disentangle the effects of the perturbations, and present some concrete realizations assuming exact μ-τ at the Lagrangian level but at the expense of adding new symmetries and matter fields. We find that all of these deformed textures are capable of accommodating the experimental data, and in all types of neutrino mass hierarchies, particularly the nonvanishing value for the smallest mixing angle.