Perturbations to μ-τ symmetry in neutrino mixing

Abstract

Many neutrino mixing scenarios that have μ-τsymmetry with θ_{13}=0 are in disagreement with recent experimental results that indicate a nonzero value for θ_{13}. We investigate the effect of small perturbations on Majorana mass matrices with μ-τsymmetry and derive analytic formulae for the corrections to the mixing angles. We find that since m_1 and m_2 are nearly degenerate, μ-τsymmetry mixing scenarios are able to explain the experimental data with about the same size perturbation for most values of θ_{12}. This suggests that the underlying unperturbed mixing need not have θ_{12} close to the experimentally preferred value. One consequence of this is that a new class of models with μ-τsymmetry is possible, with unperturbed θ_{12} equal to zero or 90 degrees for arbitrary unperturbed θ_{13}.