A partial μ–τ symmetry and its prediction for leptonic CP violation

摘要

We find that the lepton flavor mixing matrix U should possess a partial μ – τ permutation symmetry | U μ 1 | = | U τ 1 | , and the latter predicts a novel correlation between the Dirac CP-violating phase δ and three flavor mixing angles θ 12 , θ 13 and θ 23 in the standard parametrization. Inputting the best-fit values of these angles reported by Capozzi et al., we obtain the prediction δ ? 255 ° in the normal neutrino mass ordering, which is in good agreement with the best-fit result δ ? 250 ° . In this connection the inverted neutrino mass ordering is slightly disfavored. If this partial μ – τ symmetry is specified to be | U μ 1 | = | U τ 1 | = 1 / 6 , one can reproduce the phenomenologically-favored relation sin 2 ? θ 12 = ( 1 ? 2 tan 2 ? θ 13 ) / 3 and a viable two-parameter description of U which were first uncovered in 2006. Moreover, we point out that the octant of θ 23 and the quadrant of δ can be resolved due to the slight violation of | U μ 2 | = | U τ 2 | and | U μ 3 | = | U τ 3 | either at the tree level or from radiative corrections.