Broken mu-tau Symmetry and Leptonic CP Violation

Abstract

We propose that leptonic CP violation arises from a breaking of the mu-tau exchange symmetry in the neutrino mass matrix which in turn is indicated by the near maximal atmospheric neutrino mixing and the near zero \theta_{13}. We find that for the case of a normal hierarchy, present data already restricts the way CP violation may appear in the neutrino mass matrix and there is an interesting correlation between the mixing angle \theta_{13}, the solar mixing angle \theta_{12} and the Dirac CP phase. In the inverted hierarchy only \theta_{13} and the Dirac phase are linked. We also discuss the impact of this kind of CP violation on the deviation of the atmospheric mixing from its maximal value. Moreover, if corrections to mu-tau symmetry arise from the charged lepton sector, where mu-tau symmetry is known to be broken anyway, we find interesting connections between the CP-even and -odd terms as well. Our predictions are testable in the proposed long baseline neutrino experiments.