Correlation between Leptonic CP Violation and mu-tau Symmetry Breaking

Abstract

Considering the $\mu$-$\tau$ symmetry, we discuss a direct linkage between phases of flavor neutrino masses and leptonic CP violation by determining three eigenvectors associated with $\mathbf{M}=M_{\nu }^{†}{M}_{\nu }$ for a complex flavor neutrino mass matrix $M_{\nu }$ in the flavor basis. Since the Dirac CP violation is absent in the $\mu$-$\tau$ symmetric limit, leptonic CP violation is sensitive to the $\mu$-$\tau$ symmetry breaking, whose effect can be evaluated by perturbation. It is found that the Dirac phase ($\delta$) arises from the $\mu$-$\tau$ symmetry breaking part of ${\mathbf{M}}_{e\mu ,e\tau }$ and an additional phase ($\rho$) is associated with the $\mu$-$\tau$ symmetric part of ${\mathbf{M}}_{e\mu ,e\tau }$, where ${\mathbf{M}}_{ij}$ stands for an $ij$ matrix element ($i,j$=$e,\mu ,\tau$). The phase $\rho$ is redundant and can be removed but leaves its effect in the Dirac CP violation characterized by $\sin (\delta +\rho )$. The perturbative results suggest the exact formula of mixing parameters including that of $\delta$ and $\rho$, which turns out to be free from the effects of the redundant phases. As a result, it is generally shown that the maximal atmospheric neutrino mixing necessarily accompanies either $\sin {\theta }_{13}=0$ or $\cos (\delta +\rho )=0$, the latter of which indicates maximal CP violation, where ${\theta }_{13}$ is the ${\nu }_e$-${\nu }_{\tau }$ mixing angle.

16 pages, ReVTeX, references updated, typos corredcted, published version in Physical Reviews D

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Cited by in corpus (3)

• Fermion Mass Hierarchies and Flavour Mixing from a Minimal Discrete Symmetry
• Leptonic CP Violation Induced by Approximately mu-tau Symmetric Seesaw Mechanism
• Theoretical progress on the V_us determination from tau decays