* Astronomy

Title: Implications of the Daya Bay observation of _{13} on the leptonic flavour mixing structure and CP violation
Authors: Zhi-zhong Xing

The Daya Bay Collaboration has recently reported its first \bar{\nu}_e \to \bar{\nu}_e oscillation result which points to \theta_{13} \simeq 8.8° ± 0.8° (best-fit ± 1\sigma range) or \theta_{13} \neq 0° at the 5.2\sigma level. The fact that this smallest neutrino mixing angle is not strongly suppressed motivates us to look into the underlying structure of lepton flavour mixing and CP violation. Two phenomenological strategies are outlined: (1) the lepton flavour mixing matrix U consists of a constant leading term U_0 and a small perturbation term \Delta U; and (2) the mixing angles of U are associated with the lepton mass ratios. Some typical patterns of U_0 are re-examined by constraining their respective perturbations with current experimental data. We illustrate a few possible ways to minimally correct U_0 in order to fit the observed values of three mixing angles. We point out that the structure of U may exhibit an approximate \mu-\tau permutation symmetry in modulus, and reiterate the geometrical description of CP violation in terms of the leptonic unitarity triangles. The salient features of nine distinct parametrisations of U are summarised, and its Wolfenstein-like expansion is presented by taking U_0 to be the democratic mixing pattern.

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