Implications of the Daya Bay observation of θ13 on the leptonic flavor mixing structure and CP violation

The Daya Bay collaboration has recently reported its first ν-bare → ν-bare oscillation result which points to θ13 ≅ 8.8° ±0.8° (best-fit ±1φ range) or θ13 ≠0° at the 5.2a level. The fact that this smallest neutrino mixing angle is not strongly suppressed motivates us to look into the underlying structure of lepton flavor mixing and CP violation. Two phenomenological strategies are outlined: (1) the lepton flavor mixing matrix U consists of a constant leading term U0 and a small perturbation term ΔU; and (2) the mixing angles of U are associated with the lepton mass ratios. Some typical patterns of U0 are reexamined by constraining their respective perturbations with current experimental data. We illustrate a few possible ways to minimally correct U0 in order to fit the observed values of three mixing angles. We point out that the structure of U may exhibit an approximate μ-τ 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 parametrizations of U are summarized, and its Wolfenstein-like expansion is presented by taking U0 to be the democratic mixing pattern. (author)