Lepton Flavor Structures

Current experimental data can help us gain an insight into the underlying dynamics of lepton flavor mixing. In particular, we explore the lepton flavor structures by taking account of the observed value of the smallest neutrino mixing angle θ13. Two phenomenological strategies are outlined: (1) the lepton flavor mixing matrix U consists of a constant leading term and a small perturbation term; and (2) the mixing angles of U are associated with the lepton mass ratios. Either approach can be realized via a certain flavor symmetry and its breaking mechanism. The approximate μ−τ permutation symmetry of U in modulus and the leptonic CP violation are discussed in some detail. We also present a full parametrization of the 6×6 flavor mixing matrix in the (3+3) scenario with three sterile neutrinos, and give some comments on the similarities and differences between lepton and quark flavor mixing structures.