Neutrinos : How Do They Mix and Violate CP ?

We discuss a simple model of lepton mixing and CP violation based on the flavor democracy of charge leptons and the mass degeneracy of neutrinos. A nearly bi-maximal flavor mixing pattern, which is favored by current data on atmospheric and solar neutrino oscillations, emerges naturally from this model after explicit symmetry breaking. The rephasing-invariant strength of CP or T violation can be as large as one percent, leading to significant probability asymmetries between ν µ → ν e and ¯ ν µ → ¯ ν e (or ν e → ν µ) transitions in the long-baseline neutrino experiments. The possible matter effects on CP-and T-violating asymmetries are also taken into account.