Maximal Neutrino Mixing and Maximal CP Violation

We propose a phenomenological 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 νμ → νe and ν̄μ → ν̄e (or νe → νμ) transitions in the long-baseline neutrino experiments. Electronic address: [email protected] Electronic address: [email protected] 1 The recent observation of atmospheric and solar neutrino anomalies, in particular by the Super-Kamiokande experiment [1], has provided a strong indication that neutrinos are massive and lepton flavors are mixed. As there exist at least three different lepton families, the flavor mixing matrix may in general contain non-trivial complex phase terms. Hence CP or T violation is naturally expected in the lepton sector. A violation of CP invariance in the quark sector can result in a variety of observable effects in hadronic weak decays. Similarly CP or T violation in the lepton sector can manifest itself in neutrino oscillations [2]. The best (and probably the only) way to observe CP or T violating effects in neutrino oscillations is to carry out the long-baseline appearance neutrino experiments [3]. In the scheme of three lepton families, the 3×3 flavor mixing matrix V links the neutrino mass eigenstates (ν1, ν2, ν3) to the neutrino flavor eigenstates (νe, νμ, ντ ):