Large Lepton Flavor Mixing and E 6 - type Unification Models

There are experimental indications of large flavor mixing between νμ and ντ . In the unification models, in which the massless sector includes extra particles beyond the standard model, there possibly appear the mixings between quarks (leptons) and the extra particles. When large mixings occur, lepton flavor mixings can be quite different from quark flavor mixings. By taking the string inspired SU(6) × SU(2)R model with global flavor symmetries, we obtain the neutrino flavor mixing sin θ23 ≃ λ = sin θC around the unification scale. It can be expected that due to large Yukawa couplings of neutrinos, the renormalization effect increases sin 2θ23 naturally up to ∼ 1 at the electroweak scale. Fermion mass spectra and the CKM matrix of quarks obtained in this paper are also phenomenologically viable.