Large Mixing Angle MSW Solution in U(1) Flavor Symmetry

We have discussed the quark-lepton mass matrices with the U(1) flavor symmetry in SU(5), which lead to the large mixing angle MSW solution of solar neutrinos. The solar neutrino solution depends on the next-leading terms in the neutrino mass matrix. We have found the lepton mass matrices with the U(1)×Z2 symmetry, which give the LMA-MSW solution uniquely. The coefficients of the matrix elements of the charged leptons are constrained strongly due to the bound of Ue3 in the CHOOZ experiment. E-mail address: [email protected] Super-Kamiokande has almost confirmed the neutrino oscillation in atmospheric neutrinos, which favors the νμ → ντ process with sin 2θatm ≥ 0.88 and ∆m2atm = (1.5 ∼ 5) × 10−3eV [1]. For the solar neutrinos [2], the 1117 days data in SuperKamiokande favors the LMA-MSW solution [3], which is sin 2θ⊙ = 0.65 ∼ 0.97 and ∆m2⊙ = 10 −5 ∼ 10−4eV. However, there are still allowed four solutions, the small mixing angle (SMA) MSW [4], the large mixing angle (LMA) MSW, the low ∆m (LOW) and the vacuum oscillation (VO) solutions [5]. There are a lot of ideas for the single large mixing angle in the neutrino mixing matrix (MNS matrix) [6]. However, it is not easy to get the nearly bi-maximal mixings [7] with the LMA-MSW mass scale in the GUT models [8]. Therefore, it is important to search for the texture of the lepton mass matrix with the LMA-MSW solution. In this paper, we study how to get the LMA-MSW solution with the help of the U(1) flavor symmetry. Vissani [9] has already shown that the texture of the neutrino mass matrix with the U(1) flavor symmetry, Mν ∼ 