The Interplay between Neutrinos and Charged Leptons in the Minimal SU(3)_LxU(1)_N Gauge Model

Abstract

In the minimal SU(3)_LxU(1)_N gauge model with a global L_e-L_mu-L_tau (=L') symmetry and a discrete Z_4 symmetry, it is found that the interplay between neutrinos and charged leptons contained in triplets of ψ^i=(ν^i_L, \ell^i_L, \ell^{ci}_L) (i=1,2,3) naturally leads to the large mixing angle (LMA) MSW solution. The model includes two (anti)sextet Higgs scalars, S^(0) with L'=0 and S^(+) with L'=2, which, respectively, couple to ψ^1ψ^{2,3} for the electron mass and masses of atmospheric neutrinos and to ψ^{2,3}ψ^{2,3} for the μ- and τ-masses and one-loop radiative neutrino masses relevant to solar neutrinos. This mechanism is realized by utilizing an additional residual discrete symmetry supplied by explicitly broken L', which guarantees the absence of tree-level neutrino mass terms of the ψ^{2,3}ψ^{2,3}-type. Pure rotation effects due to the diagonalization of neutrino and charged-lepton mass matrices are estimated to yield Δm^2_\odot/Δm^2_{atm} \leq (m_e/m_μ)^{3/2}=O(10^{-4}) but the radiative effects supersede the rotation effects to yield Δm^2_\odot/Δm^2_{atm}=O(10^{-2}) as the LMA solution.