Large mixing angle MSW solution in an SU(3)L×U(1)N gauge model with two-loop radiative mechanism

An SU(3)L×U(1)N gauge model, where E−i (i=1,2,3) as heavy leptons are placed in the third member of lepton triplets, is shown to provide the large mixing angle (LMA) MSW solution to the solar neutrino problem. By introducing approximate conservation of Le−Lμ−Lτ (≡L′) into the model, we have estimated Δm⊙2∼2 ϵΔmatm2mE1/(mE2+mE3), where ϵ represents L′-breaking effects and mEi is a mass of E−i. Since Δmatm2∼3×10−3 eV2, the LMA solution is obtained for ϵ∼0.01–0.1 in the case of mE1∼mE2,3. This mechanism utilizes two-loop radiative mechanism, which contains a triplet version of the singly charged Zee boson, h+, given by ξ=(ξ++,ξ̄ +,h+)T. Almost bimaximal mixing is dynamically realized by the approximate equality between the ξ-couplings of the first family to the second and third families.