Almost degenerate neutrinos and bi-large lepton mixing

A scenario is proposed for bi-large lepton mixing in the framework of nearly threefold degenerate Majorana neutrinos. In our proposal, we impose Z₃ symmetry in the neutrino sector at a high energy scale to account for the threefold degenerate neutrinos and the maximal mixing between ν_μ and ν_τ. In order to obtain the atmospheric neutrino mass splitting while keeping the maximal mixing between ν_μ and ν_τ, we introduce a small perturbation to the neutrino mass matrix without breaking Z₃ symmetry. On the other hand, the solar neutrino mixing arises due to the non-diagonal charged lepton mass matrix, and the desirable large mixing and mass splitting for the solar neutrino oscillation can be obtained by radiative corrections.