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 Z(3) symmetry in the neutrino sector at a high energy scale to account for the threefold degenerate neutrinos and the maximal mixing between v(mu) and v(tau). In order to obtain the atmospheric neutrino mass splitting while keeping the maximal mixing between nu(mu) and nu(tau), we introduce a small perturbation to the neutrino mass matrix without breaking Z(3) 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. (C) 2004 Elsevier B.V. All rights reserved.