The LMA solution from bimaximal lepton mixing at the GUT scale by renormalization group running

We show that in see-saw models with bimaximal lepton mixing at the GUT scale and with zero CP phases, the solar mixing angle theta(12) generically evolves towards sizably smaller values due to renormalization group effects, whereas the evolution Of 013 and theta(23) is comparatively small. The currently favored LMA solution of the solar neutrino problem can thus be obtained in a natural way from bimaximal mixing at the GUT scale. We present numerical examples for the evolution of the leptonic mixing angles in the Standard Model and the MSSM, in which the current best-fit values of the LMA mixing angles are produced. These include a case where the mass eigenstates corresponding to the solar mass squared difference have opposite CP parity. (C) 2002 Elsevier Science B.V. All rights reserved.