Bimaximal neutrino mixings from lopsided mass matrices

Current solar and atmospheric neutrino oscillation data seem to favor a bimaximal pattern for neutrino mixings where the matrix elements U-e2 and U-mu3 are of order one, while U-e3 is much smaller. We show that such a pattern can be obtained quite easily in theories with "lopsided" mass matrices for the charged leptons and the down type quarks. A relation connecting the solar and atmospheric neutrino mixing angles is derived, tan(2)theta(atm) similar or equal to 1 + tan(2)theta(sol), which predicts sin(2)2theta(atm) similar or equal to 0.97 corresponding to the best fit LMA solution for solar neutrinos. Predictive schemes in SO(10) realizing these ideas are presented. A new class of SO(10) models with lopsided mass matrices is found which makes use of an adjoint VEV along the I-3R direction, rather than the traditional B - L direction. (C) 2002 Elsevier Science B.V. All rights reserved.