Textures for atmospheric and solar neutrino oscillations

A large theta(mu tau) mixing angle, together with hierarchies in the neutri no Delta m(2) and in the charged lepton masses, place a significant restric tion on the textures of the lepton mass matrices. In theories with three li ght neutrinos, a simple hypothesis leads to a complete list of four zeroth- order textures for lepton mass matrices is found: three for neutrinos which naturally yield theta(mu tau) approximate to 1 with vanishing theta(e tau) and Delta m(.)(2), and one for charged leptons which naturally yields thet a(mu tau) approximate to 1 with m(e) = m(mu) = theta(e tau) = 0. These text ures provide suitable starting points for constructing theories which accou nt for both atmospheric and solar neutrino fluxes. Using flavor symmetries, two schemes for such lepton masses are found, and example constructions ex hibited. (C) 1999 Elsevier Science B.V. All rights reserved.