SOLAR-NEUTRINO OSCILLATIONS AND 3RD-FLAVOR ADMIXTURE

With one Delta m(2) of the appropriate order of magnitude to solve the atmospheric neutrino problem, we study the resulting three-generation vacuum-oscillation fit to the solar neutrino flux. An explanation of the atmospheric neutrino composition in terms of pure nu(mu) --> nu(ta u) oscillations is easily compatible with the well-known two-flavour o scillation solution for solar neutrinos. The allowed parameter region in the sin(2)(2 theta(12))-Delta m(2) plane changes little with increa sing values of the mixing element U-e3, provided this is less than abo ut 0.4. We find that the threefold maximal mixing is disfavoured. (C) 1998 Elsevier Science B.V. All rights reserved.