Solar-neutrino oscillations and third-flavour admixture

With one ∆m of the appropriate order of magnitude to solve the atmospheric neutrino problem, we study the resulting three-generation vacuumoscillation fit to the solar neutrino flux. An explanation of the atmospheric neutrino composition in terms of pure νμ → ντ oscillations is easily compatible with the well-known two-flavour oscillation solution for solar neutrinos. The allowed parameter region in the sin(2θ12)–∆m 2 plane changes little with increasing values of the mixing element Ue3, provided this is less than about 0.4. We find that the threefold maximal mixing is disfavoured. CERN-TH/98-200 June 1998