Solar-neutrino oscillations and third-flavour admixture

With one Δm2 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 νμ→ντ oscillations is easily compatible with the well-known two-flavour oscillation solution for solar neutrinos. The allowed parameter region in the sin2(2θ12)–Δm2 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.