The Solar Neutrino Problem: Neither Astrophysics Nor Oscillations?

There is no consistent solar model which can describe all experimental data on the solar neutrinos. The problem can be formulated essentially in a model independent way. The key points are the comparison of the Homestake and the Kamiokande data as well as the comparison of the GALLEX and SAGE results with minimal signal estimated from the solar luminosity. It is argued than in such a comparison one should use the Homestake-II data (only after 1986) with caution. The results of the model independent analysis show strong suppression of the beryllium neutrino flux. The data can be well described by the resonant flavor conversion. For the low flux model" which can accommodate the Kamiokande signal, a consistent solution can be found for the neutrino mass squared difference $\Delta m^2 = (0.3 - 1.0)\cdot 10^{-5}$ eV$^2$ and values of mixing angle $\sin^2 2\theta > 5 \cdot 10^{-4}$ (very small mixing solution").