Solar Neutrinos

Abstract

The status of solar neutrino experiments and their implications for both nonstandard astrophysics ({\it e.g.,} cool sun models) and nonstandard neutrino properties ({\it e.g.,} MSW conversions) are discussed. Assuming that all of the experiments are correct, the relative rates observed by Kamiokande and Homestake are hard to account for by a purely astrophysical solution, while MSW conversions can describe all of the data. Assuming the standard solar model, there are two allowed regions for MSW conversions into $\nu_\mu$ or $\nu_\tau$, with the non-adiabatic solution giving a better fit than the large angle. For conversions into sterile neutrinos there is only a nonadiabatic solution. Allowing both MSW conversions and nonstandard astrophysics, the data simultaneously determine the temperature of the core of the sun to within five percent, consistent with the standard solar model prediction. The implications of the atmospheric $\nu_\mu/\nu_e$ ratio and of a hot component of the dark matter are briefly discussed, and the expectations of theoretical models motivated by grand unification are summarized.