Implications of combined solar-neutrino observations and their theoretical uncertainties.

Constraints on the core temperature (T c) of the Sun and on neutrino-oscillation parameters are obtained from the existing solar neutrino data, including the recent GALLEX and Kamiokande III results. (1) A purely astrophysical solution to the solar neutrino problem is strongly disfavored by the data: the best fit in a cooler Sun model requires an 8% reduction in T c , but the χ 2 test rejects this hypothesis at 99.99% C.L. This suggests neutrino physics (mass, mixings) that goes beyond the standard elec-troweak theory. (2) Assuming the Standard Solar Model (SSM) and matter-enhanced neutrino oscillations, the MSW parameters are constrained to two small regions: non