NEUTRINOS FROM THE SUN - EXPERIMENTAL RESULTS CONFRONTED WITH SOLAR MODELS

For standard neutrinos, recent solar neutrino results together with the assumption of a nuclear powered Sun imply severe constraints on the individual components of the total neutrino flux: Phi(Be) less than or equal to 0.7 X 10(9) cm(-2) s(-1), Phi(CNO)less than or equal to 0.6 X 10(9) cm(-2) s(-1), and 64 X 10(9) X cm(-2) s(-1) less than or equal to Phi(pp+pep) less than or equal to 65 X 10(9) cm(-2) s(-1) (at 1 sigma level). The bound on Phi(Be) is in strong disagreement with the standard solar model (SSM) prediction Phi(Be)(SSM) approximate to 5 x 10(9) cm(-2) s(-1). We study a large variety of nonstandard solar models with low inner temperature, finding that the temperature profiles T(m) follow the homology relationship T(m) = kT(SSM)(m), so that they are specified just by the central temperature T-c. There is no value of T-c which can account for all the available experimental results. Even if we only consider the gallium and Kamiokande results, they remain incompatible. Lowering the cross section p + Be-7 --> gamma + B-8 is not a remedy. The shift of the nuclear fusion chain towards the pp-I termination could be induced by a hypothetical low energy resonance in the He-3 + He-3 reaction. This mechanism gives a somehow better, but still bad, fit to the combined experimental data. We also discuss what can be learned from new generation experiments, planned for the detection of monochromatic solar neutrinos, about the properties of neutrinos and of the Sun.