SEESAW MODEL SOLUTIONS OF THE SOLAR NEUTRINO PROBLEM

We re-examine solutions to the solar neutrino problem involving neutrino oscillations, decaying neutrinos and a cooler center of the sun. Comparison of the Homestake and Kamiokande II observations implies that low-energy neutrinos are more suppressed than high-energy, disfavoring the large-mass adiabatic MSW resonance and allowing us to exclude non-standard solar models with a simple reduction of core temperature. Diagonal (sin(2)2-theta congruent-to 0.004-0.5, DELTA-m2 congruent-to 0.08-10 meV2), vertical large-angle (sin2 congruent-to 0.6-0.9, DELTA-m2 congruent-to 0.08-2, 4-60 meV2), and part of the horizontal (sin(2)2-theta congruent-to 0.02-0.6, DELTA-m2 congruent-to 80 meV2) MSW solutions are compatible with these data (meV = 10(-3) eV). The present SAGE results disfavor non-standard solar models and the horizontal MSW solution. Assuming nu(e) --> nu(mu) conversion, we show that seesaw models of neutrino masses imply m(nu(mu)) = 0.3-9 meV, intermediate-scale symmetry breaking O(10(9)-10(12)) GeV, and a tau-neutrino mass with cosmological ramifications in some cases and laboratory or atmospheric nu(mu)-nu(tau) oscillations. While seesaw predictions for neutrino masses are model-dependent and subject to large uncertainties, we prove that leptonic mixing angles are similar to quark mixings for a wide range of models. We also present two specific seesaw models compatible with electroweak neutral current and proton decay constraints, including radiative corrections to the seesaw predictions.