Seesaw model solutions of the solar neutrino problem

We re-examine solutions to the solar 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 (sin²2θ - 0.004-0.5, Δm² {reversed tilde equals} 0.08-10 meV²), vertical large-angle (sin² {reversed tilde equals} 0.6-0.9, Δm² {reversed tilde equals} 0.08-2, 4-60 meV²), and part of the horizontal (sin²2θ {reversed tilde equals} 0.02-0.6, Δm² {reversed tilde equals} 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 ν_e → ν_μ conversion, we show that seesaw models of neutrino masses imply m_νμ = 0.3-9 meV, intermediate-scale symmetry breaking O(10⁹-10¹²) GeV, and a τ-neutrino mass with cosmological ramifications in some cases and laboratory or atmospheric ν_μ - ν_τ 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.