Neutrinos on Earth and in the heavens

Abstract
Recent data suggest a simple and intriguing form of the neutrino mass matrix. We show how the data may constrain solar neutrino oscillations to be nearly maximal [and rule out the small-angle Mikheyev-Smirnov-Wolfenstein (MSW) explanation of solar neutrino observations] if relic neutrinos comprise at least three percent of the critical mass density of the universe.