Three-flavor MSW solutions of the solar neutrino problem

TL;DR

This paper updates the analysis of MSW solutions to the solar neutrino problem, considering two and three neutrino oscillations, and finds constraints on mixing angles and possible bimaximal mixing scenarios.

Contribution

It provides the first comprehensive phenomenological analysis including multiple experiments and the impact of the third neutrino flavor on MSW solutions.

Findings

Solar data constrains theta_{13} < 55--59 degrees at 95% C.L.

Bimaximal mixing is compatible with solar and atmospheric neutrino data.

MSW solutions extend beyond maximal (nu_1, nu_2) mixing under certain conditions.

Abstract

We perform an updated phenomenological analysis of the Mikheyev-Smirnov-Wolfenstein (MSW) solutions of the solar neutrino problem, assuming oscillations between two and three neutrino families. The analysis includes the total rates of the Homestake, SAGE, GALLEX, Kamiokande and Super-Kamiokande experiments, as well as the day-night asymmetry and the 18-bin energy spectrum of Super-Kamiokande. Solutions are found at several values of the theta_{13} mixing angle. Among the most interesting features, we find that solar neutrino data alone put the constraint theta_{13} < 55--59 deg at 95% C.L., and that a fraction of the MSW solutions extends at and beyond maximal (nu_1,nu_2) mixing (theta_{12} > pi/4), especially if the neutrino square mass splitting is in its lower range (m^2_2-m^2_1 ~ 10^{-7} eV^2) and if theta_{13} is nonzero. In particular, bimaximal (or nearly bimaximal) mixing is possible for atmospheric and MSW solar neutrino oscillations within the stringent reactor bounds on theta_{13}.