MSW effect for large mixing angles

Abstract

The traditional physical description of neutrino flavor conversion in the Sun focuses on the notion of resonance. However, the resonance picture is valid only in the limit of small mixing angles theta. For large values of theta, the resonance picture leads to seemingly paradoxical results. This observation is important for understanding the physics of neutrino flavor conversion in the Sun, since the latest solar neutrino data seems to prefer large mixing angles. Here we review the basic arguments and in particular show that the resonance does not in general coincide with either the point of maximal violation of adiabaticity in the nonadiabatic case or the point of maximal flavor conversion in the adiabatic case. We also discuss a modified adiabaticity criterion.