The Mikheyev-Smirnov-Wolfenstein (MSW) Effect

TL;DR

This paper reviews the development of the MSW effect, explaining how neutrino interactions with matter lead to flavor oscillations, resonance enhancement, and adiabatic conversion, crucial for understanding solar and supernova neutrinos.

Contribution

It provides a comprehensive overview of the theoretical foundations and key concepts of the MSW effect developed between 1978 and 1985, highlighting its significance in neutrino physics.

Findings

Resonance enhancement of neutrino oscillations in matter

Adiabatic flavor conversion in varying density environments

Application to solar neutrino problem and supernova neutrinos

Abstract

Developments of main notions and concepts behind the MSW effect (1978 - 1985) are described. They include (i) neutrino refraction, matter potential, and evolution equation in matter, (ii) mixing in matter, resonance and level crossing; (iii) adiabaticity condition and adiabatic propagation in matter with varying density. They are in the basis of the resonance enhancement of oscillations in matter with constant (nearly constant) density, and the adiabatic flavor conversion in matter with slowly changing density. The former is realized in matter of the Earth and can be used to establish neutrino mass hierarchy. The latter provides solution to the solar neutrino problem and play the key role in transformations of the supernova neutrinos.