Beyond the MSW effect: Neutrinos in a dense medium

TL;DR

This paper develops a comprehensive theory of neutrino oscillations in dense media, accounting for decoherence effects from neutrino-environment interactions, and reveals deviations from traditional MSW predictions at high densities and energies.

Contribution

It introduces new oscillation formulas that include decoherence effects, extending beyond the traditional MSW effect, and demonstrates their significance in high-density, high-energy scenarios.

Findings

Deviations from MSW formulae at high densities and energies.

Neutrino interactions with matter can cause decoherence.

Transition probabilities remain non-zero where MSW predicts zero.

Abstract

We present a theory of neutrino oscillations in a dense medium which goes beyond the effective matter potential used in the description of the MSW effect. We show how the purity of the neutrino state is degraded by neutrino interactions with the environment and how neutrino--matter interactions can be a source of decoherence. We present new oscillation formulae for neutrinos interacting with leptons and carry out a numerical analysis which exhibits deviations from the MSW formulae for propagation through the Earth of ultra-high energy neutrinos. In particular, we show that at high density and/or high neutrino energy, the vanishing transition probabilities derived for MSW effect, are non zero when the scattering is taken into account.