Neutrino refraction by the cosmic neutrino background

TL;DR

This paper calculates how the cosmic neutrino background affects neutrino propagation, revealing potential signatures in experiments and implications for Lorentz violation searches, despite the detection challenges due to low relic neutrino temperatures.

Contribution

It provides a detailed analysis of neutrino dispersion relations in the cosmic neutrino background, introducing a framework to identify experimental signatures and background effects for Lorentz violation tests.

Findings

Neutrino energies are modified by the cosmic background.

Refractive effects could produce observable signatures in beta-decay and oscillation experiments.

The relic neutrino background creates an ultralow background for Lorentz violation studies.

Abstract

We have determined the dispersion relation of a neutrino test particle propagating in the cosmic neutrino background. Describing the relic neutrinos and antineutrinos from the hot big bang as a dense medium, a matter potential or refractive index is obtained. The vacuum neutrino mixing angles are unchanged, but the energy of each mass state is modified. Using a matrix in the space of neutrino species, the induced potential is decomposed into a part which produces signatures in beta-decay experiments and another part which modifies neutrino oscillations. The low temperature of the relic neutrinos makes a direct detection extremely challenging. From a different point of view, the identified refractive effects of the cosmic neutrino background constitute an ultralow background for future experimental studies of nonvanishing Lorentz violation in the neutrino sector.