Cosmological radiation density with non-standard neutrino-electron interactions

TL;DR

This paper investigates how non-standard neutrino-electron interactions influence the effective number of neutrinos, $N_{eff}$, and assesses the potential of future cosmological observations to constrain these interactions.

Contribution

It provides a detailed analysis of the impact of non-universal and flavor-changing NSI on $N_{eff}$ and explores degeneracies and constraints from cosmology versus terrestrial experiments.

Findings

Future cosmological data can offer competitive constraints on certain NSI parameters.

NSI can cause measurable variations in $N_{eff}$, affecting cosmological observations.

Degeneracies among NSI parameters complicate their individual identification.

Abstract

Neutrino non-standard interactions (NSI) with electrons are known to alter the picture of neutrino decoupling from the cosmic plasma. NSI modify both flavour oscillations through matter effects, and the annihilation and scattering between neutrinos and electrons and positrons in the thermal plasma. In view of the forthcoming cosmological observations, we perform a precision study of the impact of non-universal and flavour-changing NSI on the effective number of neutrinos, $N_{eff}$. We present the variation of $N_{eff}$ arising from the different NSI parameters and discuss the existing degeneracies among them, from cosmology alone and in relation to the current bounds from terrestrial experiments. Even though cosmology is generally less sensitive to NSI than these experiments, we find that future cosmological data would provide competitive and complementary constraints for some of the couplings and their combinations.