Sterile neutrino self-interactions: $H_0$ tension and short-baseline anomalies

TL;DR

This paper investigates sterile neutrino models with self-interactions to address the H0 tension and short-baseline anomalies, updating cosmological bounds and analyzing the compatibility of these models with observational data.

Contribution

It provides an updated cosmological analysis of eV-scale sterile neutrinos with pseudoscalar interactions and assesses their viability in explaining both cosmological and short-baseline experimental results.

Findings

Sterile neutrino mass constrained to be less than ~1 eV by high-ell polarization data.

The pseudoscalar interaction model fits cosmological data and alleviates H0 tension.

Only narrow mass ranges around 1 eV are consistent with both cosmology and SBL data.

Abstract

Sterile neutrinos with a mass in the eV range have been invoked as a possible explanation of a variety of short baseline (SBL) neutrino oscillation anomalies. However, if one considers neutrino oscillations between active and sterile neutrinos, such neutrinos would have been fully thermalised in the early universe, and would be therefore in strong conflict with cosmological bounds. In this study we first update cosmological bounds on the mass and energy density of eV-scale sterile neutrinos. We then perform an updated study of a previously proposed model in which the sterile neutrino couples to a new light pseudoscalar degree of freedom. Consistently with previous analyses, we find that the model provides a good fit to all cosmological data and allows the high value of $H_0$ measured in the local universe to be consistent with measurements of the cosmic microwave background. However, new high $\ell$ polarisation data constrain the sterile neutrino mass to be less than approximately 1 eV in this scenario. Finally, we combine the cosmological bounds on the pseudoscalar model with a Bayesian inference analysis of SBL data and conclude that only a sterile mass in narrow ranges around 1 eV remains consistent with both cosmology and SBL data.