# A search for sterile neutrinos with the latest cosmological observations

## TL;DR

This paper investigates the existence of sterile neutrinos using comprehensive cosmological data, finding mild evidence for massless sterile neutrinos and tight constraints on their mass, aligning with recent experimental results.

## Contribution

It provides the first combined analysis of multiple cosmological datasets to constrain sterile neutrinos within the ΛCDM model, considering both massless and massive cases.

## Key findings

- Hint of massless sterile neutrino at 1.44σ significance
- Extra massless sterile neutrino alleviates observational tensions
- Tight upper limits on sterile neutrino mass from data

## Abstract

We report the result of a search for sterile neutrinos with the latest cosmological observations. Both cases of massless and massive sterile neutrinos are considered in the $\Lambda$CDM cosmology. The cosmological observations used in this work include the Planck 2015 temperature and polarization data, the baryon acoustic oscillation data, the Hubble constant direct measurement data, the Planck Sunyaev-Zeldovich cluster counts data, the Planck lensing data, and the cosmic shear data. We find that the current observational data give a hint of the existence of massless sterile neutrino (as dark radiation) at the 1.44$\sigma$ level, and the consideration of an extra massless sterile neutrino can indeed relieve the tension between observations and improve the cosmological fit. For the case of massive sterile neutrino, the observations give a rather tight upper limit on the mass, which implies that actually a massless sterile neutrino is more favored. Our result is consistent with the recent result of neutrino oscillation experiment done by the Daya Bay and MINOS collaborations, as well as the recent result of cosmic ray experiment done by the IceCube collaboration.