# Sterile neutrinos in cosmology

## TL;DR

This paper reviews the cosmological implications of light sterile neutrinos, including their production, role as dark matter candidates, and potential observational signatures in cosmic microwave background, large scale structure, and X-ray data.

## Contribution

It provides a comprehensive overview of the theoretical and observational aspects of light sterile neutrinos in cosmology, highlighting recent candidate detections and decay signatures.

## Key findings

- Sterile neutrinos can significantly influence early Universe cosmology.
- Detection of a 3.5 keV X-ray line suggests possible sterile neutrino decay.
- Sterile neutrinos are viable dark matter candidates with observable signatures.

## Abstract

Sterile neutrinos are natural extensions to the standard model of particle physics in neutrino mass generation mechanisms. If they are relatively light, less than approximately 10 keV, they can alter cosmology significantly, from the early Universe to the matter and radiation energy density today. Here, we review the cosmological role such light sterile neutrinos can play from the early Universe, including production of keV-scale sterile neutrinos as dark matter candidates, and dynamics of light eV-scale sterile neutrinos during the weakly-coupled active neutrino era. We review proposed signatures of light sterile neutrinos in cosmic microwave background and large scale structure data. We also discuss keV-scale sterile neutrino dark matter decay signatures in X-ray observations, including recent candidate $\sim$3.5 keV X-ray line detections consistent with the decay of a $\sim$7 keV sterile neutrino dark matter particle.