Abstract

Sterile neutrinos are neutral fermions which mix with ordinary neutrinos. They emerge in the simplest extensions of the Standard Model and their mass can range from sub-eV to GUT scales. I will briefly review the theoretical motivations for sterile neutrinos and the experimental hints in favour of their existence and the possible strategies to search for them. Thanks to their mixing, they could have been produced in the Early Universe via neutrino oscillations. They would be a component of hot or cold dark matter and would have had an important impact on the evolution of the Universe. I will discuss the mechanisms of sterile neutrino production and the constraints which can be put on their properties using the observations from the Cosmic Microwave Background and large scale structure formation. I will discuss also the (unconfirmed) 3.5 keV x-ray line which was reported last year using observations of nearby clusters by the XMM -Newton and Chandra satellites and its possible explanation in terms of sterile neutrino dark matter.