Sterile neutrinos and their role in particle physics and cosmology

Introducing new fermions into particles physics that are singlet under the gauge group of the Standard Model allows using the seesaw type-I mechanism to obtain small neutrino masses and explaining the phenomenon of neutrino oscillations. The mass scale of these fermions (sterile neutrinos) is a free parameter with values ranging widely from a subelectronvolt to $10^{15}$ GeV. The mass scale determines the direct search strategy for these particles, and depending on it, sterile neutrinos can influence the evolution of the Universe and can be responsible for the baryon asymmetry of the Universe and for the phenomenon of dark matter.