The Result of the Neutrino-4 Experiment, Sterile Neutrinos, Dark Matter, and the Standard Model Extended by Right-Handed Neutrinos

The analysis of results of the Neutrino-4 experiment and the data of the GALLEX, SAGE, and BEST experiments confirms the parameters of neutrino oscillations claimed by the Neutrino-4 experiment (\(\Delta m_{{14}}^{2}\) = 7.3 eV² and sin²2θ₁₄ = 0.36) and increases the confidence level up to 5.8σ. This sterile neutrino thermalizes in the cosmic plasma, contributes 5% to the energy density of the Universe, and can explain 15–20% of the dark matter. It is discussed that the extension of the neutrino model by introducing two more heavy sterile neutrinos in accordance with the number of types of active neutrinos, but with very small mixing angles to avoid the thermalization, makes it possible to explain the large-scale structure of the Universe and bring the contribution of sterile neutrinos to the Universe dark matter up to a level of 27%. The dynamic process of generation of the dark matter, consisting of three right-handed neutrinos, is presented. It is shown that the current astrophysical data on the \(^{4}{\text{He}}\) abundance make it impossible to draw a definite conclusion in favor of the model of three or four thermalized neutrinos.