Searches for sterile neutrinos at very short baseline reactor experiments

Abstract

For a long time there were 3 main experimental indications in favor of the existence of sterile neutrinos: $\bar{ν_e}$ appearance in the $\bar{ν_μ}$ beam in the LSND experiment, $\bar{ν_e}$ flux deficit in comparison with theoretical expectations in reactor experiments, and $ν_e$ deficit in calibration runs with radioactive sources in the Ga solar neutrino experiments SAGE and GALEX. All three problems can be explained by the existence of sterile neutrinos with the mass square difference in the ballpark of $1~\mathrm{eV^2}$. Recently the MiniBooNE collaboration observed electron (anti)neutrino appearance in the muon (anti)neutrino beams. The significance of the effect reaches 6.0$σ$ level when combined with the LSND result. Even more recently the NEUTRINO-4 collaboration claimed the observation of $\bar{ν_e}$ oscillations to sterile neutrinos with a significance slightly higher than 3$σ$. If these results are confirmed, New Physics beyond the Standard Model would be required. More than 10 experiments are devoted to searches of sterile neutrinos. Six very short baseline reactor experiments are taking data just now. We review the present results and perspectives of these experiments.