Experimental bounds on sterile neutrino mixing angles

A bstract We derive bounds on the mixing between the Standard Model (“active”) neutrinos and their right-chiral (“sterile”) counterparts in the see-saw models, by combining neutrino oscillation data and results of direct experimental searches. We demonstrate that the mixing of sterile neutrinos with any active flavour can be significantly suppressed for the values of the angle θ 13 measured recently by Daya Bay and RENO experiments. We reinterpret the results of searches for sterile neutrinos by the PS191 and CHARM experiments, considering not only charged current but also neutral current-mediated decays, as applicable in the case of see-saw models. The resulting lower bounds on sterile neutrino lifetime are up to an order of magnitude stronger than previously discussed in the literature. Combination of these results with the upper bound on the lifetime coming from primordial nucleosynthesis rule out the possibility that two sterile neutrinos with the masses between 10 MeV and the pion mass are solely responsible for neutrino flavour oscillations. We discuss the implications of our results for the Neutrino Minimal Standard Model (the νMSM).