Experimental bounds on sterile neutrino mixing angles

TL;DR

This paper establishes new bounds on sterile neutrino mixing angles by combining oscillation data and experimental searches, showing that mixing can be suppressed and previous bounds may be less restrictive, impacting models like NuMSM.

Contribution

It provides a reinterpretation of experimental bounds on sterile neutrino lifetime and mixing, considering the effects of non-zero theta_13 and model-specific constraints.

Findings

Sterile neutrino mixing can be significantly suppressed with non-zero theta_13.

Negative search results' bounds on sterile neutrinos can be relaxed by up to an order of magnitude.

Reinterpretation of PS191 and CHARM results yields stronger bounds on sterile neutrino lifetime.

Abstract

We derive bounds on the mixing between the left-chiral ("active") and the right-chiral ("sterile") neutrinos, provided from the combination of neutrino oscillation data and direct experimental searches for sterile neutrinos. We demonstrate that the mixing of sterile neutrinos with any flavour can be significantly suppressed, provided that the angle theta_13 is non-zero. This means that the lower bounds on sterile neutrino lifetime, coming from the negative results of direct experimental searches can be relaxed (by as much as the order of magnitude at some masses). We also demonstrate that the results of the negative searches of sterile neutrinos with PS191 and CHARM experiments are not applicable directly to the see-saw models. The reinterpretation of these results provides up to the order of magnitude stronger bounds on sterile neutrino lifetime than previously discussed in the literature. We discuss the implications of our results for the Neutrino Minimal Standard Model (the NuMSM).