Very Light Sterile Neutrinos at NOvA and T2K

TL;DR

This paper investigates whether adding a very light sterile neutrino can resolve tensions between T2K and NOvA neutrino oscillation data, finding moderate evidence that supports a four-neutrino model over the standard three-neutrino paradigm.

Contribution

It introduces a four-neutrino framework with a very light sterile neutrino to address experimental tensions, providing analysis and future outlooks.

Findings

Four-neutrino model is moderately favored over three-neutrino model.

Adding a light sterile neutrino can alleviate data tensions.

Future experiments could further test this four-neutrino hypothesis.

Abstract

Over the last several years, our understanding of neutrino oscillations has developed significantly due to the long-baseline measurements of muon-neutrino disappearance and muon-to-electron-neutrino appearance at the T2K and NOvA experiments. However, when interpreted under the standard-three-massive-neutrinos paradigm, a tension has emerged between the two experiments' data. Here, we examine whether this tension can be alleviated when a fourth, very light neutrino is added to the picture. Specifically, we focus on the scenario in which this new neutrino has a mass similar to, or even lighter than, the three mostly-active neutrinos that have been identified to date. We find that, for some regions of parameter space, the four-neutrino framework is favored over the three-neutrino one with moderate (a little under two sigma) significance. Interpreting these results, we provide future outlook for near-term and long-term experiments if this four-neutrino framework is indeed true.