Very light sterile neutrinos at NOvA and T2K
André de Gouvêa, Giancarlo Jusino Sánchez, Kevin J. Kelly
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 ($\ensuremath{\lesssim}2\ensuremath{\sigma}$) significance. Interpreting these results, we provide a future outlook for near-term and long-term experiments if this four-neutrino framework is indeed true.