Sensitivity of Hyper-Kamiokande to sub-eV Sterile Neutrinos

TL;DR

This paper assesses Hyper-Kamiokande's potential to detect or constrain light sterile neutrinos with small mass-squared differences, using atmospheric and accelerator neutrino data, and finds it can significantly improve existing bounds.

Contribution

It provides the first detailed sensitivity analysis of Hyper-Kamiokande to sub-eV sterile neutrinos within the (3+1) framework, focusing on a complementary parameter space.

Findings

Hyper-K can improve current bounds on sterile neutrino parameters.

Sensitivity is competitive with future dedicated experiments.

Analysis covers the regime where Δm₄₁² ≤ 1 eV².

Abstract

In this work, we investigate the sensitivity of Hyper-Kamiokande (Hyper-K) to light sterile neutrinos within the $(3+1)$ framework, consisting of three active and one sterile neutrino state. We focus on the regime where the new mass-squared splitting satisfies $\Delta m_{41}^{2} \lesssim 1$ eV$^{2}$, a parameter space complementary to short-baseline sterile-neutrino searches. Using both accelerator and atmospheric neutrino samples, we evaluate the expected capability of Hyper-K to constrain active-sterile mixing. Our results show that Hyper-K can significantly improve current bounds on sterile-neutrino parameters and achieve sensitivity that is competitive with that of future dedicated experiments.