Impact of New Physics on the JUNO-Long-Baseline Synergy in Neutrino Mass Ordering Determination

TL;DR

This paper examines how potential new physics could impact the combined use of JUNO and long-baseline experiments in determining neutrino mass ordering, highlighting the importance of accounting for such effects.

Contribution

It analyzes the robustness of the neutrino mass ordering sum rule against new physics effects, providing conditions under which new physics could alter the inference.

Findings

Current constraints make SNSI effects negligible

Ultralight scalar coupling could affect mass ordering inference

Sum rule can be used to detect new physics signals

Abstract

The determination of the neutrino mass ordering is one of the flagship goals in particle physics. A well-known and powerful synergy emerges when combining high-precision measurements of the effective atmospheric mass-squared splitting from electron antineutrino disappearance in reactor experiments with that from muon (anti)neutrino disappearance in accelerator-based long-baseline experiments. To fully exploit this synergy, percent-level precision in the atmospheric mass splitting is required-a target that JUNO is expected to achieve within a few months of data taking. This motivated the formulation of a mass ordering sum rule for neutrino disappearance channels, which shows that by combining data from T2K and NOvA with JUNO after one year of operation, the neutrino mass ordering can be determined at the $3\sigma$ confidence level. Since JUNO has recently started taking data, it is timely to ask whether this sum rule remains robust in the presence of new physics. We identify the necessary conditions for new physics to affect the sum rule and demonstrate that, in some cases, such effects could lead to an incorrect inference of the mass ordering. As concrete examples, we consider Scalar Non-Standard Interactions (SNSI) and neutrinos coupled to an ultralight scalar field. We find that, for SNSI, current constraints render any modification of the sum rule negligible, whereas in the latter case, the inference of the ordering requires caution. Nevertheless, these effects can be disentangled, illustrating how the sum rule can also be used to search for new physics.