Diagnosing Unmodeled Neutrino Physics via DUNE and T2HK Complementarity

TL;DR

This paper proposes using the complementary baselines of DUNE and T2HK to diagnose unmodeled neutrino physics, specifically non-standard interactions, by detecting inconsistencies in their parameter fits.

Contribution

It introduces a method to identify propagation BSM effects through baseline complementarity, demonstrated with NSI scenarios affecting DUNE but not T2HK.

Findings

DUNE's measurements are systematically distorted by NSI effects.

A 3-sigma tension between DUNE and T2HK results indicates potential BSM physics.

Baseline complementarity is crucial for uncovering new physics in neutrino experiments.

Abstract

Unmodeled beyond Standard Model (BSM) physics in neutrino propagation can masquerade as parameter degeneracies in future precision measurements. Because the upcoming DUNE and T2HK experiments will operate at substantially different baselines, interpreting their data under the standard three-flavor framework provides a powerful diagnostic tool: any propagation BSM effect will inevitably manifest as an artificial tension between their extracted parameters. We demonstrate this principle using the complex non-standard interactions (NSI) currently favored to resolve the $\sim2\sigma$ tension between NO$\nu$A and T2K. If these NSI solutions are realized, the NSI-induced interference term $\propto\sin(\delta_{\rm CP}+\phi)$ systematically distorts the DUNE appearance rates, leading to a correlated misidentification of the atmospheric mixing octant and the CP phase $\delta_{\rm CP}$. Specifically, for $\varepsilon_{e\mu}$ ($\varepsilon_{e\tau}$) NSI, the DUNE fit shifts toward CP- conserving values (the opposite CP half-plane) along with a preference for the wrong octant. In contrast, the shorter-baseline T2HK experiment remains largely insensitive to this effect. The resulting $\sim3\sigma$ incompatibility between the DUNE and T2HK standard-fit results (after 6 years of data collection for each experiment) provides a robust experimental diagnostic for propagation NSI, illustrating how baseline complementarity is essential to uncover new physics in the precision era.