Status of tension between NOvA and T2K after Neutrino 2024 and possible role of nonstandard neutrino interactions

In a previous work, we have shown that the data presented by the two long-baseline accelerator
experiments NOvA and T2K at the Neutrino 2020 conference displayed a tension and that it could be
alleviated by nonstandard neutrino interactions (NSI) of the flavor changing type involving the e − μ or the
e − τ sectors with couplings jεeμj ∼ jεeτj ∼ 0.1. As a consequence, a hint in favor of NSI emerged. In the
present paper, we reassess the issue in light of the new data released by the two experiments at the Neutrino
2024 conference. We find that the tension in the determination of the standard CP-phase δCP extracted by
the two experiments in the normal neutrino mass ordering persists and has a statistical significance of ∼2σ.
Concerning the NSI, we find that including their effects in the fit, the two values of δCP preferred by NOvA
and T2K return in very good agreement. The current statistical significance of the hint of nonzero NSI is
∼1.8σ. Further experimental data are needed in order to settle the issue.