Status of tension between NO$ν$A and T2K after Neutrino 2024 and possible role of non-standard neutrino interactions

Abstract: In a previous work we have shown that the data presented by the two long-baseline accelerator experiments NO$\nu$A and T2K at the Neutrino 2020 conference displayed a tension, and that it could be alleviated by non-standard neutrino interactions (NSI) of the flavor changing type involving the $e-\mu$ or the $e-\tau$ sectors with couplings $|\varepsilon_{e\mu}| \sim |\varepsilon_{e\tau}|\sim 0.1$. 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 $\delta_{\mathrm {CP}}$ extracted by the two experiments in the normal neutrino mass ordering persists and has a statistical significance of $\sim2\sigma$. Concerning the NSI, we find that including their effects in the fit, the two values of $\delta_{\mathrm {CP}}$ preferred by NO$\nu$A and T2K return in very good agreement. The current statistical significance of the hint of non zero NSI is $\sim1.8\sigma$. Further experimental data are needed in order to settle the issue.