Resolving the NOvA and T2K tension in the presence of Neutrino Non-Standard Interactions

Abstract

The current data of the two long-baseline accelerator experiments NO$\nu$A and T2K, shows a tension at more than 90$\%$ C.L. for 2 degrees of freedom, in the determination of the standard CP-phase $\delta_{\mathrm {CP}}$ in case of neutrino normal ordering (NO). NO$\nu$A measures the value close to $\delta_{\mathrm {CP}} \sim 0.8 \pi$, while T2K prefers the value of $\delta_{\mathrm {CP}} \sim 1.4 \pi$. We show that such a tension can be resolved if one hypothesizes the existence of neutral-current non-standard interactions (NSI) of neutrinos involving the flavor changing type $e-\mu$ or the $e-\tau$ sectors with couplings $|\varepsilon_{e\mu}| \sim |\varepsilon_{e\tau}|\sim 0.2$. Remarkably, our analyses show that in the presence of such NSI, both the experiments point towards the same common value of the standard CP-phase $\delta_{\mathrm {CP}} \sim 3\pi/2$, thereby indicating towards the maximal CP-violation in the standard $3\nu$ framework. We also show that the best fit values of the new CP-phases $\phi_{e\mu}$ or $ \phi_{e\tau}$ are close to $\sim 3\pi/2$, hence pointing towards the maximal CP-violation in the NSI sector.