Non-standard neutrino interactions as a solution to the NO$\nu$A and T2K discrepancy

TL;DR

This paper proposes that non-standard neutrino interactions can reconcile the differing CP-phase measurements from NOvA and T2K experiments, suggesting new physics beyond the standard model.

Contribution

It introduces complex neutral-current non-standard interactions as a solution to experimental discrepancies in neutrino CP-phase measurements.

Findings

NSI resolve the tension between NOvA and T2K CP-phase estimates.

Both experiments favor a common CP-phase near 3π/2 with NSI.

Evidence suggests maximal CP-violation in the non-standard sector.

Abstract

The latest data of the two long-baseline accelerator experiments NO$\nu$A and T2K, interpreted in the standard 3-flavor scenario, display a discrepancy. A mismatch in the determination of the standard CP-phase $\delta_{\mathrm {CP}}$ extracted by the two experiments is evident in the normal neutrino mass ordering. While NO$\nu$A prefers values close to $\delta_{\mathrm {CP}} \sim 0.8 \pi$, T2K identifies values of $\delta_{\mathrm {CP}} \sim 1.4 \pi$. Such two estimates are in disagreement at more than 90$\%$ C.L. for 2 degrees of freedom. We show that such a tension can be resolved if one hypothesizes the existence of complex neutral-current non-standard interactions (NSI) of the flavor changing type involving the $e-\mu$ or the $e-\tau$ sectors with couplings $|\varepsilon_{e\mu}| \sim |\varepsilon_{e\tau}|\sim 0.2$. Remarkably, in the presence of such NSI, both experiments point towards the same common value of the standard CP-phase $\delta_{\mathrm {CP}} \sim 3\pi/2$. Our analysis also highlights an intriguing preference for maximal CP-violation in the non-standard sector with the NSI CP-phases having best fit close to $\phi_{e\mu} \sim \phi_{e\tau}\sim 3\pi/2$, hence pointing towards imaginary NSI couplings.