Nonstandard Neutrino Interactions as a Solution to the NOν A and T2K Discrepancy

The latest data of the two long-baseline accelerator experiments NOνA and T2K, interpreted in the standard three-flavor scenario, display a discrepancy. A mismatch in the determination of the standard CP phase δCP extracted by the two experiments is evident in the normal neutrino mass ordering. While NOνA prefers values close to δCP∼0.8π, T2K identifies values of δCP∼1.4π. 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 nonstandard interactions (NSIs) of the flavor changing type involving the e-μ or the e-τ sectors with couplings | µeμ|∼| µeτ|∼0.2. Remarkably, in the presence of such NSIs, both experiments point towards the same common value of the standard CP phase δCP∼3π/2. Our analysis also highlights an intriguing preference for maximal CP violation in the nonstandard sector with the NSI CP phases having best fit close to φeμ∼φeτ∼3π/2, hence pointing towards imaginary NSI couplings.