Nonstandard Neutrino Interactions as a Solution to the NOνA and T2K Discrepancy

The latest data of the two long-baseline accelerator experiments NO nu A and T2K, interpreted in the standard three-flavor scenario, display a discrepancy. A mismatch in the determination of the standard CP phase delta(CP) extracted by the two experiments is evident in the normal neutrino mass ordering. While NO nu A prefers values close to delta(CP) similar to 0.8 pi, T2K identifies values of delta(CP) similar to 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 nonstandard interactions (NSIs) of the flavor changing type involving the e - mu or the e - tau sectors with couplings vertical bar epsilon(e mu)vertical bar similar to vertical bar epsilon(e tau)vertical bar similar to 0.2. Remarkably, in the presence of such NSIs, both experiments point towards the same common value of the standard CP phase delta(CP) similar to 3 pi/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 phi(e mu) similar to phi(e tau) similar to 3 pi/2, hence pointing towards imaginary NSI couplings.

Automated summary

The latest data from the NO nu A and T2K long-baseline accelerator experiments show a discrepancy in the determination of the standard CP phase, which may be resolved by considering the existence of complex neutral-current nonstandard interactions (NSIs). This tension could be explained if NSIs of the flavor changing type involving the e - mu or the e - tau sectors with specific couplings are hypothesized. Both experiments point towards the same common value of the standard CP phase in the presence of such NSIs, highlighting a preference for maximal CP violation in the nonstandard sector.