C P -Violating Neutrino Nonstandard Interactions in Long-Baseline-Accelerator Data

Neutrino oscillations in matter provide a unique probe of new physics. Leveraging the advent of neutrino appearance data from NOvA and T2K in recent years, we investigate the presence of C P -violating neutrino nonstandard interactions in the oscillation data. We first show how to very simply approximate the expected NSI parameters to resolve differences between two long-baseline appearance experiments analytically. Then, by combining recent NOvA and T2K data, we find a tantalizing hint of C P -violating NSI preferring a new complex phase that is close to maximal: ϕ_{e μ} or ϕ_{e τ}≈3 π /2 with |ε_{e μ}| or |ε_{e τ}|∼0.2 . We then compare the results from long-baseline data to constraints from IceCube and COHERENT.