Imprints of CP violation induced by sterile neutrinos in T2K data

Abstract: We investigate the impact of light ($\sim$ eV) sterile neutrinos in the long-baseline experiment T2K. We show that, within the 3+1 scheme, for mass-mixing parameters suggested by the short-baseline anomalies, the interference among the sterile and the atmospheric oscillation frequencies induces a new term in the $\nu_\mu \to \nu_e$ transition probability, which has the same order of magnitude of the standard 3-flavor solar-atmospheric interference term. We show, for the first time, that current T2K data, taken together with the results of the $\theta_{13}$-dedicated reactor experiments, are sensitive to two of the three CP-violating phases involved in the 3+1 scheme. Both the standard CP-phase and the new one ($\delta_{13} \equiv \delta$ and $\delta_{14}$ in our parameterization choice) tend to have a common best fit value $\delta_{13} \simeq \delta_{14} \simeq -\pi/2$. Quite intriguingly, the inclusion of sterile neutrino effects leads to better agreement between the two estimates of $\theta_{13}$ obtained, respectively, from reactors and T2K, which in the 3-flavor framework are slightly different.