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.

Comments: 11 pages; 8 figures; minor changes; matches version published in PRD