Imprints of CP violation induced by sterile neutrinos in T2K data

TL;DR

This paper explores how sterile neutrinos could influence CP violation signals in T2K data, revealing potential new CP phases and improving consistency between different measurements.

Contribution

It demonstrates for the first time that current T2K data can be sensitive to two CP-violating phases in the 3+1 sterile neutrino scheme, highlighting new interference effects.

Findings

Current T2K data sensitive to two CP phases in 3+1 scheme

Sterile neutrinos induce interference terms comparable to standard oscillations

Including sterile neutrinos improves agreement between reactor and T2K measurements

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.