Probing Non-unitary Neutrino Mixing

Evidences in many of the experiments regarding neutrino oscillation today indicate that there is an existence of non-unitarity of the PMNS matrix, signaling the existence of additional flavors (sterile neutrinos) beyond the three standard oscillation flavors. An important question for future experiments is: what is the minimum deviation from the unitary case that can be used to probe the existence of non-unitarity? To address this question, we first investigate different entries of the PMNS matrix by testing them with the NuFIT data, checking the correlation between different entries by varying the theta and delta CP values within the 3 sigma range indicated by NuFIT. We then take a step further to investigate the case where the mixing matrix is no longer unitary after parametrization.