Non-unitary lepton mixing in an inverse seesaw and its impact on the physics potential of long-baseline experiments

Abstract

In this paper, we consider the low-energy scale inverse seesaw mechanism in which the observed neutrino mass and lepton mixing are explained by introducing right handed neutrinos and the gauge-singlet fermions with experimentally testable energy scale. Moreover, the presence of such new fermions leads to unitarity violation in lepton mixing due to significantly large mixing between active neutrinos and the heavy fermions. In addition to this, such large lepton mixing also gives rise to potentially large lepton flavor violation, which allows to constrain the non-unitarity parameters via lepton flavor violating decays ($l_i \to l_j \gamma$). We make use of these constraints on non-unitarity parameters and investigate their effects on the determination of current unknown oscillation parameters at long-baseline experiments. We find that non-unitarity parameters are sensitive to NO$\nu$A experiment. However, it is observed that NO$\nu$A experiment is not expected to improve the current knowledge of non-unitarity parameter $\eta_{21}$. We also find that the sensitivities to current unknowns are deteriorated significantly in presence of non-unitary lepton mixing and these sensitivities crucially depend upon the new CP-violating phase in the non-unitary mixing. Further, we find that the degeneracy resolution capability of NO$\nu$A experiment is reduced in the presence of non-unitarity parameters. However, the synergy between the currently running experiments T2K and NO$\nu$A can improve the parameter degeneracy resolution and hence there is enhancement in the sensitivities of unknowns.