Impact of unitarity violation on sensitivity of the leptonic CP phase at Hyper-Kamiokande and DUNE

We study the impact of unitarity violation on the sensitivity of the leptonic CP phase, $δ_{CP}$, considering the next generation of long-baseline neutrino experiments, Hyper-Kamiokande and DUNE. By simulating near and far detectors and assuming different scenarios for non-unitarity, we verify how it can affect the sensitivity to measure the $δ_{ CP}$ violating phase. We also probe the capability of these experiments to constrain the non-unitarity parameters and how their capability could be improved if the impact of non-unitarity at both near and the far detectors were properly taken into account. We find that the Hyper-Kamiokande experiment is robust in the presence of non-unitarity mixing, achieving a sensitivity above $5σ$ for our all considered cases. On the other hand, DUNE suffers somewhat more impact due to unitarity violation, reaching a sensitivity below 5$σ$ for some values of $δ_{CP}$. However, depending on the scenario adopted for non-unitarity, DUNE demonstrates robustness in the sensitivity to $δ_{ CP}$ phase.