Probing Direct and Indirect Unitarity Violation in Future Accelerator Neutrino Facilities

TL;DR

This paper evaluates how future accelerator neutrino experiments can detect and distinguish between direct and indirect unitarity violations in the neutrino mixing matrix, enhancing understanding of sterile neutrinos and CP violation.

Contribution

It analyzes the potential of DUNE, T2HK, and LENF to probe unitarity violation effects and improve measurements of leptonic CP violation and mixing angles.

Findings

Future experiments can effectively constrain unitarity violation parameters.

Combining different experiments improves robustness against parameter degeneracies.

Distinct effects of direct and indirect violations can be distinguished with multiple channels.

Abstract

The possible existence of light and heavy sterile neutrinos may give rise to direct and indirect unitarity violation of the $3\times3$ lepton mixing matrix respectively. In the current work we study the potential of future accelerator neutrino facilities in probing the unitarity violation effects. Taking DUNE, T2HK and a low-energy Neutrino Factory (LENF) as working examples of future accelerator neutrino facilities, we study the distinct effects of direct and indirect unitarity violation on the discovery reach of the leptonic CP violation and precision measurements of $\theta_{23}$ in the three neutrino framework. In addition, constraints on the additional mixing parameters of direct and indirect unitarity violation are also discussed. Finally, we stress that the combination of experiments with different oscillation channels, different neutrino beams and different detector techniques will be an effective solution to the parameter degeneracy problem and give the robust measurement of leptonic CP violation even if the direct and indirect unitarity violation are taken into account.