Testing non-unitarity of neutrino mixing matrices at neutrino factories

TL;DR

This paper investigates how non-unitary neutrino mixing affects oscillation probabilities, especially at neutrino factories, and proposes methods to constrain unitarity violation parameters and distinguish true solutions from degeneracies.

Contribution

It analyzes the impact of non-unitary mixing on neutrino oscillations and suggests experimental strategies to constrain unitarity violation parameters using multiple baselines.

Findings

Constraints on unitarity violation parameters can be obtained at neutrino factories.

New CP violation phases can cause degeneracies in parameter space.

Combining measurements at several baselines helps resolve degeneracies.

Abstract

In this paper we explore the effect of non-unitary neutrino mixing on neutrino oscillation probabilities both in vacuum and matter. In particular, we consider the $\nu_\mu \to \nu_\tau$ channel and using a Neutrino Factory as the source for $\nu_\mu$'s discuss the constraints that can be obtained on the moduli and phases of the parameters characterizing the violation of unitarity. We point out how the new CP violation phases present in the case where the non-unitary mixings give rise to spurious ``degenerate'' solutions in the parameter space and discuss how the true solutions can be extricated by combining measurements at several baselines.