Testing nonunitarity of neutrino mixing matrices at neutrino factories

Abstract

In this paper we explore the effect of nonunitary neutrino mixing on neutrino oscillation probabilities both in vacuum and matter. In particular, we consider the ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\rightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ channel and, using a neutrino factory as the source for ${\ensuremath{\nu}}_{\ensuremath{\mu}}$'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 nonunitary mixings give rise to spurious ``degenerate'' solutions in the parameter space. We also discuss how the true solutions can be extricated by combining measurements at several baselines.