Orbit Equivalence of actions on Cartan pairs

Abstract: We introduce and study the notion of continuous orbit equivalence of actions of countable discrete groups on Cartan pairs in (twisted) groupoid context. We characterize orbit equivalence of actions in terms of the corresponding C$^*$-algebraic crossed products using Kumjian-Renault theory. We relate our notion to the classical notion of orbit equivalence of actions on topological spaces by showing that, under certain conditions, orbit equivalence of actions on (twisted) groupoids follows from orbit equivalence of restricted actions on unit spaces. We illustrate our results with concrete examples of continuous orbit equivalent actions on groupoids coming from odometer transformations.