Similar Relatively Hyperbolic Actions of a Group

Abstract

Let a discrete group G possess two convergence actions by homeomorphisms on compacta X and Y . Consider the following question: does there exist a convergence action GyZ on a compactum Z and continuous equivariant maps X ← Z → Y ? We call the space Z (and action of G on it) pullback space (action). In such general setting a negative answer follows from a recent result of O. Baker and T. Riley [BR]. Suppose, in addition, that the initial actions are relatively hyperbolic that is they are non-parabolic and the induced action on the distinct pairs are cocompact. Then the existence of the pullback space if G is finitely generated follows from [Ge2]. The main result of the paper claims that the pullback space exists if and only if the maximal parabolic subgroups of one of the actions are dynamically quasiconvex for the other one. We provide an example of two relatively hyperbolic actions of the free group G of countable rank for which the pullback action does not exist. We study an analog of the notion of geodesic flow for relatively hyperbolic groups. Further these results are used to prove the main theorem.