EZ-structures and topological applications

Abstract

We introduce the notion of an EZ-structure on a group. Delta-hyperbolic groups and CAT(0)-groups have EZ-structures. We show torsion-free groups having an EZ-structure automatically have an action by homeomorphisms on a closed (high-dimensional) ball, which is well-behaved away from a "bad limit set" in the boundary of the ball. We show that groups having such an action satisfy the Novikov conjecture. For torsion-free delta-hyperbolic groups $G$, we also give a lower bound for the homotopy groups $π_n(P(BG))$, where $P$ is the stable topological pseudo-isotopy functor.