Finite cuts and CAT(0) boundaries

Abstract

We show that if a 1-ended group $G$ acts geometrically on a CAT(0) space $X$ and $\bd X$ is separated by $m$ points then either $G$ is virtually a surface group or $G$ splits over a 2-ended group. In the course of the proof we study nesting actions on $\mathbb{R}$-trees and we show that nesting actions with non overlapping translation intervals give rise to isometric actions.

84 pages