A 'transversal' for minimal invariant sets in the boundary of a CAT(0) group

Dan P. Guralnik, Eric L. Swenson
2012 Transactions of the American Mathematical Society  
We introduce new techniques for studying boundary dynamics of CAT(0) groups. For a group G acting geometrically on a CAT(0) space X we show there is a flat F ⊂ X of maximal dimension (denote it by d), whose boundary sphere intersects every minimal G-invariant subset of ∂ ∞ X. As applications we obtain an improved dimension-dependent bound diam ∂ T X ≤ 2π − arccos − 1 d + 1 on the Tits-diameter of ∂X for non-rank-one groups, a necessary and sufficient dynamical condition for G to be virtually
more » ... lian, and we formulate a new approach to Ballmann's rank rigidity conjectures.
doi:10.1090/s0002-9947-2012-05714-x fatcat:pa2edi3ilvctjedh3gsmazlkbi