A combinatorial higher-rank hyperbolicity condition
We investigate a coarse version of a 2(n+1)-point inequality characterizing metric spaces of combinatorial dimension at most n due to Dress.This condition, experimentally called (n,δ)-hyperbolicity, reduces to Gromov's quadruple definition of δ-hyperbolicity in case n=1. The l∞-product of n δ-hyperbolic spaces is (n,δ)-hyperbolic. Every (n,δ)-hyperbolic metric space, without any further assumptions, possesses a slim (n+1)-simplex property analogous to the slimness of quasi-geodesic triangles in Gromov hyperbolic spaces. In connection with recent work in geometric group theory, we show that every Helly group and every hierarchically hyperbolic group of (asymptotic) rank n acts geometrically on some (n,δ)-hyperbolic space. The talk is based on a joint paper with Martina Jørgensen.