Large scale geometry of metrisable groups

Abstract

We develop a theory of large scale geometry of metrisable topological groups that, in a significant number of cases, allows one to define and identify a unique quasi-isometry type intrinsic to the topological group. Moreover, this quasi-isometry type coincides with the classical notion in the case of compactly generated locally compact groups and, for the additive group of a Banach space, is simply that of the corresponding Banach space. In particular, we characterise the class of separable metrisable groups admitting metrically proper, respectively, maximal compatible left-invariant metrics. Moreover, we develop criteria for when a metrisable group admits metrically proper affine isometric actions on Banach spaces of various degress of convexity and reflexivity. A further study of the large scale geometry of automorphism groups of countable first order model theoretical structures is separated into a companion paper.