Vol. 221, No. 1, 2005

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Boundaries of hyperbolic metric spaces

Corran Webster and Adam Winchester

Vol. 221 (2005), No. 1, 147–158
Abstract

We investigate the relationship between the metric boundary and the Gromov boundary of a hyperbolic metric space. We show that the Gromov boundary is a quotient of the metric boundary and the quotient map is continuous, and that therefore a word-hyperbolic group has an amenable action on the metric boundary of its Cayley graph. Furthermore, if the space is 0-hyperbolic, the boundaries agree, and as a consequence there are no non-Busemann points on the boundary of such spaces. These results have significance for the study of Lip-norms on group C-algebras.

Keywords
hyperbolic space, hyperbolic group, Gromov boundary, Cayley graph, group C-algebra, quantum metric space
Mathematical Subject Classification 2000
Primary: 20F65
Secondary: 46L87, 53C23
Milestones
Received: 16 January 2004
Accepted: 30 September 2004
Published: 1 September 2005
Authors
Corran Webster
Department of Mathematical Sciences
University of Nevada Las Vegas
Las Vegas, NV 89154
www.nevada.edu/~cwebster/
Adam Winchester
Mathematics Department
University of California, Los Angeles
Los Angeles, CA 90095-1555