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ISSN (electronic): 1364-0380
ISSN (print): 1465-3060
Asymptotic geometry of the mapping class group and Teichmüller space

Jason A Behrstock

Geometry & Topology 10 (2006) 1523–1578

arXiv: math.GT/0502367


In this work, we study the asymptotic geometry of the mapping class group and Teichmuller space. We introduce tools for analyzing the geometry of “projection” maps from these spaces to curve complexes of subsurfaces; from this we obtain information concerning the topology of their asymptotic cones. We deduce several applications of this analysis. One of which is that the asymptotic cone of the mapping class group of any surface is tree-graded in the sense of Druţu and Sapir; this tree-grading has several consequences including answering a question of Druţu and Sapir concerning relatively hyperbolic groups. Another application is a generalization of the result of Brock and Farb that for low complexity surfaces Teichmüller space, with the Weil–Petersson metric, is δ–hyperbolic. Although for higher complexity surfaces these spaces are not δ–hyperbolic, we establish the presence of previously unknown negative curvature phenomena in the mapping class group and Teichmüller space for arbitrary surfaces.

mapping class group, Teichmüller space, curve complex, asymptotic cone
Mathematical Subject Classification 2000
Primary: 20F67
Secondary: 30F60, 57M07, 20F65
Forward citations
Received: 15 August 2005
Revised: 15 July 2006
Accepted: 26 September 2006
Published: 21 October 2006
Proposed: Benson Farb
Seconded: Walter Neumann, Rob Kirby
Jason A Behrstock
Department of Mathematics
Barnard College
Columbia University
New York, NY 10027