#### Volume 14, issue 2 (2010)

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Hausdorff dimension and the Weil–Petersson extension to quasifuchsian space

### Martin Bridgeman

Geometry & Topology 14 (2010) 799–831
##### Abstract

We consider a natural nonnegative two-form $G$ on quasifuchsian space that extends the Weil–Petersson metric on Teichmüller space. We describe completely the positive definite locus of $G$, showing that it is a positive definite metric off the fuchsian diagonal of quasifuchsian space and is only zero on the “pure-bending” tangent vectors to the fuchsian diagonal. We show that $G$ is equal to the pullback of the pressure metric from dynamics. We use the properties of $G$ to prove that at any critical point of the Hausdorff dimension function on quasifuchsian space the Hessian of the Hausdorff dimension function must be positive definite on at least a half-dimensional subspace of the tangent space. In particular this implies that Hausdorff dimension has no local maxima on quasifuchsian space.

##### Keywords
quasifuchsian space, Weil–Petersson metric, Hausdorff dimension
##### Mathematical Subject Classification 2000
Primary: 30F60, 30F40, 37D35
##### Publication
Revised: 3 January 2010
Accepted: 29 December 2009
Published: 2 March 2010
Proposed: Shigeyuki Morita
Seconded: Benson Farb, Martin Bridson
##### Authors
 Martin Bridgeman Department of Mathematics Boston College Chestnut Hill, MA 02167 http://www2.bc.edu/~bridgem/