Thurston obstructions and Ahlfors regular conformal dimension

Peter Haïssinsky (1) , Kevin Pilgrim (2)

1 Picard
2 Dept. of Mathematics

Let $f: S^2 \to S^2$ be an expanding branched covering map of the sphere to itself with finite postcritical set $P_f$. Associated to $f$ is a canonical quasisymmetry class $\GGG(f)$ of Ahlfors regular metrics on the sphere in which the dynamics is (non-classically) conformal. We show \[ \inf_{X \in \GGG(f)} \hdim(X) \geq Q(f)=\inf_\Gamma \{Q \geq 2: \lambda(f_{\Gamma,Q}) \geq 1\}.\] The infimum is over all multicurves $\Gamma \subset S^2-P_f$. The map $f_{\Gamma,Q}: \R^\Gamma \to \R^\Gamma$ is defined by \[ f_{\Gamma, Q}(\gamma) =\sum_{[\gamma']\in\Gamma} \sum_{\delta \sim \gamma'} \deg(f:\delta \to \gamma)^{1-Q}[\gamma'],\] where the second sum is over all preimages $\delta$ of $\gamma$ freely homotopic to $\gamma'$ in $S^2-P_f$, and $ \lambda(f_{\Gamma,Q})$ is its Perron-Frobenius leading eigenvalue. This generalizes Thurston's observation that if $Q(f)>2$, then there is no $f$-invariant classical conformal structure.

Mots clés: postcritically finite; conformal dimension; finite subdivision rule; combinatorial moduli

Domaines: Systèmes dynamiques [math.DS]

Peter Haïssinsky, Kevin Pilgrim. Thurston obstructions and Ahlfors regular conformal dimension. Journal de Mathématiques Pures et Appliquées, 2008, 90 (no. 3), pp.229--241. ⟨hal-00152983v3⟩