Minimal Ahlfors regular conformal dimension of coarse conformal dynamics on the sphere

Abstract

We prove that if the Ahlfors regular conformal dimension $Q$ of a topologically cxc map on the sphere $f:S^2\to S^2$ is realized by some metric $d$ on $S^2$, then either Q=2 and $f$ is topologically conjugate to a semihyperbolic rational map with Julia set equal to the whole Riemann sphere, or $Q>2$ and $f$ is topologically conjugate to a map which lifts to an affine expanding map of a torus whose differential has distinct real eigenvalues. This is an analog of a known result for Gromov hyperbolic groups with two-sphere boundary, and our methods apply to give a new proof.