Non-uniform hyperbolicity in complex dynamics

TL;DR

This paper investigates complex rational functions under summability conditions, establishing properties like unique conformal measures, Julia set dimensions, and stability criteria, with implications for polynomial and Blaschke product dynamics.

Contribution

It introduces new summability conditions that lead to comprehensive dynamical properties and dimension results for Julia sets in complex dynamics.

Findings

Existence of a unique ergodic conformal measure with Hausdorff dimension

Julia set has Minkowski dimension less than 2

Julia set is either the whole sphere or the dynamics are unstable

Abstract

We study rational functions satisfying summability conditions - a family of weak conditions on the expansion along the critical orbits. Assuming their appropriate versions, we derive many nice properties: There exists a unique, ergodic, and non-atomic conformal measure with exponent equal to the Hausdorff dimension of the Julia set. There is an absolutely continuous invariant measure with respect to this conformal measure. The Minkowski dimension of the Julia set is strictly less than 2. Either the Julia set is the whole sphere, or the dynamics is unstable. For such polynomials and Blaschke products the Julia set is conformally removable. The connected components of the boundary of invariant Fatou components are locally connected. Finally, we derive a conformal analogue of Jakobson-Benedicks-Carleson theorem and prove the external continuity of the Hausdorff dimension of Julia sets for almost all points in the Mandelbrot set with respect to the harmonic measure. Some of the results extend to the multimodal maps of an interval.