Assouad type dimensions of parabolic Julia sets

Abstract

We prove that the Assouad dimension of a parabolic Julia set is max{1, h} where h is the Hausdorff dimension of the Julia set. Since h may be strictly less than 1, this provides examples where the Assouad and Hausdorff dimension are distinct. The box and packing dimensions of the Julia set are known to coincide with h and, moreover, h can be characterised by a topological pressure function. This distinctive behaviour of the Assouad dimension invites further analysis of the Assouad type dimensions, including the Assouad and lower spectra. We compute all of the Assouad type dimensions for parabolic Julia sets and the associated h-conformal measure. Further, we show that if a Julia set has a Cremer point, then the Assouad dimension is 2.