The extended Hausdorff dimension spectrum of a conformal iterated function system is maximal

TL;DR

This paper proves that the set of Hausdorff dimensions of all limit sets generated by a conformal iterated function system (CIFS) covers all possible dimensions up to the limit set’s dimension, demonstrating maximality.

Contribution

It establishes that the extended Hausdorff dimension spectrum of any CIFS with finitely or countably many maps is maximal, including for conformal graph directed Markov systems.

Findings

The dimension spectrum is maximal for all CIFS.

Hausdorff dimension varies continuously with parameters in β-shifts.

The result applies to systems with nearest-neighbor restrictions.

Abstract

For any conformal iterated function system (CIFS) consisting of finitely or countably many maps, and any closed shift-invariant set of right-infinite sequences of such maps, one can associate a limit set, which we call a shift-generated conformal iterated construction. We define the extended Hausdorff dimension spectrum of a CIFS to be the set of Hausdorff dimensions of all such limit sets. We prove that for any CIFS with finitely or countably many maps, the extended Hausdorff dimension spectrum is maximal, i.e. all nonnegative dimensions less than or equal to the dimension of the limit set of the CIFS are realized. We also prove a version of this result even for so-called conformal graph directed Markov systems, obtained via nearest-neighbor restrictions on the CIFS. %when there are nearest-neighbor restrictions on the CIFS (similar to those in the so-called conformal graph directed Markov systems). The main step of the proof is to show that for the family $(X_\beta)$ of so-called $\beta$-shifts, the Hausdorff dimension of the limit set associated to $X_\beta$ varies continuously as a function of $\beta$.