A multifractal analysis for escaping trajectories on free groups

TL;DR

This paper studies the multifractal properties of escaping trajectories in free groups, establishing dimension bounds and symmetry conditions, with applications to geodesic flows on Schottky surfaces.

Contribution

It introduces a multifractal analysis framework for escaping trajectories in free groups and identifies conditions for dimension bounds and symmetry effects.

Findings

Established positive lower bounds for the u-dimensions of escaping sets.

Proved equality of lower bounds and actual dimensions under symmetry conditions.

Identified a dimension gap in geodesic flows on free group covers of Schottky surfaces.

Abstract

We consider a free group extension of a subshift of finite type $\sigma:\Sigma\rightarrow\Sigma$, and consider three sets of points in $\Sigma$ to which the corresponding trajectories on the free group escape to a given point in the Gromov boundary of the free group in three different senses. Under very mild conditions, we provide a common positive lower bound for the $u$-dimensions of these three sets. We also show that the lower bound is equal to the $u$-dimensions of these three sets when the extension and $u$ have certain symmetries. Moreover, we apply our results to geodesic flows on free group covers of Schottky surfaces, and show that there exists a dimension gap between the three sets we considered and the entire escaping set.