Invariant measures with full support and approximation by zero-entropy systems in the $C^0$-Gromov--Hausdorff topology

TL;DR

This paper demonstrates that homeomorphisms with full support invariant measures can be approximated by zero-entropy systems in the $C^0$-Gromov--Hausdorff topology, revealing instability of entropy under such perturbations.

Contribution

It establishes the approximation of homeomorphisms with full support invariant measures by zero-entropy systems and explores implications for entropy stability and periodic points.

Findings

Homeomorphisms with full support invariant measures can be approximated by zero-entropy systems.

Topological entropy is not stable under $C^0$-Gromov--Hausdorff perturbations within this class.

For topologically $GH$-stable homeomorphisms, periodic points are dense.

Abstract

In this paper we prove that every homeomorphism of a compact metric space admitting an invariant probability measure with full support can be approximated in the $C^0$-Gromov--Hausdorff topology by homeomorphisms with zero topological entropy. The argument relies on the ergodic decomposition theorem and on the existence of points with dense positive orbit in the supports of suitable ergodic components. As a consequence, topological entropy is not stable under $C^0$-Gromov--Hausdorff perturbations within this class. We also show that if, in addition, the homeomorphism is topologically $GH$-stable, then its periodic points are dense in the ambient space. Finally, by combining this framework with a previous result on transitive and topologically $GH$-stable homeomorphisms, we deduce that every dynamics in this class admits an invariant measure with full support and therefore falls within the scope of the general approximation theorem by zero-entropy systems.