Joint invariant sets for non-commutative expanding Markov maps of the circle

TL;DR

This paper investigates the structure and properties of joint invariant sets for non-commutative expanding Markov maps on the circle, addressing a less understood area beyond the commuting case.

Contribution

It analyzes the topological structure of invariant sets for a single circle map and explores the prevalence of maps with non-trivial joint invariant sets in the non-commutative setting.

Findings

Characterizes the topological structure of invariant sets for $C^{ ext{alpha}}$ maps.

Shows the size of the subset of maps with non-trivial joint invariants.

Establishes a dimensional relation between maximal invariant sets and their endpoints.

Abstract

A long-standing question is what invariant sets can be shared by two maps acting on the same space. A similar question stands for invariant measures. A particular interesting case are expanding Markov maps of the circle. If the two involved maps are commuting the answer is almost complete. However very little is known in the non-commutative case. A first step is to analyze the structure of the invariant sets of a single map. For a mapping of the circle of class $C^{\alpha}$, $\alpha>1$, we study the topological structure of the set containing all compact invariant sets. Furthermore for a fixed such mapping we examine locally, in the category sense, how big is the subset of all maps that have at least one non trivial joint invariant compact set. Lastly we show the strong dimensional relation of the maximal invariant set of a given Markov map contained in a subinterval of $[0,1)$ and the set of all right endpoints of its invariants sets contained in the same subinterval as well as the continuity dependence of the dimension on the endpoints of the subinterval.