The dynamics of partial inverse semigroup actions

TL;DR

This paper explores the structure of partial inverse semigroup actions on topological spaces, constructing associated groupoids and algebras, and establishes isomorphisms and equivalences that generalize previous global action results.

Contribution

It introduces a new framework for partial inverse semigroup actions, linking groupoid of germs and Steinberg algebras, and extends orbit equivalence concepts to these partial actions.

Findings

Isomorphism between Steinberg algebra of groupoid of germs and crossed product $A_R(X)\rtimes S$

Characterization of topologically principal partial actions and their groupoids

Comparison of orbit equivalence notions for actions and graphs

Abstract

Given an inverse semigroup $S$ endowed with a partial action on a topological space $X$, we construct a groupoid of germs $S\ltimes X$ in a manner similar to Exel's groupoid of germs, and similarly a partial action of $S$ on an algebra $A$ induces a crossed product $A\rtimes S$. We then prove, in the setting of partial actions, that if $X$ is locally compact Hausdorff and zero-dimensional, then the Steinberg algebra of the groupoid of germs $S\ltimes X$ is isomorphic to the crossed product $A_R(X)\rtimes S$, where $A_R(X)$ is the Steinberg algebra of $X$. We also prove that the converse holds, that is, that under natural hypotheses, crossed products of the form $A_R(X)\rtimes S$ are Steinberg algebras of appropriate groupoids of germs of the form $S\ltimes X$. We introduce a new notion of topologically principal partial actions, which correspond to topologically principal groupoids of germs, and study orbit equivalence for these actions in terms of isomorphisms of the corresponding groupoids of germs. This generalizes previous work of the first-named author as well as from others, which dealt mostly with global actions of semigroups or partial actions of groups. We finish the article by comparing our notion of orbit equivalence of actions and orbit equivalence of graphs.