Haar systems, KMS states on von Neumann algebras and $C^*$-algebras on dynamically defined groupoids and Noncommutative Integration

TL;DR

This paper explores Haar systems, KMS states, and noncommutative integration on groupoids derived from dynamical equivalence relations, connecting operator algebras with thermodynamic formalism and providing a detailed survey of the subject.

Contribution

It introduces new results on Haar systems and KMS states on groupoid-related algebras, linking them to thermodynamic formalism and offering a comprehensive survey with detailed examples.

Findings

Characterization of Haar systems for dynamical groupoids

Description of KMS states and their relation to Gibbs states

Analysis of non-commutative integration in this context

Abstract

We analyse certain Haar systems associated to groupoids obtained by certain natural equivalence relations of dynamical nature on sets like $\{1,2,...,d\}^\mathbb{Z}$, $\{1,2,...,d\}^\mathbb{N}$, $S^1\times S^1$, or $(S^1)^\mathbb{N}$, where $S^1$ is the unitary circle. We also describe properties of transverse functions, quasi-invariant probabilities and KMS states for some examples of von Neumann algebras (and also $C^*$-Algebras) associated to these groupoids. We relate some of these KMS states with Gibbs states of Thermodynamic Formalism. While presenting new results, we will also describe in detail several examples and basic results on the above topics. In other words it is also a survey paper. Some known results on non-commutative integration are presented, more precisely, the relation of transverse measures, cocycles and quasi-invariant probabilities. We describe the results in a language which is more familiar to people in Dynamical Systems. Our intention is to study Haar systems, quasi-invariant probabilities and von Neumann algebras as a topic on measure theory (intersected with ergodic theory) avoiding questions of algebraic nature (which, of course, are also extremely important).