KMS states on $C^*$-algebras associated to a family of $*$-commuting local homeomorphisms

TL;DR

This paper investigates KMS states on $C^*$-algebras derived from a family of $*$-commuting local homeomorphisms, analyzing their structure under various dynamics and identifying critical inverse temperatures.

Contribution

It constructs a new class of $C^*$-algebras from $*$-commuting local homeomorphisms and characterizes their KMS states across different temperature regimes.

Findings

Describes the simplex of KMS states at large inverse temperatures.

Identifies a unique KMS state at a critical inverse temperature.

Applies results to backward shifts on infinite-path spaces of $k$-graphs.

Abstract

We consider a family of $*$-commuting local homeomorphisms on a compact space, and build a compactly aligned product system of Hilbert bimodules (in the sense of Fowler). This product system has a Nica-Toeplitz algebra and a Cuntz-Pimsner algebra. Both algebras carry a gauge action of a higher-dimensional torus, and there are many possible dynamics obtained by composing with different embeddings of the real line in this torus. We study the KMS states of these dynamics. For large inverse temperatures, we describe the simplex of KMS states on the Nica-Toeplitz algebra. To study KMS states for smaller inverse temperature, we consider a preferred dynamics for which there is a single critical inverse temperature. We find a KMS state on the Nica-Toeplitz algebra at this critical inverse temperature which factors through the Cuntz-Pimsner algebra. We then illustrate our results by considering backward shifts on the infinite-path spaces of a class of $k$-graphs.