KMS states on the C*-algebras of Fell bundles over groupoids

TL;DR

This paper characterizes KMS states on the C*-algebras of Fell bundles over étale groupoids using measurable fields of traces, extending existing results to twisted groupoid C*-algebras and finite k-graphs.

Contribution

It generalizes Neshveyev's theorem to twisted groupoid C*-algebras and applies the framework to finite k-graphs, providing a comprehensive description of equilibrium states.

Findings

Describes KMS states in terms of measurable fields of traces.

Extends Neshveyev's main theorem to twisted groupoid C*-algebras.

Applies results to twisted C*-algebras of finite k-graphs.

Abstract

We consider fiberwise singly generated Fell-bundles over etale groupoids. Given a continuous real-valued 1-cocycle on the groupoid, there is a natural dynamics on the cross-sectional algebra of the Fell bundle. We study the Kubo-Martin-Schwinger equilibrium states for this dynamics. Following work of Neshveyev on equilibrium states on groupoid C*-algebras, we describe the equilibrium states of the cross-sectional algebra in terms of measurable fields of traces on the C*-algebras of the restrictions of the Fell bundle to the isotropy subgroups of the groupoid. As a special case, we obtain a description of the trace space of the cross-sectional algebra. We apply our result to generalise Neshveyev's main theorem to twisted groupoid C*-algebras, and then apply this to twisted C*-algebras of strongly connected finite k-graphs.