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We show that every strongly $\mathbb{Z}$-graded C*-algebra (equivalently, every C*-algebra carrying a strongly continuous $\mathbb{T}$-action with full spectral subspaces) is a Cuntz--Pimsner algebra, and describe subalgebras and subspaces…

Operator Algebras · Mathematics 2025-07-08 Efren Ruiz , Aidan Sims

We establish exact sequences in $KK$-theory for graded relative Cuntz-Pimsner algebras associated to nondegenerate $C^*$-correspondences. We use this to calculate the graded $K$-theory and $K$-homology of relative Cuntz-Krieger algebras of…

Operator Algebras · Mathematics 2021-10-26 Quinn Patterson , Adam Sierakowski , Aidan Sims , Jonathan Taylor

We study the KMS states of the C*-algebra of a strongly connected finite k-graph. We find that there is only one 1-parameter subgroup of the gauge action that can admit a KMS state. The extreme KMS states for this preferred dynamics are…

Operator Algebras · Mathematics 2014-04-29 Astrid an Huef , Marcelo Laca , Iain Raeburn , Aidan Sims

I introduce yet another way to associate a C*-algebra to a graph and construct a simple nuclear C*-algebra that has irreducible representations both on a separable and a nonseparable Hilbert space.

Operator Algebras · Mathematics 2009-10-24 Ilijas Farah

We investigate the question: when is a higher-rank graph C*-algebra approximately finite dimensional? We prove that the absence of an appropriate higher-rank analogue of a cycle is necessary. We show that it is not in general sufficient,…

Operator Algebras · Mathematics 2018-10-19 D. Gwion Evans , Aidan Sims

We prove that a graph C*-algebra with exactly one proper nontrivial ideal is classified up to stable isomorphism by its associated six-term exact sequence in K-theory. We prove that a similar classification also holds for a graph C*-algebra…

Operator Algebras · Mathematics 2009-06-26 Soren Eilers , Mark Tomforde

We examine a certain type of abelian C*-subalgebras that allow one to give a unified treatment of two uniqueness theorems: for graph C*-algebras and for certain reduced crossed products.

Operator Algebras · Mathematics 2013-08-30 Gabriel Nagy , Sarah Reznikoff

In this paper, two sufficient and necessary conditions are given. The first one characterizes when the boundary path groupoid of a topological graph without singular vertices has closed interior of its isotropy group bundle, and the second…

Operator Algebras · Mathematics 2016-10-18 Jonathan Brown , Hui Li , Dilian Yang

We prove a version of the result in the title that makes use of maximal coactions in the context of discrete groups. Earlier Gauge-Invariant Uniqueness theorems for $C^*$-algebras associated to $P$-graphs and similar $C^*$-algebras…

Operator Algebras · Mathematics 2023-12-25 Robert Huben , S. Kaliszewski , Nadia S. Larsen , John Quigg

In this paper, we study multiplicative structures on the K-theory of the core $A:=C^*(E)^{U(1)}$ of the C*-algebra $C^*(E)$ of a directed graph $E$. In the first part of the paper, we study embeddings $E\to E\times E$ that induce a…

K-Theory and Homology · Mathematics 2026-04-15 Francesco D'Andrea

We augment Restorff's classification of purely infinite Cuntz-Krieger algebras by describing the range of his invariant on purely infinite Cuntz-Krieger algebras. We also describe its range on purely infinite graph C*-algebras with finitely…

Operator Algebras · Mathematics 2014-03-17 Sara E. Arklint , Rasmus Bentmann , Takeshi Katsura

Let X be a product system over a quasi-lattice ordered group. Under mild hypotheses, we associate to X a C*-algebra which is co-universal for injective Nica covariant Toeplitz representations of X which preserve the gauge coaction. Under…

Operator Algebras · Mathematics 2012-03-09 Toke Meier Carlsen , Nadia S. Larsen , Aidan Sims , Sean Vittadello

We prove a new uniqueness theorem for the tight C*-algebras of an inverse semigroup by generalizing the uniqueness theorem given for \'etale groupoid C*-algebras by Brown, Nagy, Reznikoff, Sims, and Williams. We use this to show that in the…

Operator Algebras · Mathematics 2022-08-18 Charles Starling

We show that the Cuntz splice induces stably isomorphic graph $C^*$-algebras.

Operator Algebras · Mathematics 2021-09-20 Søren Eilers , Gunnar Restorff , Efren Ruiz , Adam P. W. Sørensen

There has recently been much interest in the $C^*$-algebras of directed graphs. Here we consider product systems $E$ of directed graphs over semigroups and associated $C^*$-algebras $C^*(E)$ and $\mathcal{T}C^*(E)$ which generalise the…

Operator Algebras · Mathematics 2016-09-07 Iain Raeburn , Aidan Sims

An ultragraph gives rise to a labelled graph with some particular properties. In this paper we describe the algebras associated to such labelled graphs as groupoid algebras. More precisely, we show that the known groupoid algebra…

Rings and Algebras · Mathematics 2020-09-04 Gilles G. de Castro , Daniel Gonçalves , Daniel W. van Wyk

For a finitely aligned k-graph $\Lambda$ with X a set of vertices in $\Lambda$ we define a universal C*-algebra called $C^*(\Lambda,X)$ generated by partial isometries. We show that $C^*(\Lambda,X)$ is isomorphic to the corner…

Operator Algebras · Mathematics 2007-05-23 Stephen Allen

A universal coefficient theorem is proved for C*-algebras over an arbitrary finite T_0-space X which have vanishing boundary maps. Under bootstrap assumptions, this leads to a complete classification of unital/stable real-rank-zero…

Operator Algebras · Mathematics 2013-11-05 Rasmus Bentmann

This dissertation concerns the classification of groupoid and higher-rank graph C*-algebras and has two main components. Firstly, for a groupoid it is shown that the notions of strength of convergence in the orbit space and…

Operator Algebras · Mathematics 2013-05-28 Robert Hazlewood

We present a uniqueness theorem for the reduced C*-algebra of a twist $\mathcal{E}$ over a Hausdorff \'etale groupoid $\mathcal{G}$. We show that the interior $\mathcal{I}^\mathcal{E}$ of the isotropy of $\mathcal{E}$ is a twist over the…

Operator Algebras · Mathematics 2022-06-06 Becky Armstrong