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We consider the higher-rank graphs introduced by Kumjian and Pask as models for higher-rank Cuntz-Krieger algebras. We describe a variant of the Cuntz-Krieger relations which applies to graphs with sources, and describe a local convexity…

Operator Algebras · Mathematics 2007-05-23 Iain Raeburn , Aidan Sims , Trent Yeend

As a generalization of the Exel-Pardo's notion of self-similar graph, we introduce self-similar group actions on ultragraphs and their $C^*$-algebras. We then approach to the $C^*$-algebras by inverse semigroup and tight groupoid models.

Operator Algebras · Mathematics 2025-05-20 Hossein Larki , Najmeh Rajabzadeh-Hasiri

We introduce a bivariant version of the Cuntz semigroup as equivalence classes of order zero maps generalizing the ordinary Cuntz semigroup. The theory has many properties formally analogous to KK-theory including a composition product. We…

Operator Algebras · Mathematics 2016-02-08 Joan Bosa , Gabriele Tornetta , Joachim Zacharias

Associating graph algebras to directed graphs leads to both covariant and contravariant functors from suitable categories of graphs to the category k-Alg of algebras and algebra homomorphisms. As both functors are often used at the same…

Rings and Algebras · Mathematics 2026-04-30 Gilles G. de Castro , Francesco D'Andrea , Piotr M. Hajac

We associate a $C^*$-algebra to a partial action of the integers acting on the base space of a vector bundle, using the framework of Cuntz--Pimsner algebras. We investigate the structure of the fixed point algebra under the canonical gauge…

Operator Algebras · Mathematics 2025-06-23 Aaron Kettner

Given an arbitrary countable directed graph $G$ we prove the C*-envelope of the tensor algebra $T_+(G)$ coincides with the universal Cuntz-Krieger algebra associated with $G$. Our approach is concrete in nature and does not rely on Hilbert…

Operator Algebras · Mathematics 2007-05-23 Elias Katsoulis , David Kribs

We prove directly that if E is a directed graph in which every cycle has an entrance, then there exists a C*-algebra which is co-universal for Toeplitz-Cuntz-Krieger E-families. In particular, our proof does not invoke ideal-structure…

Operator Algebras · Mathematics 2010-01-13 Aidan Sims , Samuel B. G. Webster

We consider graphs E which have been obtained by adding one or more sinks to a fixed directed graph G. We classify the C*-algebra of E up to a very strong equivalence relation, which insists, loosely speaking, that C*(G) is kept fixed. The…

Operator Algebras · Mathematics 2007-05-23 Iain Raeburn , Mark Tomforde , Dana P. Williams

Given a graph of C*-algebras, we prove a long exact sequence in KK-theory for both the maximal and the vertex-reduced fundamental C*-algebras in the presence of possibly non GNS-faithful conditional expectations. We deduce from it the…

Operator Algebras · Mathematics 2016-12-28 Fima Pierre , Germain Emmanuel

We consider directed graphs E which have been obtained by adding a sink to a fixed graph G. We associate an element of Ext(C*(G)) to each such E, and show that the classes of two such graphs are equal in Ext(C*(G)) if and only if the…

Operator Algebras · Mathematics 2007-05-23 Mark Tomforde

The construction of the C*-algebra associated to a directed graph $E$ is extended to incorporate a family $C$ consisting of partitions of the sets of edges emanating from the vertices of $E$. These C*-algebras $C^*(E,C)$ are analyzed in…

Operator Algebras · Mathematics 2011-07-12 P. Ara , K. R. Goodearl

Let $X$ be a product system over a quasi-lattice ordered groupoid $(G,P)$. Under mild hypotheses, we associate to $X$ a $C^*$-algebra which is couniversal for injective Nica covariant Toeplitz representations of $X$ which preserve the gauge…

Operator Algebras · Mathematics 2024-01-10 Massoud Amini , Mahdi Moosazadeh

In the first part of the article we introduce $C^*$-algebras associated to self-similar groups and study their properties and relations to known algebras. The algebras are constructed as sub-algebras of the Cuntz-Pimsner algebra (and its…

Group Theory · Mathematics 2007-05-23 Rostislav Grigorchuk , Volodymyr Nekrashevych

Let (G,P) be a quasi-lattice ordered group and let X be a compactly aligned product system over P of Hilbert bimodules. Under mild hypotheses we associate to X a C*-algebra which we call the Cuntz-Nica-Pimsner algebra of X. Our construction…

Operator Algebras · Mathematics 2009-01-08 Aidan Sims , Trent Yeend

We describe how boundary paths in a graph can be used to construct irreducible representations of the associated graph C*-algebra and the associated Leavitt path algebra. We use this construction to establish two sets of results: First, we…

Rings and Algebras · Mathematics 2025-02-07 Kulumani M. Rangaswamy , Mark Tomforde

We prove gauge-invariant uniqueness theorems with respect to maximal and normal coactions for $C^*$-algebras associated to product systems of $C^*$-correspondences. Our techniques of proof are developed in the abstract context of Fell…

Operator Algebras · Mathematics 2012-05-29 S. Kaliszewski , Nadia S. Larsen , John Quigg

We prove a version of uniqueness theorem for Cuntz-Pimsner algebras of discrete product systems over semigroups of Ore type. To this end, we introduce Doplicher-Roberts picture of Cuntz-Pimsner algebras, and the semigroup dual to a product…

Operator Algebras · Mathematics 2016-12-01 B. K. Kwasniewski , W. Szymanski

Topological quivers generalize the notion of directed graphs in which the sets of vertices and edges are locally compact (second countable) Hausdorff spaces. Associated to a topological quiver $Q$ is a $C^*$-correspondence, and in turn, a…

Operator Algebras · Mathematics 2013-01-31 Shawn J. McCann

We compute K-theory for ring C*-algebras in the case of higher roots of unity and thereby completely determine the K-theory for ring C*-algebras attached to rings of integers in arbitrary number fields.

Operator Algebras · Mathematics 2025-04-08 Xin Li , Wolfgang Lück

We extend the usual theory of universal C*-algebras from generators and relations in order to allow some relations to be described using the strong operator topology. In particular, we can allow some infinite sum relations. We prove a…

Operator Algebras · Mathematics 2020-08-13 Giuliano Boava , Gilles G. de Castro
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