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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

Graph C*-algebras have been celebrated as C*-algebras that can be seen, because many important properties may be determined by looking at the underlying graph. This paper introduces the permutation graph for a permutative endomorphism of a…

Operator Algebras · Mathematics 2015-01-15 James Emil Avery , Rune Johansen , Wojciech Szymanski

In this article, we extend a well known result about real rank zero C* Algebras to higher real rank C* Algebras. The main technique used here is similar to the method in which we approximate continuous functions using projections. What we…

Operator Algebras · Mathematics 2026-04-24 Aranya Sarkar

Given a directed graph, there exists a universal operator algebra and universal C*-algebra associated to the directed graph. In this paper we give intrinsic constructions of these objects. We provide an explicit construction for the maximal…

Operator Algebras · Mathematics 2007-05-23 Benton L. Duncan

We consider *-linear maps into a commutative C*-algebra C (X) of continuous functions on a locally compact Hausdorff space X with certain specified properties and prove two results: (1) an extension result for a class of *-linear maps Y -->…

Functional Analysis · Mathematics 2013-07-24 Ulrich Haag

Given a graph, we associate each edge with the transposition which exchanges the endvertices. Fixing a linear order on the edge set, we obtain a permutation of the vertices. D\'enes proved that the permutation is a full cyclic permutation…

Combinatorics · Mathematics 2024-04-04 Shuhei Tsujie , Ryo Uchiumi

Topological quivers are generalizations of directed graphs in which the sets of vertices and edges are locally compact Hausdorff spaces. Associated to such a topological quiver Q is a C*-correspondence, and from this correspondence one may…

Operator Algebras · Mathematics 2007-05-23 Paul S. Muhly , Mark Tomforde

We construct explicit generating sets S_n and \tilde S_n of the for the alternating and the symmetric groups, which turn the Cayley graphs C(Alt(n), S_n) and C(Sym(n), \tilde S_n) into a family of bounded degree expanders for all n. This…

Group Theory · Mathematics 2007-05-23 Martin Kassabov

In this article we survey some of the recent goings-on in the classification programme of C$^*$-algebras, following the interesting link found between the Cuntz semigroup and the classical Elliott invariant and the fact that the Elliott…

Operator Algebras · Mathematics 2009-02-20 Pere Ara , Francesc Perera , Andrew S. Toms

In this paper, we discuss a method of constructing separable representations of the $C^*$-algebras associated to strongly connected row-finite $k$-graphs $\Lambda$. We begin by giving an alternative characterization of the…

Operator Algebras · Mathematics 2018-03-26 Carla Farsi , Elizabeth Gillaspy , Palle E. T. Jorgensen , Sooran Kang , Judith Packer

On a separable C*-algebra A every (completely) bounded map, which preserves closed two sided ideals, can be approximated uniformly by elementary operators if and only if A is a finite direct sum of C*-algebras of continuous sections…

Operator Algebras · Mathematics 2009-02-03 Bojan Magajna

Let $\A$ be a unital separable nuclear $C^*$--algebra which belongs to the bootstrap category $\N$ and $\B$ be a separable stable $C^*$--algebra. In this paper, we consider the group $\Ext_u(\A,\B)$ consisting of the unitary equivalence…

Operator Algebras · Mathematics 2010-08-10 Yifeng Xue

Given a self-similar groupoid action $(G,E)$ on the path space of a finite graph, we study the associated Exel-Pardo \'etale groupoid ${\mathcal G}(G,E)$ and its $C^*$-algebra $C^*(G,E)$. We review some facts about groupoid actions, skew…

Operator Algebras · Mathematics 2021-01-01 Valentin Deaconu

We study the representation theory and enveloping $C^*$-algebras for Wick analogues of CAR and twisted CAR algebras. The realization of the $C^*$-algebras under consideration as algebras of continuous matrix-functions satisfying certain…

Operator Algebras · Mathematics 2007-05-23 Daniil Proskurin , Yurii Savchuk , Lyudmila Turowska

We characterise the strictly closed left invariant C*-subalgebras of the C*-algebra C_b(G) of bounded continuous functions on a locally compact group G. On the dual side, we characterise the strictly closed invariant C*-subalgebras of the…

Operator Algebras · Mathematics 2011-10-26 Pekka Salmi

We investigate which topological spaces can be constructed as topological realisations of higher-rank graphs. We describe equivalence relations on higher-rank graphs for which the quotient is again a higher-rank graph, and show that…

Operator Algebras · Mathematics 2016-06-09 Alex Kumjian , David Pask , Aidan Sims , Michael F. Whittaker

We show that the C*-algebra of a row-finite source-free k-graph is Rieffel-Morita equivalent to a crossed product of an AF algebra by the fundamental group of the k-graph. When the k-graph embeds in its fundamental groupoid, this AF algebra…

Operator Algebras · Mathematics 2024-03-05 Nathan Brownlowe , Alex Kumjian , David Pask , Aidan Sims

We introduce $C^*$-algebras associated to directed graphs of groups. In particular, we associate a combinatorial $C^*$-algebra to each row-finite directed graph of groups with no sources, and show that this $C^*$-algebra is Morita…

Operator Algebras · Mathematics 2024-03-06 Victor Wu

We show that c-planarity is solvable in quadratic time for flat clustered graphs with three clusters if the combinatorial embedding of the underlying graph is fixed. In simpler graph-theoretical terms our result can be viewed as follows.…

Computational Geometry · Computer Science 2016-08-26 Radoslav Fulek

We study the Wold decomposition for representations of a self-similar semigroup $P$ action on a directed graph $E$. We then apply this decomposition to the case where $P=\mathbb{N}$ to study the C*-envelope of the associated universal…

Operator Algebras · Mathematics 2024-05-14 Boyu Li , Dilian Yang
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