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We study groupoids and semigroup C*-algebras arising from graphs of monoids, in the setting of right LCM monoids. First, we establish a general criterion when a graph of monoids gives rise to a submonoid of the fundamental group which is…

Operator Algebras · Mathematics 2022-12-06 Cheng Chen , Xin Li

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

This paper investigates the structure of C*-algebras built from one-sided Sturmian subshifts. They are parametrised by irrationals in the unit interval and built from a local homeomorphism associated to the subshift. We provide an explicit…

Operator Algebras · Mathematics 2021-07-23 Kevin Aguyar Brix

We explore the recently introduced local-triviality dimensions by studying gauge actions on graph $C^*$-algebras, as well as the restrictions of the gauge action to finite cyclic subgroups. For $C^*$-algebras of finite acyclic graphs and…

Operator Algebras · Mathematics 2021-06-09 Alexandru Chirvasitu , Benjamin Passer , Mariusz Tobolski

We give a complete description of which unital graph C*-algebras are semiprojective, and use it to disprove two conjectures by Blackadar. To do so, we perform a detailed analysis of which projections are properly infinite in such…

Operator Algebras · Mathematics 2015-12-24 Søren Eilers , Takeshi Katsura

We prove that a discrete group $G$ is amenable iff it is strongly unitarizable in the following sense: every unitarizable representation $\pi$ on $G$ can be unitarized by an invertible chosen in the von Neumann algebra generated by the…

Operator Algebras · Mathematics 2014-12-23 Gilles Pisier

Following our previous works on $C^*$-graph algebras and the associated Cuntz-Krieger graph families, in this paper we will try to have a look at the colored version of these structures and to see what a $C^*$-colored graph algebra might…

Operator Algebras · Mathematics 2025-04-25 Farrokh Razavinia

In this paper, we introduce a notion of a self-similar action of a group $G$ on a $k$-graph $\Lambda$, and associate it a universal C*-algebra $\O_{G,\Lambda}$. We prove that $\O_{G,\Lambda}$ can be realized as the Cuntz-Pimsner algebra of…

Operator Algebras · Mathematics 2018-01-16 Hui Li , Dilian Yang

Let $E$ and $F$ be Hilbert $C^*$-modules over a $C^*$-algebra $\CAlg{A}$. New classes of (possibly unbounded) operators $t:E\to F$ are introduced and investigated. Instead of the density of the domain $\Def(t)$ we only assume that $t$ is…

Operator Algebras · Mathematics 2015-07-09 René Gebhardt , Konrad Schmüdgen

We introduce an algebraic version of the Katsura $C^*$-algebra of a pair $A,B$ of integer matrices and an algebraic version of the Exel-Pardo $C^*$-algebra of a self-similar action on a graph. We prove a Graded Uniqueness Theorem for such…

Rings and Algebras · Mathematics 2019-12-30 Roozbeh Hazrat , David Pask , Adam Sierakowski , Aidan Sims

We study purely atomic representations of C*-algebras associated to row-finite and source-free higher-rank graphs. We describe when purely atomic representations are unitarily equivalent and we give necessary and sufficient conditions for a…

Operator Algebras · Mathematics 2018-06-14 Carla Farsi , Elizabeth Gillaspy , Palle Jorgensen , Sooran Kang , Judith Packer

Given a directed graph $E$ and a labeling $\mathcal{L}$, one forms the labelled graph $C^*$-algebra by taking a weakly left--resolving labelled space $(E, \mathcal{L}, \mathcal{B})$ and considering a universal generating family of partial…

Operator Algebras · Mathematics 2019-07-16 Menassie Ephrem

It is shown that the *-algebra of all (closed densely defined linear) operators affiliated with a finite type I von Neumann algebra admits a unique center-valued trace, which turns out to be, in a sense, normal. It is also demonstrated that…

Operator Algebras · Mathematics 2017-05-26 Piotr Niemiec , Adam Wegert

We initiate the study of computable presentations of real and complex C*-algebras under the program of effective metric structure theory. With the group situation as a model, we develop corresponding notions of recursive presentations and…

Logic · Mathematics 2023-04-17 Alec Fox

An example is given of a simple, unital C*-algebra which contains an infinite and a non-zero finite projection. This C*-algebra is also an example of an infinite simple C*-algebra which is not purely infinite. A corner of this C*-algebra is…

Operator Algebras · Mathematics 2010-11-24 Mikael Rordam

We give various necessary and sufficient conditions for an AF-algebra to be isomorphic to a graph C*-algebra, an Exel-Laca algebra, and an ultragraph C*-algebra. We also explore consequences of these results. In particular, we show that all…

Operator Algebras · Mathematics 2009-05-24 Takeshi Katsura , Aidan Sims , Mark Tomforde

We investigate the closed convex hull of unitary orbits of selfadjoint elements in arbitrary unital C*-algebras. Using a notion of majorization against unbounded traces, a characterization of these closed convex hulls is obtained.…

Operator Algebras · Mathematics 2016-08-16 Ping Wong Ng , Leonel Robert , Paul Skoufranis

We provide inverse semigroup and groupoid models for the Toeplitz and Cuntz-Krieger algebras of finitely aligned higher-rank graphs. Using these models, we prove a uniqueness theorem for the Cuntz-Krieger algebra.

Operator Algebras · Mathematics 2007-05-23 Cynthia Farthing , Paul S. Muhly , Trent Yeend

We classify the unital embeddings of a unital separable nuclear $C^*$-algebra satisfying the universal coefficient theorem into a unital simple separable nuclear $C^*$-algebra that tensorially absorbs the Jiang--Su algebra. This gives a new…

Operator Algebras · Mathematics 2023-12-25 José R. Carrión , James Gabe , Christopher Schafhauser , Aaron Tikuisis , Stuart White

If A is a C*-algebra, G a locally compact group, K{\subset}G a compact subgroup and {\alpha}:G{\to}Aut(A) a continuous homomorphism, let Ax_{{\alpha}}G denote the crossed product. In this paper we prove that Ax_{{\alpha}}G is nuclear…

Operator Algebras · Mathematics 2019-08-07 Raluca Dumitru , Costel Peligrad