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In [5] the author conjectures and partially shows that the Cuntz semigroup classifies unitary elements of unital AF-algebras. We provide a complete proof by addressing the existence part of the conjecture, under a mild adjustment of both…

Operator Algebras · Mathematics 2025-03-04 Laurent Cantier

We prove that a number of classes of separable unital C*-algebras are closed under crossed products by finite group actions with the Rokhlin property, including: (1) AI algebras, AT algebras, and related classes characterized by direct…

Operator Algebras · Mathematics 2009-02-06 Hiroyuki Osaka , N. Christopher Phillips

Let $A$ be a unital simple $A\T$-algebra of real rank zero. Given an isomorphism $\gamma_1: K_1(A)\to K_1(A),$ we show that there is an automorphism $\af: A\to A$ such that $\af_{*1}=\gamma_1$ which has the tracial Rokhlin property.…

Operator Algebras · Mathematics 2007-05-23 Huaxin Lin , Hiroyuki Osaka

Let A be a unital simple separable C*-algebra with strict comparison of positive elements. We prove that the Cuntz semigroup of A is recovered functorially from the Murray-von Neumann semigroup and the tracial state space T(A) whenever the…

Operator Algebras · Mathematics 2009-12-04 Marius Dadarlat , Andrew S. Toms

Cuntz algebras $\mathcal{O}_n$, $n>1$, are celebrated examples of a separable infinite simple C*-algebra with a number of fascinating properties. Their K-theory allows an embedding of $\mathcal O_m$ in $\mathcal O_n$ whenever $n-1$ divides…

Operator Algebras · Mathematics 2025-02-21 Piotr M. Hajac , Yang Liu

Given a separable, AF-algebra A and an inductive limit action on A of a finitely generated abelian group with finite Rokhlin dimension with commuting towers, we give a local description of the associated crossed product C*-algebra. In…

Operator Algebras · Mathematics 2026-02-13 Sureshkumar M , Prahlad Vaidyanathan

The Calkin algebra is not isomorphic to the corona of the stabilization of the Cuntz algebra~${\mathcal O}_\infty$, any other Kirchberg algebra, or even the corona of the stabilization of any unital, ${\mathcal Z}$-stable ${\mathrm…

Operator Algebras · Mathematics 2023-10-02 Ilijas Farah

We show that there exists a purely infinite AH-algebra. The AH-algebra arises as an inductive limit of C*-algebras of the form C_0([0,1),M_k) and it absorbs the Cuntz algebra O_\infty tensorially. Thus one can reach an O_\infty-absorbing…

Operator Algebras · Mathematics 2010-11-24 Mikael Rordam

We examine crossed product C*-algebras associated with non-minimal free actions of countably infinite discrete abelian groups on the circle, extending the work of Putnam, Schmidt, and Skau. We obtain a large class of unital separable…

Operator Algebras · Mathematics 2026-04-21 Jamie Bell

We give an example of a simple separable C*-algebra which is not isomorphic to its opposite algebra. Our example is nonnuclear and stably finite, has real rank zero and stable rank one, and has a unique tracial state. It has trivial K_1,…

Operator Algebras · Mathematics 2007-05-23 N. Christopher Phillips

Let X be a path connected, compact metric space and let A be a unital separable simple nuclear Z-stable real rank zero C*-algebra. We classify all the unital *-embeddings (up to approximate unitary equivalence) of C(X) into A. Specifically,…

Operator Algebras · Mathematics 2007-09-11 P. W. Ng , Wilhelm Winter

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

We show that it is consistent with ZFC that there is a simple nuclear non-separable C*-algebra which is not isomorphic to its opposite algebra. We can furthermore guarantee that this example is an inductive limit of unital copies of the…

Operator Algebras · Mathematics 2022-06-08 Ilijas Farah , Ilan Hirshberg

This paper explores the following regularity properties and their relationships for simple, not-necessarily-unital C*-algebras: (i) Jiang-Su stability, (ii) Unperforation in the Cuntz semigroup, and (iii) slow dimension growth (applying…

Operator Algebras · Mathematics 2012-07-18 Aaron Tikuisis

Using Cuntz semigroup techniques, we characterize when limit traces are dense in the space of all traces on a free ultrapower of a C*-algebra. More generally, we consider density of limit quasitraces on ultraproducts of C*-algebras. Quite…

Operator Algebras · Mathematics 2023-03-14 Ramon Antoine , Francesc Perera , Leonel Robert , Hannes Thiel

We introduce the notion of the partial group algebra with projections and relations and show that this C*-algebra is a partial crossed product. Examples of partial group algebras with projections and relations are the Cuntz-Krieger algebras…

Operator Algebras · Mathematics 2018-08-06 Danilo Royer

In a recent paper, Pardo and the first named author introduced a class of C*-algebras which which are constructed from an action of a group on a graph. This class was shown to include many C*-algebras of interest, including all Kirchberg…

Operator Algebras · Mathematics 2014-06-30 Ruy Exel , Charles Starling

Let $A$ be a unital separable simple \CA with $\tr(A)\le 1$ and $\alpha$ be an automorphism. We show that if $\alpha$ satisfies the tracially cyclic Rokhlin property then $\tr(A\rtimes_{\alpha}\Z)\le 1.$ We also show that whenever $A$ has a…

Operator Algebras · Mathematics 2007-05-23 Huaxin Lin , Hiroyuki Osaka

We study the class of pseudocompact C*-algebras, which are the logical limits of finite-dimensional C*-algebras. The pseudocompact C*-algebras are unital, stably finite, real rank zero, stable rank one, and tracial. We show that the…

Operator Algebras · Mathematics 2016-09-26 Stephen Hardy

We present a systematic study of the structure of crossed products and fixed point algebras by compact group actions with the Rokhlin property on not necessarily unital C*-algebras. Our main technical result is the existence of an…

Operator Algebras · Mathematics 2016-05-31 Eusebio Gardella