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We construct a simple C*-algebra with nuclear dimension zero that is not isomorphic to its tensor product with the Jiang-Su algebra Z, and a hyperfinite II_1 factor not isomorphic to its tensor product with the separable hyperfinite II_1…

Operator Algebras · Mathematics 2016-01-11 Ilijas Farah , Dan Hathaway , Takeshi Katsura , Aaron Tikuisis

We present the first examples of higher-rank lattices whose reduced $C^{*}$-algebras satisfy strict comparison, stable rank one, selflessness, uniqueness of embeddings of the Jiang--Su algebra, and allow explicit computations of the Cuntz…

Operator Algebras · Mathematics 2025-10-07 Itamar Vigdorovich

We give an example of an exact, stably finite, simple. separable C*-algebra D which is not isomorphic to its opposite algebra. Moreover, D has the following additional properties. It is stably finite, approximately divisible, has real rank…

Operator Algebras · Mathematics 2014-01-22 N. Christopher Phillips , Maria Grazia Viola

The cone of lower semicontinuous traces is studied with a view to its use as an invariant. Its properties include compactness, Hausdorffness, and continuity with respect to inductive limits. A suitable notion of dual cone is given. The cone…

Operator Algebras · Mathematics 2009-01-21 George A. Elliott , Leonel Robert , Luis Santiago

We present a stable uniqueness theorem for non-unital C*-algebras. Generalized tracial rank one is defined for stably projectionless simple C*-algebras. Let $A$ and $B$ be two stably projectionless separable simple amenable C*-algebras with…

Operator Algebras · Mathematics 2017-02-28 Guihua Gong , Huaxin Lin

We consider three notions of divisibility in the Cuntz semigroup of a C*-algebra, and show how they reflect properties of the C*-algebra. We develop methods to construct (simple and non-simple) C*-algebras with specific divisibility…

Operator Algebras · Mathematics 2014-02-26 Leonel Robert , Mikael Rordam

For a C$^*$-algebra $A$, it is an important problem to determine the Cuntz semigroup $\mathrm{Cu}(A\otimes\mathcal{Z})$ in terms of $\mathrm{Cu}(A)$. We approach this problem from the point of view of semigroup tensor products in the…

Operator Algebras · Mathematics 2016-10-20 Ramon Antoine , Francesc Perera , Henning Petzka

We study semiprojective, subhomogeneous C*-algebras and give a detailed description of their structure. In particular, we find two characterizations of semiprojectivity for subhomogeneous C*-algebras: one in terms of their primitive ideal…

Operator Algebras · Mathematics 2017-01-03 Dominic Enders

It is shown that if a C*-algebra has nuclear dimension $n$ then its Cuntz semigroup has the property of $n$-comparison. It then follows from results by Ortega, Perera, and Rordam that $\sigma$-unital C*-algebras of finite nuclear dimension…

Operator Algebras · Mathematics 2010-03-09 Leonel Robert

We define and study large and stably large subalgebras of simple unital C*-algebras. The basic example is the orbit breaking subalgebra of a crossed product by Z, as follows. Let X be an infinite compact metric space, let h be a minimal…

Operator Algebras · Mathematics 2014-08-26 N. Christopher Phillips

We introduce stabilised property Gamma, a C*-algebraic variant of property Gamma which is invariant under stable isomorphism. We then show that simple separable nuclear C*-algebras with stabilised property Gamma and $\mathrm{Cu}(A) \cong…

Operator Algebras · Mathematics 2021-02-02 Jorge Castillejos , Samuel Evington

We prove that the category of abstract Cuntz semigroups is bicomplete. As a consequence, the category admits products and ultraproducts. We further show that the scaled Cuntz semigroup of the (ultra)product of a family of C*-algebras agrees…

Operator Algebras · Mathematics 2020-05-27 Ramon Antoine , Francesc Perera , Hannes Thiel

In this paper we analyse the structure of the Cuntz semigroup of certain $C(X)$-algebras, for compact spaces of low dimension, that have no $\mathrm{K}_1$-obstruction in their fibres in a strong sense. The techniques developed yield…

Operator Algebras · Mathematics 2011-01-26 Ramon Antoine , Francesc Perera , Luis Santiago

Let Z denote the simple limit of prime dimension drop algebras that has a unique tracial state. Let A != 0 be a unital C^*-algebra with A = A tensor Z. Then the homotopy groups of the group U(A) of unitaries in A are stable invariants,…

Operator Algebras · Mathematics 2009-09-25 Xinhui Jiang

A group may be considered $C^*$-stable if almost representations of the group in a $C^*$-algebra are always close to actual representations. We initiate a systematic study of which discrete groups are $C^*$-stable or only stable with…

Operator Algebras · Mathematics 2021-04-21 Søren Eilers , Tatiana Shulman , Adam P. W. Sørensen

We introduce the notion of locally finite decomposition rank, a structural property shared by many stably finite nuclear C*-algebras. The concept is particularly relevant for Elliott's program to classify nuclear C*-algebras by K-theory…

Operator Algebras · Mathematics 2007-05-23 Wilhelm Winter

The Cuntz semigroup of a C*-algebra is an important invariant in the structure and classification theory of C*-algebras. It captures more information than K-theory but is often more delicate to handle. We systematically study the lattice…

Operator Algebras · Mathematics 2019-04-26 Ramon Antoine , Francesc Perera , Hannes Thiel

In this paper we study structural properties of the Cuntz semigroup and its functionals for continuous fields of C*-algebras over finite dimensional spaces. In a variety of cases, this leads to an answer to a conjecture posed by Blackadar…

Operator Algebras · Mathematics 2013-06-07 Ramon Antoine , Joan Bosa , Francesc Perera , Henning Petzka

We study C*-algebras associated with subsemigroups of groups. For a large class of such semigroups including positive cones in quasi-lattice ordered groups and left Ore semigroups, we describe the corresponding semigroup C*-algebras as…

Operator Algebras · Mathematics 2012-05-14 Xin Li

I give an overview of recent developments in the structure and classification theory of separable, simple, nuclear C*-algebras. I will in particular focus on the role of quasidiagonality and amenability for classification, and on the…

Operator Algebras · Mathematics 2017-12-04 Wilhelm Winter