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We give an example of a unital C*-algebra $\mathbf{A}$ with a computable presentation and for which neither $K_0(\mathbf{A})$ nor $K_1(\mathbf{A})$ has a computable presentation.

Operator Algebras · Mathematics 2026-02-18 Christopher J. Eagle , Isaac Goldbring , Timothy H. McNicholl , Russell Miller

We construct an example of a simple approximately homogeneous C*-algebra such that its Elliott invariant admits an automorphism which is not induced by an automorphism of the algebra.

Operator Algebras · Mathematics 2023-06-07 Ilan Hirshberg , N. Christopher Phillips

We prove that the reduced C*-algebras of centerless mapping class groups and outer automorphism groups of free groups are simple, as are the irreducible pure subgroups of mapping class groups and the analogous subgroups of outer…

Operator Algebras · Mathematics 2007-05-23 Martin R. Bridson , Pierre de la Harpe

In this paper we consider shift operators, self-adjoint, unitary and normal operators on the standard module over a unital C*-algebra A. We define various generalized spectra in A of these operators, give description of such spectra of…

Operator Algebras · Mathematics 2020-07-13 Stefan Ivkovic

In order to realize all possible KMS-bundles on the Jiang-Su algebra, we introduce a class of C*-algebras which we call rationally approximately finite dimensional (RAF). Using these, we show that for a given proper simplex bundle $(S,…

Operator Algebras · Mathematics 2022-09-27 George A. Elliott , Yasuhiko Sato

We classify equivariant *-homomorphisms between C*-dynamical systems associated to actions of finite groups on C*-algebras with the Rokhlin property. In addition, the given actions are classified. An obstruction is obtained for the Cuntz…

Operator Algebras · Mathematics 2018-01-08 Eusebio Gardella , Luis Santiago

We study properties of C*-algebras obtained from the nonstandard hull construction (a generalization of the ultraproduct of C*-algebras). Among others, we prove that the properties of being an infinite and a properly infinite C*-algebra are…

Operator Algebras · Mathematics 2009-10-28 Stefano Baratella , Siu-Ah Ng

A C*-metric algebra consists of a unital C*-algebra and a Leibniz Lip-norm on the C*-algebra. We show that if the Lip-norms concerned are lower semicontinuous, then any unital *-homomorphism from a C*-metric algebra to another one is…

Operator Algebras · Mathematics 2009-01-23 Wei Wu

We prove that the pure state space is homogeneous under the action of the automorphism group (or a certain smaller group of approximately inner automorphisms) for a fairly large class of simple separable nuclear C*-algebras, including the…

Operator Algebras · Mathematics 2007-05-23 H. Futamura , N. Kataoka , A. Kishimoto

We classify isomorphism types of unital commutative algebras of rank 7 over an algebraically closed field of characteristic not 2 or 3 completely.

Commutative Algebra · Mathematics 2021-07-13 Naoto Onda

Let $\mathfrak{A}$ and $\mathfrak{A}'$ be two $C^*$-algebras with identities $I_{\mathfrak{A}}$ and $I_{\mathfrak{A}'}$, respectively, and $P_1$ and $P_2 = I_{\mathfrak{A}} - P_1$ nontrivial symmetric projections in $\mathfrak{A}$. In this…

We consider various lifting problems for C*-algebras. As an application of our results we show that any commuting family of order zero maps from matrices to a von Neumann central sequence algebra can be lifted to a commuting family of order…

Operator Algebras · Mathematics 2019-10-30 Don Hadwin , Tatiana Shulman

We classify $^*$-homomorphisms from nuclear $C^*$-algebras into uniform tracial sequence algebras of nuclear $\mathcal Z$-stable $C^*$-algebras via tracial data.

Operator Algebras · Mathematics 2023-07-13 Jorge Castillejos , Samuel Evington , Aaron Tikuisis , Stuart White

We investigate how a C*-algebra could consist of functions on a noncommutative set: a discretization of a C*-algebra $A$ is a $*$-homomorphism $A \to M$ that factors through the canonical inclusion $C(X) \subseteq \ell^\infty(X)$ when…

Operator Algebras · Mathematics 2017-02-16 Chris Heunen , Manuel L. Reyes

We characterize exotic C*-algebras of twisted, principal \'etale groupoids, together with the abelian subalgebra associated to the unit space, as precisely being the inclusions "$A\subseteq B$" of C*-algebras in which $A$ is abelian,…

Operator Algebras · Mathematics 2021-10-26 Ruy Exel

We study what we call topological cylindric algebras and tense cylindric algebras defined for every ordinal $\alpha$. The former are cylindric algebras of dimension $\alpha$ expanded with $\sf S4$ modalities indexed by $\alpha$. The…

Logic · Mathematics 2014-02-26 Tarek Sayed Ahmed

We describe the C*-algebras of the Heisenberg group H_n, n\geq 1, and the thread-like Lie group G_N, N\geq 3, in terms of C*-algebras of operator fields.

Operator Algebras · Mathematics 2009-04-23 Jean Ludwig , Lyudmila Turowska

We obtain two characterizations of the bi-inner Hopf *-automorphisms of a finite-dimensional Hopf C*-algebra, by means of an analysis of the structure of convolution products in this class of Hopf C*-algebra.

Operator Algebras · Mathematics 2014-06-11 Dan Z. Kučerovskyý

From a planar algebra, we give a functorial construction to produce numerous associated $C^*$-algebras. Our main construction is a Hilbert $C^*$-bimodule with a canonical real subspace which produces Pimsner-Toeplitz, Cuntz-Pimsner, and…

Operator Algebras · Mathematics 2014-01-14 Michael Hartglass , David Penneys

We define an ultragraph, which is a generalization of a directed graph, and describe how to associate a C*-algebra to it. We show that the class of ultragraph algebras contains the C*-algebras of graphs as well as the Exel-Laca algebras. We…

Operator Algebras · Mathematics 2007-05-23 Mark Tomforde