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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

We give a number of examples of exotic actions of locally compact groups on separable nuclear C*-algebras. In particular, we give examples of the following: (1) Minimal effective actions of ${\mathbb{Z}}$ and $F_n$ on unital nonsimple prime…

Operator Algebras · Mathematics 2023-12-08 Eberhard Kirchberg , N. Christopher Phillips

Let $P \subset A$ be an inclusion of $\sigma$-unital C*-algebras with a finite index in the sense of Izumi. Then we introduce the Rokhlin property for a conditional expectation $E$ from $A$ onto $P$ and show that if $A$ is simple and…

Operator Algebras · Mathematics 2018-03-23 Hiroyuki Osaka , Tamotsu Teruya

We develop the concept of weak tracial Rokhlin property for finite group actions on simple (not necessarily unital) C*-algebras and study its properties systematically. In particular, we show that this property is stable under restriction…

Operator Algebras · Mathematics 2021-04-28 Marzieh Forough , Nasser Golestani

An action of a compact, in particular finite group on a C*-algebra is called properly outer if no automorphism of the group that is distinct from identity is implemented by a unitary element of the algebra of local multipliers of the…

Operator Algebras · Mathematics 2024-04-11 Costel Peligrad

We examine inclusions of $C^*$-algebras of the form $A^H \subseteq A \rtimes_{r} G$, where $G$ and $H$ are groups acting on a unital simple $C^*$-algebra $A$ by outer automorphisms and $H$ is finite. It follows from a theorem of Izumi that…

Operator Algebras · Mathematics 2021-11-22 Siegfried Echterhoff , Mikael Rørdam

We show an equivariant Kirchberg-Phillips-type absorption theorem for pointwise outer actions of discrete amenable groups on Kirchberg algebras with respect to natural model actions on the Cuntz algebras $\mathcal{O}_\infty$ and…

Operator Algebras · Mathematics 2018-10-04 Gabor Szabo

We review several known categorification procedures, and introduce a functorial categorification of group extensions with applications to non-abelian group cohomology. Categorification of acyclic models and of topological spaces are briefly…

Category Theory · Mathematics 2007-05-23 Lucian M. Ionescu

Continuous actions of topological groups on compact Hausdorff spaces $X$ are investigated which induce almost periodic functions in the corresponding commutative C*-algebra. The unique invariant mean on the group resulting from averaging…

Operator Algebras · Mathematics 2009-03-11 M. Frank , V. Manuilov , E. Troitsky

In this paper we will introduce the tracial Rokhlin property for an inclusion of separable simple unital C*-algebras $P \subset A$ with finite index in the sense of Watatani, and prove theorems of the following type. Suppose that $A$…

Operator Algebras · Mathematics 2014-05-01 Hiroyuki Osaka , Tamotsu Teruya

We introduce and study actions of Fell bundles over discrete groups on Hilbert bundles. Many examples of such actions are presented. We discuss the connection with positive definite bundle maps between Fell bundles, culminating in the…

Operator Algebras · Mathematics 2026-04-14 Erik Bédos , Roberto Conti

In this paper, we study partial actions of groups on $R$-algebras, where $R$ is a commutative ring. We describe the partial actions of groups on the indecomposable algebras with enveloping actions. Then we work on algebras that can be…

Rings and Algebras · Mathematics 2017-08-07 Wagner Cortes , Eduardo Marcos

We calssify actions of discrete abelian groups on some inclusions of von Neumann algebras, up to cocycle conjugacy. As an application, we classify actions of compact abelian groups on the inclusions of AFD factors of type II_1 with index…

Operator Algebras · Mathematics 2014-12-16 Koichi Shimada

We define and examine sequentially split $*$-homomorphisms between $\mathrm{C}^*$-algebras and $\mathrm{C}^*$-dynamical systems. For a $*$-homomorphism, the property of being sequentially split can be regarded as an approximate weakening of…

Operator Algebras · Mathematics 2018-01-12 Selçuk Barlak , Gábor Szabó

We begin the systematic model theoretic study of $\mathrm{C}^*$-algebras using the tools of continuous logic.

Logic · Mathematics 2018-04-17 I. Farah , B. Hart , M. Lupini , L. Robert , A. Tikuisis , A. Vignati , W. Winter

We survey some of the progress made recently in the classification of von Neumann algebras arising from countable groups and their measure preserving actions on probability spaces. We emphasize results which provide classes of…

Operator Algebras · Mathematics 2017-12-04 Adrian Ioana

We study a tracial notion of Z-absorption for simple, unital C*-algebras. We show that if A is a C*-algebra for which this property holds then A has almost unperforated Cuntz semigroup, and if in addition A is nuclear and separable we show…

Operator Algebras · Mathematics 2013-05-02 Ilan Hirshberg , Joav Orovitz

Human actions that do not conform to usual behavior are considered as anomalous and such actors are called anomalous entities. Detection of anomalous entities using visual data is a challenging problem in computer vision. This paper…

Computer Vision and Pattern Recognition · Computer Science 2021-03-10 Hamza Riaz , Muhammad Uzair , Habib Ullah

We introduce a categorical approach to classifying actions of C$^*$-tensor categories $\mathcal{C}$ on C$^*$-algebras up to cocycle conjugacy. We show that, in this category, inductive limits exist and there is a natural notion of…

Operator Algebras · Mathematics 2026-04-09 Sergio Girón Pacheco , Robert Neagu

We study Rokhlin dimension of Z^m-actions on simple separable stably finite nuclear C*-algebras. We prove that under suitable assumptions, a strongly outer Z^m-action has finite Rokhlin dimension. This extends the known result for…

Operator Algebras · Mathematics 2017-11-16 Hung-Chang Liao