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We establish conditions under which the universal and reduced norms coincide for a Fell bundle over a groupoid. Specifically, we prove that the full and reduced C*-algebras of any Fell bundle over a measurewise amenable groupoid coincide,…

Operator Algebras · Mathematics 2012-01-05 Aidan Sims , Dana P. Williams

Motivated by the beautiful work of M. A. Rieffel (1965) and of M. E. Walter (1974), we obtain characterisations of the Fourier algebra $A(G)$ of a locally compact group $G$ in terms of the class of $F$-algebras (i.e. a Banach algebra $A$…

Functional Analysis · Mathematics 2015-11-24 Anthony To-Ming Lau , Hung Le Pham

Three natural definitions for amenability of general Hopf C^*-algebras (all of them being generalizations of the case of locally compact groups) were given and the relations between them were studied. Moreover, amenability in the situation…

Operator Algebras · Mathematics 2007-05-23 Chi-Keung Ng

We show that topological amenability of an action of a countable discrete group on a compact space is equivalent to the existence of an invariant mean for the action. We prove also that this is equivalent to vanishing of bounded cohomology…

Group Theory · Mathematics 2010-04-05 Jacek Brodzki , Graham A. Niblo , Piotr Nowak , Nick Wright

We study which von Neumann algebras can be embedded into uniform Roe algebras and quasi-local algebras associated to a uniformly locally finite metric space $X$. Under weak assumptions, these $\mathrm{C}^*$-algebras contain embedded copies…

Operator Algebras · Mathematics 2023-02-20 Florent P. Baudier , Bruno de Mendonça Braga , Ilijas Farah , Alessandro Vignati , Rufus Willett

We generalize Renault's notion of measurewise amenability to actions of second countable, Hausdorff, \'etale groupoids on separable $C^*$-algebras and show that measurewise amenability characterizes nuclearity of the crossed product…

Operator Algebras · Mathematics 2023-01-31 Julian Kranz

Let $\mathbf{G}$ be an algebraic group over a local field $\mathbf k$ of characteristic zero. We show that the locally compact group $\mathbf G(\mathbf k)$ consisting of the $\mathbf k$-rational points of $\mathbf G$ is of type I. Moreover,…

Representation Theory · Mathematics 2020-03-06 Bachir Bekka , Siegfried Echterhoff

Let E be a second-countable, locally compact, Hausdorff groupoid equipped with an action of T such that G:=E/T is a principal groupoid with Haar system \lambda. The twisted groupoid C*-algebra C*(E;G,\lambda) is a quotient of the C*-algebra…

Operator Algebras · Mathematics 2012-02-21 Lisa Orloff Clark , Astrid an Huef

Building on Lin's breakthrough MIP$^{co}$ = coRE and an encoding of non-local games as universal sentences in the language of tracial von Neumann algebras, we show that locally universal tracial von Neumann algebras have undecidable…

Operator Algebras · Mathematics 2026-04-07 Jananan Arulseelan , Aareyan Manzoor

A groupoid correspondence on an etale, locally compact groupoid induces a C*-correspondence on its groupoid C*-algebra. We show that the Cuntz-Pimsner algebra for this C*-correspondence relative to an ideal associated to an open invariant…

Operator Algebras · Mathematics 2026-05-20 Ralf Meyer

In the present paper we prove a duality theory for compact groups in the case when the C*-algebra A, the fixed point algebra of the corresponding Hilbert C*-system (F,G), has a nontrivial center Z and the relative commutant satisfies the…

Operator Algebras · Mathematics 2007-05-23 Hellmut Baumgärtel , Fernando Lledó

We compare finiteness properties of locally compact groups that generalize the properties of being compactly generated and of being compactly presented. Three such families of properties have been proposed: Abels--Tiemeyer's type $C_n$,…

Group Theory · Mathematics 2024-10-10 Dorian Chanfi , Stefan Witzel

Conformal inclusions of chiral conformal field theories, or more generally inclusions of quantum field theories, are described in the von Neumann algebraic setting by nets of subfactors, possibly with infinite Jones index if one takes…

Operator Algebras · Mathematics 2022-11-01 Marcel Bischoff , Simone Del Vecchio , Luca Giorgetti

We show that nuclear C*-algebras have a refined version of the completely positive approximation property, in which the maps that approximately factorize through finite dimensional algebras are convex combinations of order zero maps. We use…

Operator Algebras · Mathematics 2012-04-27 Ilan Hirshberg , Eberhard Kirchberg , Stuart White

We study strongly outer actions of discrete groups on C*-algebras in relation to (non)amenability. In contrast to related results for amenable groups, where uniqueness of strongly outer actions on the Jiang-Su algebra is expected, we show…

Operator Algebras · Mathematics 2018-03-19 Eusebio Gardella , Martino Lupini

We study class $\mathcal S$ for locally compact groups. We characterize locally compact groups in this class as groups having an amenable action on a boundary that is small at infinity, generalizing a theorem of Ozawa. Using this…

Operator Algebras · Mathematics 2019-04-29 Tobe Deprez

We present a contribution to the structure theory of locally compact groups. The emphasis is on compactly generated locally compact groups which admit no infinite discrete quotient. It is shown that such a group possesses a characteristic…

Group Theory · Mathematics 2012-07-10 Pierre-Emmanuel Caprace , Nicolas Monod

Recent results of Laca, Raeburn, Ramagge and Whittaker show that any self-similar action of a groupoid on a graph determines a 1-parameter family of self-mappings of the trace space of the groupoid C*-algebra. We investigate the fixed…

Operator Algebras · Mathematics 2018-11-07 Joan Claramunt , Aidan Sims

We study amenability of affine algebras (based on the notion of almost-invariant finite-dimensional subspace), and apply it to algebras associated with finitely generated groups. We show that a group G is amenable if and only if its group…

Group Theory · Mathematics 2009-11-27 Laurent Bartholdi

Tracial Rokhlin property was introduced by Chris Phillips to study the structure of crossed product of actions on simple C*-algebras. It was originally defined for actions of finite groups and group of integers. Matui and Sato generalized…

Operator Algebras · Mathematics 2016-08-16 Qingyun Wang
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