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In this paper we study the nuclearity and weak containment property of reduced cross-sectional C*-algebras of Fell bundles over inverse semigroups. In order to develop the theory, we first prove an analogue of Fell's absorption trick in the…

Operator Algebras · Mathematics 2023-08-10 Alcides Buss , Diego Martínez

We introduce a natural concept of positive definiteness for bundle maps between Fell bundles over (possibly different) discrete groups and describe several examples. Such maps induce completely positive maps between the associated full…

Operator Algebras · Mathematics 2025-07-03 Erik Bédos , Roberto Conti

We show that every Fell bundle B over a locally compact group G is "proper" in a sense recently introduced by Ng. Combining our results with those of Ng we show that if B satisfies the "approximation property" then it is amenable in the…

Operator Algebras · Mathematics 2007-05-23 Ruy Exel

Building on previous papers by Anantharaman-Delaroche (AD) we introduce and study the notion of AD-amenability for partial actions and Fell bundles over discrete groups. We prove that the cross-sectional C*-algebra of a Fell bundle is…

Operator Algebras · Mathematics 2021-08-12 Fernando Abadie , Alcides Buss , Damián Ferraro

We investigate amenability for $W^*$-Fell bundles over a discrete group $G$, with a focus on its characterization via approximation properties and conditional expectations. Building on the notion of $W^*$-amenability, we construct an…

Operator Algebras · Mathematics 2025-12-19 Alcides Buss , Damián Ferraro

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

We extend the theory of tensor products of C*-algebras to the larger category of Fell bundles over locally compact groups. We prove that, like in the case of C*-algebras, there exist maximal and minimal tensor products. Given two Fell…

funct-an · Mathematics 2024-12-12 Fernando Abadie

We prove that the reduced cross-sectional algebra of a Fell bundle with the approximation property over an inverse semigroup is exact if and only if the unit fiber of the Fell bundle is exact. This generalizes a recent result of the…

Operator Algebras · Mathematics 2026-05-21 Changyuan Gao , Julian Kranz

We prove that a locally compact group has the approximation property (AP), introduced by Haagerup-Kraus, if and only if a non-commutative Fej\'{e}r theorem holds for the associated $C^*$- or von Neumann crossed products. As applications, we…

Operator Algebras · Mathematics 2020-09-15 Jason Crann , Matthias Neufang

In this paper we study amenability, nuclearity and tensor products of $C^{\ast}$-Fell bundles by the method of induced representation theory.

Operator Algebras · Mathematics 2020-04-09 Weijiao He

We show that if $p:\B\to G$ is a Fell bundle over a locally compact groupoid $G$ and that $A=\Gamma_{0}(G^{(0)};\B)$ is the \cs-algebra sitting over $G^{(0)}$, then there is a continuous $G$-action on $\Prim A$ that reduces to the usual…

Operator Algebras · Mathematics 2009-12-08 Marius Ionescu , Dana P. Williams

We study Fell bundles on groupoids from the viewpoint of quantale theory. Given any saturated upper semicontinuous Fell bundle $\pi:E\to G$ on an \'etale groupoid $G$ with $G_0$ locally compact Hausdorff, equipped with a suitable completion…

Operator Algebras · Mathematics 2017-12-11 Pedro Resende

Given a Fell bundle $\B$, over a discrete group $\Gamma$, we construct its reduced cross sectional algebra $C^*_r(\B)$, in analogy with the reduced crossed products defined for C*-dynamical systems. When the reduced and full cross sectional…

funct-an · Mathematics 2008-02-03 Ruy Exel

We prove that if A and B are Fell bundles over the locally compact groups G and H respectively, then the minimal (maximal) tensor product of the C*-algebra of kernels of A with the C*-algebra of kernels of B agrees with the C*-algebra of…

Operator Algebras · Mathematics 2024-12-18 Fernando Abadie

We establish several new characterizations of amenable $W^*$- and $C^*$-dynamical systems over arbitrary locally compact groups. In the $W^*$-setting we show that amenability is equivalent to (1) a Reiter property and (2) the existence of a…

Operator Algebras · Mathematics 2020-08-25 Alex Bearden , Jason Crann

We introduce notions of weak and strong equivalence for non-saturated Fell bundles over locally compact groups and show that every Fell bundle is strongly (resp. weakly) equivalent to a semidirect product Fell bundle for a partial (resp.…

Operator Algebras · Mathematics 2021-08-12 Fernando Abadie , Alcides Buss , Damián Ferraro

A topological group $G$ has the Approximate Fixed Point (AFP) property on a bounded convex subset $C$ of a locally convex space if every continuous affine action of $G$ on $C$ admits a net $(x_i)$, $x_i\in C$, such that…

Group Theory · Mathematics 2021-02-18 Cleon S. Barroso , Brice R. Mbombo , Vladimir G. Pestov

We study the $C^*$-algebras associated to upper-semicontinuous Fell bundles over second-countable Hausdorff groupoids. Based on ideas going back to the Packer--Raeburn "Stabilization Trick," we construct from each such bundle a groupoid…

Operator Algebras · Mathematics 2016-05-23 Marius Ionescu , Alex Kumjian , Aidan Sims , Dana P. Williams

Let $\mathbb{G}$ be a locally compact quantum group, and $A,B$ von Neumann algebras on which $\mathbb{G}$ acts. We refer to these as $\mathbb{G}$-dynamical W$^*$-algebras. We make a study of $\mathbb{G}$-equivariant $A$-$B$-correspondences,…

Operator Algebras · Mathematics 2024-09-19 K. De Commer , J. De Ro

We define possibly unsaturated, upper semicontinuous Fell bundles over Hausdorff, locally compact groupoids and establish a universal property for representations of their full section C*-algebras on Hilbert modules over arbitrary…

Operator Algebras · Mathematics 2026-04-07 Alcides Buss , Rohit Holkar , Ralf Meyer
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