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We extend a theorem of Haagerup and Kraus in the C*-algebra context: for a locally compact group with the approximation property (AP), the reduced C*-crossed product construction preserves the strong operator approximation property (SOAP).…

Operator Algebras · Mathematics 2021-01-26 Yuhei Suzuki

We first give simplified and corrected accounts of some results in \cite{PiRCP} on compactifications of pseudofinite groups. For instance, we use a classical theorem of Turing \cite{Turing} to give a simplified proof that any definable…

Logic · Mathematics 2025-06-18 Gabriel Conant , Ehud Hrushovski , Anand Pillay

In this work we introduce and study a new notion of amenability for actions of locally compact groups on $C^*$-algebras. Our definition extends the definition of amenability for actions of discrete groups due to Claire…

Operator Algebras · Mathematics 2022-05-04 Alcides Buss , Siegfried Echterhoff , Rufus Willett

For locally compact groups amenability and Kazhdan's property (T) are mutually exclusive in the sense that a group having both properties is compact. This is no longer true for more general Polish groups. However, a weaker result still…

Group Theory · Mathematics 2021-02-18 Vladimir G. Pestov

We investigate the fundamental concept of a closed quantum subgroup of a locally compact quantum group. Two definitions - one due to S.Vaes and one due to S.L.Woronowicz - are analyzed and relations between them discussed. Among many…

Operator Algebras · Mathematics 2013-01-09 Matthew Daws , Paweł Kasprzak , Adam Skalski , Piotr M. Sołtan

Let G be a locally compact group, and let A(G) and B(G) denote its Fourier and Fourier-Stieltjes algebras. These algebras are dual objects of the group and measure algebras, L^1(G) and M(G), in a sense which generalizes the Pontryagin…

Functional Analysis · Mathematics 2010-07-28 Nico Spronk

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

Let Gamma be a discrete group satisfying the rapid decay property with respect to a length function which is conditionally negative. Then the reduced C*-algebra of Gamma has the metric approximation property. The central point of our proof…

Group Theory · Mathematics 2016-09-07 Jacek Brodzki , Graham Niblo

We introduce notions of finite presentation and co-exactness which serve as qualitative and quantitative analogues of finite-dimensionality for operator modules over completely contractive Banach algebras. With these notions we begin the…

Operator Algebras · Mathematics 2021-04-12 Jason Crann

We study stability properties of amenable locally compact quantum groups under the bicrossed product construction. We obtain as our main result an equivalence between amenability of the bicrossed product and amenability of the matched…

Quantum Algebra · Mathematics 2007-05-23 P. Desmedt , J. Quaegebeur , S. Vaes

We give a definition of an amenable fusion module over a fusion algebra. A notion of relative integrability for the `coduals' of coideals of compact quantum groups was recently introduced in the joint work of de Commer and Dzokou Talla. We…

Quantum Algebra · Mathematics 2023-11-21 Benjamin Anderson-Sackaney , Leonid Vainerman

This paper concerns the study of regular Fourier hypergroups through multipliers of their associated Fourier algebras. We establish hypergroup analogues of well-known characterizations of group amenability, introduce a notion of weak…

Functional Analysis · Mathematics 2016-06-21 Mahmood Alaghmandan , Jason Crann

The following paper is devoted to the study of type I locally compact quantum groups. We show how various operators related to the modular theory of the Haar integrals on $\mathbb{G}$ and $\widehat{\mathbb{G}}$ act on the level of direct…

Quantum Algebra · Mathematics 2020-08-06 Jacek Krajczok

We continue our study of the concepts of amenability and co-amenability for algebraic quantum groups in the sense of A. Van Daele and our investigation of their relationship with nuclearity and injectivity. One major tool for our analysis…

Operator Algebras · Mathematics 2007-05-23 E. Bedos , G. J. Murphy , L. Tuset

We introduce a new combinatorial condition that characterises the amenability for locally compact groups. Our condition is weaker than the well-known F{\o}lner's conditions, and so is potentially useful as a criteria to show the amenability…

Functional Analysis · Mathematics 2023-10-31 Hung Pham

A version of group cohomology for locally compact groups and Polish modules has previously been developed using a bar resolution restricted to measurable cochains. That theory was shown to enjoy analogs of most of the standard algebraic…

Group Theory · Mathematics 2012-11-27 Tim Austin , Calvin C. Moore

Let $1 < p < \infty$. It is shown that if $G$ is a discrete group with the approximation property introduced by Haagerup and Kraus, then the non-commutative $L_p(VN(G))$ space has the operator space approximation property. If, in addition,…

Operator Algebras · Mathematics 2007-05-23 M. Junge , Z. -J. Ruan

We introduce the Property of Rapid Decay for discrete quantum groups by equivalent characterizations that generalize the classical ones. We then investigate examples, proving in particular the Property of Rapid Decay for unimodular free…

Operator Algebras · Mathematics 2020-06-04 Roland Vergnioux

We prove that weak amenability of a locally compact group imposes a strong condition on its amenable closed normal subgroups. This extends non weak amenability results of Haagerup (1988) and Ozawa--Popa (2010). A von Neumann algebra…

Operator Algebras · Mathematics 2015-01-14 Narutaka Ozawa

We establish two conditions equivalent to coamenability for type I locally compact quantum groups. The first condition is concerned with the spectra of certain convolution operators on the space…

Operator Algebras · Mathematics 2020-02-12 Jacek Krajczok