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For a topological group $G$, amenability can be characterized by the amenability of the convolution Banach algebra $L^1(G)$. Here a Banach algebra $A$ is called amenable if every bounded derivation from $A$ into any dual--type…

Functional Analysis · Mathematics 2025-07-01 Hikaru Awazu

Let $K$ be a locally compact field of characteristic 0. Let $G$ be a linear algebraic group defined over $K$, acting algebraically on an algebraic variety $V$. We prove that the action of $G(K)$ (the group of $K$-rational points of $G$) on…

Dynamical Systems · Mathematics 2024-05-13 Alain J. Valette

Let $G$ be a second countable locally compact groupoid equipped with a Haar system $\lambda$.In this work, we introduce and develop the notion of amenability for continuous unitary representations of $G$, formulated in terms of Hilbert…

Operator Algebras · Mathematics 2026-02-13 K. N. Sridharan , N. Shravan Kumar

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

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

Amenable actions of locally compact groups on von Neumann algebras are investigated by exploiting the natural module structure of the crossed product over the Fourier algebra of the acting group. The resulting characterisation of…

Operator Algebras · Mathematics 2021-01-20 Andrew McKee , Reyhaneh Pourshahami

We establish that a second countable locally compact groupoid possessing a continuous Haar system is topologically amenable if and only if it is Borel amenable. We give some examples and applications.

Dynamical Systems · Mathematics 2013-04-09 Jean Renault

We show that an amenable Invariant Random Subgroup of a locally compact second countable group lives in the amenable radical. This answers a question raised in the introduction of the paper "Kesten's Theorem for Invariant Random Subgroup"…

Group Theory · Mathematics 2021-02-03 Uri Bader , Bruno Duchesne , Jean Lecureux

Let G be a locally compact topological group and X a compact space with continuous G-action. The main result of this essay states that the following statements are equivalent : 1) The action of G on X is topologically amenable ; 2) Every…

Group Theory · Mathematics 2011-03-15 Terra Antonio

We define and study notions of amenability and skew-amenability of continuous actions of topological groups on compact topological spaces. Our main motivation is the question under what conditions amenability of a topological group passes…

Group Theory · Mathematics 2025-10-27 Vadim Alekseev , Hiroshi Ando , Friedrich Martin Schneider , Andreas Thom

After a short introduction to the general notion of Borel fields of metric spaces we introduce the notion of the action of an equivalence relation on such fields. Then, we specify the study to the Borel fields of proper CAT(0) spaces and we…

Group Theory · Mathematics 2019-02-20 Martin Anderegg , Philippe P. A. Henry

We investigate the notion of relatively amenable topological action and show that the action of Thompson's group $T$ on $S^1$ is relatively amenable with respect to Thompson's group $F$. We use this to conclude that $F$ is exact if and only…

Group Theory · Mathematics 2021-09-28 Eduardo Scarparo

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

We say that an action of a countable discrete inverse semigroup on a locally compact Hausdorff space is amenable if its groupoid of germs is amenable in the sense of Anantharaman-Delaroche and Renault. We then show that for a given inverse…

Operator Algebras · Mathematics 2015-10-14 Ruy Exel , Charles Starling

We study amenability of definable and topological groups. Among our main technical tools is an elaboration on and strengthening of the Massicot-Wagner version of the stabilizer theorem, and some results around measures. As an application we…

Logic · Mathematics 2021-11-23 Ehud Hrushovski , Krzysztof Krupiński , Anand Pillay

A topological group $G$ is called extremely amenable if every continuous action of $G$ on a compact space has a fixed point. This concept is linked with geometry of high dimensions (concentration of measure). We show that a von Neumann…

Operator Algebras · Mathematics 2007-09-03 Thierry Giordano , Vladimir Pestov

The notion of an action of a locally compact quantum group on a von Neumann algebra is studied from the amenability point of view. Various Reiter's conditions for such an action are discussed. Several applications to some specific actions…

Operator Algebras · Mathematics 2009-06-30 M. Ramezanpour , H. R. Ebrahimi Vishki

Generalizing Block and Weinberger's characterization of amenability we introduce the notion of uniformly finite homology for a group action on a compact space and use it to give a homological characterization of topological amenability for…

Group Theory · Mathematics 2010-12-14 Jacek Brodzki , Graham A. Niblo , Piotr Nowak , Nick J. Wright

We prove that a partial action is amenable if and only if so is its Morita enveloping action. As applications we prove that any partial representation of a discrete group is positive definite, and we extend a result of Zeller-Meier…

Operator Algebras · Mathematics 2009-06-09 Fernando Abadie , Laura Martí Pérez

As is well known, the equivalence between amenability of a locally compact group $G$ and injectivity of its von Neumann algebra $\mathcal{L}(G)$ does not hold in general beyond inner amenable groups. In this paper, we show that the…

Operator Algebras · Mathematics 2014-11-04 Jason Crann , Matthias Neufang
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