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We prove several results on the permanence of weak amenability and the Haagerup property for discrete quantum groups. In particular, we improve known facts on free products by allowing amalgamation over a finite quantum subgroup. We also…

Operator Algebras · Mathematics 2014-11-18 Amaury Freslon

We investigate recent uniqueness theorems for reduced $C^*$-algebras of Hausdorff \'{e}tale groupoids in the context of inverse semigroups. In many cases the distinguished subalgebra is closely related to the structure of the inverse…

Operator Algebras · Mathematics 2016-11-11 Scott M. LaLonde , David Milan

We introduce two notions of amenability for a Banach algebra $\cal A$. Let $I$ be a closed two-sided ideal in $\cal A$, we say $\cal A$ is $I$-weakly amenable if the first cohomology group of $\cal A$ with coefficients in the dual space…

Functional Analysis · Mathematics 2007-05-23 M E Gorgi , T Yazdanpanah

In this paper, we introduce actions of fusion algebras on unital $C^*$-algebras, and define amenability for fusion algebraic actions. Motivated by S.\ Neshveyev et al.'s work, considering the co-representation ring of a compact quantum…

Operator Algebras · Mathematics 2021-08-24 Xiao Chen , Debashish Goswami , Huichi Huang

We describe conditions that characterize amenability for groups in terms of positive definite functions valued in a von Neumann algebra.

Operator Algebras · Mathematics 2022-02-02 Mikaël Pichot , Erik Séguin

The notions of module pseudo-amenable and module pseudo-contractible Banach algebras are introduced. For a Banach algebra with bounded approximate identity, module pseudo-amenability and module approximate amenability are the same…

Functional Analysis · Mathematics 2015-06-10 Abasalt Bodaghi , Ali Jabbari

We introduce the notion of integrable modules over $\imath$quantum groups (a.k.a. quantum symmetric pair coideal subalgebras). After determining a presentation of such modules, we prove that each integrable module over a quantum group is…

Quantum Algebra · Mathematics 2026-01-14 Hideya Watanabe

We introduce two notions of amenability for a Banach algebra $\cal A$. Let $n\in \Bbb N$ and let $I$ be a closed two-sided ideal in $\cal A$, $\cal A$ is $n-I-$weakly amenable if the first cohomology group of $\cal A$ with coefficients in…

Functional Analysis · Mathematics 2007-05-23 M. Eshaghi Gordji , R. Memarbashi

Building on a construction of J-P. Serre, we associate to any graph of C*-algebras a maximal and a reduced fundamental C*-algebra and use this theory to construct the fundamental quantum group of a graph of discrete quantum groups. This…

Operator Algebras · Mathematics 2013-07-23 Pierre Fima , Amaury Freslon

In this paper we extend the approach of M. Cavaleri to effective amenability to the class of computably enumerable groups, i.e. in particular we do not assume that groups are finitely generated. In the case of computable groups we also…

Group Theory · Mathematics 2022-05-16 Karol Duda

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 prove that amenability of a discrete group is equivalent to dimension flatness of certain ring inclusions naturally associated with measure preserving actions of the group. This provides a group-measure space theoretic solution to a…

Group Theory · Mathematics 2013-05-16 David Kyed , Henrik Densing Petersen

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

In this article we analyze the notions of amenability and paradoxical decomposition from an algebraic perspective. We consider this dichotomy for locally finite extended metric spaces and for general algebras over commutative fields. In the…

Rings and Algebras · Mathematics 2018-08-08 Pere Ara , Kang Li , Fernando Lledó , Jianchao Wu

We prove that the following are equivalent for a locally compact group $G$: (i) $G$ is amenable; (ii) $M(G)$ is Connes-amenable; (iii) $M(G)$ has a normal, virtual diagonal.

Functional Analysis · Mathematics 2016-09-07 Volker Runde

In the present paper, the concepts of module (uniform) approximate amenability and contractibility of Banach algebras that are modules over another Banach algebra, are introduced. The general theory is developed and some hereditary…

Functional Analysis · Mathematics 2013-01-16 Hasan Pourmahmood-Aghababa , Abasalt Bodaghi

In this paper, we study the hereditary properties of module $(\phi,\varphi)$-amenability on Banach algebras. We also define the concept of module character contractibility for Banach algebras and obtain characterizations of module character…

Functional Analysis · Mathematics 2015-06-17 Abasalt Bodaghi , Hamzeh Ebrahimi , Mahmood Lashkarizadeh Bami

We introduce the notions of approximate Connes-amenability and approximate strong Connes-amenability for dual Banach algebras. Then we characterize these two types of algebras in terms of approximate normal virtual diagonals and approximate…

Functional Analysis · Mathematics 2011-01-25 G. H. Esslamzadeh , B. Shojaee

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

In this article, we establish the duality between the generalised Drinfeld double and generalised quantum codouble within the framework of modular or manageable (not necessarily regular) multiplicative unitaries, and discuss several…

Operator Algebras · Mathematics 2024-06-25 Sutanu Roy