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We develop a relative boundary theory for actions of discrete groups on compact spaces and use it to derive rigidity results for reduced crossed products. For a discrete group $\Gamma$ acting on a compact space $X$ and a subgroup $H$, we…

Operator Algebras · Mathematics 2026-01-08 Tattwamasi Amrutam , Chunlin Liu

A discrete group $\Gamma$ is called exact if the reduced group C*-algebra ${C_{\lambda}}^{*}(\Gamma)$ is exact as C*-algebras, and a discrete group $\Lambda$ is called residually exact if every nonunital element $g \in \Lambda$ admits a…

Group Theory · Mathematics 2025-12-16 Hikaru Awazu

Let $R$ be a semilocal principal ideal domain. Two algebraic objects over $R$ in which scalar extension makes sense (e.g. quadratic spaces) are said to be of the same genus if they become isomorphic after extending scalars to all…

Rings and Algebras · Mathematics 2016-01-12 Eva Bayer-Fluckiger , Uriya A. First

Almost finiteness was introduced in the seminal work of Kerr as an dynamical analogue of Z-stability in the Toms-Winter conjecture. In this article, we provide the first examples of minimal, topologically free actions of amenable groups…

Dynamical Systems · Mathematics 2023-11-07 Matthieu Joseph

A relatively hyperbolic group $G$ is said to be QCERF if all finitely generated relatively quasiconvex subgroups are closed in the profinite topology on $G$. Assume that $G$ is a QCERF relatively hyperbolic group with double coset separable…

Group Theory · Mathematics 2025-04-02 Ashot Minasyan , Lawk Mineh

We analyze Hecke pairs (G,H) and the associated Hecke algebra when G is a semidirect product N x Q and H = M x R for subgroups M of N and R of Q with M normal in N. Conditions are given in terms of N, Q, M, and R which are equivalent to the…

Operator Algebras · Mathematics 2008-04-11 S. Kaliszewski , Magnus B. Landstad , John Quigg

In this paper, we consider an equivalence relation within the class of finitely presented discrete groups attending to their asymptotic topology rather than their asymptotic geometry. More precisely, we say that two finitely presented…

Geometric Topology · Mathematics 2020-02-05 M. Cárdenas , F. F. Lasheras , A. Quintero , R. Roy

We consider II$_1$ factors of the form $M=\bar{\bigotimes}_{G}N\rtimes G$, where either i) $N$ is a non-hyperfinite II$_1$ factor and $G$ is an ICC amenable group or ii) $N$ is a weakly rigid II$_1$ factor and $G$ is ICC group and where $G$…

Operator Algebras · Mathematics 2007-05-23 Adrian Ioana

Given two finitely generated groups that coarsely embed into a Hilbert space, it is known that their wreath product also embeds coarsely into a Hilbert space. We introduce a wreath product construction for general metric spaces X,Y,Z and…

Group Theory · Mathematics 2013-07-12 Chris Cave , Dennis Dreesen , Ana Khukhro

We prove the Farrell-Jones Conjecture for (non-connective) $A$-theory with coefficients and finite wreath products for hyperbolic groups, CAT(0)-groups, cocompact lattices in almost connected Lie groups and fundamental groups of manifolds…

Geometric Topology · Mathematics 2018-10-03 Nils-Edvin Enkelmann , Wolfgang Lück , Malte Pieper , Mark Ullmann , Christoph Winges

We generalize the notion of an approximate indicator for a closed subgroup $H$ of a locally compact group $G$ introduced by Aristov, Runde, and Spronk and extend their characterization of the existence of such nets in terms of the…

Functional Analysis · Mathematics 2015-06-10 Zsolt Tanko

We show that free products of sofic groups with amalgamation over monotileably amenable subgroups are sofic. Consequently, so are HNN extensions of sofic groups relative to homomorphisms of monotileably amenable subgroups. We also show that…

Group Theory · Mathematics 2012-02-15 Benoit Collins , Ken Dykema

We show that a wreath product of two finitely generated abelian groups is LERF. Consequently the free metabelian groups are LERF.

Group Theory · Mathematics 2007-05-23 Roger C. Alperin

We prove a new weak mean ergodic theorem (Theorem A) for 1-cocycles associated to weakly mixing representations of amenable groups. Let $G$ be a finitely generated, discrete, amenable group $G$ which admits a controlled Folner sequence. We…

Group Theory · Mathematics 2012-08-06 Ionut Chifan , Thomas Sinclair

We consider the class of finitely generated groups which have a normal form computable in logspace. We prove that the class of such groups is closed under finite extensions, finite index subgroups, direct products, wreath products, and also…

Group Theory · Mathematics 2014-01-28 Murray Elder , Gillian Elston , Gretchen Ostheimer

We show that an arithmetic function which satisfies some weak multiplicativity properties and in addition has a non-decreasing or $\log$-uniformly continuous normal order is close to a function of the form $n\mapsto n^c$. As an application…

Number Theory · Mathematics 2019-12-03 Jan-Christoph Schlage-Puchta

The group property FW stands in-between the celebrated Kazdhan's property (T) and Serre's property FA. Among many characterizations, it might be defined, for finitely generated groups, as having all Schreier graphs one-ended. It follows…

Group Theory · Mathematics 2024-03-20 Paul-Henry Leemann , Grégoire Schneeberger

We investigate subgroups of the group PLo(I) of piecewise-linear, orientation-preserving homeomorphisms of the unit interval with finitely many breaks in slope, under the operation of composition, and also subgroups of the generalized…

Group Theory · Mathematics 2014-02-26 Collin Bleak

We here consider inner amenability from a geometric and group theoretical perspective. We prove that for every non-elementary action of a group $G$ on a finite dimensional irreducible CAT(0) cube complex, there is a nonempty $G$-invariant…

Group Theory · Mathematics 2021-08-16 Bruno Duchesne , Robin Tucker-Drob , Phillip Wesolek

We study topological groups having all closed subgroups (totally) minimal and we call such groups c-(totally) minimal. We show that a locally compact c-minimal connected group is compact. Using a well-known theorem of Hall and Kulatilaka…

General Topology · Mathematics 2021-06-29 Wenfei Xi , Menachem Shlossberg