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We show that several new classes of groups are measure strongly treeable. In particular, finitely generated groups admitting planar Cayley graphs, elementarily free groups, and the group of isometries of the hyperbolic plane and all its…

Group Theory · Mathematics 2026-03-20 Clinton T. Conley , Damien Gaboriau , Andrew S. Marks , Robin D. Tucker-Drob

Given a compact oriented triangulated $3$-manifold we find a non-trivial condition satisfied by certain labelings of the tetrahedra by elements of an arbitrary abelian group which we call angle structures. Smoothness of the manifold is used…

Geometric Topology · Mathematics 2020-11-25 Anton Mellit

We establish sufficient conditions for the C$^*$-simplicity of two classes of groups. The first class is that of groups acting on trees, such as amalgamated free products, HNN-extensions, and their normal subgroups; for example normal…

Group Theory · Mathematics 2012-03-06 Pierre de la Harpe , Jean-Philippe Préaux

A subgroup of a group $G$ is called algebraic if it can be expressed as a finite union of solution sets to systems of equations. We prove that a non-elementary subgroup $H$ of an acylindrically hyperbolic group $G$ is algebraic if and only…

Group Theory · Mathematics 2017-02-07 Bryan Jacobson

This paper studies the locally uniform exponential growth and product set growth for a finitely generated group $G$ acting properly on a finite product of hyperbolic spaces. Under the assumption of coarsely dense orbits or shadowing…

Group Theory · Mathematics 2024-07-23 Renxing Wan , Wenyuan Yang

We study the automorphism groups of free-by-cyclic groups and show these are finitely generated in the following cases: (i) when defining automorphism has linear growth and (ii) when the rank of the underlying free group has rank at most 3.…

Group Theory · Mathematics 2022-11-10 Naomi Andrew , Armando Martino

Serre in "Trees" laid down the fundamentals of the theory of groups acting on simplicial trees. In particular, Bass-Serre theory makes it possible to extract information about the structure of a group from its action on a simplicial tree.…

Group Theory · Mathematics 2017-10-31 Olga Kharlampovich , Alina Vdovina

We give a complete characterization of the locally compact groups that are non-elementary Gromov-hyperbolic and amenable. They coincide with the class of mapping tori of discrete or continuous one-parameter groups of compacting…

Group Theory · Mathematics 2015-10-29 Pierre-Emmanuel Caprace , Yves de Cornulier , Nicolas Monod , Romain Tessera

We analyse the existence question for essential laminations in 3-manifolds. The purpose is to prove that there are infinitely many closed hyperbolic 3-manifolds which do not admit essential laminations. This answers in the negative a…

Geometric Topology · Mathematics 2007-05-23 Sergio R. Fenley

We study hyperbolic cohomology classes in the general context of simplicial complexes and prove homological invariance statements for them. We relate the existence of hyperbolic cohomology classes to the non-amenability of the fundamental…

Geometric Topology · Mathematics 2008-08-12 M. Brunnbauer , D. Kotschick

We exhibit a closed aspherical 5-manifold of nonpositive curvature that fibers over a circle whose fundamental group is hyperbolic relative to abelian subgroups such that the fiber is a closed aspherical 4-manifold whose fundamental group…

Geometric Topology · Mathematics 2021-06-17 Koji Fujiwara

In this paper, we show that, if a group $G$ acts geometrically on a geodesically complete CAT(0) space $X$ which contains at least one point with a CAT(-1) neighborhood, then $G$ must be either virtually cyclic or acylindrically hyperbolic.…

Group Theory · Mathematics 2018-11-20 Anthony Genevois , Arnaud Stocker

We present some partial results concerning a-T-menability of groups acting on trees. Various known results are given uniform proofs.

Group Theory · Mathematics 2010-03-15 Swiatoslaw R. Gal

This is a long introduction to the theory of "branch groups": groups acting on rooted trees which exhibit some self-similarity features in their lattice of subgroups.

Group Theory · Mathematics 2009-11-27 Laurent Bartholdi , Rostislav I. Grigorchuk , Zoran Sunik

Bass-Serre theory provides a powerful framework for studying group actions on trees. While extremely effective for structural questions in group theory, it is less suited to the systematic construction of group actions with prescribed local…

Group Theory · Mathematics 2026-04-02 Florian Lehner , Christian Lindorfer , Rögnvaldur G. Möller , Wolfgang Woess

We prove groups acting cocompactly on locally finite trees with hyperbolic vertex stabilisers are asynchronously automatic. Combining this with previous work of the authors, we obtain an example of a group satisfying several non-positive…

Group Theory · Mathematics 2025-08-01 Sam Hughes , Motiejus Valiunas

The question which motivates the article is the following: given a group acting on a CAT(0) cube complex, how can we prove that it is acylindrically hyperbolic? Keeping this goal in mind, we show a weak acylindricity of the action on the…

Group Theory · Mathematics 2019-08-26 Anthony Genevois

We present a new notion of non-positively curved groups: the collection of discrete countable groups acting (AU-)acylindrically on finite products of $\delta$-hyperbolic spaces with general type factors. Inspired by the classical theory of…

Group Theory · Mathematics 2025-12-30 Sahana Balasubramanya , Talia Fernos

We propose the study of Markov chains on groups as a "quasi-isometry invariant" theory that encompasses random walks. In particular, we focus on certain classes of groups acting on hyperbolic spaces including (non-elementary) hyperbolic and…

Group Theory · Mathematics 2022-11-24 Antoine Goldsborough , Alessandro Sisto

The goal of this article is to survey some recent developments in the study of groups acting on hyperbolic spaces. We focus on the class of acylindrically hyperbolic groups; it is broad enough to include many examples of interest, yet a…

Group Theory · Mathematics 2018-05-14 D. Osin