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We construct an uncountable sequence of groups acting uniformly properly on hyperbolic spaces. We show that only countably many of these groups can be virtually torsion-free. This gives new examples of groups acting uniformly properly on…

Group Theory · Mathematics 2020-07-29 Robert Kropholler , Vladimir Vankov

Let V(KG) be the normalized group of units of the group ring KG of a non-Dedekind group G with nontrivial torsion part t(G) over the integral domain K. We give a simple method for constructing free objects in V(KG).In particular, we show…

Group Theory · Mathematics 2014-11-27 Victor Bovdi

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

We give an algorithm for solving equations and inequations with rational constraints in virtually free groups. Our algorithm is based on Rips classification of measured band complexes. Using canonical representatives, we deduce an algorithm…

Group Theory · Mathematics 2020-07-20 François Dahmani , Vincent Guirardel

We extend discrete Morse-Bott theory to the setting of loop-free (or acyclic) categories. First of all, we state a homological version of Quillen's Theorem A in this context and introduce the notion of cellular categories. Second, we…

Algebraic Topology · Mathematics 2021-07-14 Michał Lipiński , David Mosquera-Lois , Mateusz Przybylski

Let $\Phi:F\rightarrow F$ be an automorphism of the finite-rank free group $F$. Suppose that $G=F\rtimes_\Phi\mathbb Z$ is word-hyperbolic. Then $G$ acts freely and cocompactly on a CAT(0) cube complex.

Group Theory · Mathematics 2016-05-27 Mark F. Hagen , Daniel T. Wise

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 present a new method for showing that groups are virtually special. This is done by considering finite quotients and linear characters. We use this to show that an infinite family of groups, related to Bestvina-Brady groups and…

Group Theory · Mathematics 2020-02-03 Vladimir Vankov

Let $G$ be a torsion-free hyperbolic group and $\alpha$ an automorphism of $G$. We show that there exists a canonical collection of subgroups that are polynomially growing under $\alpha$, and that the mapping torus of $G$ by $\alpha$ is…

Group Theory · Mathematics 2023-10-24 François Dahmani , Suraj Krishna M S

We prove that amongst the class of free-by-cyclic groups, Gromov hyperbolicity is an invariant of the profinite completion. We show that whenever $G$ is a free-by-cyclic group with first Betti number equal to one, and $H$ is a…

Group Theory · Mathematics 2026-03-03 Sam Hughes , Monika Kudlinska

We introduce the concept of cyclicity and hypercyclicity in self-similar groups as an analogue of cyclic and hypercyclic vectors for an operator on a Banach space. We derive a sufficient condition for cyclicity of non-finitary automorphisms…

Group Theory · Mathematics 2026-01-29 Jorge Fariña-Asategui

A finitely generated group is lacunary hyperbolic if one of its asymptotic cones is an $\mathbb{R}$-tree. In this article we give a necessary and sufficient condition on lacunary hyperbolic groups in order to be stable under free product by…

Group Theory · Mathematics 2020-02-21 Krishnendu Khan

A group $G$ is said to be equationally Noetherian if every system of equations in $G$ is equivalent to a finite subsystem. We show that all free-by-cyclic groups are equationally Noetherian. As a corollary, we deduce that the set of…

Group Theory · Mathematics 2025-12-04 Monika Kudlinska , Motiejus Valiunas

The study of word hyperbolic groups is a prominent topic in geometric group theory; however word hyperbolic groups are defined by a geometric condition which does not extend naturally to semigroups. We propose a linguistic definition.…

Group Theory · Mathematics 2007-05-23 Andrew Duncan , Robert H. Gilman

We prove that the first order theory of nonabelian free groups eliminates the "there exists infinitely many" quantifier (in eq). Equivalently, since the theory of nonabelian free groups is stable, it does not have the finite cover property.…

Logic · Mathematics 2017-06-08 Rizos Sklinos

Genevois recently classified which graph braid groups on $\ge 3$ strands are word hyperbolic. In the $3$-strand case, he asked whether all such word hyperbolic groups are actually free; this reduced to checking two infinite classes of…

Group Theory · Mathematics 2024-03-22 B. Appiah , P. Dani , W. Ge , C. Hudson , S. Jain , M. Lemoine , J. Murphy , J. Murray , A. Pandikkadan , K. Schreve , H. Vo

Gromov asked whether every one-ended word-hyperbolic group contains a hyperbolic surface group. We prove that every one-ended double of a free group has a hyperbolic surface subgroup if (1) the free group has rank two, or (2) every…

Group Theory · Mathematics 2015-01-05 Sang-hyun Kim , Sang-il Oum

We study groups having the property that every non-cyclic subgroup contains its centralizer. The structure of nilpotent and supersolvable groups in this class is described. We also classify finite $p$-groups and finite simple groups with…

Group Theory · Mathematics 2014-01-28 Costantino Delizia , Urban Jezernik , Primož Moravec , Chiara Nicotera

We show that on an arbitrary finitely generated non virtually solvable linear group, any two independent random walks will eventually generate a free subgroup. In fact, this will hold for an exponential number of independent random walks.

Group Theory · Mathematics 2019-12-19 Richard Aoun

Let $F$ be a finitely generated free group. By using Bestvina-Handel theory, as well as some further improvements, the eigengroups of a given automorphism of $F$ (and its fixed subgroup among them) are globally analyzed and described. In…

Group Theory · Mathematics 2007-05-23 A. Martino , E. Ventura