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We study the boundaries of relatively hyperbolic HHGs. Using the simplicial structure on the hierarchically hyperbolic boundary, we characterize both relative hyperbolicity and being thick of order 1 among HHGs. In the case of relatively…

Group Theory · Mathematics 2023-05-29 Carolyn Abbott , Jason Behrstock , Jacob Russell

For a large class of groups, we exhibit an infinite-dimensional space of homogeneous quasimorphisms that are invariant under the action of the automorphism group. This class includes non-elementary hyperbolic groups, infinitely-ended…

Group Theory · Mathematics 2025-12-02 Francesco Fournier-Facio , Richard D. Wade

For every group $G$, we introduce the set of hyperbolic structures on $G$, denoted $\mathcal{H}(G)$, which consists of equivalence classes of (possibly infinite) generating sets of $G$ such that the corresponding Cayley graph is hyperbolic;…

Group Theory · Mathematics 2019-08-21 Carolyn Abbott , Sahana Balasubramanya , Denis Osin

Let $G$ be a right-angled Artin group with $|\mathrm{Out}(G)|<+\infty$. We prove that if a countable group $H$ with bounded torsion is measure equivalent to $G$, with an $L^1$-integrable measure equivalence cocycle towards $G$, then $H$ is…

Group Theory · Mathematics 2025-10-09 Camille Horbez , Jingyin Huang

We give a criterion which ensures that a group generated by Cartan involutions in the automorph group of a rational quadratic form of signature (n-1,1) is "thin", namely it is of infinite index in the latter. It is based on a graph defined…

Group Theory · Mathematics 2013-08-13 Elena Fuchs , Chen Meiri , Peter Sarnak

We provide a new method of constructing non-quasiconvex subgroups of hyperbolic groups by utilizing techniques inspired by Stallings' foldings. The hyperbolic groups constructed are in the natural class of right-angled Coxeter groups (RACGs…

Group Theory · Mathematics 2022-08-23 Pallavi Dani , Ivan Levcovitz

We establish a criterion that implies the acylindrical hyperbolicity of many Artin groups admitting a visual splitting. This gives a variety of new examples of acylindrically hyperbolic Artin groups, including many Artin groups of FC-type.…

Group Theory · Mathematics 2026-05-06 Ruth Charney , Alexandre Martin , Rose Morris-Wright

We characterize convex cocompact subgroups of mapping class groups that arise as subgroups of specially embedded right-angled Artin groups. That is, if the right-angled Artin group G in Mod(S) satisfies certain conditions that imply G is…

Geometric Topology · Mathematics 2017-05-17 Johanna Mangahas , Samuel J. Taylor

We give a group theoretic characterization of geodesics with superlinear divergence in the Cayley graph of a right-angled Artin group A(G) with connected defining graph G. We use this to determine when two points in an asymptotic cone of…

Group Theory · Mathematics 2010-01-26 Jason Behrstock , Ruth Charney

In this paper we provide a procedure to obtain a non-trivial HHS structure on a hyperbolic space. In particular, we prove that given a finite collection $\mathcal{F}$ of quasi-convex subgroups of a hyperbolic group $G$, there is an HHG…

Group Theory · Mathematics 2018-12-17 Davide Spriano

The present article continues the study of median groups initiated in [6, 9, 10]. Some classes of median groups are introduced and investigated with a stress upon the class of the so called A-groups which contains as remarkable subclasses…

Group Theory · Mathematics 2009-09-23 Şerban A. Basarab

We prove using a novel random matrix model that all right-angled Artin groups have a sequence of finite dimensional unitary representations that strongly converge to the regular representation. We deduce that this result applies also to:…

Group Theory · Mathematics 2023-09-26 Michael Magee , Joe Thomas

This paper considers the question of relative hyperbolicity of an Artin group with regard to the geometry of its associated Deligne complex. We prove that an Artin group is weakly hyperbolic relative to its finite (or spherical) type…

Group Theory · Mathematics 2007-05-23 Ruth Charney , John Crisp

We construct examples of free-by-cyclic hyperbolic groups which fiber in infinitely many ways over Z. The construction involves adding a specialized square 2-cell to a non-positively curved, squared 2-complex defined by labeled oriented…

Group Theory · Mathematics 2014-11-11 TaraLee Mecham , Antara Mukherjee

Consider a hyperbolic group G and a quasiconvex subgroup H of infinite index. We construct a set-theoretic section s of the quotient map (of sets) from G to G/H such that s(G/H) is a net in G; that is, any element of G is a bounded distance…

Geometric Topology · Mathematics 2007-05-23 Thomas Mack

We consider two manifestations of non-positive curvature: acylindrical actions on hyperbolic spaces and quasigeodesic stability. We study these properties for the class of hierarchically hyperbolic groups, which is a general framework for…

Group Theory · Mathematics 2020-08-06 Carolyn Abbott , Jason Behrstock , Daniel Berlyne , Matthew Gentry Durham , Jacob Russell

We define the intersection complex for the universal cover of a compact weakly special square complex and show that it is a quasi-isometry invariant. By using this quasi-isometry invariant, we study the quasi-isometric classification of…

Group Theory · Mathematics 2023-09-07 Sangrok Oh

We generalize a result of Paulin on the Gromov boundary of hyperbolic groups to the Morse boundary of proper, maximal hierarchically hyperbolic spaces admitting cocompact group actions by isometries. Namely we show that if the Morse…

Geometric Topology · Mathematics 2018-01-16 Sarah C. Mousley , Jacob Russell

In this paper we use techniques from convex projective geometry to produce many new examples of thin subgroups of lattices in special linear groups that are isomorphic to the fundamental groups of finite volume hyperbolic manifolds. More…

Geometric Topology · Mathematics 2020-07-29 Samuel Ballas , D. D. Long

We exhibit two examples of convex cocompact subgroups of the isometry groups of real hyperbolic spaces with limit set a Pontryagin sphere: one generated by $50$ reflections of $\mathbb{H}^4$, and the other by a rotation of order $21$ and a…

Geometric Topology · Mathematics 2026-04-03 Sami Douba , Gye-Seon Lee , Ludovic Marquis , Lorenzo Ruffoni