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For a given group $G$, it is natural to ask whether one can classify all isometric $G$-actions on Gromov hyperbolic spaces. We propose a formalization of this problem utilizing the complexity theory of Borel equivalence relations. In this…

Group Theory · Mathematics 2025-05-01 D. Osin , K. Oyakawa

We prove that any hyperbolic group acting properly discontinuously and cocompactly on a $\mathrm{CAT}(0)$ cube complex admits a projective Anosov representation into $\mathrm{SL}(d, \mathbb{R})$ for some $d$. More specifically, we show that…

Group Theory · Mathematics 2026-01-30 Sami Douba , Balthazar Fléchelles , Theodore Weisman , Feng Zhu

It is known that every infinite index quasi-convex subgroup $H$ of a non-elementary hyperbolic group $G$ is a free factor in a larger quasi-convex subgroup of $G$. We give a probabilistic generalization of this result. That is, we show that…

Geometric Topology · Mathematics 2021-10-04 C. Abbott , M. Hull

We look at group actions on metric spaces, particularly at group actions on geodesic hyperbolic spaces. We classify the types of automorphisms on these spaces and prove several results about the density of the hyperbolic limit set of the…

Metric Geometry · Mathematics 2013-01-29 Matthias Hamann

Aim of this article is the construction of a spanning set for the space of super cusp forms on a complex bounded symmetric super domain B of rank 1 with respect to a lattice. The main ingredients are a generalization of the Anosov closing…

Complex Variables · Mathematics 2009-09-08 Roland Knevel

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

Mapping class groups are known to admit geometric (proper, cobounded) actions on injective spaces. Starting with such an action, and relying only on geometric arguments, we show that all finite generating sets resulting from taking large…

Geometric Topology · Mathematics 2025-12-24 Lihuang Ding , Dídac Martínez-Granado , Abdul Zalloum

Let $M$ be a compact surface with boundary. We are interested in the question of how a group action on $M$ permutes a finite invariant set $X \subset int(M)$. More precisely, how the algebraic properties of the induced group of permutations…

Dynamical Systems · Mathematics 2016-05-10 John Franks , Kamlesh Parwani

We show that colorable hierarchically hyperbolic groups (HHGs) admit asymptotically CAT(0) metrics, that is, roughly, metrics where the CAT(0) inequality holds up to sublinear error in the size of the triangle. We use the asymptotically…

Geometric Topology · Mathematics 2025-04-25 Matthew Gentry Durham , Yair Minsky , Alessandro Sisto

We show that the probability that a finitely supported random walk on a non-elementary subgroup of the the mapping class group gives a non-pseudo-Anosov element decays exponentially in the length of the random walk. More generally, we show…

Geometric Topology · Mathematics 2016-07-07 Joseph Maher

Let $G$ be an acylindrically hyperbolic group. We prove that Bernoulli bond percolation on every Cayley graph of $G$ has a nonuniqueness phase, in which there are infinitely many infinite clusters. This generalizes Hutchcroft's result for…

Group Theory · Mathematics 2025-08-14 Inhyeok Choi , Donggyun Seo

In a group, a non-trivial element is called a generalized torsion element if some non-empty finite product of its conjugates equals to the identity. We say that a knot has generalized torsion if its knot group admits such an element. For a…

Geometric Topology · Mathematics 2021-06-29 Kimihiko Motegi , Masakazu Teragaito

A quasi-tree is a geodesic metric space quasi-isometric to a tree. We give a general construction of many actions of groups on quasi-trees. The groups we can handle include non-elementary (relatively) hyperbolic groups, rank 1 CAT(0)…

Group Theory · Mathematics 2014-09-09 Mladen Bestvina , Kenneth Bromberg , Koji Fujiwara

In this paper we start the inquiry into proving uniform exponential growth in the context of groups acting on CAT(0) cube complexes. We address free group actions on CAT(0) square complexes and prove a more general statement. This says that…

Group Theory · Mathematics 2019-05-29 Aditi Kar , Michah Sageev

This paper is a survey of results proved in recent years that pertain to classifying cobounded hyperbolic actions of any group $G$. In other words, we discuss results that allow us to describe the partially ordered set $\mathcal{H}(G)$,…

Group Theory · Mathematics 2023-10-17 Sahana H. Balasubramanya

We introduce the notion of \"uber-contracting element, a strengthening of the notion of strongly contracting element which yields a particularly tractable criterion to show the acylindrical hyperbolicity, and thus a strong form of…

Group Theory · Mathematics 2017-08-16 Alexandre Martin

We make a few observations on the absence of geometric and topological rigidity for acylindrically hyperbolic and relatively hyperbolic groups. In particular, we demonstrate the lack of a well-defined limit set for acylindrical actions on…

Group Theory · Mathematics 2020-02-19 Brendan Burns Healy

Generalising results of Razborov and Safin, and answering a question of Button, we prove that for every hyperbolic group there exists a constant $\alpha >0$ such that for every finite subset $U$ that is not contained in a virtually cyclic…

Group Theory · Mathematics 2020-05-27 Thomas Delzant , Markus Steenbock

In this article we prove that the set of torsion-free groups acting by isometries on a hyperbolic metric space whose entropy is bounded above and with a compact quotient is finite. The number of such groups can be estimated in terms of the…

Group Theory · Mathematics 2021-11-09 Gérard Besson , Gilles Courtois , Sylvestre Gallot , Andrea Sambusetti

Given a geodesic metric space $X$, we construct a corresponding hyperbolic space, which we call the contraction space, that detects all strongly contracting directions in the following sense; a geodesic in $X$ is strongly contracting if and…

Group Theory · Mathematics 2024-04-19 Stefanie Zbinden