Nicolas Vaskou
In this paper, we show that every irreducible $2$-dimensional Artin group $A_Γ$ of rank at least $3$ is acylindrically hyperbolic. We do this by studying the action of $A_Γ$ on its modified Deligne complex. Along the way, we prove results of independent interests on the geometry of links of this complex.
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Dyer groups: Centres, hyperbolicity, and acylindrical hyperbolicity
该研究刻画了所有Dyer群的中心，并给出了可通过Dyer图直接判定的Dyer群双曲性与柱形双曲性的完整分类结果。
We characterise acylindrical hyperbolicity of a group in terms of properties of an action of the group on a set (without any extra structure). In particular, this applies to the action of the group on itself by left multiplication, as well as the action on a (full measure subset of the) Furstenberg-Poisson boundary.
In our paper arXiv:1310.6289, we stated that acylindrical hyperbolicity of a group is invariant under commensurability up to finite kernels. Unfortunately, the proof of this fact contained a gap. The goal of this erratum is to point out the gap and to correct the statements and proofs of results of arXiv:1310.6289 and the subsequent paper arXiv:1501.03066 affected by it.
We show, using acylindrical hyperbolicity, that a finitely generated group splitting over $\Z$ cannot be simple. We also obtain SQ-universality in most cases, for instance a balanced group (one where if two powers of an infinite order element are conjugate then they are equal or inverse) which is finitely generated and splits over $\Z$ must either be SQ-universal or it is one of exactly seven virtually abelian exceptions.
We provide an analogue of Strebel's classification of geodesic triangles in classical $C'(\frac16)$ groups for groups given by Wise's cubical presentations satisfying sufficiently strong metric cubical small cancellation conditions. Using our classification, we prove that, except in specific degenerate cases, such groups are acylindrically hyperbolic.
Acylindrical hyperbolicity for Artin groups with a visual splitting
该研究建立了判定具有可视分裂的Artin群柱形双曲性的准则，提出抛物子群弱反正规性相关猜想并在多类Artin群中证明，同时建立了相关Artin群猜想间的联系。
We introduce the notion of über-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 non-simplicity, of groups acting on non locally compact spaces of arbitrary dimension. We also give a simple local criterion to construct über-contracting elements for groups acting on complexes with unbounded links of vertices. As an application, we show the acylindrical hyperbolicity of the tame automorphism group of $\mathrm{SL}_2(\mathbb{C})$, a subgroup of the $3$…
We prove that the group of outer automorphisms of the free Coxeter group $W_n$ is acylindrically hyperbolic in the sense of Osin. As an application, we observe that any CAT(0) space admitting a geometric action by Out($W_n$) must contain a rank-one geodesic. The theorem proceeds from expanding on a well-known relationship between Out($W_n$) and the outer automorphism group of free groups.
We study the acylindrical hyperbolicity of groups acting by isometries on CAT(0) cube complexes, and obtain simple criteria formulated in terms of stabilisers for the action. Namely, we show that a group acting essentially and non-elementarily on a finite dimensional irreducible CAT(0) cube complex is acylindrically hyperbolic if there exist two hyperplanes whose stabilisers intersect along a finite subgroup. We also give further conditions on the geometry of the complex so that the result holds if we only require the existence of a single pair of points whose stabilisers intersect along a fin…
Acylindrical hyperbolicity of outer automorphism groups of right-angled Artin groups
本文研究了直角Artin群外自同构群的非柱形双曲性，分别在定义图无SIL-pair和有极大SIL-pair系统时，给出了其非柱形双曲性的充要条件及分类定理，揭示了其与部分共轭存在性的关系。
Acylindrical Visual Splittings and The Tits Alternative For Artin Groups
本研究给出满足两个著名猜想条件的阿廷群可视分裂为非柱形的充要条件，借此构造出一大类满足Tits二择性的全新阿廷群实例，推进相关群论研究。
We prove that, for any irreducible Artin-Tits group of spherical type $G$, the quotient of $G$ by its center is acylindrically hyperbolic. This is achieved by studying the additional length graph associated to the classical Garside structure on $G$, and constructing a specific element $x_G$ of $G/Z(G)$ whose action on the graph is loxodromic and WPD in the sense of Bestvina-Fujiwara; following Osin, this implies acylindrical hyperbolicity. Finally, we prove that "generic" elements of $G$ act loxodromically, where the word "generic" can be understood in either of the two common usages: as a res…
In this paper we show the statement in the title. To any Garside group of finite type, Wiest and the author associated a hyperbolic graph called the \emph{additional length graph} and they used it to show that central quotients of Artin-Tits groups of spherical type are acylindrically hyperbolic. In general, a euclidean Artin-Tits group is not \emph{a priori} a Garside group but McCammond and Sulway have shown that it embeds into an \emph{infinite-type} Garside group which they call a \emph{crystallographic Garside group}. We associate a \emph{hyperbolic} additional length graph to this crysta…
Charney and Morris-Wright showed acylindrical hyperbolicity of Artin groups of infinite type associated with graphs that are not joins, by studying clique-cube complexes and actions on them. In this paper, by developing their study and formulating some additional discussion, we demonstrate that acylindrical hyperbolicity holds for more general Artin groups. Indeed, we are able to treat Artin groups of infinite type associated with graphs that are not cones.
Acylindrical Hyperbolicity and Pure Conjugating Automorphisms in Graph Products of Groups
该研究从两个视角刻画群的图乘积的轴双曲性，并确立纯共轭自同构的拓扑生成、闭性等性质，还给出阿贝尔群图乘积对应的典范拓扑半直积分解。
For a two-dimensional Artin group $A$ whose associated Coxeter group is hyperbolic, we prove that the action of $A$ on the hyperbolic space obtained by coning off certain subcomplexes of its modified Deligne complex is acylindrical. Moreover, if for each $s\in S$ there is $t\in S$ with $m_{st}< \infty$, then this action is universal. As a consequence, for $|S|\geq 3$, if $A$ is irreducible, then it is acylindrically hyperbolic. We also obtain the Tits alternative for $A$, and we classify the subgroups of $A$ that virtually split as a direct product. A key ingredient in our approach is a simple…
We prove that every countable acylindrically hyperbolic group admits a highly transitive action with finite kernel. This theorem uniformly generalizes many previously known results and allows us to answer a question of Garion and Glassner on the existence of highly transitive faithful actions of mapping class groups. It also implies that in various geometric and algebraic settings, the transitivity degree of an infinite group can only take two values, namely $1$ and $\infty$. Here by transitivity degree of a group we mean the supremum of transitivity degrees of its faithful permutation represe…
The aim of this note is to give the simplest possible proof that Mapping Class Groups of closed hyperbolic surfaces are acylindrically hyperbolic, and more specifically that their curve graphs are hyperbolic and that pseudo-Anosovs act on them as loxodromic WPDs.
Let $G$ be a finitely presented group, and let $H$ be a subgroup of $G$. We prove that if $H$ is acylindrically hyperbolic and existentially closed in $G$, then $G$ is acylindrically hyperbolic. As a corollary, any finitely presented group which is existentially equivalent to the mapping class group of a surface of finite type, to $\mathrm{Out}(F_n)$ or $\mathrm{Aut}(F_n)$ for $n\geq 2$ or to the Higman group, is acylindrically hyperbolic.
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 contact graph associated to a CAT(0) cube complex, and we prove a characterisation of WPD contracting isometries of CAT(0) cube complexes. As a first consequence, we find alternative arguments to show several criteria which were proved by Indira Chatterji and Alexandre Martin. Next, we show that if a group acts essentially and acylindrically on the hyperplanes…
Around subgroups of Artin groups: derived subgroups and acylindrical hyperbolicity in the even FC-case
该研究将直角Artin群的多项相关结果推广至更广泛的Artin群类，涵盖导子群自由性与群凝聚性的等价性、有限生成正规子群性质及FC型偶Artin群子群的柱形双曲性三方面内容。
In this paper we study group actions on quasi-median graphs, or 'CAT(0) prism complexes', generalising the notion of CAT(0) cube complexes. We consider hyperplanes in a quasi-median graph $X$ and define the contact graph $\mathcal{C}X$ for these hyperplanes. We show that $\mathcal{C}X$ is always quasi-isometric to a tree, generalising a result of Hagen, and that under certain conditions a group action $G \curvearrowright X$ induces an acylindrical action $G \curvearrowright \mathcal{C}X$, giving a quasi-median analogue of a result of Behrstock, Hagen and Sisto. As an application, we exhibit an…
We prove that the automorphism group of every infinitely-ended finitely generated group is acylindrically hyperbolic. In particular $\mathrm{Aut}(\mathbb{F}_n)$ is acylindrically hyperbolic for every $n\ge 2$. More generally, if $G$ is a group which is not virtually cyclic, and hyperbolic relative to a finite collection $\mathcal{P}$ of finitely generated proper subgroups, then $\mathrm{Aut}(G,\mathcal{P})$ is acylindrically hyperbolic. As a consequence, a free-by-cyclic group $\mathbb{F}_n\rtimes_φ\mathbb{Z}$ is acylindrically hyperbolic if and only if $φ$ has infinite order in $\mathrm{Out}(…
We provide new examples of acylindrically hyperbolic groups arising from actions on simplicial trees. In particular, we consider amalgamated products and HNN-extensions, 1-relator groups, automorphism groups of polynomial algebras, 3-manifold groups and graph products. Acylindrical hyperbolicity is then used to obtain some results about the algebraic structure, analytic properties and measure equivalence rigidity of groups from these classes.
It is conjectured that the central quotient of every irreducible Artin group is either virtually cyclic or acylindrically hyperbolic. We prove this conjecture for Artin groups associated to triangle-free graphs and Artin groups of large type associated to cones over square-free bipartite graphs. In fact, we treat Artin groups that are known to be CAT(0) groups by a result of Brady and McCammond.
Acylindrical hyperbolicity and the centers of Artin groups that are not free of infinity
本文引入约化团-立方复形，证明了与非完全图相关的不可约Artin群的非柱面双曲性，并得出此类群中心有限且多为平凡的结论。
Connections between the topology of the Morse boundary, the Morse local-to-global property and acylindrical hyperbolicity
本文研究了Morse边界拓扑与群的几何和算法性质的关系，证明了σ-紧Morse边界等价于Morse局部到全局性质，并引入了新的工具来判断群是否具有该性质。
Induced quasi-isometries of hyperbolic spaces, Markov chains, and acylindrical hyperbolicity
本文证明分层双曲群的拟等距可诱导其极大双曲空间的拟等距，并据此推出柱形双曲性的拟等距不变性及Markov链线性进展结果。
We prove that the group STame($k^3$) of special tame automorphisms of the affine 3-space is not simple, over any base field of characteristic zero. Our proof is based on the study of the geometry of a 2-dimensional simply-connected simplicial complex C on which the tame automorphism group acts naturally. We prove that C is contractible and Gromov-hyperbolic, and we prove that Tame($k^3$) is acylindrically hyperbolic by finding explicit loxodromic weakly proper discontinuous elements.
We prove that every finitely presented group with positive first $\ell^2$-Betti number that virtually surjects onto $\mathbb Z$ is acylindrically hyperbolic. In particular, this implies acylindrical hyperbolicity of finitely presented residually finite groups with positive first $\ell^2$-Betti number as well as groups of deficiency at least $2$.
This article is dedicated to the study of the acylindrical hyperbolicity of automorphism groups of graph products of groups. Our main result is that, if $Γ$ is a finite graph which contains at least two vertices and is not a join and if $\mathcal{G}$ is a collection of finitely generated irreducible groups, then either $Γ\mathcal{G}$ is infinite dihedral or $\mathrm{Aut}(Γ\mathcal{G})$ is acylindrically hyperbolic. This theorem is new even for right-angled Artin groups and right-angled Coxeter groups. Various consequences are deduced from this statement and from the techniques used to prove it…
We show that the complex of parabolic subgroups associated to the Artin-Tits group of type $B$ is hyperbolic
The main technical result of this paper is to characterize the contracting isometries of a CAT(0) cube complex without any assumption on its local finiteness. Afterwards, we introduce the combinatorial boundary of a CAT(0) cube complex, and we show that contracting isometries are strongly related to isolated points at infinity, when the complex is locally finite. This boundary turns out to appear naturally in the context of Guba and Sapir's diagram groups, and we apply our main criterion to determine precisely when an element of a diagram group induces a contracting isometry on the associated …
Random quotients preserve acylindrical and hierarchical hyperbolicity
本文提出了一种随机商模型，证明了随机商保持圆柱形和层次超几何性，并展示了其在超几何群中的应用。
The $K(π,1)$ conjecture and acylindrical hyperbolicity for relatively extra-large Artin groups
本文引入 Artin 群相对于任意抛物子群族为超大型的新概念，推广了此前仅涉及两个抛物子群的定义，并证明在该条件下 $K(π,1)$ 猜想可由子群传递到整个群，同时在温和条件下得到 acylindrical 双曲性。
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 parabolic subgroups if and only if its Deligne complex is a Gromov hyperbolic space. For a 2-dimensional Artin group the Deligne complex is Gromov hyperbolic precisely when the corresponding Davis complex is Gromov hyperbolic, that is, precisely when the underlying Coxeter group is a hyperbolic group. For Artin groups of FC type we give a sufficient condition for …
While finite type Artin groups and right-angled Artin groups are well-understood, little is known about more general Artin groups. In this paper we use the action of an infinite type Artin group $A_Γ$ on a CAT(0) cube complex to prove that $A_Γ$ has trivial center providing the graph $Γ$ is not the star of a single vertex, and is acylindrically hyperbolic providing $Γ$ is not a join.
On acylindrical tree actions and outer automorphism group of Baumslag-Solitar groups
本文研究树上非柱状作用在商化后的保持条件及最大作用判据，并据此证明不可解 Baumslag–Solitar 群的外自同构群具有非柱状双曲性。
Let $R$ be an infinite commutative ring with identity and $n\geq 2$ be an integer. We prove that for each integer $i=0,1,\cdots ,n-2,$ the $L^{2}$-Betti number $b_{i}^{(2)}(G)=0,$ $\ $when $G=\mathrm{GL}_{n}(R)$ the general linear group, $\mathrm{SL}_{n}(R)$ the special linear group, $% E_{n}(R)$ the group generated by elementary matrices. When $R$ is an infinite principal ideal domain, similar results are obtained for $\mathrm{Sp}_{2n}(R)$ the symplectic group, $\mathrm{ESp}_{2n}(R)$ the elementary symplectic group, $\mathrm{O}(n,n)(R)$ the split orthogonal group or $\mathrm{EO}(n,n)(R)$ the …
(Non-)Recognizing Spaces for Stable Subgroups
本文探讨稳定子群的识别空间，发现映射类群和右角Artin群的最大非圆柱作用可识别所有稳定子群，但构造的反例表明并非所有非圆柱双曲群都如此。
We introduce a new invariant of finitely generated groups, the ambiguity function, and prove that every finitely generated acylindrically hyperbolic group has a linearly bounded ambiguity function. We use this result to prove that the relative exponential growth rate $\lim \limits_{n \rightarrow \infty} \sqrt[n]{\vert B^{X}_H(n) \vert}$ of a subgroup $H$ of an acylindrically hyperbolic group $G$ exists with respect to every finite generating set $X$ of $G$, if $H$ contains a loxodromic element of $G$. Further we prove that the relative exponential growth rate of every finitely generated subgro…
Hyperbolicity and uniformly Lipschitz affine actions on subspaces of $L^1$
本文利用 Mineyev 的 $\mathbb{Q}$-双组合和 Balasubramanya 的拟树作用刻画，证明了双曲群和无端双曲群在 $L^1$ 空间子空间上分别具有真一致 Lipschitz 仿射作用和无界轨道的一致 Lipschitz 仿射作用。
Property $R_\infty$ for Artin and Coxeter groups whose outer automorphisms are length-preserving
该研究证明非球面Artin与Coxeter群的保长自同构具无限Reidemeister数，进而确立多类Artin、Coxeter群的$R_\infty$性质，还证明无限不可约非仿射强刚性Coxeter群的自同构群具acylindrically双曲性。
Given a finite rank free group $\mathbb{F}$ of $\mathsf{rank}(\mathbb{F})\geq 3$, we show that the mapping torus of $ϕ$ is (strongly) relatively hyperbolic if $ϕ$ is exponentially growing. We combine our result with the work of Button-Kropholler to answer a question asked by Minasyan-Osin regarding the acylindrical hyperbolicity of such free-by-cyclic extensions. As an application we construct new examples of free-by-free hyperbolic extensions where the elements of the quotient group are not necessarily fully irreducible. We also give a new proof of the Bridson-Groves quadratic isoperimetric i…
Negative curvature in locally reducible Artin groups
本文通过定义2-完全 Artin 复形并证明其 systolic 性，进而证明一类抛物子群为弱 malnormal，最终得出许多局部可约 Artin 群是 acylindrically 双曲的结论。
We conjecture that the word problem of Artin-Tits groups can be solved without introducing trivial factors ss^{-1} or s^{-1}s. Here we make this statement precise and explain how it can be seen as a weak form of hyperbolicity. We prove the conjecture in the case of Artin-Tits groups of type FC, and we discuss various possible approaches for further extensions, in particular a syntactic argument that works at least in the right-angled case.
Let $G=<a_1,..., a_n | a_ia_ja_i... = a_ja_ia_j..., i<j>$ be an Artin group and let $m_{ij}=m_{ji}$ be the length of each of the sides of the defining relation involving $a_i$ and $a_j$. We show if all $m_{ij}\ge 7$ then $G$ is relatively hyperbolic in the sense of Farb with respect to the collection of its two-generator subgroups $<a_i, a_j>$ for which $m_{ij}<\infty$.
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 studying many important families of groups, including mapping class groups, right-angled Coxeter and Artin groups, most 3-manifold groups, and many others. A group that admits an acylindrical action on a hyperbolic space may admit many such actions on different hyperbolic spaces, so it is natural to search for a "best" one. The set of all cobounded acylindric…
We show that Artin groups of extra-large type, and more generally Artin groups of large and hyperbolic type, are hierarchically hyperbolic. This implies in particular that these groups have finite asymptotic dimension and uniform exponential growth. We prove these results by using a combinatorial approach to hierarchical hyperbolicity, via the action of these groups on a new complex that is quasi-isometric both to the coned-off Deligne complex introduced by Martin-Przytycki and to a generalisation due to Morris-Wright of the graph of irreducible parabolic subgroups of finite type introduced by…
In this paper we study the hyperbolicity properties of a class of random groups arising as graph products associated to random graphs. Recall, that the construction of a graph product is a generalization of the constructions of right-angled Artin and Coxeter groups. We adopt the Erdos - Renyi model of a random graph and find precise threshold functions for the hyperbolicity (or relative hyperbolicity). We aslo study automorphism groups of right-angled Artin groups associated to random graphs. We show that with probability tending to one as $n\to \infty$, random right-angled Artin groups have f…
JSJ splittings for all Artin groups
本文刻画 Artin 群沿无限循环子群的 JSJ 分裂条件，并据此得到同构不变量、自同构群非柱形双曲性及新的 R-infinity Artin 群族。
Hyperbolicity and obstructions to PL actions of the circle
该研究探讨作用于圆周的分段线性同胚的 acylindrically 双曲群的结构，证明其为虚自由群等三类，推广直角 Artin 子群性质，还得出高维双曲流形基本群无法作用于圆周的结论。
We develop an analogy between right-angled Artin groups and mapping class groups through the geometry of their actions on the extension graph and the curve graph respectively. The central result in this paper is the fact that each right-angled Artin group acts acylindrically on its extension graph. From this result we are able to develop a Nielsen--Thurston classification for elements in the right-angled Artin group. Our analogy spans both the algebra regarding subgroups of right-angled Artin groups and mapping class groups, as well as the geometry of the extension graph and the curve graph. O…
Tiling in some nonpositively curved groups
本文证明了acylindrically超几何群是单调铺砌的，即每个有限子集都包含在有限铺砌中，为单调铺砌群提供了新例子，并推动了关于所有群是否单调铺砌的问题。
The \emph{graph of irreducible parabolic subgroups} is a combinatorial object associated to an Artin-Tits group $A$ defined so as to coincide with the curve graph of the $(n+1)$-times punctured disk when $A$ is Artin's braid group on $(n+1)$ strands. In this case, it is a hyperbolic graph, by the celebrated Masur-Minsky's theorem. Hyperbolicity for more general Artin-Tits groups is an important open question. In this paper, we give a partial affirmative answer. For $n\geqslant 3$, we prove that the graph of irreducible parabolic subgroups associated to the Artin-Tits group of spherical type $B…
Cyclic hyperbolicity in CAT(0) cube complexes
本文证明余紧特殊群不含F2×F2当且仅当循环双曲，并在CAT(0)立方复形几何作用群中给出结构定理和强Tits替代，推论SQ-普遍性。
Balanced groups and the virtually cyclic dimension of poly-surfaces groups
本文通过研究平衡性质（Lück的条件C），获得正常多面体群和正常多自由群的虚拟循环维数的线性上界，证明了平衡性质在短正合列、极限和圆柱形图群分解下的稳定性，并应用该结果证明了正常多超几何群、正常多自由群和正常多面体群均为平衡群。
On free components of Artin and Coxeter groups
研究Artin和Coxeter群的连通分量数量，探讨von Neumann代数与自由群因子问题的关系，以及测度等价中的相关情况。
Let $A\neq A_1, A_2, I_{2m}$ be an irreducible Artin--Tits group of spherical type. We show that periodic elements of $A$ and the elements preserving some parabolic subgroup of $A$ act elliptically on the additional length graph $\mathcal{C}_{AL}(A)$, an hyperbolic, infinite diameter graph associated to $A$ constructed by Calvez and Wiest to show that $A/Z(A)$ is acylindrically hyperbolic. We use these results to find an element $g\in A$ such that $\langle P,g \rangle\cong P* \langle g \rangle$ for every proper standard parabolic subgroup $P$ of $A$. The length of $g$ is uniformly bounded with…
We study the geometry of nonrelatively hyperbolic groups. Generalizing a result of Schwartz, any quasi-isometric image of a non-relatively hyperbolic space in a relatively hyperbolic space is contained in a bounded neighborhood of a single peripheral subgroup. This implies that a group being relatively hyperbolic with nonrelatively hyperbolic peripheral subgroups is a quasi-isometry invariant. As an application, Artin groups are relatively hyperbolic if and only if freely decomposable. We also introduce a new quasi-isometry invariant of metric spaces called metrically thick, which is sufficien…
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