Arjeh M. Cohen, Luis Paris
We determine the epimorphisms $A \to W$ from the Artin group $A$ of type $Γ$ onto the Coxeter group $W$ of type $Γ$, in case $Γ$ is an irreducible Coxeter graph of spherical type, and we prove that the kernel of the standard epimorphism is a characteristic subgroup of $A$. This generalizes an over 50 years old result of Artin.
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We present a complete classification for the epimorphisms from the affine Artin-Tits groups $A(\widetilde{A}_{n})$ to the corresponding Coxeter groups $W(\widetilde{A}_{n})$, for $n\geq 1$.
This paper is a sequel of [A.M. Cohen, L. Paris, {\it On a theorem of Artin}, J. Group Theory {\bf 6} (2003), 421--441]. Let $A$ be an Artin group, let $W$ be its associated Coxeter group, and let $CA$ be its associated coloured Artin group, that is, the kernel of the standard epimorphism $μ: A \to W$. We determine the homomorphisms $\f: A \to W$ that verify $\Im \f \cdot Z(W)= W$, for $A$ irreducible and of spherical type, and we prove that $CA$ is a characteristic subgroup of $A$, if $A$ is of spherical type but not necessarily irreducible.
The dual Artin isomorphism for Artin groups of XXL type
本文证明XXL型Artin群（所有定义整数m_{ij}≥5）与任意Coxeter元素对应的对偶Artin群同构，通过Hurwitz词集Q的几何性质及Coxeter群词问题的解完成证明。
Short hierarchically hyperbolic groups II: quotients and the Hopf property for Artin groups
本文证明大多数大类型和超几何类型的Artin群是Hopf群，并展示大部分五孔球面映射群的商是层次超几何的。
A simplicial complex L on n vertices determines a subcomplex T_L of the n-torus, with fundamental group the right-angled Artin group G_L. Given an epimorphism χ\colon G_L\to \Z, let T_L^χbe the corresponding cover, with fundamental group the Artin kernel N_χ. We compute the cohomology jumping loci of the toric complex T_L, as well as the homology groups of T_L^χwith coefficients in a field \k, viewed as modules over the group algebra \k\Z. We give combinatorial conditions for H_{\le r}(T_L^χ;\k) to have trivial \Z-action, allowing us to compute the truncated cohomology ring, H^{\le r}(T_L^χ;\k…
Starting from the observation that the standard presentation of a virtual braid group mixes the standard presentation of the corresponding braid group with the standard presentation of the corresponding symmetric group and some mixed relations that mimic the action of the symmetric group on its root system, we define a virtual Artin group $VA[Γ]$ of a Coxeter graph $Γ$ mixing the standard presentation of the Artin group $A[Γ]$ with the standard presentation of the Coxeter group $W[Γ]$ and some mixed relations that mimic the action of $W[Γ]$ on its root system. By definition we have two epimorp…
On a theorem of Artin and the dimension of the space spanned by the rational valued characters of a group
本文改进Artin定理，证明有限群的有理值特征标张成空间的维数等于循环子群的共轭类数目。
In a recent paper by L. A. Bokut, V. V. Chaynikov and K. P. Shum in 2007, Braid group $B_n$ is represented by Artin-Burau's relations. For such a representation, it is told that all other compositions can be checked in the same way. In this note, we support this claim and check all compositions.
A combination theorem for the twist conjecture for Artin groups
本文将Artin群的强扭猜想简化为定义图无分离顶点的Artin群，提供了新例证并深化了Artin群同构问题的理解。
We prove an analogue of the Centralizer Theorem in the context of Artin-Tits groups.
Thurston norm for coherent right-angled Artin groups via $L^2$-invariants
本文为群定义了分裂复杂性新概念，证明单端凝聚直角 Artin 群沿满射的分裂复杂性等于核的 $L^2$-Euler 特征，借此定义了 Thurston 型半范数，主要工具为 Friedl--Lück 的 $L^2$-多面体。
We generalize the peak-reduction algorithm (Whitehead's theorem) for free groups to a theorem about a general right-angled Artin group A_Gamma. As an application, we find a finite presentation for the automorphism group Aut A_Gamma that generalizes McCool's presentation for the automorphism group of a finite rank free group. We also give consider a stronger generalization of peak-reduction, giving a counterexample and proving a special case.
We show that non-abelian two-generator subgroups of right-angled Artin groups are quasi-isometrically embedded free groups. This provides an alternate proof of a theorem of A. Baudisch: that all two-generator subgroups are free or free abelian. Additionally, it shows that they are quasi-isometrically embedded. Our theorem also gives a method for detecting groups that are not isomorphic to a subgroup of any RAAG. We present some counterexamples in subgroups with more than two generators.
Equations in Products of Free Groups and 3-Manifold Groups II: Olshanskii Epimorphisms
本文证明所有奥尔桑斯基满同态均为标准的，构造性处理了Q₈情形，给出哈拉兰波娃等人所宣布结果的详细证明，未使用佩雷尔曼定理等。
We give a complete classification of conjugacy stable parabolic subgroups of Artin-Tits groups of spherical type. This answers a question posed by Ivan Marin and generalizes a theorem obtained by Juan González-Meneses in the specific case of Artin braid groups.
Morgan and Culler proved that a minimal action of a free group on a tree is determined by its translation length function. We prove an analogue of this theorem for 2-dimensional right-angled Artin groups acting on CAT(0) rectangle complexes.
In this paper we will present the results of Artin--Markov on braid groups by using the Groebner--Shirshov basis. As a consequence we can reobtain the normal form of Artin--Markov--Ivanovsky as an easy corollary.
We prove a new version of the classical peak-reduction theorem for automorphisms of free groups in the setting of right-angled Artin groups. We use this peak-reduction theorem to prove two important corollaries about the action of the automorphism group of a right-angled Artin group $A_Γ$ on the set of $k$-tuples of conjugacy classes from $A_Γ$: orbit membership is decidable, and stabilizers are finitely presentable. Further, we explain procedures for checking orbit membership and building presentations of stabilizers. This improves on a previous result of the author's. We overcome a technical…
Droms Theorems for twisted right-angled Artin groups
本文刻画了有限生成子群仍为扭曲直角Artin群的扭曲直角Artin群，基于定义图分类了该类群的凝聚性，并解决了其一个重要子类的同构问题。
Embeddability of right-angled Artin groups into hierarchically hyperbolic groups
研究分层双曲群中直角Artin群的可嵌入性，给出生成非失真直角Artin子群的充分条件，复现相关经典定理并扩展非环形非失真结果。
For any right-angled Artin group, we show that its outer automorphism group contains either a finite-index nilpotent subgroup or a nonabelian free subgroup. This is a weak Tits alternative theorem. We find a criterion on the defining graph that determines which case holds. We also consider some examples of solvable subgroups, including one that is not virtually nilpotent and is embedded in a non-obvious way.
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 the lattice ordered groups and the right-angled Artin groups. Some general results concerning A-groups are applied to a systematic study of the arboreal structure of right-angled Artin groups. Structure theorems for foldings, directions, quasidirections and centralizers are proved.
We present a method for computing the number of epimorphisms from a finitely-presented group G to a finite solvable group Γ, which generalizes a formula of Gäschutz. Key to this approach are the degree 1 and 2 cohomology groups of G, with certain twisted coefficients. As an application, we count low-index subgroups of G. We also investigate the finite solvable quotients of the Baumslag-Solitar groups, the Baumslag parafree groups, and the Artin braid groups.
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。
A theorem proved by Dobrinskaya in 2006 shows that there is a strong connection between the $K(π,1)$ conjecture for Artin groups and the classifying space of Artin monoids. More recently Ozornova obtained a different proof of Dobrinskaya's theorem based on the application of discrete Morse theory to the standard CW model of the classifying space of an Artin monoid. In Ozornova's work there are hints at some deeper connections between the above-mentioned CW model and the Salvetti complex, a CW complex which arises in the combinatorial study of Artin groups. In this work we show that such connec…
Faithful Artin induction and the Chebotarev density theorem
本研究证明有限群G的忠实不可约特征标张成的向量空间由其内单项式特征标生成，由此推出固定数域F的几乎所有G-扩张满足强有效Chebotarev密度定理，并将其用于推导数域族类群的相关结论。
Combination theorems for Wise's power alternative
本文通过引入动力学条件和统一版本，证明了Wise的power alternative在特定群构造下的稳定性，并应用于Artin群和超几何群的统一power alternative研究。
We extend previous results by Cumplido, Martin and Vaskou on parabolic subgroups of large-type Artin groups to a broader family of two-dimensional Artin groups. In particular, we prove that an arbitrary intersection of parabolic subgroups of a $(2,2)$-free two-dimensional Artin group is itself a parabolic subgroup. An Artin group is $(2,2)$-free if its defining graph does not have two consecutive edges labeled by $2$. As a consequence of this result, we solve the conjugacy stability problem for this family by applying an algorithm introduced by Cumplido. All of this is accomplished by consider…
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…
We define a family of groups that include the mapping class group of a genus g surface with one boundary component and the integral symplectic group Sp(2g,Z). We then prove that these groups are finitely generated. These groups, which we call mapping class groups over graphs, are indexed over labeled simplicial graphs with 2g vertices. The mapping class group over the graph Gamma is defined to be a subgroup of the automorphism group of the right-angled Artin group A_Gamma of Gamma. We also prove that the kernel of the map Aut A_Gamma to Aut H_1(A_Gamma) is finitely generated, generalizing a th…
Homological growth of Artin kernels in positive characteristic
该研究针对含直角Artin群、Bestvina--Brady群的一类剩余有限有理可解群，证明正特征下Lück逼近定理的类似结论，明确模p同调增长与泛可除环系数群同调维数的关系及剩余链无关性，给出一般RFRS群的不变量不等式，并拓展相关应用。
We give a short proof of the following theorem of Sang-hyun Kim: if $A(Γ)$ is a right-angled Artin group with defining graph $Γ$, then $A(Γ)$ contains a hyperbolic surface subgroup if $Γ$ contains an induced subgraph $\bar{C}_n$ for some $n \geq 5$, where $\bar{C}_n$ denotes the complement graph of an $n$-cycle. Furthermore, we give a new proof of Kim's co-contraction theorem.
In all known examples of a CAT(0) group acting on CAT(0) spaces with non-homeomorphic CAT(0) visual boundaries, the boundaries are each not path connected. In this paper, we show this does not have to be the case by providing examples of right-angled Artin groups which exhibit non-unique CAT(0) boundaries where all of the boundaries are arbitrarily connected. We also prove a combination theorem for certain amalgams of CAT(0) groups to act on spaces with non-path connected visual boundaries. We apply this theorem to some right-angled Artin groups.
A note on virtual duality and automorphism groups of right-angled Artin groups
本文利用 Brady–Meier 判据构造外自同构群非虚拟对偶群的 RAAG，部分回答 Vogtmann 问题，并由附录介绍计算机辅助搜索更多例子。
We describe a new approach to the Word Problem for Artin-Tits groups and, more generally, for the enveloping group U(M) of a monoid M in which any two elements admit a greatest common divisor. The method relies on a rewrite system R(M) that extends free reduction for free groups. Here we show that, if M satisfies what we call the 3-Ore condition about common multiples, what corresponds to type FC in the case of Artin-Tits monoids, then the system R(M) is convergent. Under this assumption, we obtain a unique representation result for the elements of U(M), extending Ore's theorem for groups of f…
We prove three results about the graph product $G=\G(Γ;G_v, v \in V(Γ))$ of groups $G_v$ over a graph $Γ$. The first result generalises a result of Servatius, Droms and Servatius, proved by them for right-angled Artin groups; we prove a necessary and sufficient condition on a finite graph $Γ$ for the kernel of the map from $G$ to the associated direct product to be free (one part of this result already follows from a result in S. Kim's Ph.D. thesis). The second result generalises a result of Hermiller and Sunic, again from right-angled Artin groups; we prove that for a graph $Γ$ with finite ch…
Artin groups of type (2,3,n)
本文证明了类型(2,3,n)的Artin群字问题可通过保长重写规则系统在二次时间内解决，为非球面秩3 Artin群提供了特定的重写解决方案。
Graphs embedded into surfaces have many important applications, in particular, in combinatorics, geometry, and physics. For example, ribbon graphs and their counting is of great interest in string theory and quantum field theory (QFT). Recently, Koch, Ramgoolam, and Wen [Nuclear Phys.\,B {\bf 870} (2013), 530--581] gave a refined formula for counting ribbon graphs and discussed its applications to several physics problems. An important factor in this formula is the number of surface-kernel epimorphisms from a co-compact Fuchsian group to a cyclic group. The aim of this paper is to give an expl…
Let $Γ$ be a Coxeter graph, let $W$ be its associated Coxeter group, and let $G$ be a group of symmetries of $Γ$.Recall that, by a theorem of H{é}e and Mühlherr, $W^G$ is a Coxeter group associated to some Coxeter graph $\hat Γ$.We denote by $Φ^+$ the set of positive roots of $Γ$ and by $\hat Φ^+$ the set of positive roots of $\hat Γ$.Let $E$ be a vector space over a field $\K$ having a basis in one-to-one correspondence with $Φ^+$.The action of $G$ on $Γ$ induces an action of $G$ on $Φ^+$, and therefore on $E$.We show that $E^G$ contains a linearly independent family of vectors naturally in o…
We study monoids generated by Zariski-van Kampen generators in the 17 fundamental groups of the complement of logarithmic free divisors in C^3 listed by Sekiguchi (Theorem 1). Five of them are Artin monoids and eight of them are free abelian monoids. The remaining four monoids are not Gaussian and, hence, are neither Garside nor Artin (Theorem 2). However, we introduce, similarly to Artin monoids, fundamental elements and show their existence (Theorem 3). One of the four non-Gaussian monoids satisfies the cancellation condition (Theorem 4).
Subgroups of even Artin groups of FC-type
本文证明了FC型偶Artin群的子群满足Tits二择一定理，并证明其抛物子群在取根下封闭。
We consider homological finiteness properties $FP_n$ of certain $\mathbb{N}$-graded Lie algebras. After proving some general results, see Theorem A, Corollary B and Corollary C, we concentrate on a family that can be considered as the Lie algebra version of the generalized Bestvina-Brady groups associated to a graph $Γ$. We prove that the homological finiteness properties of these Lie algebras can be determined in terms of the graph in the same way as in the group case. In the last version we have corrected some missprints, in particular the statement of Theorem D (from $n-1$-acyclicity to $n-…
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 A(G) are separated by a cut-point. As an application, we show that if G does not decompose as the join of two subgraphs, then A(G) has an infinite-dimensional space of non-trivial quasimorphisms. By the work of Burger and Monod, this leads to a superrigidity theorem for homomorphisms from lattices into right-angled Artin groups.
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…
We show that there is no uniform upper bound on |Out(Aut(A))| when A ranges over all right-angled Artin groups. This is in contrast with the cases where A is free or free abelian: for all n, Dyer-Formanek and Bridson-Vogtmann showed that Out(Aut(F_n)) = 1, while Hua-Reiner showed |Out(Aut(Z^n)| = |Out(GL(n,Z))| < 5. We also prove the analogous theorem for Out(Out(A)). We establish our results by giving explicit examples; one useful tool is a new class of graphs called austere graphs.
We study $2$-dimensional Artin groups of hyperbolic type from the viewpoint of measure equivalence, and establish rigidity theorems. We first prove that they are boundary amenable. So is every group acting discretely by simplicial isometries on a connected piecewise hyperbolic $\mathrm{CAT}(-1)$ simplicial complex with countably many simplices in finitely many isometry types, assuming that vertex stabilizers are boundary amenable. Consequently, they satisfy the Novikov conjecture. We then show that measure equivalent $2$-dimensional Artin groups of hyperbolic type have isomorphic fixed set gra…
From Trees to Tripods: Proof of $K(π,1)$ for Artin groups with $ABI$-type spherical parabolics
本文通过构造注入度量空间的塔，证明了具有特定球面抛物子群性质的Artin群满足K(π,1)猜想。
The aim of this thesis is to present the notion of spaces whose curvature is bounded above, and to give some of its application in the context of Combinatorial Algebra. The thesis is made of two parts, one of theoretic purpose, and the other applicative. In particular, we present an application to the notion of $CAT(0)$-space and one to the Gromov Theorem for cubical complexes. In the final part we present a new class of discrete groups generalizing the well-known right-angled Artin groups. We concoct a cubical CAT(0)-complex on which the group acts, from whom we extract some algebraic propert…
Quasiisometric embeddings between right-angled Artin groups: rigidity
通过引入定义图上的分支条件，研究了右抵消Artin群之间准等距嵌入的刚性问题，包括对准等距嵌入到树的积中的障碍、定义图的刚性特征分类以及高维RAAG作为准等距嵌入接收器的不可能性。
Periodic elements in finite type Artin-Tits groups and stability conditions
本文通过2-Calabi-Yau范畴上的作用，证明了有限型Artin-Tits群中元素为周期元素当且仅当其在稳定性流形中有不动点。
Right-angled Artin groups of large girth and finite volume hyperbolic $3$--manifold groups
本文证明：若Γ是围长至少5的有限单纯图，则有限体积双曲3-流形的基本群不能作为右角Artin群A(Γ)的子群，特别地回答了Reid关于n-圈的问题。
We solve the simultaneous conjugacy problem in Artin's braid groups and, more generally, in Garside groups, by means of a complete, effectively computable, finite invariant. This invariant generalizes the one-dimensional notion of super summit set to arbitrary dimensions. One key ingredient in our solution is the introduction of a provable high-dimensional version of the Birman--Ko--Lee cycling theorem. The complexity of this solution is a small degree polynomial in the cardinalities of our generalized super summit sets and the input parameters. Computer experiments suggest that the cardinalit…
Hilbert's Theorem 90, periodicity, and roots of Artin-Schreier polynomials
本文研究了特征为p>0的域扩张中希尔伯特定理90的周期性及Artin-Schreier多项式根的结构。
The $K(π, 1)$ conjecture for Artin groups of spherical type
介绍球型阿廷群的$K(π, 1)$猜想，目标是通过组合拓扑方法，在只移除有限个超平面的球型情形下证明该猜想，其证明灵感源于相关原始证明。
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