Combinatorial properties of virtual braids

Dynnikov coordinates on virtual braid groups

We define Dynnikov coordinates on virtual braid groups. We prove that they are faithful invariants of virtual 2-braids, and present evidence that they are also very powerful invariants for general virtual braids.

On virtual cabling and structure of 4-strand virtual pure braid group

This article is dedicate to cabling on virtual braids. This construction gives a new generating set for the virtual pure braid group $VP_n$. Consequently we describe $VP_4$ as HNN-extension. As an application to classical braids, we find a new presentation of the Artin pure braid group $P_4$ in terms of the cabled generators.

曲面辫子群与虚拟辫子群的子群可分性

Subgroup separability of surface braid groups and virtual braid groups

该工作考察曲面辫子群与虚拟（奇异）辫子群的子群可分性（LERF）及相关性质。

Virtual braids from a topological viewpoint

Virtual braids are a combinatorial generalization of braids. We present abstract braids as equivalence classes of braid diagrams on a surface, joining two distinguished boundary components. They are identified up to isotopy, compatibility, stability and Reidemeister moves. We show that virtual braids are in a bijective correspondence with abstract braids. Finally we demonstrate that for any abstract braid, its representative of minimal genus is unique up to compatibility and Reidemeister moves. The genus of such a representative is thus an invariant for virtual braids. We also give a complete …

通用虚拟辫群中的禁止关系

Forbidden relations in universal virtual braid groups

研究通用虚拟辫群 $UV_n(k)$ 的自然自同构，证明其诱导外自同构群中的对合交换并生成同构于 $\mathbb{Z}_2^k imes\mathbb{Z}_2$ 的子群，进而证明两个单禁止商群同构，并引入通用无限制虚拟辫群 $UUV_n(k)$ 推导其结构性质。

多虚拟辫群

Multi-virtual braid groups

本文研究了多虚拟辫群及其相关结构，介绍了多虚拟纯辫群、半纯辫群以及多焊合和多非限制辫群，并探讨了三股2虚拟辫群的结构及未来研究方向。

Algebraic, combinatorial and topological properties of singular virtual braid monoids

In this paper we discuss algebraic, combinatorial and topological properties of singular virtual braids. On the algebraic side we state the relations between classical and virtual singular objects, in addition we discuss a Birman-like conjecture for the virtual case. On the topological and combinatorial side, we prove that there is a bijection between singular abstract braids, horizontal Gauss diagrams and singular virtual braids, in particular using horizontal Gauss diagrams we obtain a presentation of the singular pure virtual braid monoid.

扭曲虚拟辫子群

Twisted Virtual Braid Group

本文研究扭曲虚拟辫子群TVBₙ的子群结构与半直积分解，确定了TVPₙ、TVHₙ等子群的生成元、定义关系及分解形式，得出VPₙ是TVPₙ子群的结论，丰富了虚拟辫子群的代数结构研究。

A simple solution to the word problem for virtual braid groups

We show a simple and easily implementable solution to the word problem for virtual braid groups.

Representations of virtual braids by automorphisms and virtual knot groups

In the present paper the representation of the virtual braid group $VB_n$ into the automorphism group of free product of the free group and free abelian group is constructed. This representation generalizes the previously constructed ones. The fact that these already known representations are not faithful for $n \geq 4$ is verified. Using representations of $VB_n$, the virtual link group is defined. Also representations of welded braid group $WB_n$ are constructed and the welded link group is defined.

Classifying spaces for the family of virtually cyclic subgroups of braid groups

We prove that, for $n\geq 3$, the minimal dimension of a model of the classifying space of the full braid group $B_n$, and of the pure braid group $P_n$, with respect to the family of virtually cyclic groups is $n$.

纯辫群是RFRS

Pure braid groups are RFRS

该研究证明纯辫群是RFRS，肯定了Agol2014年提出的辫群是否为虚拟RFRS的问题，还为Artin群是否虚拟特殊的问题提供了证据。

Multi-switches and representations of braid groups

In the paper, we introduce the notion of a (virtual) multi-switch which generalizes the notion of a (virtual) switch. Using (virtual) multi-switches we introduce a general approach on how to construct representations of (virtual) braid groups by automorphisms of algebraic systems. As a corollary, we introduce new representations of virtual braid groups which generalize several previously known representations.

虚拟奇异辫群研究

On virtual singular braid groups

本文研究了虚拟奇异辫群的代数性质，引入了基于单词指数和的数值不变量，确定了到对称群的同态，并给出了核的半直积分解。

On virtual embeddings of braid groups into mapping class groups of surfaces

In this article, we give a necessary and sufficient condition for embedding a finite index subgroup of Artin's braid group into the mapping class group of a connected orientable surface.

虚拟奇异辫子之间的代数结构

Algebraic structures among virtual singular braids

该研究证明n股虚拟奇异辫子幺半群可嵌入群VSGₙ，给出其半直积结构与VSPGₙ的表示及子群分解，为虚拟奇异辫子的代数结构分析提供基础。

Lifting theorem for the virtual pure braid groups

In this article we prove theorem on Lifting for the set of virtual pure braid groups. This theorem says that if we know presentation of virtual pure braid group $VP_4$, then we can find presentation of $VP_n$ for arbitrary $n > 4$. Using this theorem we find the set of generators and defining relations for simplicial group $T_*$ which was defined in the previuos article of the authors. We find a decomposition of the Artin pure braid group $P_n$ in semi-direct product of free groups in the cabled generators.

On the pure virtual braid group $PV_3$

In this article, we investigate various properties of the pure virtual braid group PV_3. From its canonical presentation, we obtain a free product decomposition of PV_3. As a consequence, we show that PV_3 is residually torsion free nilpotent, which implies that the set of finite type invariants in the sense of Goussarov-Polyak-Viro is complete for virtual pure braids with three strands. Moreover we prove that the presentation of PV_3 is aspherical. Finally we determine the cohomology ring and the associated graded Lie algebra of PV_3.

虚拟辫子群、虚拟孪生群与晶体群

Virtual braid groups, virtual twin groups and crystallographic groups

本文证明虚拟辫子群与虚拟孪生群模去对应纯群换位子群后的商为晶体群，刻画其有限阶元素与共轭类，并实现 Bieberbach 群及无限虚拟循环群。

奇异扭曲虚拟辫子的幺半群结构

The monoid structure of singular twisted virtual braids

本文研究奇异扭曲虚拟辫子幺半群$STVB_n$的子幺半群结构，确定$STVP_n$为$STVB_n$到$S_n$满同态的核及其生成元与关系，构造类似满同态并推广表示，证明$STVB_n$可嵌入群。

虚拟平面辫群与置换

Virtual planar braid groups and permutations

本文完整刻画了虚拟孪生群到对称群的同态，由此确定其自同构群结构，并证明孪生群嵌入虚拟孪生群，类比辫群结果。

The conjugacy problem and virtually cyclic subgroups in the Artin braid group quotient $B_n/[P_n,P_n]$

Let $n\geq 3$. In this paper we deal with the conjugacy problem in the Artin braid group quotient $B_n/[P_n,P_n]$. To solve it we use systems of equations over the integers arising from the action of $B_n/[P_n,P_n]$ over the abelianization of the pure Artin braid group $P_n/[P_n,P_n]$. Using this technique we also realize explicitly infinite virtually cyclic subgroups in $B_n/[P_n,P_n]$.

Classification of the virtually cyclic subgroups of the pure braid groups of the projective plane

We classify the (finite and infinite) virtually cyclic subgroups of the pure braid groups $P_{n}(RP^2)$ of the projective plane. The maximal finite subgroups of $P_{n}(RP^2)$ are isomorphic to the quaternion group of order 8 if $n=3$, and to $\Z_{4}$ if $n\geq 4$. Further, for all $n\geq 3$, up to isomorphism, the following groups are the infinite virtually cyclic subgroups of $P_{n}(RP^2)$: $\Z$, $\Z_{2} \times \Z$ and the amalgamated product $\Z_{4} \ast_{\Z_{2}} \Z_{4}$.

Pure virtual braids, resonance, and formality

We investigate the resonance varieties, lower central series ranks, and Chen ranks of the pure virtual braid groups and their upper-triangular subgroups. As an application, we give a complete answer to the 1-formality question for this class of groups. In the process, we explore various connections between the Alexander-type invariants of a finitely generated group and several of the graded Lie algebras associated to it, and discuss possible extensions of the resonance-Chen ranks formula in this context.

通用虚拟编织群

Universal virtual braid groups

本文引入了通用虚拟编织群UV_n(c)，提供了一种统一的代数框架，用于虚拟编织结构，证明其具有残余有限性、线性、解字和共轭问题等性质，并分类了子群分离性和Howson性质。

Virtual and universal braid groups, their quotients and representations

In the present paper we study structural aspects of certain quotients of braid groups and virtual braid groups. In particular, we construct and study linear representations $B_n\to {\rm GL}_{n(n-1)/2}\left(\mathbb{Z}[t^{\pm1}]\right)$, $VB_n\to {\rm GL}_{n(n-1)/2}\left(\mathbb{Z}[t^{\pm1}, t_1^{\pm1},t_2^{\pm1},\ldots, t_{n-1}^{\pm1}]\right)$ which are connected with the famous Lawrence-Bigelow-Krammer representation. It turns out that these representations are faithful representations of crystallographic groups $B_n/P_n'$, $VB_n/VP_n'$, respectively. Using these representations we study certa…

Representations of flat virtual braids which do not preserve the forbidden relations

In the paper, we construct a representation $θ:FVB_n\to{\rm Aut}(F_{2n})$ of the flat virtual braid group $FVB_n$ on $n$ strands by automorphisms of the free group $F_{2n}$ with $2n$ generators which does not preserve the forbidden relations in the flat virtual braid group. This representation gives a positive answer to the problem formulated by V. Bardakov in the list of unsolved problems in virtual knot theory and combinatorial knot theory by R. Fenn, D. Ilyutko, L. Kauffman and V. Manturov. Using this representation we construct a new group invariant for flat welded links. Also we find the …

关于虚拟Artin群的可分解性

On Decomposability of Virtual Artin Groups

本文研究了虚拟Artin群的可分解性，证明了任何连通Coxeter图对应的虚拟Artin群都是不可分解的，虚拟辫群也不例外。

Virtual Thompson 群

Virtual Thompson's group

本文受虚拟辫群推广自辫群且可生成虚拟链环、Thompson群$F$可构造有向链环的研究启发，定义了Thompson群$F$的虚拟版本并证明其可构造任意虚拟链环。

Finite Thurston type orderings on dual braid monoids

For a finite Thurston type ordering < of the braid group B_{n}, we introduce a new normal form of a dual positive braid which we call the C-normal form. This normal form extends Fromentin's rotating normal form and the author's C-normal form of positive braids. Using the C-normal form, we give a combinatorial description of the restriction of the ordering < to the dual braid monoids B_{n}^{+*}. We prove that the restriction to the dual positive monoid (B_{n}^{+*},<) is a well-ordered set of order type ω^{ω^{n-2}}.

Finite image homomorphisms of the braid group and its generalizations

Using totally symmetric sets, Chudnovsky, Kordek, Li, and Partin gave a superexponential lower bound on the cardinality of non-abelian finite quotients of the braid group. In this paper, we develop new techniques using multiple totally symmetric sets to count elements in non-abelian finite quotients of the braid group. Using these techniques, we improve the lower bound found by Chudnovsky et al. We exhibit totally symmetric sets in the virtual and welded braid groups, and use our new techniques to find superexponential bounds for the finite quotients of the virtual and welded braid groups.

基于非负欧拉特征表面纯辫群虚阿贝尔子群族的分类空间

Classifying spaces for families of virtually abelian subgroups of surface braid groups

本文研究了表面纯辫群虚阿贝尔子群族的分类空间的最小维数，证明其等于群的虚上同调维数加n，并应用于计算可算子群族的分类空间最小维数。

On finite Thurston type orderings of braid groups

We prove that for any finite Thurston-type ordering $<_{T}$ on the braid group\ $B_{n}$, the restriction to the positive braid monoid $(B_{n}^{+},<_{T})$ is a\ well-ordered set of order type $ω^{ω^{n-2}}$. The proof uses a combi\ natorial description of the ordering $<_{T}$. Our combinatorial description is \ based on a new normal form for positive braids which we call the $\C$-normal fo\ rm. It can be seen as a generalization of Burckel's normal form and Dehornoy's \ $Φ$-normal form (alternating normal form).

Commutator Subgroups of Virtual and Welded Braid Groups

Let $VB_n$, resp. $WB_n$ denote the virtual, resp. welded, braid group on $n$ strands. We study their commutator subgroups $VB_n' = [VB_n, VB_n]$ and, $WB_n' = [WB_n, WB_n]$ respectively. We obtain a set of generators and defining relations for these commutator subgroups. In particular, we prove that $VB_n'$ is finitely generated if and only if $n \geq 4$, and $WB_n'$ is finitely generated for $n \geq 3$. Also we prove that $VB_3'/VB_3'' =\mathbb{Z}_3 \oplus \mathbb{Z}_3 \oplus\mathbb{Z}_3 \oplus \mathbb{Z}^{\infty}$, $VB_4' / VB_4'' = \mathbb{Z}_3 \oplus \mathbb{Z}_3 \oplus \mathbb{Z}_3$, $WB…

关于通用虚拟和焊接辫群及其线性表示

On Universal Virtual and Welded Braid Groups and Their Linear Representations

本文研究了通用虚拟辫群的线性表示，并探讨了其焊接辫群的结构与性质，包括其交换化、完美交换子群及有限商群等特征。

The classification of the virtually cyclic subgroups of the sphere braid groups

We study the problem of determining the isomorphism classes of the virtually cyclic subgroups of the n-string braid groups B_n(S^2) of the 2-sphere S^2. If n is odd, or if n is even and sufficiently large, we obtain the complete classification. For small even values of n, the classification is complete up to an explicit finite number of open cases. In order to prove our main theorem, we obtain a number of other results of independent interest, notably the characterisation of the centralisers and normalisers of the finite cyclic and dicyclic subgroups of B_n(S^2), a result concerning conjugate …

与虚拟阿廷群相关的空间

Spaces Related to Virtual Artin Groups

本文为任意Coxeter图定义CW复形Ω(Γ)，其基本群同构于纯虚拟阿廷群，并证明当Γ为球型或仿射型时Ω(Γ)是零调的，从而将其刻画为分类空间，通过连接Salvetti复形和K(π,1)猜想实现。

字母编织：连接组合群论与拓扑学

Letter-braiding: bridging combinatorial group theory and topology

该研究提出字母编织不变量，其为维数序列的完全不变量，可用于定义Johnson滤子和同态变体以约束有限p群自同构，连接组合群论与拓扑学。

曲面辫群和多曲面群的渐近维数和上同调维数

Asymptotic and cohomological dimension of surface braid groups and poly-surface groups

本文确定了所有曲面辫群（包括非定向和无限类型曲面相关群）的渐近维数，以及无 torsion 多有限生成曲面群的渐近维数。证明了这两类群的虚拟上同调维数与渐近维数相同，并展示了这些群在 Bieri-Eckmann 意义下是虚拟对偶群。

A braided simplicial group

By studying braid group actions on Milnor's construction of the 1-sphere, we show that the general higher homotopy group of the 3-sphere is the fixed set of the pure braid group action on certain combinatorially described group. We also give certain representation of higher differentials in the Adams spectral sequence for the homotopy groups of the 2-sphere.

Interval Garside Structures for the Complex Braid Groups B(e,e,n)

We define geodesic normal forms for the general series of complex reflection groups G(e,e,n). This requires the elaboration of a combinatorial technique in order to explicitly determine minimal word representatives of the elements of G(e,e,n) over the generating set of the presentation of Corran-Picantin. Using these geodesic normal forms, we construct intervals in G(e,e,n) that are lattices. This gives rise to interval Garside groups. We determine which of these groups are isomorphic to the complex braid group B(e,e,n) and get a complete classification. For the other Garside groups that appea…

Actions of the braid group, and new algebraic proofs of results of Dehornoy and Larue

This article surveys many standard results about the braid group with emphasis on simplifying the usual algebraic proofs. We use van der Waerden's trick to illuminate the Artin-Magnus proof of the classic presentation of the algebraic mapping-class group of a punctured disc. We give a simple, new proof of the Dehornoy-Larue braid-group trichotomy, and, hence, recover the Dehornoy right-ordering of the braid group. We then turn to the Birman-Hilden theorem concerning braid-group actions on free products of cyclic groups, and the consequences derived by Perron-Vannier, and the connections with t…

$K(π,1)$ and word problems for infinite type Artin-Tits groups, and applications to virtual braid groups

Let $Γ$ be a Coxeter graph, let $(W,S)$ be its associated Coxeter system, and let $(A,Σ$) be its associated Artin-Tits system. We regard $W$ as a reflection group acting on a real vector space $V$. Let $I$ be the Tits cone, and let $E_Γ$ be the complement in $I +iV$ of the reflecting hyperplanes. Recall that Charney, Davis, and Salvetti have constructed a simplicial complex $Ω(Γ)$ having the same homotopy type as $E_Γ$. We observe that, if $T \subset S$, then $Ω(Γ_T)$ naturally embeds into $Ω(Γ)$. We prove that this embedding admits a retraction $π_T: Ω(Γ) \to Ω(Γ_T)$, and we deduce several to…

置换 wreath 拉回与带框架的辫型群

Permutational wreath pullbacks and framed braid-type groups

本文引入置换 wreath 拉回结构，研究其中心和交换化，并探讨其作为经典 wreath 产品拉回的解释，同时建立有限生成阿贝尔群的条件，以继承 R_∞ 性质。

The inclusion of configuration spaces of surfaces in Cartesian products, its induced homomorphism, and the virtual cohomological dimension of the braid groups of S^2 and RP^2

Let M be a surface, perhaps with boundary, and either compact, or with a finite number of points removed from the interior of the surface. We consider the inclusion i: F\_n(M) --\textgreater{} M^n of the nth configuration space F\_n(M) of M into the n-fold Cartesian product of M, as well as the induced homomorphism i\_\#: P\_n(M) --\textgreater{} (π\_1(M))^n, where P\_n(M) is the n-string pure braid group of M. Both i and i\_\# were studied initially by J.Birman who conjectured that Ker(i\_\#) is equal to the normal closure of the Artin pure braid group P\_n in P\_n(M). The conjecture was late…

拟阿贝尔化辫群的上同调

Cohomology of quasi-abelianized braid groups

本研究针对广义辫群模纯辫群换位子群的商群有理上同调问题，通过图族同构类给出组合描述，建立了庞加莱对偶性并证明了无穷反射群序列的稳定性质。

Virtual Artin groups

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…

配置李群胚与轨道折叠辫群

Configuration Lie groupoids and orbifold braid groups

本文提出配置李群胚的两种定义，证明一类李群胚的Fadell-Neuwirth型纤维化定理，并利用纯轨道折叠辫群的多重几乎自由结构，推导出相应Artin群及轨道折叠辫群的Farrell-Jones猜想。

The pure braid groups and their relatives

In this mostly survey paper, we investigate the resonance varieties, the lower central series ranks, and the Chen ranks, as well as the residual and formality properties of several families of braid-like groups: the pure braid groups $P_n$, the welded pure braid groups $wP_n$, the virtual pure braid groups $vP_n$, as well as their `upper' variants, $wP_n^+$ and $vP_n^+$. We also discuss several natural homomorphisms between these groups, and various ways to distinguish among the pure braid groups and their relatives.

Uniform measures on braid monoids and dual braid monoids

We aim at studying the asymptotic properties of typical positive braids, respectively positive dual braids. Denoting by $μ_k$ the uniform distribution on positive (dual) braids of length $k$, we prove that the sequence $(μ_k)_k$ converges to a unique probability measure $μ_{\infty}$ on infinite positive (dual) braids. The key point is that the limiting measure $μ_{\infty}$ has a Markovian structure which can be described explicitly using the combinatorial properties of braids encapsulated in the Möbius polynomial. As a by-product, we settle a conjecture by Gebhardt and Tawn (J. Algebra, 2014) …

下中心序列、曲面辫群、满射与置换

Lower central series, surface braid groups, surjections and permutations

本文推广了Artin和Lin关于经典辫群的结果，确定了无边界可定向曲面辫群间满射存在的条件，并给出了有边界及不可定向曲面的部分结果及对称群表示分类。

The lower algebraic $K$-theory of virtually cyclic subgroups of the braid groups of the sphere and of $\mathbb{Z}[B\_4(\mathbb{S}^2)]$

We study $K$-theoretical aspects of the braid groups $B\_n(\mathbb{S}^{2})$ on $n$ strings of the $2$-sphere, which by results of the second two authors, are known to satisfy the Farrell-Jones fibred isomorphism conjecture~\cite{JM}. In light of this, in order to determine the algebraic $K$-theory of the group ring $\mathbb{Z}[B\_n(\mathbb{S}^{2})]$, one should first compute that of its virtually cyclic subgroups, which were classified by D.~L.~Gon{\c c}alves and the first author. We calculate the Whitehead and $K\_{-1}$-groups of the group rings of the finite subgroups (dicyclic and binary po…

Commutator Subgroups of Singular Braid Groups

The singular braids with $n$ strands, $n \geq 3$, were introduced independently by Baez and Birman. It is known that the monoid formed by the singular braids is embedded in a group that is known as singular braid group, denoted by $SG_n$. There has been another generalization of braid groups, denoted by $GVB_n$, $n \geq 3$, which was introduced by Fang as a group of symmetries behind quantum quasi-shuffle structures. The group $GVB_n$ simultaneously generalizes the classical braid group, as well as the virtual braid group on $n$ strands. We investigate the commutator subgroups $SG_n'$ and $GVB…

虚 torsion 自由和虚自由群的组合特征

Combinatorial Characterizations of Virtually Torsion-Free and Virtually Free Groups

本文通过图分解理论，研究了虚 torsion 自由和虚自由群的组合特征，并建立了相应的等价条件。