Braids on surfaces and finite type invariants

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。

Lower central series for surface braid groups

We determine the lower central series and corresponding residual properties for braid groups and pure braid groups of orientable surfaces.

Ordering pure braid groups on closed surfaces

We prove that the pure braid groups on closed, orientable surfaces are bi-orderable, and that the pure braid groups on closed, non-orientable surfaces have generalized torsion, thus they are not bi-orderable.

New presentations of surface braid groups

In this paper we give new presentations of the braid groups and the pure braid groups of a closed surface. We also give an algorithm to solve the word problem in these groups, using the given presentations.

Automorphisms of surface braid groups

In this paper, we prove that each automorphism of a surface braid group is induced by a homeomorphism of the underlying surface, provided that this surface is a closed, connected, orientable surface of genus at least 2, and the number of strings is at least three. This result generalizes previous results for classical braid groups, mapping class groups, and Torelli groups.

Birman's conjecture for singular braids on closed surfaces

Let $M$ be a closed oriented surface of genus $g\ge 1$, let $B_n(M)$ be the braid group of $M$ on $n$ strings, and let $SB_n(M)$ be the corresponding singular braid monoid. Our purpose in this paper is to prove that the desingularization map $η: SB_n(M) \to \Z [B_n(M)]$, introduced in the definition of the Vassiliev invariants (for braids on surfaces), is injective.

A family of representations of braid groups on surfaces

We propose a family of new representations of the braid groups on surfaces that extend linear representations of the braid groups on a disc such as the Burau representation and the Lawrence-Krammer-Bigelow representation.

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.

Exact sequences, lower central series and representations of surface braid groups

We consider exact sequences and lower central series of surface braid groups and we explain how they can prove to be useful for obtaining representations for surface braid groups. In particular, using a completely algebraic framework, we describe the notion of extension of a representation introduced and studied recently by An and Ko and independently by Blanchet.

On the singular braid monoid of an orientable surface

In this paper we show that the singular braid monoid of an orientable surface can be embedded in a group. The proof is purely topological, making no use of the monoid presentation.

Presentations for the monoids of singular braids on closed surfaces

We give presentations, in terms of generators and relations, for the monoids of singular braids on closed surfaces. The proof of the validity of these presentations can also be applied to verify, in a new way, the presentations given by Birman for the monoids of Singular Artin braids.

Embeddings of the braid groups of covering spaces, classification of the finite subgroups of the braid groups of the real projective plane, and linearity of braid groups of low-genus surfaces

Let M be a compact, connected surface, possibly with a finite set of points removed from its interior. Let d,n be positive integers, and let N be a d-fold covering space of M. We show that the covering map induces an embedding of the n-th braid group B_n(M) of M in the (dn)-th braid group B_{dn}(N) of N, and give several applications of this result. First, we classify the finite subgroups of the n-th braid group of the real projective plane, from which we deduce an alternative proof of the classification of the finite subgroups of the mapping class group of the n-punctured real projective plan…

Brunnian Braids on Surfaces

We determine a set of generators for the Brunnian braids on a general surface $M$ for $M\not=S^2$ or $\RP^2$. For the case $M=S^2$ or $\RP^2$, a set of generators for the Brunnian braids on $M$ is given by our generating set together with the homotopy groups of a 2-sphere.

The BNS-invariant for the pure braid groups

In 1987 Bieri, Neumann and Strebel introduced a geometric invariant for discrete groups. In this article we compute and explicitly describe the BNS-invariant for the pure braid groups.

Separation in the BNSR-invariants of the pure braid groups

We inspect the BNSR-invariants $Σ^m(P_n)$ of the pure braid groups $P_n$, using Morse theory. The BNS-invariants $Σ^1(P_n)$ were previously computed by Koban, McCammond and Meier. We prove that for any $3\le m\le n$, the inclusion $Σ^{m-2}(P_n)\subseteq Σ^{m-3}(P_n)$ is proper, but $Σ^\infty(P_n)=Σ^{n-2}(P_n)$. We write down explicit character classes in each relevant $Σ^{m-3}(P_n)\setminus Σ^{m-2}(P_n)$. In particular we get examples of normal subgroups $N\le P_n$ with $P_n/N\cong\mathbb{Z}$ such that $N$ is of type $F_{m-3}$ but not $F_{m-2}$, for all $3\le m\le n$.

Free groups and finite type invariants of pure braids

Finite type invariants (also known as Vassiliev invariants) of pure braids are considered from a group-theoretic point of view. New results include a construction of a universal invariant with integer coefficients based on the Magnus expansion of a free group and a calculation of numbers of independent invariants of each type for all pure braid groups.

剪切坐标与辫群不变量

Shear coordinates and braid invariants

本文利用双曲几何中的剪切坐标构造辫群不变量，并指出该方法存在热带几何类比。

Link invariants from $L^2$-Burau maps of braids

A previous work of A. Conway and the author introduced $L^2$-Burau maps of braids, which are generalizations of the Burau representation whose coefficients live in a more general group ring than the one of Laurent polynomials. This same work established that the $L^2$-Burau map of a braid at the group of the braid closure yields the $L^2$-Alexander torsion of the braid closure in question, as a variant of the well-known Burau-Alexander formula. In the present paper, we generalize the previous result to $L^2$-Burau maps defined over all quotients of the group of the braid closure. The link inva…

Commensurators of surface braid groups

We prove that if g and n are integers at least two, then the abstract commensurator of the braid group with n strands on a closed orientable surface of genus g is naturally isomorphic to the extended mapping class group of a compact orientable surface of genus g with n boundary components.

The Burau matrix and Fiedler's invariant for a closed braid

It is shown how Fiedler's `small state-sum' invariant for a braid can be calculated from the 2-variable Alexander polynomial of the link which consists of the closed braid together with the braid axis.

Crossing matrix and a polynomial invariant of braid systems up to Hurwitz equivalence

Crossing matrix and a polynomial invariant of braid systems up to Hurwitz equivalence

研究辫子的交叉矩阵，引入一个在Hurwitz等价下不变的辫子系统多项式不变量，并应用于曲面辫子和曲面链接，定义了一个指示辫子系统之间是否需要欧拉融合或分裂的不变量。

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。

关于纯辫子的一个不变量

On an invariant of pure braids

本文利用重耦合理论构造纯辫子群的一个表示，并证明其非平凡性，从而给出纯辫子的一个不变量。

Polynomial braid combing

Braid combing is a procedure defined by Emil Artin to solve the word problem in braid groups for the first time. It is well-known to have exponential complexity. In this paper, we use the theory of straight line programs to give a polynomial algorithm which performs braid combing. This procedure can be applied to braids on surfaces, providing the first algorithm (to our knowledge) which solves the word problem for braid groups on surfaces with boundary in polynomial time and space. In the case of surfaces without boundary, braid combing needs to use a section from the fundamental group of the …

八边形与热带八边形生成辫子不变量

Octagon and tropical octagon yield braid invariants

本文构造了实射影平面中辫子的不变量，对应辫子对$\text{RP}^2$中带标签特定图的作用，是相关文献的续篇，证明不同形式八边形关系解可生成辫子不变量。

曲面轨形纯辫群的四项正合序列

A four-term exact sequence of surface orbifold pure braid groups

本文证明了亏格大于等于1且带锥点的二维可定向曲面轨形纯辫群存在四项正合序列，并纠正了此前arXiv.2106.08110中的结果。

A remark on the Hopf invariant for spherical 4-braids

An approach by J.Wu describes homotopy groups $π_{n}(S^2)$ of the standard 2-sphere as isotopy classes of spherical $n+1$--strand Brunnian braids is investigated in the case $n=3$ for applications.

The co-Hopfian property of surface braid groups

Let g and n be integers at least two, and let G be the pure braid group with n strands on a closed orientable surface of genus g. We describe any injective homomorphism from a finite index subgroup of G into G. As a consequence, we show that any finite index subgroup of G is co-Hopfian.

Representations of the braid group by automorphisms of groups, invariants of links, and Garside groups

From a group $H$ and a non-trivial element $h$ of $H$, we define a representation $ρ: B_n \to \Aut(G)$, where $B_n$ denotes the braid group on $n$ strands, and $G$ denotes the free product of $n$ copies of $H$. Such a representation shall be called the Artin type representation associated to the pair $(H,h)$. The goal of the present paper is to study different aspects of these representations. Firstly, we associate to each braid $β$ a group $Γ_{(H,h)} (β)$ and prove that the operator $Γ_{(H,h)}$ determines a group invariant of oriented links. We then give a topological construction of the Arti…

Braid and knot invariants via triangulations and Ptolemy relations I

In this paper, we construct invariants of braids, knots and links by studying dynamics of points in $\R^{2}$ and applying the Ptolemy relation $ac+bd=xy$.

Invariants of Classical Braids Valued in $G_{n}^{2}$

The aim of the present note is to construct invariants of the Artin braid group valued in $G_{N}^{2}$, and further study of groups related to $G_{n}^{3}$. In the groups $G_{n}^{2}$, the word problem is solved; these groups are much simpler than $G_{n}^{3}$.

曲面辫群的最小非交换商

Smallest nonabelian quotients of surface braid groups

本文给出曲面辫群非交换商大小的精确下界，并分类达到下界的商为对称群或2步幂零p-群。

Minimum Braids: A Complete Invariant of Knots and Links

Minimum braids are a complete invariant of knots and links. This paper defines minimum braids, describes how they can be generated, presents tables for knots up to ten crossings and oriented links up to nine crossings, and uses minimum braids to study graph trees, amphicheirality, unknotting numbers, and periodic tables.

可定向曲面上辫群的 R$_{\infty}$-性质

The R$_{\infty}$-property for braid groups over orientable surfaces

本文研究了可定向曲面上纯辫群与全辫群的 R$_{\infty}$-性质，并证明除少数例外，这些群均具有该性质。

带点 rack 及其在辫子理论中的应用

Pointed Racks and Their Applications to Braid Theory

该研究定义了带点 rack 这一新代数结构，构造出 n-辫子的环境同痕不变量，包括整数值与矩阵值不变量，其可确定已有 rack 着色不变量，还给出了能被区分的辫子示例。

One-cocycle invariants for closed braids

We introduce new polynomial isotopy invariants for closed braids. They are constructed as polynomial valued {\em Gauss diagram 1-cocycles} evaluated on the full rotation of the closed braid $\hat β$ around the core of the corresponding solid torus. They can be calculated with polynomial complexity with respect to the braid length and their derivatives evaluated at $x=1$ are finite type invariants of closed braids. Let the solid torus V be standardly embedded in the 3-sphere and let L be the core of the complementary solid torus $S^3\setminus V$. We give examples which show that a natural refin…

Annular Rasmussen invariants: Properties and 3-braid classification

We prove that for a fixed braid index there are only finitely many possible shapes of the annular Rasmussen $d_t$ invariant of braid closures. Applying the same perspective to the knot Floer invariant $Υ_K(t)$, we show that for a fixed concordance genus of $K$ there are only finitely many possibilities for $Υ_K(t)$. Focusing on the case of 3-braids, we compute the Rasmussen $s$ invariant and the annular Rasmussen $d_t$ invariant of all 3-braid closures. As a corollary, we show that the vanishing/non-vanishing of the $ψ$ invariant is entirely determined by the $s$ invariant and the self-linking…

On p-almost direct products and residual properties of pure braid groups of nonorientable surfaces

We prove that the n th pure braid group of a nonorientable surface (closed or with boundary, but different from RP2) is residually 2-finite. Consequently, this group is residually nilpotent. The key ingredient in the closed case is the notion of p-almost direct product, which is a generalization of the notion of almost direct product. We prove therefore also some results on lower central series and augmentation ideals of p-almost direct products.

Vassiliev invariants and knots modulo pure braid subgroups

We show that two knots have matching Vassiliev invariants of order less than n if and only if they are equivalent modulo the nth group of the lower central series of some pure braid group, thus characterizing Vassiliev's knot invariants in terms of the structure of the braid groups. We also prove some results about knots modulo the nth derived subgroups of the pure braid groups, and about knots modulo braid subgroups in general.

On a Map From Pure Braids to Knots

We study a certain type of braid closure which resembles the plat closure but has certain advantages; for example, it maps pure braids to knots. The main results of this note are a Markov-type theorem and a description of how Vassiliev invariants behave under this braid closure.

Isotopy and homeomorphism of closed surface braids

The closure of a braid in a closed orientable surface $Σ$ is a link in $Σ\times S^1$. We classify such closed surface braids up to isotopy and homeomorphism (with a small indeterminacy for isotopy of closed sphere braids), algebraically in terms of the surface braid group. We find that in positive genus, braids close to isotopic links if and only if they are conjugate, and close to homeomorphic links if and only if they are in the same orbit of the outer action of the mapping class group on the surface braid group modulo its center.

On cobordisms between knots, braid index, and the Upsilon-invariant

We use Ozsváth, Stipsicz, and Szabó's Upsilon-invariant to provide bounds on cobordisms between knots that `contain full-twists'. In particular, we recover and generalize a classical consequence of the Morton-Franks-Williams inequality for knots: positive braids that contain a positive full-twist realize the braid index of their closure. We also establish that quasi-positive braids that are sufficiently twisted realize the minimal braid index among all knots that are concordant to their closure. Finally, we provide inductive formulas for the Upsilon invariant of torus knots and compare it to t…

机器学习发现辫群与平辫的不变量

Machine learning discovers invariants of braids and flat braids

本研究采用基于多层感知机的监督学习对辫与平辫做平凡性分类，通过解读模型结构提出并证明数学猜想，发现了新的辫不变量及平辫完全不变量。

Single-colored ADO-3 invariant is a specialization of Links-Gould invariant for closures of 5-braids

We prove that for knots and links that are closures of 5-braids, single-colored ADO-invariant of third order coincides with Links-Gould polynomial with specific choice of variables. We also conjecture that this is true for any knots and links and provide some arguments for that.

Long--Moody 构造与扭曲 Alexander 不变量

The Long--Moody construction and twisted Alexander invariants

本文证明 Long--Moody 构造的矩阵表示可用 Fox 导数表达，并揭示其与扭曲 Alexander 不变量的关系。

Isotopy invariants for closed braids and almost closed braids via loops in stratified spaces

Let $ϕ: S^1\times D^2\to S^1$ be the natural projection. An oriented knot $K\hookrightarrow V = S^1\times D^2$ is called an almost closed braid if the restriction of $ϕ$ to K has exactly two (non-degenerate) critical points (and K is a closed braid if the restriction of $ϕ$ has no critical points at all). We introduce new isotopy invariants for closed braids and almost closed braids in the solid torus V. These invariants refine finite type invariants. They are still calculable with polynomial complexity with respect to the number of crossings of K. Let the solid torus V be standardly embedded …

New groups and invariants of classical braids valued in $G_{n}^{2}$

The aim of the present note is to enhance groups $G_{n}^{3}$ and to construct new invariants of classical braids. In particular, we construct invariants valued in $G_{N}^{2}$ groups. In groups $G_{n}^{2}$, the identity problem is solved, besides, their structure is much simpler than that of $G_{n}^{3}$. I am grateful to Huyue Yan for pointing out a small mistake in the previous version.

Braid commutators and delta finite-type invariants

Delta finite-type invariants are defined analogously to finite-type invariants, using delta moves instead of crossing changes. We show that they are closely related to the lower central series of the commutator subgroup of the pure braid group.

On presentation of Surface Braid Groups

We give presentations of braid groups and pure braid groups on surfaces.

Surface framed braids

In this paper we introduce the framed pure braid group on $n$ strands of an oriented surface, a topological generalisation of the pure braid group $P_n$. We give different equivalents definitions for framed pure braid groups and we study exact sequences relating these groups with other generalisations of $P_n$, usually called surface pure braid groups. The notion of surface framed braid groups is also introduced.

基本群、3-辫群与不变量的有效估计

Fundamental Groups, 3-Braids, and Effective Estimates of Invariants

本研究定义辫群不变量，通过纯3-辫的自然音节分解给出其不变量及熵的有效上下界（界间差为不依赖字的乘法常数），并推广至所有3-辫，证明涉及双穿孔复平面基本群曲线的极值长度研究。

来自Yang-Baxter算子的曲面辫子不变量及其上同调

Surface Braid Invariants from Yang-Baxter Operators and Their Cohomology

本文提出利用Yang-Baxter算子通过辫子系统构造曲面辫子不变量，并借助图表使用其3-上循环，推广了quandle上循环不变量，讨论了闭包定义纽结曲面不变量的方法。

Markov trace on the algebra of braids and ties

We prove that the so-called t algebra of braids and ties supports a Markov trace. Further, by using this trace in the Jones' recipe, we define invariant polynomials for classical knots and singular knots. Our invariants have three parameters. The invariant of classical knots is an extension of the Homflypt polynomial and the invariant of singular knots is an extension of an invariant of singular knots previously defined by S. Lambropoulou and the second author.

Invariants of closed braids via counting surfaces

A Gauss diagram is a simple, combinatorial way to present a link. It is known that any Vassiliev invariant may be obtained from a Gauss diagram formula that involves counting subdiagrams of certain combinatorial types. In this paper we present simple formulas for an infinite family of invariants in terms of counting surfaces of a certain genus and number of boundary components in a Gauss diagram associated with a closed braid. We then identify the resulting invariants with partial derivatives of the HOMFLY-PT polynomial.