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Luis Paris

Publications and source records attributed to Luis Paris.

At least 19 recordsLinked to original sources
arXiv2026

A cube complex for virtual Artin groups

Let $\Gamma$ be a Coxeter graph, and let $S$ be its vertex set. An elemental complex over $\Gamma$ is an abstract simplicial complex $\mathcal D$ on $S$ that contains every pair $\{s, t\}$ with $s \neq t$ and $m_{s,t} \neq \infty$. To each elemental complex $\mathcal D$, we associate a cube complex $\Xi_\mathcal D$ on which the virtual Artin group $\rm VA [\Gamma]$ acts. We prove that $\Xi_\mathcal D$ is connected, simply connected, and locally regular; that the action of $\rm VA[\Gamma]$ on $\Xi_\mathcal D$ is regular, cocompact, and by isometries; and that the stabilizers of cells are parabolic subgroups. We finally prove that $\XiÆ’_\mathcal D$ is CAT(0) if and only if $\mathcal D$ is a flag complex.

math.GR↗
arXiv2026

The braid group Bn is not a quotient of a quasi-Coxeter interval group of type Dn

We prove that, for $n \ge 5$, an interval group associated with a proper quasi-Coxeter element of the Coxeter group of type $D_n$ admits no surjective homomorphism onto the braid group on $n$ strands. In particular, this provides an alternative proof that such a group is not isomorphic to the Artin group of type $D_n$. The proof relies on techniques from the theory of mapping class groups, and a large part of the paper provides an exposition of this theory for non-specialists.

math.GR↗
arXiv2026

Automorphisms of the Artin group of type $D_5$

For the Artin group of type $D_5$, we determine its automorphism group and the automorphism group of its quotient by the center. This settles the only remaining case, $n=5$, in the classification of automorphisms of Artin groups of spherical type $D_n$.

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arXiv2026

Classification of Artin groups admitting retractions onto their parabolic subgroups

We classify the Artin groups that admit retractions onto all of their parabolic subgroups. Our approach relies on a detailed analysis of triangular subgroups, with a key ingredient being the classification of homomorphisms between dihedral Artin groups that map one of the standard generators to a standard generator. As a consequence, we show that whenever an Artin group admits retractions to parabolic subgroups, it also admits ordinary ones - that is, retractions that send each standard generator either to a standard generator or to the identity.

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arXiv2026

Parabolic subgroups and word problem in virtual Artin groups

We begin by establishing two fundamental results on standard parabolic subgroups of virtual Artin groups. We first show that a standard parabolic subgroup is naturally isomorphic to a virtual Artin group. Second, we prove that the intersection of two standard parabolic subgroups is a standard parabolic subgroup. Our main result is that, if all free of infinity standard parabolic subgroups of a given virtual Artin group VA[{\Gamma}] have a solvable word problem, then VA[{\Gamma}] itself has a solvable word problem. It follows that virtual Artin groups of FC type and, more generally, of affine-FC type, have a solvable word problem. We also prove that, if a virtual Artin group VA[{\Gamma}] has a solvable word problem, then the strong membership problem for any standard parabolic subgroup in VA[{\Gamma}] is solvable.

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arXiv2024

Trickle groups

A new family of groups, called trickle groups, is presented. These groups generalize right-angled Artin and Coxeter groups, as well as cactus groups. A trickle group is defined by a presentation with relations of the form $xy = zx$ and $x^\mu = 1$, that are governed by a simplicial graph, called a trickle graph, endowed with a partial ordering on the vertices, a vertex labeling, and an automorphism of the star of each vertex. We show several examples of trickle groups, including extended cactus groups, certain finite-index subgroups of virtual cactus groups, Thompson group F, and ordered quandle groups. A terminating and confluent rewriting system is established for trickle groups, enabling the definition of normal forms and a solution to the word problem. An alternative solution to the word problem is also presented, offering a simpler formulation akin to Tits' approach for Coxeter groups and Green's for graph products of cyclic groups. A natural notion of a parabolic subgraph of a trickle graph is introduced. The subgroup generated by the vertices of such a subgraph is called a standard parabolic subgroup and it is shown to be the trickle group associated with the subgraph itself. The intersection of two standard parabolic subgroups is also proven to be a standard parabolic subgroup. If only relations of the form $xy = zx$ are retained in the definition of a trickle group, then the resulting group is called a preGarside trickle group. Such a group is proved to be a preGarside group, a torsion-free group, and a Garside group if and only if its associated trickle graph is finite and complete.

math.GR↗
arXiv2024

When is a TRAAG orderable?

We characterize, in terms of the defining graph, when a twisted right-angled Artin group (a group whose only relations among pairs of generators are either commuting or Klein-bottle type relations) is left-orderable.

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arXiv2024

Intersection of Parabolic Subgroups in Euclidean Braid Groups: a short proof

We give a short proof for the fact, already proven by Thomas Haettel, that the arbitrary intersection of parabolic subgroups in Euclidean Braid groups $A[\tilde{A}_n]$ is again a parabolic subgroup. To that end, we use that the spherical-type Artin group $A[B_{n+1}]$ is isomorphic to $A[\tilde{A}_n] \rtimes \mathbb{Z}$.

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arXiv2023

Endomorphisms of Artin groups of type D

In this paper we determine a classification of the endomorphisms of the Artin group $A [D_n]$ of type $D_n$ for $n\ge 6$. In particular we determine its automorphism group and its outer automorphism group. We also determine a classification of the homomorphisms from $A[D_n]$ to the Artin group $A [A_{n-1}]$ of type $A_{n-1}$ and a classification of the homomorphisms from $A[A_{n-1}]$ to $A[D_n]$ for $n\ge 6$. We show that any endomorphism of the quotient $A [D_n] / Z (A [D_n])$ lifts to an endomorphism of $A [D_n]$ for $n \ge 4$. We deduce a classification of the endomorphisms of $A [D_n] / Z (A [D_n])$, we determine the automorphism and outer automorphism groups of $A [D_n] / Z (A [D_n])$, and we show that $A [D_n] / Z (A [D_n])$ is co-Hopfian, for $n \ge 6$. The results are algebraic in nature but the proofs are based on topological arguments (curves on surfaces and mapping class groups).

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arXiv2023

The growth series of Dyer groups

Graph products of cyclic groups and Coxeter groups are two families of groups that are defined by labeled graphs. The family of Dyer groups contains these both families and gives us a framework to study these groups in a unified way. This paper focuses on the growth series of a Dyer group $D$ with respect to the standard generating set. We give a recursive formula for the growth series of $D$ in terms of the growth series of standard parabolic subgroups. As an application we obtain the rationality of the growth series of a Dyer group. Furthermore, we show that the growth series of $D$ is closely related to the Euler characteristic of $D$.

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arXiv2022

Word problem and parabolic subgroups in Dyer groups

One can observe that Coxeter groups and right-angled Artin groups share the same solution to the word problem. On the other hand, in his study of reflection subgroups of Coxeter groups Dyer introduces a family of groups, which we call Dyer groups, which contains both, Coxeter groups and right-angled Artin groups. We show that all Dyer groups have this solution to the word problem, we show that a group which admits such a solution belongs to a little more general family of groups that we call quasi-Dyer groups, and we show that this inclusion is strict. Then we show several results on parabolic subgroups in quasi-Dyer groups and in Dyer groups. Notably, we prove that any intersection of parabolic subgroups in a Dyer group of finite type is a parabolic subgroup.

math.GR↗
arXiv2022

Parabolic subgroups inside parabolic subgroups of Artin groups

We prove that a parabolic subgroup $P$ contained in another parabolic subgroup $P'$ of an Artin group $A$ is a parabolic subgroup of $P'$. This answers a question of Godelle which is not obvious despite appearances. In order to achieve our result we construct a set-retraction $A \to P$ of the inclusion map from a parabolic subgroup $P$ into $A$. This retraction was implicitly constructed in a previous paper by Charney and the second author.

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arXiv2022

On parabolic subgroups of Artin groups

Given an Artin group $A_\Gamma$, a common strategy in the study of $A_\Gamma$ is the reduction to parabolic subgroups whose defining graphs have small diameter, i.e. showing that $A_\Gamma$ has a specific property if and only if all "small" parabolic subgroups of $A_\Gamma$ have this property. Since "small" parabolic subgroups are the puzzle pieces of $A_\Gamma$ one needs to study their behavior, in particular their intersections. The conjecture we address here says that the class of parabolic subgroups of $A_\Gamma$ is closed under intersection. Under the assumption that intersections of parabolic subgroups in complete Artin groups are parabolic, we show that the intersection of a complete parabolic subgroup with an arbitrary parabolic subgroup is parabolic. Further, we connect the intersection behavior of complete parabolic subgroups of $A_\Gamma$ to fixed point properties and to automatic continuity of $A_\Gamma$ using Bass-Serre theory and a generalization of the Deligne complex.

math.GR↗
arXiv2021

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 $VA[\Gamma]$ of a Coxeter graph $\Gamma$ mixing the standard presentation of the Artin group $A[\Gamma]$ with the standard presentation of the Coxeter group $W[\Gamma]$ and some mixed relations that mimic the action of $W[\Gamma]$ on its root system. By definition we have two epimorphisms $\pi_K:VA[\Gamma]\to W[\Gamma]$ and $\pi_P:VA[\Gamma]\to W[\Gamma]$ whose kernels are denoted by $KVA[\Gamma]$ and $PVA[\Gamma]$ respectively. We calculate presentations for these two subgroups. In particular $KVA[\Gamma]$ is an Artin group. We prove that the center of any virtual Artin group is trivial. In the case where $\Gamma$ is of spherical type or of affine type, we show that each free of infinity parabolic subgroup of $KVA[\Gamma]$ is also of spherical type or of affine type, and we show that $VA[\Gamma]$ has a solution to the word problem. In the case where $\Gamma$ is of spherical type we show that $KVA[\Gamma]$ satisfies the $K(\pi,1)$ conjecture and we infer the cohomological dimension of $KVA[\Gamma]$ and the virtual cohomological dimension of $VA[\Gamma]$. In the case where $\Gamma$ is of affine type we determine upper bounds for the cohomological dimension of $KVA[\Gamma]$ and for the virtual cohomological dimension of $VA[\Gamma]$.

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