Burau representation of $B_4$ and quantization of the rational projective plane

The braid group $B_4$ naturally acts on the rational projective plane $\mathbb{P}^2(\mathbb{Q})$, this action corresponds to the classical integral reduced Burau representation of $B_4$. The first result of this paper is a classification of the orbits of this action. The Burau representation then de...

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Bibliographic Details
Main Author: Jouteur, Perrine
Format: Article
Language:English
Published: Académie des sciences 2025-03-01
Series:Comptes Rendus. Mathématique
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Online Access:https://comptes-rendus.academie-sciences.fr/mathematique/articles/10.5802/crmath.702/
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Summary:The braid group $B_4$ naturally acts on the rational projective plane $\mathbb{P}^2(\mathbb{Q})$, this action corresponds to the classical integral reduced Burau representation of $B_4$. The first result of this paper is a classification of the orbits of this action. The Burau representation then defines an action of $B_4$ on $\mathbb{P}^2\bigl (\mathbb{Z}(q)\bigr )$, where $q$ is a formal parameter and $\mathbb{Z}(q)$ is the field of rational functions in $q$ with integer coefficients. We study orbits of the $B_4$-action on $\mathbb{P}^2\bigl (\mathbb{Z}(q)\bigr )$, and show existence of embeddings of the $q$-deformed projective line $\mathbb{P}^1\bigl (\mathbb{Z}(q)\bigr )$ that precisely correspond to the notion of $q$-rationals due to Morier-Genoud and Ovsienko.
ISSN:1778-3569