Algebraic characterization of reversibility in the quaternionic Möbius group

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Main Authors: Gongopadhyay, Krishnendu, Lohan, Tejbir, Mukherjee, Abhishek
Format: Preprint
Published: 2024
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author Gongopadhyay, Krishnendu
Lohan, Tejbir
Mukherjee, Abhishek
author_facet Gongopadhyay, Krishnendu
Lohan, Tejbir
Mukherjee, Abhishek
contents An element of a group is called \emph{reversible} if it is conjugate to its inverse. While reversibility in the quaternionic Möbius group $\mathrm{PSL}(2,\mathbb{H})$ has traditionally been studied using geometric and dynamical methods, we develop a purely algebraic approach. We obtain an explicit, computable criterion for the reversibility of a quaternionic Möbius transformation, expressed solely in terms of the entries of a matrix representative. More precisely, we prove that \[ [A]\in \mathrm{PSL}(2,\mathbb{H}) \text{ is reversible} \quad \Longleftrightarrow \quad β_A^{2}=δ_A^{2}, \] where $β_A$ and $δ_A$ are real conjugacy invariants associated with a lift $A\in \mathrm{SL}(2,\mathbb{H})$. Furthermore, we give a complete characterization of reversing symmetries of reversible elements in $\mathrm{SL}(2,\mathbb{H})$ and $\mathrm{PSL}(2,\mathbb{H})$.
format Preprint
id arxiv_https___arxiv_org_abs_2401_15374
institution arXiv
publishDate 2024
record_format arxiv
spellingShingle Algebraic characterization of reversibility in the quaternionic Möbius group
Gongopadhyay, Krishnendu
Lohan, Tejbir
Mukherjee, Abhishek
Geometric Topology
Group Theory
Primary 51B10, 20E45, Secondary 15A21, 15B33 [2010]
An element of a group is called \emph{reversible} if it is conjugate to its inverse. While reversibility in the quaternionic Möbius group $\mathrm{PSL}(2,\mathbb{H})$ has traditionally been studied using geometric and dynamical methods, we develop a purely algebraic approach. We obtain an explicit, computable criterion for the reversibility of a quaternionic Möbius transformation, expressed solely in terms of the entries of a matrix representative. More precisely, we prove that \[ [A]\in \mathrm{PSL}(2,\mathbb{H}) \text{ is reversible} \quad \Longleftrightarrow \quad β_A^{2}=δ_A^{2}, \] where $β_A$ and $δ_A$ are real conjugacy invariants associated with a lift $A\in \mathrm{SL}(2,\mathbb{H})$. Furthermore, we give a complete characterization of reversing symmetries of reversible elements in $\mathrm{SL}(2,\mathbb{H})$ and $\mathrm{PSL}(2,\mathbb{H})$.
title Algebraic characterization of reversibility in the quaternionic Möbius group
topic Geometric Topology
Group Theory
Primary 51B10, 20E45, Secondary 15A21, 15B33 [2010]
url https://arxiv.org/abs/2401.15374