On fixed-point-free involutions in actions of finite exceptional groups of Lie type
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| Format: | Preprint |
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2025
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| author | Burness, Timothy C. Korhonen, Mikko |
| author_facet | Burness, Timothy C. Korhonen, Mikko |
| contents | Let $G$ be a nontrivial transitive permutation group on a finite set $Ω$. By a classical theorem of Jordan, $G$ contains a derangement, which is an element with no fixed points on $Ω$. Given a prime divisor $r$ of $|Ω|$, we say that $G$ is $r$-elusive if it does not contain a derangement of order $r$. In a paper from 2011, Burness, Giudici and Wilson essentially reduce the classification of the $r$-elusive primitive groups to the case where $G$ is an almost simple group of Lie type. The classical groups with an $r$-elusive socle have been determined by Burness and Giudici, and in this paper we consider the analogous problem for the exceptional groups of Lie type, focussing on the special case $r=2$. Our main theorem describes all the almost simple primitive exceptional groups with a $2$-elusive socle. In other words, we determine the pairs $(G,M)$, where $G$ is an almost simple exceptional group of Lie type with socle $T$ and $M$ is a core-free maximal subgroup that intersects every conjugacy class of involutions in $T$. Our results are conclusive, with the exception of a finite list of undetermined cases for $T = E_8(q)$, which depend on the existence (or otherwise) of certain almost simple maximal subgroups of $G$ that have not yet been completely classified. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2503_03423 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | On fixed-point-free involutions in actions of finite exceptional groups of Lie type Burness, Timothy C. Korhonen, Mikko Group Theory Let $G$ be a nontrivial transitive permutation group on a finite set $Ω$. By a classical theorem of Jordan, $G$ contains a derangement, which is an element with no fixed points on $Ω$. Given a prime divisor $r$ of $|Ω|$, we say that $G$ is $r$-elusive if it does not contain a derangement of order $r$. In a paper from 2011, Burness, Giudici and Wilson essentially reduce the classification of the $r$-elusive primitive groups to the case where $G$ is an almost simple group of Lie type. The classical groups with an $r$-elusive socle have been determined by Burness and Giudici, and in this paper we consider the analogous problem for the exceptional groups of Lie type, focussing on the special case $r=2$. Our main theorem describes all the almost simple primitive exceptional groups with a $2$-elusive socle. In other words, we determine the pairs $(G,M)$, where $G$ is an almost simple exceptional group of Lie type with socle $T$ and $M$ is a core-free maximal subgroup that intersects every conjugacy class of involutions in $T$. Our results are conclusive, with the exception of a finite list of undetermined cases for $T = E_8(q)$, which depend on the existence (or otherwise) of certain almost simple maximal subgroups of $G$ that have not yet been completely classified. |
| title | On fixed-point-free involutions in actions of finite exceptional groups of Lie type |
| topic | Group Theory |
| url | https://arxiv.org/abs/2503.03423 |