English

Fixed point subgroups of a supertight automorphism

Group Theory 2024-01-26 v1 Logic

Abstract

Let GG be an infinite simple group of finite Morley rank and α\alpha a supertight automorphism of GG so that the fixed point subgroup Pn:=CG(αn)P_n:=C_G(\alpha^n) is pseudofinite for all nN{0}n\in \mathbb{N}\setminus\{0\}. It is know (using CFSG) that the socle Sn:=Soc(Pn)S_n:={\rm Soc}(P_n) is a (twisted) Chevalley group over a pseudofinite field. We prove that there is rN{0}r\in \mathbb{N}\setminus\{0\} so that for each nn we have [Pn:Sn]<r[P_n:S_n] < r and that there is no mN{0}m \in \mathbb{N}\setminus \{0\} so that for each nn the sizes of the Sylow 22-subgroups of SnS_n are bounded by mm. We also note that in the recent identification result of GG under the assumption pr2(G)=1{\rm pr}_2(G)=1, the use of CFSG is not needed.

Keywords

Cite

@article{arxiv.2401.14222,
  title  = {Fixed point subgroups of a supertight automorphism},
  author = {Ulla Karhumäki},
  journal= {arXiv preprint arXiv:2401.14222},
  year   = {2024}
}
R2 v1 2026-06-28T14:27:09.847Z