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Algebra Logika, 2023 Volume 62, Number 1, Pages 114–134 (Mi al2751)

Finite groups with a soluble group of coprime automorphisms whose fixed points have bounded Engel sinks

E. I. Khukhroab, P. Shumyatskiic

a Sobolev Institute of Mathematics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk
b Charlotte Scott Research Centre for Algebra, Univ. Lincoln, Lincoln, UK
c University of Brasilia

Abstract: Suppose that a finite group $G$ admits a soluble group of coprime automorphisms $A$. We prove that if, for some positive integer $m$, every element of the centralizer $C_G(A)$ has a left Engel sink of cardinality at most $m$ (or a right Engel sink of cardinality at most $m$), then $G$ has a subgroup of $(|A|,m)$-bounded index which has Fitting height at most $2\alpha (A)+2$, where $\alpha (A)$ is the composition length of $A$. We also prove that if, for some positive integer $r$, every element of the centralizer $C_G(A)$ has a left Engel sink of rank at most $r$ (or a right Engel sink of rank at most $r$), then $G$ has a subgroup of $(|A|,r)$-bounded index which has Fitting height at most $4^{\alpha (A)}+4\alpha (A)+3$. Here, a left Engel sink of an element $g$ of a group $G$ is a set ${\mathscr E}(g)$ such that for every $x\in G$ all sufficiently long commutators $[...[[x,g],g],\dots,g]$ belong to ${\mathscr E}(g)$. (Thus, $g$ is a left Engel element precisely when we can choose ${\mathscr E}(g)=\{ 1\}$.) A right Engel sink of an element $g$ of a group $G$ is a set ${\mathscr R}(g)$ such that for every $x\in G$ all sufficiently long commutators $[...[[g,x],x],\dots,x]$ belong to ${\mathscr R}(g)$. Thus, $g$ is a right Engel element precisely when we can choose ${\mathscr R}(g)=\{ 1\}$.

Keywords: Engel condition, Fitting subgroup, Fitting height, automorphism.

UDC: 512.542.2

Received: 28.12.2022
Revised: 30.10.2023

DOI: 10.33048/alglog.2023.62.108



© Steklov Math. Inst. of RAS, 2024