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