English

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

Group Theory 2023-01-31 v1

Abstract

Suppose that a finite group GG admits a soluble group of coprime automorphisms AA. We prove that if, for some positive integer mm, every element of the centralizer CG(A)C_G(A ) has a left Engel sink of cardinality at most mm (or a right Engel sink of cardinality at most mm), then GG has a subgroup of (A,m)(|A|,m)-bounded index which has Fitting height at most 2α(A)+22\alpha (A)+2, where α(A)\alpha (A) is the composition length of AA. We also prove that if, for some positive integer rr, every element of the centralizer CG(A)C_G(A ) has a left Engel sink of rank at most rr (or a right Engel sink of rank at most rr), then GG has a subgroup of (A,r)(|A|,r)-bounded index which has Fitting height at most 4α(A)+4α(A)+34^{\alpha (A)}+4\alpha (A)+3. Here, a left Engel sink of an element gg of a group GG is a set E(g){\mathscr E}(g) such that for every xGx\in G all sufficiently long commutators [...[[x,g],g],,g][...[[x,g],g],\dots ,g] belong to E(g){\mathscr E}(g). (Thus, gg is a left Engel element precisely when we can choose E(g)={1}{\mathscr E}(g)=\{ 1\}.) A right Engel sink of an element gg of a group GG is a set R(g){\mathscr R}(g) such that for every xGx\in G all sufficiently long commutators [...[[g,x],x],,x][...[[g,x],x],\dots ,x] belong to R(g){\mathscr R}(g). (Thus, gg is a right Engel element precisely when we can choose R(g)={1}{\mathscr R}(g)=\{ 1\}.)

Keywords

Cite

@article{arxiv.2301.12397,
  title  = {Finite groups with a soluble group of coprime automorphisms whose fixed points have bounded Engel sinks},
  author = {E. I. Khukhro and P. Shumyatsky},
  journal= {arXiv preprint arXiv:2301.12397},
  year   = {2023}
}

Comments

arXiv admin note: text overlap with arXiv:2010.08616

R2 v1 2026-06-28T08:25:14.504Z