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Frobenius groups of automorphisms and their fixed points

Abstract

Suppose that a finite group GG admits a Frobenius group of automorphisms FHFH with kernel FF and complement HH such that the fixed-point subgroup of FF is trivial: CG(F)=1C_G(F)=1. In this situation various properties of GG are shown to be close to the corresponding properties of CG(H)C_G(H). By using Clifford's theorem it is proved that the order G|G| is bounded in terms of H|H| and CG(H)|C_G(H)|, the rank of GG is bounded in terms of H|H| and the rank of CG(H)C_G(H), and that GG is nilpotent if CG(H)C_G(H) is nilpotent. Lie ring methods are used for bounding the exponent and the nilpotency class of GG in the case of metacyclic FHFH. The exponent of GG is bounded in terms of FH|FH| and the exponent of CG(H)C_G(H) by using Lazard's Lie algebra associated with the Jennings--Zassenhaus filtration and its connection with powerful subgroups. The nilpotency class of GG is bounded in terms of H|H| and the nilpotency class of CG(H)C_G(H) by considering Lie rings with a finite cyclic grading satisfying a certain `selective nilpotency' condition. The latter technique also yields similar results bounding the nilpotency class of Lie rings and algebras with a metacyclic Frobenius group of automorphisms, with corollaries for connected Lie groups and torsion-free locally nilpotent groups with such groups of automorphisms. Examples show that such nilpotency results are no longer true for non-metacyclic Frobenius groups of automorphisms.Comment: 31 page

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