On finite soluble groups with almost fixed-point-free automorphisms of non-coprime order

Abstract

It is proved that if a finite $p$-soluble group $G$ admits an automorphism $\phi$ of order $p^n$ having at most $m$ fixed points on every $\phi$-invariant elementary abelian $p^{\prime }$-section of $G$, then the $p$-length of $G$ is bounded above in terms of $p^n$ and $m$; if in addition the group $G$ is soluble, then the Fitting height of $G$ is bounded above in terms of $p^n$ and $m$. It is also proved that if a finite soluble group $G$ admits an automorphism $\psi$ of order $p^a{q}^b$ for some primes $p,q$, then the Fitting height of $G$ is bounded above in terms of $|\psi |$ and $|C_G(\psi )|$.