Finite groups admitting a coprime automorphism satisfying an additional polynomial identity

Abstract

It is known that a finite group with an automorphism $\varphi$ of coprime order has a soluble radical of $(|\varphi|,|C_G(\varphi)|)$-bounded Fitting height and index. We extend this classic result as follows. Let $f(x) = a_0 + a_1 \cdot x + \cdots + a_d \cdot x^d \in \mathbb{Z}[x]$ be a primitive polynomial and let $G$ be a finite group with an automorphism $\varphi$ of coprime order satisfying $ g^{a_0} \cdot \varphi(g)^{a_1} \cdots \varphi^d(g)^{a_d} = 1 $, for all $g \in G$. Then the soluble radical of $G$ has $(d,|C_G(\varphi)|)$-boundex Fitting height and index. The bounds are made explicit and are particularly good for small values of the degree $d$.