Finite groups with an affine map of large order

Abstract

Let $G$ be a group. A function $G\to G$ of the form $x\mapsto x^{\alpha }g$ for a fixed automorphism $\alpha$ of $G$ and a fixed $g\in G$ is called an affine map of $G$. In this paper, we study finite groups $G$ with an affine map of large order. More precisely, we show that if $G$ admits an affine map of order larger than $\frac{1}{2}|G|$, then $G$ is solvable of derived length at most $3$. We also show that more generally, for each $\rho \in \left(0,1\right]$, if $G$ admits an affine map of order at least $\rho |G|$, then the largest solvable normal subgroup of $G$ has derived length at most $4\lfloor {\log }_2({\rho }^{-1})\rfloor +3$.

19 pages; some small corrections from v1, and more details added in some proofs