On the intersection of the $\cal F$-maximal subgroups and the generalized ${\cal F}$-hypercentre of a finite group

Abstract

Let $\cal F$ be a class of groups. A chief factor $H/K$ of a group $G$ is called \emph{${\cal F}$-central in $G$} provided $(H/K)\rtimes (G/C_{G}(H/K)) \in {\cal F}$. We write $Z_{\pi{\cal F}}(G)$ to denote the product of all normal subgroups of $G$ whose $G$-chief factors of order divisible by at least one prime in $\pi$ are $\cal F$-central. We call $Z_{\pi{\cal F}}(G)$ the $\pi{\cal F}$-hypercentre of $G$. A subgroup $U$ of a group $G$ is called \emph{$\cal F$-maximal} in $G$ provided that (a) $U\in {\cal F}$, and (b) if $U\leq V\leq G$ and $V\in {\cal F}$, then $U=V$. In this paper we study the properties of the intersection of all $\cal F$-maximal subgroups of a finite group. In particular, we analyze the condition under which $Z_{\pi{\cal F}}(G)$ coincides with the intersection of all $\cal F$-maximal subgroups of $G$.