On Normal Subgroups of Twisted Chevalley Groups over Commutative Rings

Abstract

In this paper, we prove two structure theorems for twisted Chevalley groups $G_\sigma (R)$ over a commutative ring $R$ with unity. The first theorem concerns the normality of $E'_\sigma (R,J)$, the elementary congruence subgroups at level $J$, in the group $G_\sigma (R)$. The second theorem classifies all subgroups of $G_\sigma (R)$ normalized by its elementary subgroup $E'_\sigma (R)$. Along the way, we obtain several interesting results. For instance, when $R$ is a semilocal ring, we show that $G_\sigma(R)$ can be expressed as the (internal) product of $E'_\sigma (R)$ and the maximal torus $T_\sigma (R)$ of $G_\sigma (R)$.