Overgroups of subsystem subgroups in exceptional groups: inside a sandwich

Abstract

The current paper is an addition to the previous paper by author, where the overgroup lattice of the elementary subsystem subgroup $E(\Delta,R)$ of the Chevalley group $G(\Phi,R)$ for a large enough root subsystem $\Delta$ was studied. Now we study the connection between the elementary subgroup $\hat{E}(\sigma)$ given by the net of ideals of the ring $R$ and the stabilizer $S(\sigma)$ of the corresponding Lie subalgebra of the Chevalley algebra. In particular, we prove that under a certain condition the subgroup $\hat{E}(\sigma)$ is normal in $S(\sigma)$, and we also study some properties of the corresponding quotient group.