On open normal subgroups of parahorics

Abstract

Let $F$ be a local complete field with discrete valuation, and let $G$ be a quasi-split group over $F$ which splits over some unramified extension of $F$. Let $P$ be a parahoric subgroup of the group $G(F)$ of $F$-points of $G$; t he open normal pro-nilpotent subgroups of $P$ can be classified using the standa rd normal filtration subgroups of Prasad and Raghanathan. More precisely, we sho w that if $G$ is quasi-simple and satisfies some additional conditions, $H$ is, modulo a subgroup of some maximal torus of $G$, either one of these filtration s ubgroups or the product of one of them by a standard normal filtration subgroup of $P\cap M$, where $M$ is a proper Levi subgroup of $G$.