On the centralizer of a balanced nilpotent section

Abstract

Let $G$ be a split reductive algebraic group defined over a complete discrete valuation ring $\mathbb{O}$, with residue field $\mathbb{F}$ and fraction field $\mathbb{K}$, where the fiber $G_{\mathbb{F}}$ is geometrically standard. A balanced nilpotent section $x\in \text{Lie}(G)$ can roughly be thought of as an $\mathbb{O}$-point in a $\mathbb{K}$ nilpotent orbit such that the corresponding orbits over $\mathbb{K}$ and $\mathbb{F}$ have the same Bala--Carter label. In this paper, we will establish a number of results on the structure of the centralizer $G^x\subseteq G$ of $x$. This includes a proof that $G^x$ is a smooth group scheme, and that the component groups of its geometric fibers are isomorphic.

21 pages