Regular characters of classical groups over complete discrete valuation rings

TL;DR

This paper classifies and counts regular characters of symplectic and special orthogonal groups over complete discrete valuation rings with odd residue characteristic, and computes their contribution to the representation zeta function.

Contribution

It provides a complete construction and enumeration of regular characters for these classical groups over such rings, extending understanding of their representation theory.

Findings

All regular characters are explicitly constructed and counted.

The regular part of the representation zeta function is computed.

Results are valid for residue characteristic greater than two.

Abstract

Let $\mathfrak{o}$ be a complete discrete valuation ring with finide residue field $\mathsf{k}$ of odd characteristic, and let $\mathbf{G}$ be a symplectic or special orthogonal group scheme over $\mathfrak{o}$. For any $\ell\in\mathbb{N}$ let $G^\ell$ denote the $\ell$-th principal congruence subgroup of $\mathbf{G}(\mathfrak{o})$. An irreducible character of the group $\mathbf{G}(\mathfrak{o})$ is said to be regular if it is trivial on a subgroup $G^{\ell+1}$ for some $\ell$, and if its restriction to $G^\ell/G^{\ell+1}\simeq \mathrm{Lie}(\mathbf{G})(\mathsf{k})$ consists of characters of minimal $\mathbf{G}(\mathsf{k}^{\rm alg})$ stabilizer dimension. In the present paper we consider the regular characters of such classical groups over $\mathfrak{o}$, and construct and enumerate all regular characters of $\mathbf{G}(\mathfrak{o})$, when the characteristic of $\mathsf{k}$ is greater than two. As a result, we compute the regular part of their representation zeta function.