Principal series component of Gelfand-Graev representation

TL;DR

This paper investigates the structure of principal series components of Gelfand-Graev representations for reductive groups over non-archimedean fields, generalizing previous results to non-trivial characters and non-split tori.

Contribution

It extends the understanding of Gelfand-Graev representations by analyzing their $ ho$-isotypical components and describing their structure as cyclic modules over Hecke algebras, including explicit cases.

Findings

The $ ho$-isotypical component is a cyclic module over the Hecke algebra.

Explicit description when the torus $T$ is split.

Generalization of previous results to non-trivial characters and non-split tori.

Abstract

Let $G$ be a connected reductive group defined over a non-archimedean local field $F$. Let $B$ be a minimal $F$-parabolic subgroup with Levi factor $T$ and unipotent radical $U$. Let $\psi$ be a non-degenerate character of $U(F)$ and $\lambda$ a character of $T(F)$. Let $(K,\rho)$ be a Bushnell-Kutzko type associated to the Bernstein block of $G(F)$ determined by the pair $(T,\lambda)$. We study the $\rho$-isotypical component $(c\text{-ind}_{U(F)}^{G(F)}\psi)^{\rho}$ of the induced space $c\text{-ind}_{U(F)}^{G(F)}\psi$ of functions compactly supported mod $U(F)$. We show that $(c\text{-ind}_{U(F)}^{G(F)}\psi)^{\rho}$ is cyclic module for the Hecke algebra $\mathcal{H}(G,\rho)$ associated to the pair $(K,\rho)$. When $T$ is split, we describe it more explicitly in terms of $\mathcal{H}(G,\rho)$. We make assumptions on the residue characteristic of $F$ and later also on the characteristic of $F$ and the center of $G$ depending on the pair $(T,\lambda)$. Our results generalize the main result of Chan and Savin in \cite{CS18} who treated the case of $\lambda=1$ for $T$ split.