Lusztig Induction, Unipotent Supports, and Character Bounds

TL;DR

This paper extends a recent exponential character bound for finite reductive groups by removing the split Levi subgroup condition, assuming a weak version of Lusztig's conjecture, thus broadening its applicability.

Contribution

It generalizes the exponential character bound to cases where the Levi subgroup is not necessarily split, under a weak Lusztig conjecture assumption.

Findings

Bound applies without the split Levi subgroup condition

Applicable to groups with connected center or classical groups over large fields

Relies on a weak form of Lusztig's conjecture

Abstract

Recently, a strong exponential character bound has been established in [3] for all elements $g \in \mathbf{G}^F$ of a finite reductive group $\mathbf{G}^F$ which satisfy the condition that the centraliser $C_{\mathbf{G}}(g)$ is contained in a $(\mathbf{G},F)$-split Levi subgroup $\mathbf{M}$ of $\mathbf{G}$ and that $\mathbf{G}$ is defined over a field of good characteristic. In this paper, assuming a weak version of Lusztig's conjecture relating irreducible characters and characteristic functions of character sheaves holds, we considerably generalize this result by removing the condition that $\mathbf{M}$ is split. This assumption is known to hold whenever $Z(\mathbf{G})$ is connected or when $\mathbf{G}$ is a special linear or symplectic group and $\mathbf{G}$ is defined over a sufficiently large finite field.