A Note on primitive pairs for graded Lie algebras

TL;DR

This paper develops a theory of primitive pairs for graded Lie algebras over fields of positive characteristic, extending the Springer correspondence and revealing deep geometric and representation-theoretic connections.

Contribution

It introduces a graded analogue of cuspidal pairs, showing they organize the category of parity sheaves and are compatible with Fourier transform in positive characteristic.

Findings

Every indecomposable parity sheaf is a summand of an induced primitive data

Primitive pairs on the nilpotent cone induce primitive pairs in the graded setting

Primitivity is preserved under Fourier--Sato transform

Abstract

We develop a theory of primitive pairs for $\mathbb{Z}$-graded Lie algebras when the sheaves have coefficients in a field $\Bbbk$ of positive characteristic, providing a graded analogue of the role played by cuspidal pairs in the generalized Springer correspondence. We consider the centralizer $G_0$ of a fixed cocharacter $\chi$ in a connected, reductive, algebraic group $G$ and its action on the eigenspaces $\mathfrak{g}_n$ of $\chi$. Building on the framework of parity sheaves and the Fourier transform established in \cite{Ch,Ch1}, we show that every indecomposable parity sheaf on $\mathfrak{g}_n$ can be expressed as a direct summand of a complex induced from primitive data on a Levi subgroup. This result extends the fact that, in the graded setting, any indecomposable parity sheaf is direct summand of an induced cuspidal datum \cite{Ch}. This confirms the organizing role of primitive pairs in the block decomposition of the category of $G_0$-equivariant parity sheaves on $\mathfrak{g}_n$. We further establish that primitive pairs on the nilpotent cone induce primitive pairs in the graded setting, and we prove that primitivity is preserved under the Fourier--Sato transform. These results reveal a deep compatibility between the geometry of graded Lie algebras and their representation-theoretic structures, forming the foundation for a graded version of the generalized Springer correspondence in positive characteristic.