The Derived $l$-Modular Unipotent Block of $p$-adic $\mathrm{GL}_n$

Abstract

For a non-Archimedean local field $F$ of residue cardinality $q=p^r$, we give an explicit classical generator $V$ for the bounded derived category $D_{fg}^b(\mathsf{H}_1(G))$ of finitely generated unipotent representations of $G=\mathrm{GL}_n(F)$ over an algebraically closed field of characteristic $l\neq p$. The generator $V$ has an explicit description that is much simpler than any known progenerator in the underived setting. This generalises a previous result of the author in the case where $n=2$ and $l$ is odd dividing $q+1$, and provides a triangulated equivalence between $D_{fg}^b(\mathsf{H}_1(G))$ and the category of perfect complexes over the dg algebra of dg endomorphisms of a projective resolution of $V$. This dg algebra can be thought of as a dg-enhanced Schur algebra. As an intermediate step, we also prove the analogous result for the case where $F$ is a finite field.