Finite generation properties of the pro-$p$ Iwahori-Hecke $\operatorname{Ext}$-algebra

Abstract

The pro-$p$ Iwahori-Hecke $\operatorname{Ext}$-algebra $E^\ast$ is a graded algebra that has been introduced and studied by Ollivier-Schneider, with the long-term goal of investigating the category of smooth mod-$p$ representations of $p$-adic reductive groups and its derived category. Its $0$th graded piece is the pro-$p$ Iwahori-Hecke algebra studied by Vign\'eras and others. In the present article, we first show that the $\operatorname{Ext}$-algebra $E^\ast$ associated with the group $\operatorname{SL}_2(\mathfrak{F})$, $\operatorname{PGL}_2(\mathfrak{F})$ or $\operatorname{GL}_2(\mathfrak{F})$, where $\mathfrak{F}$ is an unramified extension of $\mathbb{Q}_p$ with $p \neq 2,3$, is finitely generated as a (non-commutative) algebra. We then specialize to the case of the group $\operatorname{SL}_2(\mathbb{Q}_p)$, with $p \neq 2,3$, and we show that in this case the natural multiplication map from the tensor algebra $T^\ast_{E^0} E^1$ to $E^\ast$ is surjective and that its kernel is finitely generated as a two-sided ideal. Using this fact as main input, we then show that $E^\ast$ is finitely presented as an algebra. We actually compute an explicit presentation.