Sur les $\ell$-blocs de niveau z\'ero des groupes $p$-adiques II

Abstract

Let $G$ be a $p$-adic group which splits over an unramified extension and $Rep_{\Lambda}^{0}(G)$ the abelian category of smooth level $0$ representations of $G$ with coefficients in $\Lambda=\overline{\mathbb{Q}}_{\ell}$ or $\overline{\mathbb{Z}}_{\ell}$. We study the finest decomposition of $Rep_{\Lambda}^{0}(G)$ into a product of subcategories that can be obtained by the method introduced in an article of Lanard (arXiv:1703.08689), which is currently the only one available when $\Lambda=\overline{\mathbb{Z}}_{\ell}$ and $G$ is not an inner form of $GL_n$. We give two descriptions of it, a first one on the group side \`a la Deligne-Lusztig, and a second one on the dual side \`a la Langlands. We prove several fundamental properties, like for example the compatibility with parabolic induction and restriction or the compatibility with the local Langlands correspondence. The factors of this decomposition are not blocks, but we show how to group them to obtain "stable" blocks.