Euler-Poincar\'{e} formulae for positive depth Bernstein projectors

TL;DR

This paper extends Euler-Poincaré formulae for Bernstein projectors to positive depth cases, using associate classes of cuspidal pairs, and applies these to resolutions in representation theory.

Contribution

It introduces a new decomposition of the Euler-Poincaré presentation for positive depth Bernstein projectors based on cuspidal pair classes.

Findings

Decomposition of Euler-Poincaré presentation for positive depth projectors.

Application to resolutions of Schneider-Stuhler and Bestvina-Savin.

Enhanced understanding of Bernstein projectors in p-adic groups.

Abstract

Work of Bezrukavnikov-Kazhdan-Varshavsky uses an equivariant system of trivial idempotents of Moy-Prasad groups to obtain an Euler-Poincar\'{e} formula for the r-depth Bernstein projector. Barbasch-Ciubotaru-Moy use depth-zero cuspidal representations of parahoric subgroups to decompose the Euler-Poincar\'{e} presentation of the depth-zero projector. For positive depth $r$, we establish a decomposition of the Euler-Poincar\'{e} presentation of the r-depth Bernstein projector based on a notion of associate classes of cuspidal pairs for Moy-Prasad quotients. We apply these new Euler-Poincar\'{e} presentations to the obtain decompositions of the resolutions of Schneider-Stuhler and Bestvina-Savin.