Acyclic coefficient systems on buildings

Abstract

For cohomological (respectively homological) coefficient systems ${\mathcal F}$ (respectively ${\mathcal V}$ ) on affine buildings X with Coxeter data of type $\widetilde{A}_d$ , we give for any $k\ge1$ a sufficient local criterion which implies $H^k(X,{\mathcal F})=0$ (respectively $H_k(X,{\mathcal V})=0$ ). Using this criterion we prove a conjecture of de Shalit on the acyclicity of coefficient systems attached to hyperplane arrangements on the Bruhat–Tits building of the general linear group over a local field. We also generalize an acyclicity theorem of Schneider and Stuhler on coefficient systems attached to representations.