Local systems over complements of hyperplanes and the Kac-Kazhdan conditions for singular vectors

Abstract

In this paper we strenghten a theorem by Esnault-Schechtman-Viehweg, [3], which states that one can compute the cohomology of a complement of hyperplanes in a complex affine space with coefficients in a local system using only logarithmic global differential forms, provided certain ”Aomoto non-resonance conditions” for monodromies are fulfilled at some ”edges” (intersections of hyperplanes). We prove that it is enough to check these conditions on a smaller subset of edges, see Theorem 4.1. We show that for certain known one dimensional local systems over configuration spaces of points in a projective line defined by a root system and a finite set of affine weights (these local systems arise in the geometric study of Knizhnik-Zamolodchikov differential equations, cf. [8]), the Aomoto resonance conditions at non-diagonal edges coincide with Kac-Kazhdan conditions of reducibility of Verma modules over affine Lie algebras, see Theorem 7.1.