On discriminants and incidence resolutions

Abstract

In this paper we study the incidence complex of an arbitrary morphism of locally free sheaves relative to an arbitrary quasi compact morphism of schemes. We prove it is a local complete intersection in the case when the sheaf morphism is surjective. We construct a complex - the incidence complex - which is a candidate for a resolution of the ideal sheaf of the incidence scheme. When the initial scheme is Cohen-Macaulay we prove the incidence complex is a resolution. We also study the rational points of the incidence scheme and discriminant scheme of any linear system on the projective line over any field of characteristic zero. We use this study to relate the discriminant to the classical discriminant of degree d polynomials.