De Rham cohomology of local cohomology modules: The graded case

Abstract

AbstractLetKbe a field of characteristic zero, and letR = K[X1,… ,Xn]. Let An(K) = K⟨X1,… ,Xn,∂1,… ,∂n⟩ be thenth Weyl algebra overK. We consider the case whenRandAn(K) are graded by giving degXi= ωiand deg∂i=–ωifori= 1,…,n(hereωiare positive integers). Set. LetIbe a graded ideal inR. By a result due to Lyubeznik the local cohomology modulesare holonomic (An(K))-modules for eachi≥0. In this article we prove that the de Rham cohomology modulesare concentrated in degree —ω; that is,forj ≠ –ω. As an application whenA = R/(f) is an isolated singularity, we relatetoHn-1(∂(f);A), the (n –1)th Koszul cohomology ofAwith respect to∂1(f),…,∂n(f).