Twisted logarithmic complexes of positively weighted homogeneous divisors

Abstract

For a rank 1 local system on the complement of a reduced divisor on a complex manifold X X , its cohomology is calculated by the twisted meromorphic de Rham complex. Assuming the divisor is everywhere positively weighted homogeneous, we study necessary or sufficient conditions for a quasi-isomorphism from its twisted logarithmic subcomplex, called the logarithmic comparison theorem (LCT), by using a stronger version in terms of the associated complex of D X D_X -modules. In case the connection is a pullback by a defining function f f of the divisor and the residue is α \alpha , we prove among others that if LCT holds, the annihilator of f α − 1 f^{\alpha -1} in D X D_X is generated by first order differential operators and α − 1 − j \alpha -1-j is not a root of the Bernstein-Sato polynomial for any positive integer j j . The converse holds assuming either of the two conditions in case the associated complex of D X D_X -modules is acyclic except for the top degree. In the case where the local system is constant, the divisor is defined by a homogeneous polynomial, and the associated projective hypersurface has only weighted homogeneous isolated singularities, we show that LCT is equivalent to that − 1 -1 is the unique integral root of the Bernstein-Sato polynomial. We also give a simple proof of LCT in the hyperplane arrangement case under appropriate assumptions on residues, which is an immediate corollary of higher cohomology vanishing associated with Castelnuovo-Mumford regularity. Here the zero-extension case is also treated.