A universal metric for the canonical bundle of a holomorphic family of projective algebraic manifolds

Abstract

We prove that the canonical bundle of any holomorphic family of compact complex algebraic manifolds carries a singular Hermitian metric having non-negative curvature current and such that every holomorphic section of the canonical bundle of the central fiber is L^2 with respect to this metric. This result was proved by Siu when the members of the family are general type, and used to establish the deformation invariance of plurigenera in that case. In fact, we prove our result in a more general setting of a smooth hypersurface with not-necessarily normal trivial bundle in a manifold that is Stein outside an analytic subvariety. Such a setting was first considered by Takayama. (In the case of a family, the normal bundle is trivial.) The method of proof involves an adaptation of recent work of Paun.