Positivity criteria for log canonical divisors and hyperbolicity

Abstract

Let X be a complex projective variety and D a reduced divisor on X. Under a natural minimal condition on the singularities of the pair (X, D), which includes the case of smooth X with simple normal crossing D, we ask for geometric criteria guaranteeing various positivity conditions for the log-canonical divisor K_X+D. By adjunction and running the log minimal model program, natural to our setting, we obtain a geometric criterion for K_X+D to be numerically effective as well as a geometric version of the cone theorem, generalizing to the context of log pairs these results of Mori. A criterion for K_X+D to be pseudo-effective with mild hypothesis on D follows. We also obtain, assuming the abundance conjecture and the existence of rational curves on Calabi-Yau manifolds, an optimal geometric sharpening of the Nakai-Moishezon criterion for the ampleness of a divisor of the form K_X+D, a criterion verified under a canonical hyperbolicity assumption on (X,D). Without these conjectures, we verify this ampleness criterion with assumptions on the number of ample and non ample components of D.