English

Positivity criteria for log canonical divisors and hyperbolicity

Algebraic Geometry 2018-09-24 v4 Complex Variables Differential Geometry

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.

Keywords

Cite

@article{arxiv.1207.7346,
  title  = {Positivity criteria for log canonical divisors and hyperbolicity},
  author = {Steven S. Y. Lu and De-Qi Zhang},
  journal= {arXiv preprint arXiv:1207.7346},
  year   = {2018}
}

Comments

Journal f\"ur die reine und angewandte Mathematik (to appear); final version; this arXiv version contains the proof of Remark 4.9 (2-dimensional case for dlt pairs) as Appendix