English

Numerical dimension and locally ample curves

Algebraic Geometry 2019-07-10 v2

Abstract

In the paper \cite{Lau16}, it was shown that the restriction of a pseudoeffective divisor DD to a subvariety YY with nef normal bundle is pseudoeffective. Assuming the normal bundle is ample and that DYD|_Y is not big, we prove that the numerical dimension of DD is bounded above by that of its restriction, i.e. κσ(D)κσ(DY)\kappa_{\sigma}(D)\leq \kappa_{\sigma}(D|_Y). The main motivation is to study the cycle classes of "positive" curves: we show that the cycle class of a curve with ample normal bundle lies in the interior of the cone of curves, and the cycle class of an ample curve lies in the interior of the cone of movable curves. We do not impose any condition on the singularities on the curve or the ambient variety. For locally complete intersection curves in a smooth projective variety, this is the main result of Ottem \cite{Ott16}. The main tool in this paper is the theory of qq-ample divisors.

Keywords

Cite

@article{arxiv.1703.08265,
  title  = {Numerical dimension and locally ample curves},
  author = {Chung-Ching Lau},
  journal= {arXiv preprint arXiv:1703.08265},
  year   = {2019}
}
R2 v1 2026-06-22T18:55:31.104Z