Numerical triviality and pullbacks
arXiv:1109.4382
Abstract
Let f: X \to Z be a surjective morphism of smooth complex projective varieties with connected fibers. Suppose that L is a pseudo-effective divisor on X that is f-numerically trivial. We show that there is a divisor D on Z such that L is numerically equivalent to f^*D.
13 pages, v2: substantial revision fixing errors and typos, v3: minor typos fixed