Vanishing theorems for Hodge numbers and the Calabi curvature operator

Abstract

It is shown that a compact $n$-dimensional Kähler manifold with $\frac{n}{2}$-positive Calabi curvature operator has the rational cohomology of complex projective space. For even $n,$ this is sharp in the sense that the complex quadric with its symmetric metric has $\frac{n}{2}$-nonnegative Calabi curvature operator, yet $b_n=2.$ Furthermore, the compact Kähler manifolds with an $\frac{n}{2}$-nonnegative Calabi curvature operator are classified. In addition, the previously known results for the Kähler curvature operator are improved when the metric is Kähler--Einstein.

Revised introduction, 28 pages