Hirzebruch manifolds and positive holomorphic sectional curvature

Abstract

This paper is the first step in a systematic project to study examples of Kahler manifolds with positive holomorphic sectional curvature ($H > 0$). Previously Hitchin proved that any compact Kahler surface with $H>0$ must be rational and he constructed such examples on Hirzebruch surfaces $M_{2, k}=\mathbb{P}(H^{k}\oplus 1_{\mathbb{CP}^1})$. We generalize Hitchin's construction and prove that any Hirzebruch manifold $M_{n, k}=\mathbb{P}(H^{k}\oplus 1_{\mathbb{CP}^{n-1}})$ admits a Kahler metric of $H>0$ in each of its Kahler classes. We demonstrate that the pinching behaviors of holomorphic sectional curvatures of new examples differ from those of Hitchin's which were studied in the recent work of Alvarez-Chaturvedi-Heier. Some connections to recent works on the Kahler-Ricci flow on Hirzebruch manifolds are also discussed. It seems interesting to study the space of all Kahler metrics of $H>0$ on a given Kahler manifold. We give higher dimensional examples such that some Kahler classes admit Kahler metrics with $H>0$ and some do not.