Oka manifolds are ubiquitous

Abstract

We prove that every smooth complex projective rationally connected manifold, and hence every smooth complex Fano manifold, is Oka by applying the analytic criteria of Du, Guo, Wang, and Xie. We also establish the Oka property for the smooth Calabi--Yau threefolds in Schoen's construction: fiber products over the projective line of relatively minimal rational elliptic surfaces with sections and disjoint sets of singular values. For a smooth hypersurface of degree $d$ in $\PP^n$, its complement is Oka, equivalently holomorphically elliptic, if and only if $d\le n+1$. A connected smooth projective variety with reduced simple normal crossings boundary has Oka complement if it admits a nonconstant rational curve whose inverse image of the boundary consists of at most one point and whose pulled-back logarithmic tangent bundle is ample. The main positive results follow from holomorphic families of entire curves constructed by deformations of rational curves, holomorphic actions along genus-one fibers, and successive polar equations. The obstruction in higher degree is due to Carlson and Griffiths.