Extending holomorphic maps from Stein manifolds into affine toric varieties

TL;DR

This paper explores the extension of holomorphic maps from Stein manifolds to affine toric varieties, establishing new results on the interpolation property and its limitations for singular targets within Oka theory.

Contribution

It is the first to develop Oka theory for singular targets, specifically affine toric varieties, and demonstrates that these varieties satisfy a weakened interpolation property.

Findings

Affine toric varieties satisfy a strong weakened interpolation property.

Most affine toric varieties do not satisfy the full interpolation property.

The full interpolation property fails even for simple sources like products of two annuli.

Abstract

A complex manifold $Y$ is said to have the interpolation property if a holomorphic map to $Y$ from a subvariety $S$ of a reduced Stein space $X$ has a holomorphic extension to $X$ if it has a continuous extension. Taking $S$ to be a contractible submanifold of $X=\mathbb{C}^n$ gives an ostensibly much weaker property called the convex interpolation property. By a deep theorem of Forstneri\v{c}, the two properties are equivalent. They (and about a dozen other nontrivially equivalent properties) define the class of Oka manifolds. This paper is the first attempt to develop Oka theory for singular targets. The targets that we study are affine toric varieties, not necessarily normal. We prove that every affine toric variety satisfies a weakening of the interpolation property that is much stronger than the convex interpolation property, but the full interpolation property fails for most affine toric varieties, even for a source as simple as the product of two annuli embedded in $\mathbb{C}^4$.