# A counterexample to Hartogs' type extension of holomorphic line bundles

## TL;DR

This paper constructs counterexamples showing that holomorphic line bundles do not always extend over certain compact subsets in complex domains, challenging previous positive extension results in complex analysis.

## Contribution

It provides the first counterexamples in all dimensions for non-pseudoconvex sets, using a novel gluing lemma to demonstrate non-extendability.

## Key findings

- Counterexamples exist in all dimensions for non-pseudoconvex sets
- Holomorphic line bundles may fail to extend over certain compact subsets
- A new gluing lemma facilitates the construction of these counterexamples

## Abstract

Consider a domain $\varOmega$ in $\mathbb{C}^n$ with $n\geqslant 2$ and a compact subset $K\subset\varOmega$ such that $\varOmega\backslash K$ is connected. We address the problem whether a holomorphic line bundle defined on $\varOmega\backslash K$ extends to $\varOmega$. In 2013, Forn\ae ss, Sibony and Wold gave a positive answer in dimension $n\geqslant 3$, when $\varOmega$ is pseudoconvex and $K$ is a sublevel set of a strongly plurisubharmonic exhaustion function. However, for $K$ of general shape, we construct counterexamples in any dimension $n\geqslant 2$. The key is a certain gluing lemma by means of which we extend any two holomorphic line bundles which are isomorphic on the intersection of their base spaces.