When are braid groups of manifolds K\"ahler?

TL;DR

This paper investigates when braid groups of manifolds can be K"ahler, concluding that most pure braid groups of Riemann surfaces are not K"ahler, while certain higher-dimensional cases are K"ahler.

Contribution

It extends previous results by showing that, except for trivial cases, pure braid groups of Riemann surfaces are not K"ahler, and identifies conditions under which braid groups are K"ahler.

Findings

Pure braid groups of Riemann surfaces with ≥2 strands are generally not K"ahler.

Braid groups of complex dimension ≥2 projective manifolds are K"ahler.

Homological properties and the Beauville-Catanese-Siu theorem are used in proofs.

Abstract

Sometime ago, we showed that a pure Artin braid group is not K\"ahler, i.e. it is not the fundamental group of a compact K\"ahler manifold. This used a result of Bressler, Ramachandran and the author that K\"ahler groups cannot be too "big". The goal here is to study the problem of K\"ahlerness for other braid groups. The main result is that, with some trivial exceptions, the pure braid group of a Riemann surface with at least 2 strands is never K\"ahler. In some cases the proof uses the previous strategy, for others it plays off some homological properties of braid groups established beforehand against consequences of the Beauville-Catanese-Siu theorem. The braid group of a projective manifold of complex dimension 2 or more is shown to the fundamental group of a projective manifold, and hence K\"ahler.