# Localized Donaldson-Thomas theory of surfaces

## TL;DR

This paper develops a localized Donaldson-Thomas theory for surfaces, relating moduli spaces of sheaves to nested Hilbert schemes and Seiberg-Witten invariants, with implications for Vafa-Witten invariants and modularity.

## Contribution

It introduces a new localized DT invariant framework for surfaces, connecting fixed loci of moduli spaces to nested Hilbert schemes and Seiberg-Witten invariants.

## Key findings

- Identifies fixed loci components with nested Hilbert schemes and torsion free sheaves.
- Expresses localized DT invariants in terms of nested Hilbert scheme invariants and Seiberg-Witten invariants.
- Links Vafa-Witten invariants to localized DT invariants, supporting modularity conjectures.

## Abstract

Let $S$ be a projective simply connected complex surface and $\mathcal{L}$ be a line bundle on $S$. We study the moduli space of stable compactly supported 2-dimensional sheaves on the total spaces of $\mathcal{L}$. The moduli space admits a $\mathbb{C}^*$-action induced by scaling the fibers of $\mathcal{L}$. We identify certain components of the fixed locus of the moduli space with the moduli space of torsion free sheaves and the nested Hilbert schemes on $S$. We define the localized Donaldson-Thomas invariants of $\mathcal{L}$ by virtual localization in the case that $\mathcal{L}$ twisted by the anti-canonical bundle of $S$ admits a nonzero global section. When $p_g(S)>0$, in combination with Mochizuki's formulas, we are able to express the localized DT invariants in terms of the invariants of the nested Hilbert schemes defined by the authors in [GSY17a], the Seiberg-Witten invariants of $S$, and the integrals over the products of Hilbert schemes of points on $S$. When $\mathcal{L}$ is the canonical bundle of $S$, the Vafa-Witten invariants defined recently by Tanaka-Thomas, can be extracted from these localized DT invariants. VW invariants are expected to have modular properties as predicted by S-duality.