Wall-crossing of Instantons on the Blow-up

TL;DR

This paper investigates instanton counting on the blow-up of ^2 in ^2 supersymmetric gauge theories, using quiver varieties, stability parameters, and combinatorial objects to analyze wall-crossing phenomena.

Contribution

It introduces a novel formalism connecting instanton moduli spaces, stability conditions, and combinatorial classifications to study wall-crossing effects.

Findings

Characterized contributions in terms of bipartite graphs and super-partitions.

Derived explicit formulas for instanton partition functions across walls.

Reproduced the Nakajima-Yoshioka blow-up formula in a specific chamber.

Abstract

We study the instanton counting in four dimensional $\mathcal{N}=2$ supersymmetric gauge theories on the blow-up of $\mathbb{C}^2$: we start by formulating the instanton moduli space as a quiver variety, which we regularise by introducing two stability parameters, thus endowing it with a structure of infinitely many chambers separated by walls. Within a given chamber, we formulate the instanton partition function as a contour integral, which can be evaluated using the Jeffrey-Kirwan residue prescription. We characterise the physically relevant contributions in terms of bipartite oriented graphs and show that they can more efficiently be classified in terms of combinatorial objects called super-partitions. Within a given chamber, only certain types of super-partitions contribute and we show that the corresponding selection criteria are equivalent to stability conditions that have previously been proposed in the literature. We use this formalism to compare how the instanton counting changes when moving across walls between neighbouring chambers and provide explicit expressions for the corresponding partition functions. In a limiting chamber and using our approach, we show how to reproduce the Nakajima-Yoshioka blow-up formula.