Large N techniques for Nekrasov partition functions and AGT conjecture

TL;DR

This paper employs large N techniques and saddle point methods to analyze Nekrasov partition functions and the AGT conjecture, connecting gauge theories with 2D CFTs through a novel formalism and transformation laws.

Contribution

It introduces a saddle point approach to the Nekrasov-Shatashvili limit, defining a beta-deformed Seiberg-Witten curve and relating it to the Dijkgraaf-Vafa beta-ensemble, advancing understanding of the AGT correspondence.

Findings

Defined beta-deformed Seiberg-Witten curve and differential form.

Proposed a transformation law relating wave functions on both sides of the conjecture.

Discovered that instanton contributions can be derived from perturbative analysis.

Abstract

The AGT conjecture relates \mathcal{N}=2 4d SUSY gauge theories to 2d CFTs. Matrix model techniques can be used to investigate both sides of this relation. The large N limit refers here to the size of Young tableaux in the expression of the gauge theory partition function. It corresponds to the vanishing of Omega-background equivariant deformation parameters, and should not be confused with the t'Hooft expansion at large number of colors. In this paper, a saddle point approach is employed to study the Nekrasov-Shatashvili limit of the gauge theory, leading to define beta-deformed, or quantized, Seiberg-Witten curve and differential form. Then this formalism is compared to the large N limit of the Dijkgraaf-Vafa beta-ensemble. A transformation law relating the wave functions appearing at both sides of the conjecture is proposed. It implies a transformation of the Seiberg-Witten 1-form in agreement with the definition specified earlier. As a side result, a remarkable property of \mathcal{N}=2 theories emerged: the instanton contribution to the partition function can be determined from the perturbative term analysis.