2D CFT blocks for the 4D class $\mathcal{S}_k$ theories

Generalizations of the AGT correspondence between 4D $\mathcal{N}=2$ $SU(2)$ supersymmetric gauge theory on ${\mathbb {C}}^2$ with $\Omega$-deformation and 2D Liouville conformal field theory include a correspondence between 4D $\mathcal{N}=2$ $SU(N)$ supersymmetric gauge theories, $N = 2, 3, \ldots$, on ${\mathbb {C}}^2/{\mathbb {Z}}_n$, $n = 2, 3, \ldots$, with $\Omega$-deformation and 2D conformal field theories with $\mathcal{W}^{\, para}_{N, n}$ ($n$-th parafermion $\mat...

The representation theories of the SU(2)$_k$-extended $N$=4 superconformal algebras (SCAs) with $arbitrary$ level $k$ are developed being based on their Feigin-Fuchs representations found recently by the present author. A basic unit of the representation blocks consisting of eight \lq\lq boson-like\rq\rq\ and eight \lq\lq fermion-like\rq\rq\ conformal fields is found to describe arbitrary representations of the $N$=4 SU(2)$_k$ SCAs, including {\it unitary} and {\it nonunitary...

In this first of a series of three papers we outline an approach to classifying 4d $\mathcal{N}{=}2$ superconformal field theories at rank 2. The classification of allowed scale invariant $\mathcal{N}=2$ Coulomb branch geometries of dimension (or rank) greater than one is a famous open problem whose solution will greatly constrain the space of $\mathcal{N}{=}2$ superconformal field theories. At rank 2 the problem is equivalent to finding all possible genus 2 Seiberg-Witten cu...

We consider the problem of computing (irregular) conformal blocks in 2d CFTs whose chiral symmetry algebra is the N=2 superconformal algebra. Our construction uses two ingredients: (i) the relation between the representation theories of the N=2 superconformal algebra and the affine sl(2) algebra, extended to the level of the conformal blocks, and (ii) the relation between affine sl(2) conformal blocks and instanton partition functions in the 4d N=2 SU(2) gauge theory with a s...

In this paper we present a beautifully consistent web of evidence for the existence of interacting 4d rank-1 $\mathcal{N}=2$ SCFTs obtained from gauging discrete subgroups of global symmetries of other existing 4d rank-1 $\mathcal{N}=2$ SCFTs. The global symmetries that can be gauged involve a non-trivial combination of discrete subgroups of the $U(1)_R$, low-energy EM duality group $SL(2,\mathbb{Z})$, and the outer automorphism group of the flavor symmetry algebra, Out($F$)....

It was recently suggested that the su(N)_k+su(N)_p/su(N)_{k+p} coset conformal field theories should be related to N=2 SU(N) gauge theories on R^4/Z_p. In this paper we study various aspects of this proposal. We perform explicit checks of the relation for (N,p)=(2,4), where the symmetry algebra of the coset is the so called S_3 parafermion algebra. Even though the symmetry algebra of the coset is unknown for generic (N,p) models, we manage to perform non-trivial checks in the...

In their recent paper \cite{Alday:2009aq} Alday, Gaiotto and Tachikawa proposed a relation between $\mathcal{N}=2$ four-dimensional supersymmetric gauge theories and two-dimensional conformal field theories. As part of their conjecture they gave an explicit combinatorial formula for the expansion of the conformal blocks inspired from the exact form of instanton part of the Nekrasov partition function. In this paper we study the origin of such an expansion from a CFT point of ...

An introduction to Seiberg-Witten theory and its relation to theories which include gravity.

A surprising connection between N=2 gauge theory instanton partition functions and conformal blocks has been recently proposed. We illustrate through simple examples the generalization to asymptotically free N=2 gauge theories

Superconformal field theory with $\mathcal{N}=2$ supersymmetry in four dimensional spacetime provides a prime playground to study strongly coupled phenomena in quantum field theory. Its rigid structure ensures valuable analytic control over non-perturbative effects, yet the theory is still flexible enough to incorporate a large landscape of quantum systems. Here we aim to offer a guidebook to fundamental features of the 4d $\mathcal{N}=2$ superconformal field theories and bas...