Re-Recounting Dyons in N=4 String Theory

The purpose of this brief note is to understand the reason for the appearance of a genus two Riemann surface in the expression for the microscopic degeneracy of 1/4 BPS dyons in N=4 String Theory.Comment: 5 pages, 2 figure

Kazama-Suzuki models and BPS domain wall junctions in N=1 SU(n) Super Yang-Mills

Domain walls in N=1 supersymmetric Yang-Mills theory conjecturally support topological degrees of freedom at low energy. Domain wall junctions are thus expected to support gapless degrees of freedom. We propose a natural candidate for the low-energy description of such junctions.Comment: 17 pages, 5 figure

Boundary F-maximization

We discuss a variant of the F-theorem and F-maximization principles which applies to (super)conformal boundary conditions of 4d (S)CFTs.Comment: 11 page

Opers and TBA

In this note we study the "conformal limit" of the TBA equations which describe the geometry of the moduli space of four-dimensional N=2 gauge theories compactified on a circle. We argue that the resulting conformal TBA equations describe a generalization of the oper submanifold in the space of complex flat connections on a Riemann surface. In particular, the conformal TBA equations for theories in the A1 class produce solutions of the Schr\"odinger equation with a rational potential.Comment: 20 page

Families of N=2 field theories

This is the first article in the collection of reviews "Exact results on N=2 supersymmetric gauge theories", ed. J. Teschner. It describes how large families of field theories with N=2 supersymmetry can be described by means of Lagrangian formulations, or by compactification from the six-dimensional theory with (2,0) supersymmetry on spaces of the form $M^4 \times C$, with C being a Riemann surface. The class of theories that can be obtained in this way is called class $\cal S$. This description allows us to relate key aspects of the four-dimensional physics of class $\cal S$ theories to geometric structures on C.Comment: 27 pages, see also overview article arXiv:1412.714

Asymptotically free N=2 theories and irregular conformal blocks

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 theoriesComment: 7 page

N=2 dualities

We study the generalization of S-duality and Argyres-Seiberg duality for a large class of N=2 superconformal gauge theories. We identify a family of strongly interacting SCFTs and use them as building blocks for generalized superconformal quiver gauge theories. This setup provides a detailed description of the ``very strongly coupled'' regions in the moduli space of more familiar gauge theories. As a byproduct, we provide a purely four dimensional construction of N=2 theories defined by wrapping M5 branes over a Riemann surface.Comment: 59 pages, 43 figure

Monster symmetry and Extremal CFTs

We test some recent conjectures about extremal selfdual CFTs, which are the candidate holographic duals of pure gravity in $AdS_3$. We prove that no $c=48$ extremal selfdual CFT or SCFT may possess Monster symmetry. Furthermore, we disprove a recent argument against the existence of extremal selfdual CFTs of large central charge.Comment: 10 page

Genus Two Partition Functions of Extremal Conformal Field Theories

Recently Witten conjectured the existence of a family of "extremal" conformal field theories (ECFTs) of central charge c=24k, which are supposed to be dual to three-dimensional pure quantum gravity in AdS3. Assuming their existence, we determine explicitly the genus two partition functions of k=2 and k=3 ECFTs, using modular invariance and the behavior of the partition function in degenerating limits of the Riemann surface. The result passes highly nontrivial tests and in particular provides a piece of evidence for the existence of the k=3 ECFT. We also argue that the genus two partition function of ECFTs with k<11 are uniquely fixed (if they exist).Comment: 14 page

Quantum Langlands dualities of boundary conditions, D-modules, and conformal blocks

We review and extend the vertex algebra framework linking gauge theory constructions and a quantum deformation of the Geometric Langlands Program. The relevant vertex algebras are associated to junctions of two boundary conditions in a 4d gauge theory and can be constructed from the basic ones by following certain standard procedures. Conformal blocks of modules over these vertex algebras give rise to twisted D-modules on the moduli stacks of G-bundles on Riemann surfaces which have applications to the Langlands Program. In particular, we construct a series of vertex algebras for every simple Lie group G which we expect to yield D-module kernels of various quantum Geometric Langlands dualities. We pay particular attention to the full duality group of gauge theory, which enables us to extend the standard qGL duality to a larger duality groupoid. We also discuss various subtleties related to the spin and gerbe structures and present a detailed analysis for the U(1) and SU(2) gauge theories.Comment: 87 pages, minor edit