N=2 S-duality Revisited
Matthew Buican, Zoltan Laczko, Takahiro Nishinaka
TL;DR
This work identifies a minimal Argyres-Douglas S-duality setup in which the exotic T_{3,{3\over2}} theory factorizes into a free hypermultiplet and an interacting TX sector. Using chiral algebra bootstrap, the authors determine chi(TX) and its vacuum character via AKM representations, enabling a precise 4D/2D link to the Schur index of TX. They conjecture a compact, consistent chiral algebra for TX built from a Virasoro stress tensor at c_{2d}=-26, AKM currents at critical levels, and a single h=\tfrac{3}{2} AKM primary W_{aI}, and they bootstrap its OPEs to verify closure and null relations. The TX Schur index is expressed in AKM characters, revealing connections to T_N structures and enabling checks against Hall-Littlewood data and the S^3 partition function through a small S^1 reduction, with Witten anomalies offering intriguing constraints on 2D/4D correspondences.
Abstract
Using the chiral algebra bootstrap, we revisit the simplest Argyres-Douglas (AD) generalization of Argyres-Seiberg S-duality. We argue that the exotic AD superconformal field theory (SCFT), $T_{3,{3\over2}}$, emerging in this duality splits into a free piece and an interacting piece, T_X, even though this factorization seems invisible in the Seiberg-Witten (SW) curve derived from the corresponding M5-brane construction. Without a Lagrangian, an associated topological field theory, a BPS spectrum, or even an SW curve, we nonetheless obtain exact information about T_X by bootstrapping its chiral algebra, chi(T_X), and finding the corresponding vacuum character in terms of Affine Kac-Moody characters. By a standard 4D/2D correspondence, this result gives us the Schur index for T_X and, by studying this quantity in the limit of small S^1, we make contact with a proposed S^1 reduction. Along the way, we discuss various properties of T_X: as an N=1 theory, it has flavor symmetry SU(3)XSU(2)XU(1), the central charge of chi(T_X) matches the central charge of the bc ghosts in bosonic string theory, and its global SU(2) symmetry has a Witten anomaly. This anomaly does not prevent us from building conformal manifolds out of arbitrary numbers of T_X theories (giving us a surprisingly close AD relative of Gaiotto's T_N theories), but it does lead to some open questions in the context of the chiral algebra / 4D N=2 SCFT correspondence.
