$SL(2,\mathbb{Z})$ dualities of boundary conditions in Abelian M2-brane SCFTs
Tadashi Okazaki, Douglas J. Smith
TL;DR
The paper investigates boundary conditions in Abelian M2-brane SCFTs and uncovers an action of SL(2,$\mathbb{Z}$) dualities on chiral boundary data. It develops and matches half-indices and ’t Hooft anomalies for a web of dual pairs, including ADHM theories, ADHM quivers, ABJM, and circular quiver CS theories, using brane realizations in Type IIB to motivate the dualities. A key result is that diagonal breaking of U(1) gauge factors in ABJM-like setups yields a residual $\mathbb{Z}_k$ gauge theory on the boundary, which pairs with dual ADHM boundary data under $S$- and $T$-transformations. The findings illuminate a rich boundary-duality structure in 3d $\mathcal{N}=4$ and $\mathcal{N}=2$ contexts, with precise, testable index and anomaly equivalences that could guide future holographic and defect-operator studies.
Abstract
We propose $SL(2,\mathbb{Z})$ dualities of supersymmetric boundary conditions in the three-dimensional supersymmetric field theories describing a semi-infinite M2-brane terminating on M5-branes. Specifically, we present dualities of boundary conditions for Abelian (quiver) ADHM theories and circular quiver Chern-Simons matter theories including the ABJM model. For the circular quiver Chern-Simons theories we take boundary conditions breaking a $U(1)_1 \times U(1)_{-1}$ gauge group to its diagonal subgroup which is decoupled. This can be generalized to break $U(1)_k \times U(1)_{-k}$, leaving a $\mathbb{Z}_k$ gauge theory. We find matching of the 't Hooft anomalies and supersymmetric half-indices for all the proposed dual boundary conditions.
