Large $N$ matrix models for 3d ${\cal N}=2$ theories: twisted index, free energy and black holes
Seyed Morteza Hosseini, Alberto Zaffaroni
TL;DR
The paper develops a comprehensive large-$N$ analysis of the topologically twisted index for 3d ${\cal N}\ge2$ gauge theories with M-theory or massive IIA duals. It shows that the index scales as $N^{3/2}$ in the M-theory phase and as $N^{5/3}$ in the massive IIA phase, derives a universal index extraction formula from the Bethe potential, and uncovers a deep link between the index and the $S^3$ free energy, as well as with the AdS$_4$ black-hole attractor mechanism. A central result is an index theorem that expresses $\mathbb{R}e\log Z$ in terms of the extremal Bethe potential $\overline{\mathcal{V}}$, enabling practical computation from $S^3$ data. The work also outlines precise constraints on quiver content for large-$N$ consistency and provides explicit ABJM and SPP examples, highlighting a remarkable map between field theory functionals and holographic volumes. Overall, the results illuminate microscopic black-hole entropy counting in a broad class of 3d theories and suggest a unifying geometric structure connecting $F$, $\overline{\mathcal{V}}$, and prepotentials.
Abstract
We provide general formulae for the topologically twisted index of a general three-dimensional ${\cal N}\geq 2$ gauge theory with an M-theory or massive type IIA dual in the large $N$ limit. The index is defined as the supersymmetric path integral of the theory on $S^2\times S^1$ in the presence of background magnetic fluxes for the R- and global symmetries and it is conjectured to reproduce the entropy of magnetically charged static BPS AdS$_4$ black holes. For a class of theories with an M-theory dual, we show that the logarithm of the index scales indeed as $N^{3/2}$ (and $N^{5/3}$ in the massive type IIA case). We find an intriguing relation with the (apparently unrelated) large $N$ limit of the partition function on $S^3$. We also provide a universal formula for extracting the index from the large $N$ partition function on $S^3$ and its derivatives and point out its analogy with the attractor mechanism for AdS black holes.
