$\mathcal{N}=2$ Universality at Strong Coupling

TL;DR

This paper uncovers a universal pattern in strong-coupling scattering amplitudes for a class of $ ext{N}=2$ superconformal theories, revealing deep connections with $ ext{N}=4$ SYM and modular invariance.

Contribution

It demonstrates a universal structure in mixed gluon-graviton correlators at strong coupling, extending known results from $ ext{N}=4$ SYM to $ ext{N}=2$ theories with D7-branes.

Findings

Universal asymptotic series govern large-$N$ contributions.

Confirmed equivalence with $ ext{N}=4$ SYM for graviton-only correlators.

Proposed an $ ext{SL}(2, ext{Z})$-invariant completion using Eisenstein series.

Abstract

We present a detailed analysis of integrated correlators for an $\mathcal{N}=2$ superconformal field theory on a squashed sphere with SU$(N)$ gauge group and fundamental/anti-symmetric matter. Employing the matrix model arising from supersymmetric localisation, we compute derivatives of the partition function $\mathcal{Z}$ with respect to the fundamental mass ($\mu$), the anti-symmetric mass ($m$) and the squashing parameter ($b$), corresponding to integrated insertions of the $\mathcal{N}=2$ flavour-current and stress-tensor multiplets, which are holographically dual to gluon and graviton scatterings in the presence of D7-branes. For correlators dual to only graviton scatterings, we confirm the planar-limit equivalence with $\mathcal{N}=4$ SYM. Our main result is a remarkable universality for the mixed gluon-graviton scattering amplitudes off D7-branes, obtained from $\partial_\mu^2 \partial_m^2 \log \mathcal{Z}$ and $\partial_\mu^2 \partial_b^2 \log \mathcal{Z}$. We show that the leading and sub-leading large-$N$ contributions in the strong-coupling regime are governed by universal asymptotic series, identical to those found for integrated giant-graviton correlators in $\mathcal{N}=4$ SYM. We also propose an $\text{SL}(2, \mathbb{Z})$-invariant completion of these results in terms of non-holomorphic Eisenstein series. This completion provides exact constraints on higher-derivative terms in the dual $\text{AdS}_5$ brane-string amplitudes and highlights an unexpected universality across distinct superconformal theories at strong coupling.