Exceptionally simple integrated correlators in $\mathcal{N}=4$ supersymmetric Yang-Mills theory

Abstract: Supersymmetric localisation has led to several modern developments in the study of integrated correlators in $\mathcal{N}=4$ supersymmetric Yang-Mills (SYM) theory. In particular, exact results have been derived for certain integrated four-point functions of superconformal primary operators in the stress tensor multiplet valid for all classical gauge groups, $SU(N)$, $SO(N)$, and $USp(2N)$, and for all values of the complex coupling, $\tau=\theta/(2\pi)+4\pi i/g^2_{_{YM}}$. In this work we extend this analysis and provide a unified two-dimensional lattice sum representation for all simple gauge groups, in particular for the exceptional series $E_r$ (with $r=6,7,8$), $F_4$ and $G_2$. These expressions are manifestly covariant under Goddard-Nuyts-Olive duality which for $F_4$ and $G_2$ is given by particular Fuchsian groups. We show that the perturbation expansion of these integrated correlators is universal in the sense that it can be written as a single function of three parameters, called Vogel parameters, and a suitable 't Hooft-like coupling. To obtain the perturbative expansion for the integrated correlator with a given gauge group we simply need substituting in this universal expression specific values for the Vogel parameters. At the non-perturbative level we conjecture a formula for the one-instanton Nekrasov partition function with simple gauge group and general $\Omega$-deformation background. We check that our expression reduces in various limits to known results and that it produces, via supersymmetric localisation, the same one-instanton contribution to the integrated correlator as the one derived from the lattice sum. Finally, we consider the action of the hyperbolic Laplace operator in $\tau$ on the integrated correlators with exceptional gauge groups and derive inhomogeneous Laplace equations very similar to the ones previously obtained for classical gauge groups.