Exact expressions for $n$-point maximal $U(1)_Y$-violating integrated correlators in $SU(N)$ $\mathcal{N}=4$ SYM

TL;DR

This paper derives exact, modular-invariant formulas for n-point maximal U(1)_Y-violating correlators in SU(N) N=4 SYM, revealing their dependence on N, coupling, and instanton effects, and connecting to string theory amplitudes.

Contribution

It provides the first exact expressions for integrated n-point MUV correlators in SU(N) N=4 SYM using supersymmetric localisation, extending previous four-point results and revealing their modular structure.

Findings

Correlators expressed as sums of Eisenstein modular forms.

Correlators satisfy Laplace-difference equations relating different N.

Perturbative expansion starts at order (g_{YM}^2 N)^w.

Abstract

The exact expressions for integrated maximal $U(1)_Y$ violating (MUV) $n$-point correlators in $SU(N)$ ${\mathcal N}=4$ supersymmetric Yang--Mills theory are determined. The analysis generalises previous results on the integrated correlator of four superconformal primaries and is based on supersymmetric localisation. The integrated correlators are functions of $N$ and $\tau=\theta/(2\pi)+4\pi i/g_{_{YM}}^2$, and are expressed as two-dimensional lattice sums that are modular forms with holomorphic and anti-holomorphic weights $(w,-w)$ where $w=n-4$. The correlators satisfy Laplace-difference equations that relate the $SU(N+1)$, $SU(N)$ and $SU(N-1)$ expressions and generalise the equations previously found in the $w=0$ case. The correlators can be expressed as infinite sums of Eisenstein modular forms of weight $(w,-w)$. For any fixed value of $N$ the perturbation expansion of this correlator is found to start at order $( g_{_{YM}}^2 N)^w$. The contributions of Yang--Mills instantons of charge $k>0$ are of the form $q^k\, f(g_{_{YM}})$, where $q=e^{2\pi i \tau}$ and $f(g_{_{YM}})= O(g_{_{YM}}^{-2w})$ when $g_{_{YM}}^2 \ll 1$. Anti-instanton contributions have charge $k<0$ and are of the form $\bar q^{|k|} \, \hat f(g_{_{YM}})$, where $\hat f(g_{_{YM}}) = O(g_{_{YM}}^{2w})$ when $g_{_{YM}}^2 \ll 1$. Properties of the large-$N$ expansion are in agreement with expectations based on the low energy expansion of flat-space type IIB superstring amplitudes. We also comment on the identification of $n$-point free-field MUV correlators with the integrands of $(n-4)$-loop perturbative contributions to the four-point correlator. In particular, we emphasise the important r\^ole of $SL(2, \mathbb{Z})$-covariance in the construction.