Wilson Loops and QCD/String Scattering Amplitudes

TL;DR

This paper extends the duality between Wilson loops and scattering amplitudes from ${ m extstyle extbf{N}=4}$ SYM to large $N$ QCD, deriving relations and analyzing string amplitude properties, revealing a duality in certain regimes.

Contribution

It introduces a general relation between QCD meson scattering amplitudes and Wilson loops, and explores the emergence of the Veneziano amplitude in a large particle number limit.

Findings

QCD scattering amplitudes can be expressed as convolutions involving Wilson loops.

The kernel in the amplitude becomes constant at large particle numbers.

The Veneziano amplitude naturally arises when Wilson loops are approximated by area behavior.

Abstract

We generalize modern ideas about the duality between Wilson loops and scattering amplitudes in ${\cal N}=4$ SYM to large $N$ QCD by deriving a general relation between QCD meson scattering amplitudes and Wilson loops. We then investigate properties of the open-string disk amplitude integrated over reparametrizations. When the Wilson loop is approximated by the area behavior, we find that the QCD scattering amplitude is a convolution of the standard Koba-Nielsen integrand and a kernel. As usual poles originate from the first factor, whereas no (momentum dependent) poles can arise from the kernel. We show that the kernel becomes a constant when the number of external particles becomes large. The usual Veneziano amplitude then emerges in the kinematical regime where the Wilson loop can be reliably approximated by the area behavior. In this case we obtain a direct duality between Wilson loops and scattering amplitudes when spatial variables and momenta are interchanged, in analogy with the $\cal N$=4 SYM case.