QCD Worldsheet Axion from the Bootstrap

TL;DR

This paper uses the S-matrix Bootstrap to construct non-perturbative scattering amplitudes for the QCD worldsheet axion, revealing its dominant role in the UV behavior of flux tube dynamics.

Contribution

It introduces a bootstrap-based method to model the worldsheet axion's properties and demonstrates its significant influence on the flux tube amplitudes in different regimes.

Findings

Axion resonance matches lattice measurements

Axion dominates the UV completion of flux tube amplitudes

Axion can be non-parametrically light or heavy depending on regime

Abstract

The worldsheet axion plays a crucial role in the dynamics of the Yang-Mills confining flux tubes. According to the lattice measurements, its mass is of order the string tension and its coupling is close to a certain critical value. Using the S-matrix Bootstrap, we construct non-perturbative $2 \to 2$ branon scattering amplitudes which also feature a weakly coupled axion resonance with these properties. We study the extremal bootstrap amplitudes in detail and show that the axion plays a dominant role in their UV completion in two distinct regimes, in one of which it cannot be considered a parametrically light particle. We conjecture that the actual flux tube amplitudes exhibit a similar behavior.