Confining strings, axions and glueballs in the planar limit

TL;DR

This paper investigates the spectra of confining flux tubes and glueballs in SU(N) gauge theories using lattice simulations, revealing evidence for massive axions on flux-tube world-sheets and providing updated glueball mass spectra in the planar limit.

Contribution

It presents new lattice results on flux-tube and glueball spectra across various N, demonstrating the presence of massive axions and updating the glueball spectrum in the planar limit.

Findings

Most flux-tube states fit Nambu-Goto spectrum

Evidence for massive axions on flux-tube world-sheets

Updated glueball mass spectrum in the planar limit

Abstract

We present recent results on the spectrum of a confining flux tube that is closed around a spatial torus as a function of its length as well as the spectrum of glueballs. The extraction of the spectra has been realized by simulating four dimensional $SU(N)$ gauge theories and performing measurements using lattice techniques. Regarding flux-tubes, we have performed calculations for $N=3,5,6$ and for various values of spin, parity and longitudinal momentum. Long flux-tubes can be thought of as infinitesimally thin strings; hence their spectrum is expected to be described by an effective string theory. Furthermore, the flux-tube's internal structure makes possible the existence of massive states in addition to string modes. Our calculations demonstrate that although most states exhibit a spectrum which can be approximated adequately by Nambu-Goto there is strong evidence for the existence of a massive axion on the world-sheet of the QCD flux-tube as well as a bound state of two such axions. Regarding glueballs, we extracted spectra from $N=2$ to $N=12$ which enables us to extrapolate to $N= \infty$. Our main aim was to calculate the lightest glueball masses for all different configurations of the quantum numbers of spin, parity and charge conjugation. This provides a major update on the spectrum of glueballs in the planar limit.