The spectrum of open confining strings in the large-$N_c$ limit

TL;DR

This paper investigates the spectra of open flux tubes in large-$N_c$ gauge theories, revealing new phenomena like massive axions and comparing results with string models across multiple gauge groups.

Contribution

It provides the first detailed spectra of open flux tubes for various gauge groups and flux representations, highlighting the presence of massive axions and their consistency across different flux sectors.

Findings

Spectra computed for $N_c=3$ to $6$ and eight flux representations.

Identification of massive axions in the flux tube spectrum.

Consistency of axion mass between open and closed flux tube sectors.

Abstract

We compute the spectra of open flux tubes formed between a static quark-antiquark pair for various gauge groups in the large-$N_c$ limit, focusing on different symmetries manifested by the quantum numbers of angular momentum, parity, and charge conjugation. Specifically, we present spectra from $N_c=3$ up to $N_c=6$ and for eight different irreducible representations of the symmetry characterizing the flux tube. In this study, we employed an anisotropic Wilson action, a large number of suitable spacial operators, and solved the generalized eigenvalue problem (GEVP) to obtain a significant number of excitations for different combinations of flux tube quantum numbers. The spectra are compared with the Nambu-Goto string model, revealing novel phenomena such as the presence of massive axions in the flux tube spectrum. We find that the mass of the axion in the open flux tube spectra sector is consistent with the mass obtained in the closed flux tube sector.