Fine Structure of the QCD String Spectrum

TL;DR

This paper uses lattice QCD methods to identify three distinct scales in the gluon field excitation spectrum around a static quark-antiquark pair, revealing a transition from local gluon excitations to string-like behavior.

Contribution

It uncovers the detailed structure of the QCD string spectrum across different length scales, highlighting a crossover region and fine structure that inform effective string models.

Findings

Three excitation scales identified in the QCD spectrum.

A crossover region with rearranged level orderings below 2 fm.

Spectrum at large distances matches string model predictions with fine structure.

Abstract

Using advanced lattice methods in Quantum Chromodynamics, three distinct scales are established in the excitation spectrum of the gluon field around a static quark-antiquark pair as the color source separation R is varied. On the shortest length scale, the excitations are consistent with states created by local gluon field operators arising from a multipole operator product expansion. An intermediate crossover region below 2 fm is identified with a dramatic rearrangement of the level orderings. On the largest length scale of 2-3 fm, the spectrum agrees with that expected for string-like excitations. The energies nearly reproduce asymptotic pi/R string gaps, but exhibit a fine structure, providing important clues for developing an effective bosonic string description.