Semiclassical string spectrum in a string model dual to large N QCD

TL;DR

This paper analyzes the spectrum of classical strings in a holographic QCD model, deriving energy formulas for glueballs and Kaluza-Klein states, and explores their behavior across different coupling regimes.

Contribution

It provides new classical string solutions and energy formulas in a holographic QCD model, connecting string configurations to glueball spectra and their dependence on the coupling.

Findings

Energies of states increase as 't Hooft coupling decreases, except for horizon strings.

Classical solutions can be extrapolated to small coupling regimes.

Reproduction of glueball energy formulas via supergravity point-like string oscillations.

Abstract

We explore the string spectrum in the Witten QCD model by considering classical string configurations, thereby obtaining energy formulas for quantum states with large excitation quantum numbers representing glueballs and Kaluza-Klein states. In units of the string tension, the energies of all states increase as the 't Hooft coupling $\lambda $ is decreased, except the energies of glueballs corresponding to strings lying on the horizon, which remain constant. We argue that some string solutions can be extrapolated to the small $\lambda $ regime. We also find the classical mechanics description of supergravity glueballs in terms of point-like string configurations oscillating in the radial direction, and reproduce the glueball energy formula previously obtained by solving the equation for the dilaton fluctuation.