The spectrum of (h)QCD in the Veneziano limit

TL;DR

This paper analyzes the zero-temperature spectra of glueballs and mesons in holographic QCD using the V-QCD model, revealing discrete spectra, Miransky scaling near the conformal transition, and no dilaton presence.

Contribution

It provides a detailed holographic analysis of meson and glueball spectra in the Veneziano limit, including the behavior near the conformal transition and the S-parameter calculation.

Findings

Spectra are discrete and gapped below the critical x_c.

Masses approach zero following Miransky scaling as x approaches x_c.

No evidence of a dilaton in the spectrum.

Abstract

In this note we report on the analysis of the zero temperature spectra of glueballs and mesons for holographic QCD in the Veneziano limit. We work within a holographic bottom-up model named V-QCD which takes into account the full backreaction of the flavor degrees of freedom. By studying the fluctuations of this model we compute spectra of mesons and glueballs as a function of x=N_f/N_c. The spectra are discrete and gapped (modulo the pions) in the QCD regime, where x is below the critical value x_c at which the conformal transition takes place. The masses uniformly converge to zero in the walking region x -> x_c following Miransky scaling. Moreover, all the ratios of masses asymptote to finite constants as x -> x_c. Therefore there is no "dilaton" in the spectrum. Finally, we compute the S-parameter, which is found to be of O(1) in the walking regime.