Toward a Systematic Holographic QCD: A Braneless Approach

TL;DR

The paper develops a braneless AdS/QCD framework in which QCD vacuum condensates are incorporated as bulk scalar fields that backreact on the 5D geometry, dynamically producing an IR confinement scale. It then introduces an asymptotically free background with a dilaton potential that yields logarithmic running, computing the gluon condensate and a spectrum of glueball states; it further includes a Tr F^3 condensate and analyzes the sensitivity of spectra to its scale via Gubser's criterion. The running coupling is connected to Analytic Perturbation Theory through a Lambert W form, yielding a finite $\alpha_s(\mu)$ at all scales. The work also discusses limitations, including radion modes and Regge physics, and proposes tachyon condensation as a possible route to linear confinement.

Abstract

Recently a holographic model of hadrons motivated by AdS/CFT has been proposed to fit the low energy data of mesons. We point out that the infrared physics can be developed in a more systematic manner by exploiting backreaction of the nonperturbative condensates. We show that these condensates can naturally provide the IR cutoff corresponding to confinement, thus removing some of the ambiguities from the original formulation of the model. We also show how asymptotic freedom can be incorporated into the theory, and the substantial effect it has on the glueball spectrum and gluon condensate of the theory. A simple reinterpretation of the holographic scale results in a non-perturbative running for alpha_s which remains finite for all energies. We also find the leading effects of adding the higher condensate into the theory. The difficulties for such models to reproduce the proper Regge physics lead us to speculate about extensions of our model incorporating tachyon condensation.