Tests of Universality in AdS/QCD

TL;DR

This paper investigates the universality of certain predictions in AdS/QCD models, analyzing how low-energy hadronic observables depend on model parameters and testing the robustness of these models against experimental data.

Contribution

It provides a detailed analysis of the sensitivity of low-energy hadronic observables to various parameters in the hard-wall AdS/QCD model and explores the universality of specific predictions.

Findings

Certain predictions like viscosity-to-entropy ratio are universal.

Low-energy observables show limited sensitivity to model parameter variations.

A generalized Gell-Mann-Oakes-Renner relation is derived.

Abstract

Estimates of the light hadron masses, decay constants and couplings in AdS/QCD models are generally more accurate than should have been expected. Certain predictions based on the AdS/CFT correspondence, such as the ratio of the equilibrium viscosity to entropy density, are universal and therefore provide firm experimental tests of these models. Other observables, while not completely universal, may be relatively insensitive to model details. We calculate the dependence of a number of low-energy hadronic observables on details of the hard-wall AdS/QCD model. In particular, we vary the infrared boundary conditions, the 5D gauge coupling, and the mass of the field responsible for chiral symmetry breaking, while holding fixed a small number of observables. We also find a generalized Gell-Mann-Oakes-Renner relation which helps to justify the identification of model parameters with the product of physical quark mass and chiral condensate as per the AdS/CFT correspondence.