Dynamic AdS/QCD and the Spectrum of Walking Gauge Theories

TL;DR

This paper introduces a dynamic AdS/QCD model that predicts the spectrum of walking gauge theories, revealing a BKT phase transition, enhanced condensate, and a light Higgs-like particle as the theory approaches the conformal window.

Contribution

It presents a novel AdS/QCD framework incorporating dynamical chiral symmetry breaking driven by the anomalous dimension gamma, applied to study the spectrum near the conformal window in walking gauge theories.

Findings

Identification of a BKT phase transition with Miransky scaling.

Enhanced quark condensate near the conformal window.

Prediction of a light Higgs-like excitation and vanishing non-perturbative S parameter.

Abstract

We present a simple AdS/QCD model in which the formation of the chiral condensate is dynamically determined. The gauge dynamics is input through the running of the quark bilinear's anomalous dimension, gamma. The condensate provides a dynamically generated infra-red wall in the computation of mesonic bound state masses and decay constants. As an example, we use the model, with perturbative computations of the running of gamma, to study SU(3) gauge theory with a continuous number of quark flavours, Nf. We follow the behaviour of the spectrum as we approach the conformal window through a walking gauge theory regime. We show such walking theories display a BKT phase transition, with Miransky scaling, as one approaches the edge of the conformal window at the critical value of Nf. We show that these walking theories possess an enhanced quark condensate, a light Higgs like excitation and argue that the non-perturbative contribution to S falls to zero. We also study the deformation of the BKT transition when the quarks have a current mass which may be of use for understanding lattice simulations of walking theories.