Dynamic AdS/QCD and the spectrum of walking gauge theories
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, ?. The condensate provides a dynamically generated infrared 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 ?, to study SU(3) gauge theory with a continuous number of quark flavors, Nf. We follow the behavior of the spectrum as we approach the conformal window through a walking gauge theory regime. We show such walking theories display a Berezinskii–Kosterlitz–Thoules 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 nonperturbative contribution to S falls to zero. We also study the deformation of the Berezinskii–Kosterlitz–Thoules transition when the quarks have a current mass, which may be of use for understanding lattice simulations of walking theories.