The discontinuities of conformal transitions and mass spectra of V-QCD

A bstract Zero temperature spectra of mesons and glueballs are analyzed in a class of holographic bottom-up models for QCD in the Veneziano limit, N c → ∞, N f → ∞, with x = N f /N c fixed(V-QCD).The back reaction of flavor on color is fully included. It is found that spectra are discrete and gapped (modulo the pions) in the QCD regime, for x below the critical value x c where the conformal transition takes place. The masses uniformly converge to zero in the walking region due to Miransky scaling. All the ratios of masses asymptote to non-zero constants as and therefore there is no “dilaton” in the spectrum. The S-parameter is computed and found to be of in units of N f N c in the walking regime, while it is always an increasing function of x . This indicates the presence of a subtle discontinuity of correlation functions across the conformal transition at x = x c .