Massive holographic QCD in the Veneziano limit

Abstract

QCD at finite, flavor independent quark mass is analyzed by using bottom-up holography in the Veneziano limit, where the backreaction of quarks to the gluon dynamics is fully included. The dependence on the quark mass of observables such as the bound state masses, the chiral condensate, the S-parameter, and the critical temperatures is studied. Many of the results are argued to be universal, i.e., independent of the details of the holographic model, and compared to explicit computations in the V-QCD models. The effect of adding four-fermion operators in QCD is also discussed.

Holography and the conformal window in the Veneziano limit

“…By universality, we mean that the phase diagram is largely independent on the exact choice of the potentials in the V-QCD action, and qualitatively similar to all potentials which smoothly interpolate between the UV and IR asymptotics discussed in the previous section. In addition, many results near the conformal transition hold for a little more general class of models than just V-QCD [19] as we will explain below.…”

“…The normalized S-parameter is enhanced rather than suppressed in the walking region (as x → x c from below). For finite quark mass, the S-parameter is also nontrivial inside the conformal window [19], whereas at zero quark mass it vanishes there because chiral symmetry is intact. Notice that as a tiny quark mass is turned on in the conformal window, the S-parameter immediately jumps to a finite O (N f N c ) value.…”

“…The glue and flavor sectors are fully backreacted in the Veneziano limit. The structure of V-QCD at finite temperature and chemical potential [13][14][15][16] as well as the two-point correlators and bound state masses [17][18][19] have also been analyzed.…”

Improved Holographic QCD and the Quark--Gluon Plasma

“…We want to know if these solutions satisfy (54). Near the asymptotically AdS boundary we universally have B ∼ 3/2A and A ∼ −log(r)+· · · .…”

“…Then V f 0 , w and κ are new potentials (in addition to V in (6)) that, in the bottom-up approximation should be fixed by phenomenological requirements as in the previous sections. The theory is further developed in the subsequent works in [46,48,49,51,52,53,54,55]. One typically also makes a simplifying assumption and takes κ(λ, T ) and w(λ, T ) independent of T .…”