Abstract
V-QCD is a class of effective holographic models for QCD which fully includes the backreaction of quarks to gluon dynamics. The physics of the theta-angle and the axial anomaly can be consistently included in these models. We analyze their phase diagrams over ranges of values of the quark mass, N_f/N_c, and theta, computing observables such as the topological susceptibility and the meson masses. At small quark mass, where effective chiral Lagrangians are reliable, they agree with the predictions of V-QCD.
Highlights
Most of the literature on holographic QCD assumes the’t Hooft limit, Nc → ∞, λ = g2YM Nc = fixed, (1)and keeping the number of flavors N f fixed
The quarks act as probes in the dynamics determined by the gluon degrees of freedom
The conformal window in QCD is found for the values of the ratio N f /Nc ≡ x larger than three of four, whereas in the ’t Hooft limit this ratio tends to zero
Summary
Most of the literature on holographic QCD (and holographic Yang-Mills theory) assumes the. Born-Infeld (DBI) action, which describe the dynamics of a pair of space filling D4−D4 branes [9, 10] This method has been successfully tested in the probe limit [11, 12]: tachyon condensation in the bulk, triggered by confinement, was seen to produce the desired picture of chiral symmetry breaking and the spectrum of light mesons was very close to that observed in experiments. The physical parameter is the combination θ = θ + a φa, where φa are the phases in the masses of the various quark flavors, which is invariant in the axial U(1)A transformation In this talk the V-QCD models at zero θwill be reviewed first. V-QCD, the CP-odd dynamics, and results for related observables will be discussed
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