Holographic dual of QCD from black D5 branes

Abstract

We study the dynamics of probe D7 flavor probe branes in the background of near extremal D5 branes. This model is a holographic dual to a gauge theory with spontaneous breaking of a U(Nf)L × U(Nf)R chiral symmetry. The spectrum of two such D7 embeddings, contains a single massive 4D meson coming from the world volume U(1) gauge field, the pion, and a single massive 4D scalar meson coming from fluctuations of the embedding of the brane. In addition, there are continuum five dimensional states due to the finite height of the effective potential in the radial direction. We investigate baryons in this model, and find that the size is stabilized due to the Chern-Simons term in the D7 world volume action. The model admits a Hagedorn temperature of 1/2πR where R is the radius parameter in the D5 branes metric. We investigate the pattern of chiral symmetry breaking in the deconfined phase as a function of the asymptotic separation of the branes L. We find that for πR/3 < L 1.068R that chiral symmetry is restored, and that chiral symmetry is broken for L outside this window. We further argue that the solutions with L < π/3 are only classically stable, and in fact no D7 embedding exists with these boundary conditions.