Holographic Dual of QCD from Black D5 Branes

TL;DR

This paper explores a holographic model of QCD using D5 branes, analyzing chiral symmetry breaking, meson spectra, and baryon stabilization, revealing phase transitions and stability conditions in the dual gauge theory.

Contribution

It introduces a D5 brane-based holographic dual of QCD, detailing meson spectra, baryon stabilization, and chiral symmetry behavior in the deconfined phase.

Findings

Identifies a single massive pion and scalar meson in the spectrum.

Finds a specific range of brane separation where chiral symmetry is restored.

Demonstrates baryon size stabilization via the Chern-Simons term.

Abstract

We study the dynamics of probe D7 $\overline{\rm D7}$ 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 $U(N_f)_L\times U(N_f)_R$ chiral symmetry. The spectrum of two such D7 $\overline{\rm D7}$ 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 $\frac{1}{2\pi R}$ 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 $\frac{\pi}{3}R<L\lessapprox 1.068 R$ that chiral symmetry is restored, and that chiral symmetry is broken for $L$ outside this window. We further argue that the solutions with $L<\frac{\pi}{3}$ are only classically stable, and in fact no D7 embedding exists with these boundary conditions.