Brane-induced Skyrmion on S3: Baryonic matter in holographic QCD

We study baryonic matter in holographic QCD with D4/D8/D8̄ multi-D brane system in type IIA superstring theory. The baryon is described as the "brane-induced Skyrmion," which is a topologically nontrivial chiral soliton in the four-dimensional meson effective action induced by holographic QCD. We employ the "truncated-resonance model" approach for the baryon analysis, including pion and ρ meson fields below the ultraviolet cutoff scale MKK∼1GeV, to keep the holographic duality with QCD. We describe the baryonic matter in large Nc as single brane-induced Skyrmion on the three-dimensional closed manifold S3 with finite radius R. The interactions between baryons are simulated by the curvature of the closed manifold S3, and the decrease of the size of S3 represents the increase of the total baryon-number density in the medium in this modeling. We investigate the energy density, the field configuration, the mass and the root-mean-square radius of single baryon on S3 as the function of its radius R. We find a new picture of "pion dominance" near the critical density in the baryonic matter, where all the (axial) vector meson fields disappear and only the pion fields survive. We also find the swelling phenomena of the baryons as the precursor of the deconfinement, and propose the mechanism of the swelling in the general context of QCD. The properties of the deconfinement and the chiral symmetry restoration in the baryonic matter are examined by taking the proper order parameters. We also compare our truncated-resonance model with another instanton description of the baryon in holographic QCD, considering the role of cutoff scale MKK. © 2009 The American Physical Society.