Progress of Theoretical Physics Supplement No. 186, 2010 463 Holographic Chiral Currents in a Magnetic Field

In the presence of a quark chemical potential, a magnetic field induces an axial current in the direction of the magnetic field. We compute this current in the Sakai-Sugimoto model, a holographic model which, in a certain limit, is dual to large-Nc QCD. We also compute the analogous vector current, for which an axial chemical potential is formally introduced. This vector current can potentially be observed via charge separation in heavy-ion collisions. After implementing the correct axial anomaly in the Sakai-Sugimoto model we find an axial current in accordance with previous studies and a vanishing vector current, in apparent contrast to previous weak-coupling calculations. The Sakai-Sugimoto model1),2) is a realization of the gauge/gravity duality3) which provides a top-down approach to a holographic model of QCD. While at present no gravity dual to QCD is known, the Sakai-Sugimoto model exhibits some of the most important properties of QCD, most notably confinement and chira