Chiral currents and static properties of nucleons in holographic QCD

Abstract

We analyze static properties of nucleons in the two flavor holographic QCD model of Sakai and Sugimoto described effectively by a five-dimensional $U(2)$ Yang-Mills theory with the Chern-Simons term on a curved background. The baryons are represented in this model as a soliton, which at a time slice is approximately the Belavin-Polyakov-Shvarts-Tyupkin (BPST) instanton with a fixed size. First, we construct a chiral current in four dimensions from the Noether current of local gauge transformations which are nonvanishing on the boundaries of the extra dimension. We examine this chiral current for nucleons with quantized collective coordinates to compute their charge distribution, charge radii, magnetic moments, and axial-vector coupling. Most of the results are better close to the experimental values than in the Skyrme model. We discuss the problems of our chiral current, nonuniqueness of the local gauge transformation for defining the current, and its gauge-noninvariance.