Chiral dynamics of baryons from string theory

Abstract

We study baryons in a holographic model of QCD by Sakai and Sugimoto, realized as small instantons with fundamental string hairs. We introduce an effective field theory of the baryons in the five-dimensional setting, and show that the instanton interpretation implies a particular magnetic coupling. Dimensional reduction to four dimensions reproduces the usual chiral effective action, and, in particular, we estimate the axial coupling ${g}_{A}$ between baryons and pions and the magnetic dipole moments, both of which are proportional to ${N}_{c}$. We extrapolate to finite ${N}_{c}$ and discuss subleading corrections.