Chiral dynamics of baryons from string theory

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 gA between baryons and pions and the magnetic dipole moments, both of which are proportional to Nc. We extrapolate to finite Nc and discuss subleading corrections.