A holographic QCD and baryons from string theory

A holographic QCD deals with the gauge invariant observables of QCD in the large Nc and large 't Hooft coupling limit, according to the general idea of gauge/gravity duality. A very appealing example is based on a D4-D8 brane complex in string theory. In this note, we review how this model is capable of reproducing physics of pions, vector mesons and baryons, in a unifying picture based on a holographic flavor gauge field. In particular, the baryon show up as quantized instanton soliton of the flavor gauge field, which gives us a natural and extremely simple framework for determining all baryon-meson interactions. We give some of the simplest predictions of the model which are remarkably good when compared to experimental data. We close with comments. (author)