Dynamics of Baryons from String Theory and Vector Dominance

We consider a holographic model of QCD from string theory, à la Sakai and Sugimoto, and study baryons. In this model, mesons are collectively realized as a five-dimensional U(NF ) = U(1) × SU(NF ) Yang-Mills field and baryons are classically identified as SU(NF ) solitons with a unit Pontryagin number and Nc electric charges. The soliton is shown to be very small in the large ’t Hooft coupling limit, allowing us to introduce an effective field B. Its coupling to the mesons are dictated by the soliton structure, and consists of a direct magnetic coupling to the SU(NF ) field strength as well as a minimal coupling to the U(NF ) gauge field. Upon the dimensional reduction, this effective action reproduces all interaction terms between nucleons and an infinite tower of mesons in a manner consistent with the large Nc expansion. We further find that all electromagnetic interactions, as inferred from the same effective action via a holographic prescription, are mediated by an infinite tower of vector mesons, rendering the baryon electromagnetic form factors completely vector-dominated as well. We estimate nucleon-meson couplings and also the anomalous magnetic moments, which compare well with nature. [email protected] [email protected] [email protected] [email protected]