Electromagnetic Baryon Form Factors from Holographic QCD

TL;DR

This paper uses holographic QCD to model baryons as chiral solitons sourced by D4 instantons, deriving electromagnetic properties and magnetic moments with strong vector-baryon interactions at the core boundary.

Contribution

It introduces a semiclassical quantization of D4 instantons in holographic QCD, revealing detailed electromagnetic structure and magnetic moments of baryons within this framework.

Findings

Electromagnetic charge radius is of order ^0.

Proton and neutron magnetic moments are related by a model-independent relation.

Vector-meson dominated electromagnetic current at the core boundary.

Abstract

In the holographic model of QCD suggested by Sakai and Sugimoto, baryons are chiral solitons sourced by D4 instantons in bulk of size 1/\sqrt{\lambda} with \lambda=g^2N_c. We quantize the D4 instanton semiclassically using \hbar=1/(N_c\lambda) and non-rigid constraints on the vector mesons. The holographic baryon is a small chiral bag in the holographic direction with a Cheshire cat smile. The vector-baryon interactions occur at the core boundary of the instanton in D4. They are strong and of order 1/\sqrt{\hbar}. To order \hbar^0 the electromagnetic current is entirely encoded on the core boundary and vector-meson dominated. To this order, the electromagnetic charge radius is of order \lambda^0. The meson contribution to the baryon magnetic moments sums identically to the core contribution. The proton and neutron magnetic moment are tied by a model independent relation similar to the one observed in the Skyrme model.