Electromagnetic nucleon-to-delta transition in holographic QCD

We study nucleon-to-delta electromagnetic transition form factors and relations between them within the framework of the holographic dual model of QCD proposed by Sakai and Sugimoto. In this setup, baryons appear as topological solitons of the five-dimensional holographic gauge theory that describes a tower of mesons and their interactions. We find a relativistic extension of the nucleon-delta-vector meson interaction vertices and use these to calculate transition form factors from holographic QCD. We observe that at low momentum transfer, magnetic dipole, electric and Coulomb quadrupole form factors, and their ratios follow the patterns expected in the large $N_c$ limit. Our results at this approximation are in reasonable agreement with experiment.

Figure 1

The plot of the ratio $G_M^{*}(Q^2)/(3G_D(Q^2))$ as a function of $Q^2$, where $G_D(Q^2)=1/(1+Q^2/{\Lambda }^2{)}^2$ with ${\Lambda }^2=0.71(\mathrm{GeV}/c{)}^2$. The solid and dotted lines are the predictions from the holographic type I and type II models, respectively. The dashed (dash-dotted) curves are from taking the parameter $a$ of Eq. (20) to be 20% larger (smaller) than the value $a\sim 0.240$. The experimental data points are taken from 50.