Couplings of the Rho Meson in a Holographic dual of QCD with Regge Trajectories

Abstract

The couplings $g_{ρHH}$ of the $ρ$ meson with any hadron H are calculated in a holographic dual of QCD where the Regge trajectories for mesons are manifest. The resulting couplings grow linearly with the exciting number of H, thus are far from universal. A simple argument has been given for this behavior based on quasi-classical picture of excited hadrons. It seems that in holographic duals with exact Regge trajectories the $g_{ρHH}$ universality should be violated. The $ρ$-dominance for the electromagnetic form factors of H are also strongly violated, except for the lowest state, the pion. Quite unexpected, the form factor of the pion is completely saturated by the contribution of the $ρ$. The asymptotic behavior of the form factors are also calculated, and are found to be perfectly accordant with the prediction of conformal symmetry and pertubative QCD.