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

TL;DR

This paper calculates the rho meson couplings in a holographic QCD model with Regge trajectories, revealing non-universality and specific behaviors of form factors consistent with QCD and conformal symmetry.

Contribution

It introduces a holographic model with Regge trajectories to compute rho meson couplings, showing their linear growth and violation of universality, and analyzes form factors with QCD consistency.

Findings

Couplings grow linearly with hadron excitation number.

Universality of rho couplings is violated in models with Regge trajectories.

Pion form factor is saturated by rho contribution and matches QCD predictions.

Abstract

The couplings $g_{\rho HH}$ of the $\rho$ 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 $g_{\rho HH}$ universality should be violated. The $\rho$-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 $\rho$. 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.