On the Couplings of Vector Mesons in AdS/QCD

TL;DR

This paper investigates the universality of rho meson couplings in AdS/QCD models, showing it generally does not hold but emerges in specific regimes, and examining the approximate validity of the rho-dominance relation.

Contribution

It demonstrates conditions under which rho meson couplings become universal in AdS/QCD models and identifies regimes where the rho-dominance relation approximately holds.

Findings

Universality of rho couplings fails generally but emerges in specific limits.

The rho-dominance relation is approximately valid in studied models.

Certain models exhibit exact universality for rho couplings.

Abstract

We address, in the AdS/CFT context, the issue of the universality of the couplings of the rho meson to other hadrons. Exploring some models, we find that generically the rho-dominance prediction f_\rho g_{\rho H H}=m_\rho^2 does not hold, and that g_{\rho H H} is not independent of the hadron H. However, we prove that, in any model within the AdS/QCD context, there are two limiting regimes where the g_{\rho H H}, along with the couplings of all excited vector mesons as well, become H-independent: (1) when H is created by an operator of large dimension, and (2) when H is a highly-excited hadron. We also find a sector of a particular model where universality for the rho coupling is exact. Still, in none of these cases need it be true that f_\rho g_\rho=m_\rho^2, although we find empirically that the relation does hold approximately (up to a factor of order two) within the models we have studied.