Decay constants in soft wall AdS/QCD revisited

TL;DR

This paper revisits the soft wall AdS/QCD model and introduces a modification with an additional energy scale to accurately reproduce the decreasing decay constants of radially excited heavy vector mesons.

Contribution

The authors propose a modified soft wall AdS/QCD framework with an extra energy scale to better match experimental decay constant behavior.

Findings

Decay constants decrease with radial excitation level in the modified model.

The model aligns better with experimental data for heavy vector mesons.

Two-point functions are computed at a finite AdS radial coordinate.

Abstract

Phenomenological AdS/QCD models, like hard wall and soft wall, provide hadronic mass spectra in reasonable consistency with experimental and (or) lattice results. These simple models are inspired in the AdS/CFT correspondence and assume that gauge/ gravity duality holds in a scenario where conformal invariance is broken through the introduction of an energy scale. Another important property of hadrons: the decay constant, can also be obtained from these models. However, a consistent formulation of an AdS/QCD model that reproduces the observed behavior of decay constants of vector meson excited states is still lacking. In particular: for radially excited states of heavy vector mesons, the experimental data lead to decay constants that decrease with the radial excitation level. We show here that a modified framework of soft wall AdS/QCD involving an additional dimensionfull parameter, associated with an ultraviolet energy scale, provides decay constants decreasing with radial excitation level. In this version of the soft wall model the two point function of gauge theory operators is calculated at a finite position of the anti-de Sitter space radial coordinate.