Decay constants in soft wall AdS/QCD revisited

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.Comment: Shorter (letter) version. Results unchanged. More references included. We now explain that the large UV scale of the model is associated with the non-hadronic decay of the heavy vector meson into light leptons. Version Published in Phys. Lets.

Light meson masses using AdS/QCD modified soft wall model

“…This extra brane will work as the boundary were the particles live and also will fix, altogether with the dilatonic energy scale, the mass and decay constant spectra of the particles. The application of this idea gives good results describing the first four vector states of charmonium and also the first four of bottomonion with a total error near to 30% for fitting eight quarkonium states with three parameters [34]. The extension to finite temperature of this model gives a complete holographic view of the melting processes of these heavy quarkonium states, with results in agreement with the observed phenomenology [35].…”

“…Following [34], we can test the predictability of the model developed here with the RMS error for estimating N parameters using N p parameters as…”

“…Despite having different values for κ and z 0 for heavy [34] and light mesons, an universality class can be established for these sort of models. In fact, there is a huge phenomelogical difference between heavy and light quarks due to the heavy quark symmetry: heavy quark systems are considered as non-relativistic, e.g., Schroedinger-like heavy quarkonium potentials.…”

“…Thus, we can fix ∆ = 3 and p = 0 such that m 2 5 R 2 = −3 [31]. The geometric background is given by the sliced AdS Poincare patch [34,35] …”

“…Recently, a new approach was developed in [34], where the usual soft wall model is upgraded by including an extra UV cutoff given by a D-brane. This extra brane will work as the boundary were the particles live and also will fix, altogether with the dilatonic energy scale, the mass and decay constant spectra of the particles.…”