SVZ⊕1/q2-expansion versus some QCD holographic models

Considering the classical two-point correlators built from (axial-) vector, scalar q¯q and gluonium currents, we confront results obtained using the SVZ⊕1/q2-expansion to the ones from some QCD holographic models in the Euclidean region and with negative dilaton Φi(z)=−|ci2|z2. We conclude that the presence of the 1/q2-term in the SVZ-expansion due to a tachyonic gluon mass appears naturally in the Minimum Soft-Wall (MSW) and the Gauge/String Dual (GSD) models which can also reproduce semi-quantitatively some of the higher dimension condensate contributions appearing in the OPE. The Hard-Wall model shows a large departure from the SVZ⊕1/q2-expansion in the vector, scalar and gluonium channels due to the absence of any power corrections. The equivalence of the MSW and GSD models is manifest in the vector channel through the relation of the dilaton parameter with the tachyonic gluon mass. For approximately reproducing the phenomenological values of the dimension d=4,6 condensates, the holographic models require a tachyonic gluon mass (αs/π)λ2≈−(0.12-0.14) GeV2, which is about twice the fitted phenomenological value from e+e− data. The relation of the inverse length parameter ci to the tachyonic gluon mass also shows that ci is channel dependent but not universal for a given holographic model. Using the MSW model and Mρ=0.78 GeV as input, we predict a scalar q¯q mass MS≈(0.95-1.10) GeV and a scalar gluonium mass MG≈(1.1-1.3) GeV.