Connections between chiral Lagrangians and QCD sum-rules

TL;DR

This paper establishes a method connecting QCD sum-rules with chiral Lagrangians, enabling detailed analysis of light scalar meson substructures and mixing effects through a novel relationship between quark and mesonic correlation functions.

Contribution

It introduces a framework that relates quark-level correlation functions to mesonic two-point functions using scale factor matrices, validated on the $a_0$ meson system.

Findings

Successful determination of scale factors from QCD sum-rules and chiral Lagrangians.

Remarkable agreement between QCD quark condensates and mesonic vacuum expectation values.

Sensitivity of results to the $a_0$-system mixing angle.

Abstract

It is shown how a chiral Lagrangian framework can be used to derive relationships connecting quark-level QCD correlation functions to mesonic-level two-point functions. Crucial ingredients of this connection are scale factor matrices relating each distinct quark-level substructure (e.g., quark-antiquark, four-quark) to its mesonic counterpart. The scale factors and mixing angles are combined into a projection matrix to obtain the physical (hadronic) projection of the QCD correlation function matrix. Such relationships provide a powerful bridge between chiral Lagrangians and QCD sum-rules that are particularly effective in studies of the substructure of light scalar mesons with multiple complicated resonance shapes and substantial underlying mixings. The validity of these connections is demonstrated for the example of the isotriplet $a_0(980)$-$a_0(1450)$ system, resulting in an unambiguous determination of the scale factors from the combined inputs of QCD sum-rules and chiral Lagrangians. These scale factors lead to a remarkable agreement between the quark condensates in QCD and the mesonic vacuum expectation values that induce spontaneous chiral symmetry breaking in chiral Lagrangians. This concrete example shows a clear sensitivity to the underlying $a_0$-system mixing angle, illustrating the value of this methodology in extensions to more complicated mesonic systems.