The Extended Chiral Quark Model confronts QCD

TL;DR

This paper develops an extended chiral quark model to connect low-energy QCD effective theories with fundamental QCD, deriving meson properties and constraints from chiral symmetry considerations and matching to QCD.

Contribution

It introduces a comprehensive truncation of the effective QCD action including operators up to dimension 6 and performs bosonization to derive meson spectra and couplings.

Findings

Scalar meson mass around 1 GeV

Small axial pion-quark coupling g_A ≈ 0.55

Consistent fit of meson parameters and chiral constants

Abstract

We discuss the truncation of low energy effective action of QCD below the chiral symmetry breaking (CSB) scale, including all operators of dimensionality less or equal to 6 which can be built with quark and chiral fields. We perform its bosonization in the scalar, pseudoscalar, vector and axial-vector channels in the large-N_c and leading-log approximation. Constraints on the coefficients of the effective lagrangian are derived from the requirement of Chiral Symmetry Restoration (CSR) at energies above the CSB scale in the scalar-pseudoscalar and vector-axial-vector channels, from matching to QCD at intermediate scales, and by fitting some hadronic observables. In this truncation two types of pseudoscalar states (massless pions and massive Pi'-mesons), as well as a scalar, vector and axial-vector one arise as a consequence of dynamical chiral symmetry breaking. Their masses and coupling constants as well as a number of chiral structural constants are derived. A reasonable fit of all parameters supports a relatively heavy scalar meson (quarkonium) with the mass \sim 1 GeV and a small value of axial pion-quark coupling constant g_A \simeq 0.55.