Three-flavour order parameters of chiral symmetry in low-energy QCD

TL;DR

This paper reviews the current understanding of chiral symmetry order parameters in low-energy QCD, highlighting differences between two- and three-flavour cases and presenting new constraints from Bayesian analysis of eta decays.

Contribution

It provides a comprehensive review of the order parameters in low-energy QCD and introduces new Bayesian constraints on three-flavour parameters from eta decay data.

Findings

Better understanding of two-flavour chiral symmetry parameters.

New Bayesian constraints on three-flavour order parameters.

Implications for QCD vacuum structure in three-flavour case.

Abstract

The current state of knowledge of the order parameters of the spontaneously broken chiral symmetry, the quark condensate and the pseudoscalar decay constant in the chiral limit, is briefly reviewed, based on available phenomenological fits and lattice QCD calculations. We argue that while the theory is pretty well understood in the two-flavour case, there is still a gap in the knowledge of the characteristics of the QCD vacuum in the three-flavour one. Our constraints for the three-flavour parameters obtained by a Bayesian statistical analysis of the decays of eta to three pions are presented. Possible implications of a new analysis of subthreshold parameters of pion-pion scattering is outlined.