Chiral dynamics with strange quarks in the light of recent lattice simulations

TL;DR

This paper discusses a reordering of chiral expansions, called Resummed Chiral Perturbation Theory, to better fit lattice QCD data involving strange quarks, revealing insights into chiral symmetry breaking patterns.

Contribution

It introduces and applies Resummed Chiral Perturbation Theory to lattice data, improving fits and understanding of chiral symmetry breaking with strange quarks.

Findings

Resummed Chiral Perturbation Theory provides good fits to lattice data.

Chiral symmetry breaking shows strong dependence on strange quark mass.

Significant differences between Nf=2 and Nf=3 chiral limits are observed.

Abstract

Several lattice collaborations performing simulations with 2+1 light dynamical quarks have experienced difficulties in fitting their data with standard Nf=3 chiral expansions at next-to-leading order, yielding low values of the quark condensate and/or the decay constant in the Nf=3 chiral limit. A reordering of these expansions seems required to analyse these data in a consistent way. We discuss such a reordering, known as Resummed Chiral Perturbation Theory, in the case of pseudoscalar masses and decay constants, pion and kaon electromagnetic form factors and Kl3} form factors. We show that it provides a good fit of the recent results of two lattice collaborations (PACS-CS and RBC/UKQCD). We describe the emerging picture for the pattern of chiral symmetry breaking, marked by a strong dependence of the observables on the strange quark mass and thus a significant difference between chiral symmetry breaking in the Nf=2 and Nf=3 chiral limits. We discuss the consequences for the ratio of decay constants F_K/F_pi and the Kl3 form factor at vanishing momentum transfer.