f_K/f_pi in Full QCD with Domain Wall Valence Quarks

TL;DR

This paper calculates the ratio of kaon to pion decay constants using domain-wall valence quarks and rooted Kogut-Susskind sea quarks, employing chiral perturbation theory to extrapolate to physical values and compare systematic errors.

Contribution

It provides a precise determination of f_K/f_pi with domain-wall valence quarks and assesses systematic errors related to lattice quark choices.

Findings

f_K/f_pi = 1.218 with statistical and systematic errors

Results agree with MILC collaboration within uncertainties

Systematic errors from valence quark choice are small

Abstract

We compute the ratio of pseudoscalar decay constants f_K/f_pi using domain-wall valence quarks and rooted improved Kogut-Susskind sea quarks. By employing continuum chiral perturbation theory, we extract the Gasser-Leutwyler low-energy constant L_5, and extrapolate f_K/f_pi to the physical point. We find: f_K/f_pi = 1.218 (+- 0.002) (+0.011 -0.024) where the first error is statistical and the second error is an estimate of the systematic due to chiral extrapolation and fitting procedures. This value agrees within the uncertainties with the determination by the MILC collaboration, calculated using Kogut-Susskind valence quarks, indicating that systematic errors arising from the choice of lattice valence quark are small.