Dynamical Quark Effects on Light Quark Masses

TL;DR

This study uses lattice QCD with two dynamical quark flavors to accurately determine light quark masses, showing that dynamical effects significantly lower these masses compared to quenched approximations.

Contribution

First systematic lattice QCD calculation of light quark masses with two dynamical flavors using improved actions and continuum extrapolation.

Findings

Light quark masses are approximately 3.44 MeV for up/down quarks.

Strange quark mass is around 88-90 MeV depending on input.

Dynamical quarks reduce quark masses by about 25% compared to quenched results.

Abstract

We present results for light quark masses from a systematic lattice QCD study with two degenerate flavors of dynamical quarks. Simulations are made with a renormalization-group improved gauge action and a mean-field improved clover quark action for sea quark masses corresponding to $m_{\rm PS}/m_{\rm V} \approx 0.8$--0.6 and the lattice spacing $a=0.22$--0.11 fm. In the continuum limit we find $m_{ud}^{\bar{MS}}(2 {\rm GeV})=3.44^{+0.14}_{-0.22}$ MeV using the $\pi$ and $\rho$ meson masses as physical input, and $m_s^{\bar{MS}}(2 {\rm GeV})=88^{+4}_{-6}$ MeV or $90^{+5}_{-11}$ MeV with the $K$ or $\phi$ meson mass as additional input. The quoted errors represent statistical and systematic combined, the latter including those from continuum and chiral extrapolations, and from renormalization factors. Compared to quenched results, two flavors of dynamical quarks reduce quark masses by about 25%.