MILC Gauge Configurations

The greatest challenge to performing accurate numerical calculations of quantum chromodynamics (QCD) is the inclusion of the full effects of sea quarks, quarks that are created and destroyed during the course of a process, rather than being part of the initial and final states. The simulations we have carried out over the last several years are the first to fully take into account the effects of up, down and strange sea quarks [1]. These three flavors of quarks are the only ones with masses comparable to the energy scale of QCD, and are therefore the only ones light enough to have a significant impact on realistic calculations. The computational resources needed to generate configurations grows rapidly as the sea quark masses decrease. Although it is possible to work directly at the mass of the strange quark, with current computers it is too expensive to do so for the much lighter up and down quarks, whose masses are much smaller than any other energy scale in QCD. Instead one generates configurations for a range of u and d quark masses, and extrapolates to their physical values with the aid of chiral perturbation theory [2], an effective field theory which predicts the dependence of physical observables on the light quark masses. In our simulations, we take the masses of the up and down quarks to be equal, which has a negligible effect (< 1%) on isospin-averaged quantities.