Full nonperturbative QCD simulations with 2+1 flavors of improved staggered quarks
Abstract
For several years the MILC collaboration has carried out nonperturbative simulations of full QCD with two degenerate flavors of light quarks, up and down, and with one heavier flavor, the strange quark. Several light quark masses, down to about three times the physical light quark mass, and several lattice spacings have been used. These allow for controlled continuum and chiral extrapolations of many low energy QCD observables. Use of an improved staggered quark formalism, "asqtad" fermions, has been crucial in achieving this goal. Here we review the improved staggered formalism, emphasizing both advantages and drawbacks. In particular, we review the procedure, known as the "fourth root trick" for removing unwanted staggered species in the continuum limit. We then describe the lattice ensembles created so far, and the physics results obtained on them. These include the heavy quark potential, spectrum of light hadrons, quark masses, decay constants of light and heavy-light pseudoscalar mesons, semileptonic form factors, computation of the strong coupling constant, spectroscopy of quarkonia, neutral meson mixing, and more. We illustrate the impact of some of these results on the determination of CKM matrix elements. All MILC lattice ensembles are publicly available. Some of the results mentioned were obtained by other groups using these MILC ensembles, some were obtained by MILC in collaboration with other groups, and some by the MILC collaboration alone.Keywords
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