Non-perturbative Renormalization of Improved Staggered Bilinears

We compute Z-factors for general staggered bilinears on fine (a \approx 0.09 fm) MILC ensembles using both asqtad and HYP-smeared valence actions, comparing the results to the predictions of one-loop perturbation theory. This is an extension of previous work on the coarse (a \approx 0.12 fm) MILC ensembles. It provides a laboratory for studying NPR methodology in the staggered context, and is an important stepping stone for fully non-perturbative matching factors in ongoing computations of B_K and other weak matrix elements. We also implement non-exceptional RI/SMOM renormalization conditions using the asqtad action and present first results.Comment: 7 pages, 4 figures. Contribution to the 30th International Symposium on Lattice Field Theory, June 24-29, 2012, Cairns, Australi

Current Physics Results from Staggered Chiral Perturbation Theory

We review several results that have been obtained using lattice QCD with the staggered quark formulation. Our focus is on the quantities that have been calculated numerically with low statistical errors and have been extrapolated to the physical quark mass limit and continuum limit using staggered chiral perturbation theory. We limit our discussion to a brief introduction to staggered quarks, and applications of staggered chiral perturbation theory to the pion mass, decay constant, and heavy-light meson decay constants.Comment: 18 pages, 4 figures, commissioned review article, to appear in Mod. Phys. Lett.

Non-perturbative improvement of bilinears in unquenched QCD

We describe how the improvement of quark bilinears generalizes from quenched to unquenched QCD, and discuss which of the additional improvement constants can be determined using Ward Identities.Comment: LATTICE99 (Improvement and Renormalization). 3 pages, no figures. Corrected error (improvement coefficient $g_T$ is not needed

Mass dependence of the hairpin vertex in quenched QCD

The pseudoscalar ``hairpin'' vertex (i.e. quark-disconnected vertex) plays a key role in quenched chiral perturbation theory. Direct calculations using lattice simulations find that it has a significant dependence on quark mass. I show that this mass dependence can be used to determine the quenched Gasser-Leutwyler constant L5. This complements the calculation of L5 using the mass dependence of the axial decay constant of the pion. In an appendix, I discuss power counting for quenched chiral perturbation theory and describe the particular scheme used in this paper.Comment: 12 pages, 4 figures. Version to appear in Phys. Rev. D. Central result unchanged, but explanation of calculation improved and minor errors corrected. New appendix discusses power counting schemes in quenched chiral perturbation theor