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

A Simple Algebraic Grid Adaptation Scheme with Applications to Two- and Three-dimensional Flow Problems

An algebraic adaptive grid scheme based on the concept of arc equidistribution is presented. The scheme locally adjusts the grid density based on gradients of selected flow variables from either finite difference or finite volume calculations. A user-prescribed grid stretching can be specified such that control of the grid spacing can be maintained in areas of known flowfield behavior. For example, the grid can be clustered near a wall for boundary layer resolution and made coarse near the outer boundary of an external flow. A grid smoothing technique is incorporated into the adaptive grid routine, which is found to be more robust and efficient than the weight function filtering technique employed by other researchers. Since the present algebraic scheme requires no iteration or solution of differential equations, the computer time needed for grid adaptation is trivial, making the scheme useful for three-dimensional flow problems. Applications to two- and three-dimensional flow problems show that a considerable improvement in flowfield resolution can be achieved by using the proposed adaptive grid scheme. Although the scheme was developed with steady flow in mind, it is a good candidate for unsteady flow computations because of its efficiency

Using Wilson flow to study the SU(3) deconfinement transition

We explore the use of Wilson flow to study the deconfinement transition in SU(3) gauge theory. We use the flowed Polyakov loop as a renormalized order parameter for the transition, and use it to renormalize the Polyakov loop. We also study the flow properties of the electric and magnetic gluon condensates, and demonstrate that the difference of the flowed operators shows rapid change across the transition point.Comment: 13 pages, 10 figures. Small changes in figures and discussion, results unchanged. Published versio

Wilson flow with naive staggered quarks

Scale setting for QCD with two flavours of staggered quarks is examined using Wilson flow over a factor of four change in both the lattice spacing and the pion mass. The statistics needed to keep the errors in the flow scale fixed is found to increase approximately as the inverse square of the lattice spacing. Tree level improvement of the scales t_0 and w_0 is found to be useful in most of the range of lattice spacings we explore. The scale uncertainty due to remaining lattice spacing effects is found to be about 3%. The ratio w_0/\sqrt{t_0} is N_f dependent and we find its continuum limit to be 1.106 \pm 0.007 (stat) \pm 0.005 (syst) for m_\pi w_0 \simeq 0.3

Light meson form factors at high Q2Q^2 from lattice QCD

Measurements and theoretical calculations of meson form factors are essential for our understanding of internal hadron structure and QCD, the dynamics that bind the quarks in hadrons. The pion electromagnetic form factor has been measured at small space-like momentum transfer $|q^2| < 0.3$~GeV$^2$ by pion scattering from atomic electrons and at values up to $2.5$~GeV$^2$ by scattering electrons from the pion cloud around a proton. On the other hand, in the limit of very large (or infinite) $Q^2=-q^2$, perturbation theory is applicable. This leaves a gap in the intermediate $Q^2$ where the form factors are not known. As a part of their 12 GeV upgrade Jefferson Lab will measure pion and kaon form factors in this intermediate region, up to $Q^2$ of $6$~GeV$^2$. This is then an ideal opportunity for lattice QCD to make an accurate prediction ahead of the experimental results. Lattice QCD provides a from-first-principles approach to calculate form factors, and the challenge here is to control the statistical and systematic uncertainties as errors grow when going to higher $Q^2$ values. Here we report on a calculation that tests the method using an $\eta_s$ meson, a 'heavy pion' made of strange quarks, and also present preliminary results for kaon and pion form factors. We use the $n_f=2+1+1$ ensembles made by the MILC collaboration and Highly Improved Staggered Quarks, which allows us to obtain high statistics. The HISQ action is also designed to have small discretisation errors. Using several light quark masses and lattice spacings allows us to control the chiral and continuum extrapolation and keep systematic errors in check.Comment: Presented at Lattice 2017, the 35th International Symposium on Lattice Field Theory at Granada, Spain (18-24 June 2017

The B(s)→D(s)lνB_{(s)} \to D_{(s)}l\nu Decay with Highly Improved Staggered Quarks and NRQCD

We report on progress of a lattice QCD calculation of the $B\to Dl\nu$ and $B_s\to D_s l\nu$ semileptonic form factors. We use a relativistic staggered action (HISQ) for light and charm quarks, and an improved non-relativistic (NRQCD) action for bottom, on the second generation MILC ensembles.Comment: Presented at Lattice 2017, the 35th International Symposium on Lattice Field Theory at Granada, Spain (18-24 June 2017