We study the ability of a variety of fitting techniques to extract the ground state matrix elements of the vector current from ratios of nucleon three- and two-point functions that contain contaminations from excited states. Extending our high-statis
tics study of nucleon form factors, we are able to demonstrate that the treatment of excited-state contributions in conjunction with approaching the physical pion mass has a significant impact on the $Q^2$-dependence of the form factors.
We apply the background field (BF) method to Non-Relativistic QCD (NRQCD) on the lattice in order to determine the one-loop radiative corrections to the coefficients of the NRQCD action in a manifestly gauge-covariant manner by matching the NRQCD pre
diction for particular on-shell processes with those of relativistic continuum QCD. We explain how the BF method is implemented in automated perturbation theory and discuss the technique for matching the relativistic and non-relativistic theories. We compute the one-loop radiative corrections to the sigma.B and Darwin terms for the NRQCD action currently used in simulations, as well as the one-loop coefficients of the spin-dependent O(alpha^2) four-fermion contact terms. The effect of the corrections on the hyperfine splitting of bottomonium is estimated using earlier simulation results; the corrected lattice prediction is found to be in agreement with experiment. Agreement of the hyperfine splitting of bottomonium and the B-meson system is confirmed by recent simulation studies (Dowdall et al.) which include our NRQCD radiative corrections for the first time.
We present an algorithm to automatically derive Feynman rules for lattice perturbation theory in background field gauge. Vertices with an arbitrary number of both background and quantum legs can be derived automatically from both gluonic and fermioni
c actions. The algorithm is a generalisation of our earlier algorithm based on prior work by Luscher and Weisz. We also present techniques allowing for the parallelisation of the evaluation of the often rather complex lattice Feynman rules that should allow for efficient implementation on GPUs, but also give a significant speed-up when calculating the derivatives of Feynman diagrams with respect to external momenta.
We present a preliminary analysis of the charm quark mass and the mass and decay constant $f_{D_s}$ of the $D_s$ meson obtained from dynamical simulations of $N_f = 2$ Wilson QCD on the large and fine lattices simulated by the CLS effort.
We present a new (and general) algorithm for deriving lattice Feynman rules which is capable of handling actions as complex as the Highly Improved Staggered Quark (HISQ) action. This enables us to perform a perturbative calculation of the influence o
f dynamical HISQ fermions on the perturbative improvement of the gluonic action in the same way as we have previously done for asqtad fermions. We find the fermionic contributions to the radiative corrections in the Luscher-Weisz gauge action to be somewhat larger for HISQ fermions than for asqtad.
The effects of unquenching on the perturbative improvement coefficients in the Symanzik action are computed within the framework of Luscher-Weisz on-shell improvement. We find that the effects of quark loops are surprisingly large, and their omission
may well explain the scaling violations observed in some unquenched studies.
The effects of unquenching on the perturbative improvement coefficients in the Symanzik action are computed within the framework of Luscher-Weisz on-shell improvement. We find that the effects of quark loops are surprisingly large, and their omission
may well explain the scaling violations observed in some unquenched studies.
