1,712 research outputs found
FLIC-Overlap Fermions and Topology
APE smearing the links in the irrelevant operators of clover fermions
(Fat-Link Irrelevant Clover (FLIC) fermions) provides significant improvement
in the condition number of the Hermitian-Dirac operator and gives rise to a
factor of two savings in computing the overlap operator. This report
investigates the effects of using a highly-improved definition of the lattice
field-strength tensor F_mu_nu in the fermion action, made possible through the
use of APE-smeared fat links in the construction of the irrelevant operators.
Spurious double-zero crossings in the spectral flow of the Hermitian-Wilson
Dirac operator associated with lattice artifacts at the scale of the lattice
spacing are removed with FLIC fermions composed with an O(a^4)-improved lattice
field strength tensor. Hence, FLIC-Overlap fermions provide an additional
benefit to the overlap formalism: a correct realization of topology in the
fermion sector on the lattice.Comment: Lattice2002(chiral
Renormalization Group Therapy
We point out a general problem with the procedures commonly used to obtain
improved actions from MCRG decimated configurations. Straightforward
measurement of the couplings from the decimated configurations, by one of the
known methods, can result into actions that do not correctly reproduce the
physics on the undecimated lattice. This is because the decimated
configurations are generally not representative of the equilibrium
configurations of the assumed form of the effective action at the measured
couplings. Curing this involves fine-tuning of the chosen MCRG decimation
procedure, which is also dependent on the form assumed for the effective
action. We illustrate this in decimation studies of the SU(2) LGT using
Swendsen and Double Smeared Blocking decimation procedures. A single-plaquette
improved action involving five group representations and free of this pathology
is given.Comment: 18 pages, 9 figures, 9 table
An accurate calculation of the nucleon axial charge with lattice QCD
We report on a lattice QCD calculation of the nucleon axial charge, ,
using M\"{o}bius Domain-Wall fermions solved on the dynamical HISQ
ensembles after they are smeared using the gradient-flow algorithm. The
calculation is performed with three pion masses,
MeV. Three lattice spacings ( fm) are used with the
heaviest pion mass, while the coarsest two spacings are used on the middle pion
mass and only the coarsest spacing is used with the near physical pion mass. On
the MeV, fm point, a dedicated volume study is
performed with . Using a new strategy
motivated by the Feynman-Hellmann Theorem, we achieve a precise determination
of with relatively low statistics, and demonstrable control over the
excited state, continuum, infinite volume and chiral extrapolation systematic
uncertainties, the latter of which remains the dominant uncertainty. Our final
determination at 2.6\% total uncertainty is , with the
first uncertainty including statistical and systematic uncertainties from
fitting and the second including model selection systematics related to the
chiral and continuum extrapolation. The largest reduction of the second
uncertainty will come from a greater number of pion mass points as well as more
precise lattice QCD results near the physical pion mass.Comment: 17 pages + 11 pages of references and appendices. 15 figures.
Interested readers can download the Python analysis scripts and an hdf5 data
file at https://github.com/callat-qcd/project_gA_v
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