117 research outputs found
Three Dirac operators on two architectures with one piece of code and no hassle
A simple minded approach to implement three discretizations of the Dirac
operator (staggered, Wilson, Brillouin) on two architectures (KNL and core i7)
is presented. The idea is to use a high-level compiler along with OpenMP
parallelization and SIMD pragmas, but to stay away from cache-line optimization
and/or assembly-tuning. The implementation is for N_v right-hand-sides, and
this extra index is used to fill the SIMD pipeline. On one KNL node single
precision performance figures for N_c=3, N_v=12 read 475 Gflop/s, 345 Gflop/s,
and 790 Gflop/s for the three discretization schemes, respectively.Comment: 1+6 pages, 3 figures, proceedings of Lattice 2018; v2: typos in eqs.
(3.1) and (4.2) corrected, results unchange
Physics of eta-prime with rooted staggered quarks
The quark-mass dependence of the eta in the Schwinger model, which -- like
the eta-prime in QCD -- becomes massive through the axial anomaly, is studied
on the lattice with N_f=0,1,2. Staggered quarks are used, with a rooted
determinant for N_f=1. In the chiral limit the Schwinger mass is reproduced,
which suggests that the anomaly is being treated correctly.Comment: 11 pages, 7 figures, 2 tables; v2: presentation improved, 4 refs
adde
Recent Progress in Lattice QCD
Recent progress in Lattice QCD is highlighted. After a brief introduction to
the methodology of lattice computations the presentation focuses on three main
topics: Hadron Spectroscopy, Hadron Structure and Lattice Flavor Physics. In
each case a summary of recent computations of selected quantities is provided.Comment: Review talk given at Physics in Collision 2012, Strbske Pleso,
Slovakia; 14 pages, 4 tables, 6 figure
Convergence issues in ChPT: a lattice perspective
This review addresses the practical convergence of the ChPT series in the
p-regime. In the SU(2) framework there is a number of new results, and improved
estimates of \bar\ell_3 and \bar\ell_4 are available. In the SU(3) framework
few new lattice computations have appeared and the improvement in the precision
of the low-energy constants L_i is comparatively slow. I sketch some of the
convergence issues genuine to extensions of ChPT which include additional
sources of chiral symmetry breaking (finite lattice spacing) and/or violations
of unitarity (different sea and valence quark masses). Finally, it is pointed
out that the quark mass ratios m_u/m_d, m_s/m_d happen to be such that no
reordering of the chiral series is needed to accommodate the experimental pion
and kaon masses.Comment: 10 pages, 11 figures, review talk given at "Kaon 13", Ann Arbo
Validity of ChPT -- is M_\pi=135 MeV small enough ?
I discuss the practical convergence of the SU(2) ChPT series in the meson
sector, based on 2+1 flavor lattice data by the Wuppertal-Budapest and
Budapest-Marseille-Wuppertal collaborations. These studies employ staggered and
clover-improved Wilson fermions, respectively. In both cases large box volumes
and several lattice spacings are used, and the pion masses reach down to the
physical mass point. We conclude that LO and NLO low-energy constants can be
determined with controlled systematics, if there is sufficient data between the
physical mass point and about 350 MeV pion mass. Exploratory LO+NLO+NNLO fits
with a wider range reveal some distress of the chiral series near M_\pi ~ 400
MeV and suggest a complete breakdown beyond M_\pi ~ 500 MeV.Comment: 14 pages, 16 figures; written form of plenary talk at Lattice 201
Lattice fermions with complex mass
We present evidence in the Schwinger model that rooted staggered fermions may
correctly describe the m<0 sector of a theory with an odd number of flavors. We
point out that in QCD-type theories with a complex-valued quark mass every
non-chiral action essentially "borrows" knowledge about the
theta-transformation properties from the overlap action.Comment: 8 pages, 4 figures. v2: eqn. (20) corrected, figs. 3,4 adjusted,
conclusions unchanged. v3: text improved, 2 refs. added (version to appear in
PRD
Physics prospects of UV-filtered overlap quarks
Some key features of the overlap operator with a UV-filtered Wilson kernel
are discussed. The first part concerns spectral properties of the underlying
shifted hermitean Wilson operator and the relation to the observed speedup of
the overlap construction. Next, the localization of the filtered overlap and
its axial-vector renormalization constant are discussed. Finally, results of an
exploratory scaling study for and are presented.Comment: Talk given at Workshop on Computational Hadron Physics, Nicosia,
Cyprus, 14-17 Sep 200
Testing UV-filtered ("fat-link") clover fermions
We investigate filtered clover fermions, built from fat gauge links, both in
one-loop perturbation theory and in numerical simulations. We use a variety of
filtering recipes (APE, HYP, EXP, HEX), some of which are suitable for a HMC
with dynamical fermions. A generic filtering together with a (fat-link) clover
term yields fermions with much reduced chiral symmetry breaking.Comment: 7 pages, Lattice 2006 (Quark Masses, Gauge Couplings, and
Renormalization
Details of a staggered fermion data analysis
We present technical details of an analysis of pseudo-scalar data from a QCD
simulation with staggered fermions. The data were obtained close to the
physical point with an inverse lattice spacing of about 3 GeV, and .
We compare different methods of extracting effective masses and decay constants
in lattice units. The results of several correlated and uncorrelated fitting
methods are compared, both on the simulated data set, and on a synthetically
generated data set.Comment: 7 pages, 8 figures. Contribution to proceedings of Lattice 201
Determination of SU(2) ChPT LECs from 2+1 flavor staggered lattice simulations
By fitting pion masses and decay constants from 2+1 flavor staggered lattice
simulations to the predictions of NLO and NNLO SU(2) chiral perturbation theory
we determine the low-energy constants l_3 and l_4. The lattice ensembles were
generated by the Wuppertal-Budapest collaboration and cover pion masses in the
range of 135 to 435 MeV and lattice scales between 0.7 and 2.0 GeV. By choosing
a suitable scaling trajectory, we were able to demonstrate that precise and
stable results for the LECs can be obtained from continuum ChPT to NLO. The
pion masses available in this work also allow us to study the applicability of
using ChPT to extrapolate from higher masses to the physical pion mass.Comment: 8 pages, 8 figures, 1 table, talk presented at Xth Quark Confinement
and the Hadron Spectrum, Munich, October 201
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