87 research outputs found
Scaling tests with dynamical overlap and rooted staggered fermions
We present a scaling analysis in the 1-flavor Schwinger model with the full
overlap and the rooted staggered determinant. In the latter case the chiral and
continuum limit of the scalar condensate do not commute, while for overlap
fermions they do. For the topological susceptibility a universal continuum
limit is suggested, as is for the partition function and the Leutwyler-Smilga
sum rule. In the heavy-quark force no difference is visible even at finite
coupling. Finally, a direct comparison between the complete overlap and the
rooted staggered determinant yields evidence that their ratio is constant up to
effects.Comment: 28 pages, 20 figures containg 37 graphs. v2: 6 new references, 2 new
footnotes (to match published version
A comparative study of overlap and staggered fermions in QCD
We perform a comparative study of the infrared properties of overlap and
staggered fermions in QCD. We observe that the infrared spectrum of the APE/HYP
improved staggered Dirac operator develops a four-fold near-degeneracy and is
in quantitative agreement with the infrared spectrum of the overlap operator.
The near-degeneracy allows us to identify the zero modes of the staggered
operator and we find that the number of zero modes is in line with the
topological index of the overlap operator.Comment: Talk presented at Lattice2004(chiral), Fermilab, June 21-26, 2004, 3
pages, 2 figure
Chiral behavior of pseudo-Goldstone boson masses and decay constants in 2+1 flavor QCD
We present preliminary results for the chiral behavior of charged
pseudo-Goldstone-boson masses and decay constants. These are obtained in
simulations with N_f=2+1 flavors of tree-level, O(a)-improved Wilson sea
quarks. In these simulations, mesons are composed of either valence quarks
discretized in the same way as the sea quarks (unitary simulations) or of
overlap valence quarks (mixed-action simulations). We find that the chiral
behavior of the pseudoscalar meson masses in the mixed-action calculations
cannot be explained with continuum, partially-quenched chiral perturbation
theory. We show that the inclusion of O(a^2) unitarity violations in the chiral
expansion resolves this discrepancy and that the size of the unitarity
violations required are consistent with those which we observe in the
zero-momentum, scalar-isotriplet-meson propagator.Comment: 7 pages, 3 figures, talk by L. Lellouch at the XXV International
Symposium on Lattice Field Theory (LATTICE 2007), 30 July - 4 August 2007,
Regensburg, German
The ratio FK/Fpi in QCD
We determine the ratio FK/Fpi in QCD with Nf=2+1 flavors of sea quarks, based
on a series of lattice calculations with three different lattice spacings,
large volumes and a simulated pion mass reaching down to about 190 MeV. We
obtain FK/Fpi=1.192 +/- 0.007(stat) +/- 0.006(syst). This result is then used
to give an updated value of the CKM matrix element |Vus|. The unitarity
relation for the first row of this matrix is found to be well observed.Comment: 15 pages, 4 figures, 2 table
Precision computation of the kaon bag parameter
Indirect CP violation in K \rightarrow {\pi}{\pi} decays plays a central role
in constraining the flavor structure of the Standard Model (SM) and in the
search for new physics. For many years the leading uncertainty in the SM
prediction of this phenomenon was the one associated with the nonperturbative
strong interaction dynamics in this process. Here we present a fully controlled
lattice QCD calculation of these effects, which are described by the neutral
kaon mixing parameter B_K . We use a two step HEX smeared clover-improved
Wilson action, with four lattice spacings from a\approx0.054 fm to
a\approx0.093 fm and pion masses at and even below the physical value.
Nonperturbative renormalization is performed in the RI-MOM scheme, where we
find that operator mixing induced by chiral symmetry breaking is very small.
Using fully nonperturbative continuum running, we obtain our main result
B_K^{RI}(3.5GeV)=0.531(6)_{stat}(2)_{sys}. A perturbative 2-loop conversion
yields B_K^{MSbar-NDR}(2GeV)=0.564(6)_{stat}(3)_{sys}(6)_{PT}, which is in good
agreement with current results from fits to experimental data.Comment: 10 pages, 7 figures. v2: Added one reference and one figure, replaced
2 figures for better readability and updated ensembles, conclusions
unchanged. Final, published versio
Electromagnetic corrections to light hadron masses
At the precision reached in current lattice QCD calculations, electromagnetic
effects are becoming numerically relevant. We will present preliminary results
for electromagnetic corrections to light hadron masses, based on simulations in
which a degree of freedom is superimposed on QCD
configurations from the BMW collaboration.Comment: 7 pages, 2 figures, The XXVIII International Symposium on Lattice
Field Theory, June 14-19,2010, Villasimius, Sardinia Ital
Light hadron spectra and wave functions in quenched QCD with overlap quarks on a large lattice
A simulation of quenched QCD with the overlap Dirac operator has been
completed using 100 Wilson gauge configurations at beta=6 on an 18^3x64
lattice. We present results for meson and baryon masses, meson final state
"wave functions'' and other observables.Comment: 5 LaTeX pages (espcrc2.sty), 13 figures. Combined contributions by
J.H., L.L. and C.R. at Lattice2004(spectrum), Fermilab, June 21-26, 200
Hadronic vacuum polarization contribution to the anomalous magnetic moments of leptons from first principles
We compute the leading, strong-interaction contribution to the anomalous
magnetic moment of the electron, muon and tau using lattice quantum
chromodynamics (QCD) simulations. Calculations include the effects of , ,
and quarks and are performed directly at the physical values of the
quark masses and in volumes of linear extent larger than . All
connected and disconnected Wick contractions are calculated. Continuum limits
are carried out using six lattice spacings. We obtain
,
and
, where the first error
is statistical and the second is systematic.Comment: 17 pages, 8 figures (in 13 PDF files), RevTeX 4.1. Minor changes to
results and to text. References updated. Matches version published in
Physical Review Letter
Spectra of heavy-light and heavy-heavy mesons containing charm quarks, including higher spin states for
We study the spectra of heavy-light and heavy-heavy mesons containing charm
quarks, including higher spin states. We use two sets of gauge
configurations, one set from QCDSF using the SLiNC action, and the other
configurations from the Budapest-Marseille-Wuppertal collaboration, using the
HEX smeared clover action. To extract information about the excited states, we
choose a suitable basis of operators to implement the variational method.Comment: 7 pages, 5 figures, Talk presented at the XXIX International
Symposium on Lattice Field Theory, Lattice2011, July 11-16, 2011, The Village
at Squaw Valley, California, US
Lattice QCD at the physical point: light quark masses
Ordinary matter is described by six fundamental parameters: three couplings
(gravitational, electromagnetic and strong) and three masses: the electron's
(m_e) and those of the up (m_u) and down (m_d) quarks. An additional mass
enters through quantum fluctuations: the strange quark mass (m_s). The three
couplings and m_e are known with an accuracy of better than a few per mil.
Despite their importance, , (their average m_{ud}) and m_s are
relatively poorly known: e.g. the Particle Data Group quotes them with
conservative errors close to 25%. Here we determine these quantities with a
precision below 2% by performing ab initio lattice quantum chromodynamics (QCD)
calculations, in which all systematics are controlled. We use pion and quark
masses down to (and even below) their physical values, lattice sizes of up to 6
fm, and five lattice spacings to extrapolate to continuum spacetime. All
necessary renormalizations are performed nonperturbatively.Comment: 9 pages, 2 figures, 1 table. v2: published version, one reference
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