3,756 research outputs found
Improving the dynamical overlap algorithm
We present algorithmic improvements to the overlap Hybrid Monte Carlo
algorithm, including preconditioning techniques and improvements to the
correction step, used when one of the eigenvalues of the Kernel operator
changes sign, which is now O(\Delta t^2) exact.Comment: 6 pages, 3 figures; poster contribution at Lattice 2005(Algorithms
and machines
Freeze-out parameters: lattice meets experiment
We present our results for ratios of higher order fluctuations of electric
charge as functions of the temperature. These results are obtained in a system
of 2+1 quark flavors at physical quark masses and continuum extrapolated. We
compare them to preliminary data on higher order moments of the net electric
charge distribution from the STAR collaboration. This allows us to determine
the freeze-out temperature and chemical potential from first principles. We
also show continuum-extrapolated results for ratios of higher order
fluctuations of baryon number. These will allow to test the consistency of the
approach, by comparing them to the corresponding experimental data (once they
become available) and thus extracting the freeze-out parameters in an
independent way.Comment: 5 pages, 7 figures, revte
Freeze-out parameters from electric charge and baryon number fluctuations: is there consistency?
Recent results for moments of multiplicity distributions of net-protons and
net-electric charge from the STAR collaboration are compared to lattice QCD
results for higher order fluctuations of baryon number and electric charge by
the Wuppertal-Budapest collaboration, with the purpose of extracting the
freeze-out temperature and chemical potential. All lattice simulations are
performed for a system of 2+1 dynamical quark flavors, at the physical mass for
light and strange quarks; all results are continuum extrapolated. We show that
it is possible to extract an upper value for the freeze-out temperature, as
well as precise baryo-chemical potential values corresponding to the four
highest collision energies of the experimental beam energy scan. Consistency
between the freeze-out parameters obtained from baryon number and electric
charge fluctuations is found. The freeze-out chemical potentials are now in
agreement with the statistical hadronization model.Comment: 5 pages, 4 figures, references added, discussion added to the
introduction, results unchange
QCD thermodynamics with dynamical overlap fermions
We study QCD thermodynamics using two flavors of dynamical overlap fermions
with quark masses corresponding to a pion mass of 350 MeV. We determine several
observables on N_t=6 and 8 lattices. All our runs are performed with fixed
global topology. Our results are compared with staggered ones and a nice
agreement is found.Comment: 14 pages, 6 figures, 1 tabl
Nucleon electromagnetic form factors from lattice QCD using a nearly physical pion mass
We present lattice QCD calculations of nucleon electromagnetic form factors
using pion masses = 149, 202, and 254 MeV and an action with
clover-improved Wilson quarks coupled to smeared gauge fields, as used by the
Budapest-Marseille-Wuppertal collaboration. Particular attention is given to
removal of the effects of excited state contamination by calculation at three
source-sink separations and use of the summation and generalized
pencil-of-function methods. The combination of calculation at the nearly
physical mass = 149 MeV in a large spatial volume ( = 4.2)
and removal of excited state effects yields agreement with experiment for the
electric and magnetic form factors and up to = 0.5
GeV.Comment: v2: published version; 30 pages, 25 figures, 6 table
Dynamical overlap simulations using HMC
We apply the Hybrid Monte Carlo method to the simulation of overlap fermions.
We give the fermionic force for the molecular dynamics update. We present early
results on a small dynamical chiral ensemble.Comment: Lattice2004(machines), 3 pages; references updated, minor changes to
tex
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
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