42 research outputs found
Heavy-quark free energy at finite temperature with 2+1 flavors of improved Wilson quarks in fixed scale approach
The free energy between a static quark and an antiquark is studied by using
the color-singlet Polyakov-line correlation at finite temperature. We perform
simulations on , 10, 8, 6, 4 lattices in the high temperature
phase with the RG-improved gluon action and 2+1 flavors of the clover-improved
Wilson quark action. Since the simulations are based on the fixed scale
approach that the temperature can be varied without changing the spatial volume
and renormalization factor, it is possible to investigate temperature
dependence of the heavy-quark free energy without any adjustment of the overall
constant. We find that, the heavy-quark free energies at short distance
converge to the heavy-quark potential evaluated from the Wilson-loop operator
at zero temperature, in accordance with the expected insensitivity of short
distance physics to the temperature. At long distance, the heavy-quark free
energies approach to twice the single-quark free energies, implying that the
interaction between heavy quarks is screened. The Debye screening mass obtained
from the long range behavior of the heavy-quark free energy is compared with
results of the thermal perturbation theory and those of and
lattice simulations.Comment: To appear in the proceedigns of 27th International Symposium on
Lattice Field Theory (Lattice 2009), Beijing, China, 25-31 July 200
Thermodynamics of SU(3) gauge theory at fixed lattice spacing
We study thermodynamics of SU(3) gauge theory at fixed scales on the lattice,
where we vary temperature by changing the temporal lattice size
N_t=(Ta_t)^{-1}. In the fixed scale approach, finite temperature simulations
are performed on common lattice spacings and spatial volumes. Consequently, we
can isolate thermal effects in observables from other uncertainties, such as
lattice artifact, renormalization factor, and spatial volume effect.
Furthermore, in the EOS calculations, the fixed scale approach is able to
reduce computational costs for zero temperature subtraction and parameter
search to find lines of constant physics, which are demanding in full QCD
simulations. As a test of the approach, we study the thermodynamics of the
SU(3) gauge theory on isotropic and anisotropic lattices. In addition to the
equation of state, we calculate the critical temperature and the static quark
free energy at a fixed scale.Comment: 7pages, 3figures, proceedings of Lattice 2008, Williamsburg,
Virginia, USA, July 14-19, 200
Heavy-Quark Free Energy, Debye Mass, and Spatial String Tension at Finite Temperature in Two Flavor Lattice QCD with Wilson Quark Action
We study Polyakov loop correlations and spatial Wilson loop at finite
Temperature in two-flavor QCD simulations with the RG-improved gluon action and
the clover-improved Wilson quark action on a lattice. From the
line of constant physics at and 0.80, we extract
the heavy-quark free energies, the effective running coupling
and the Debye screening mass for various color channels of heavy
quark--quark and quark--anti-quark pairs above the critical temperature. The
free energies are well approximated by the screened Coulomb form with the
appropriate Casimir factors at high temperature. The magnitude and the
temperature dependence of the Debye mass are compared to those of the
next-to-leading order thermal perturbation theory and to a phenomenological
formula in terms of . We make a comparison between our results
with the Wilson quark action and the previous results with the staggered quark
action. The spatial string tension is also studied in the high temperature
phase and is compared to the next-to-next-leading order prediction in an
effective theory with dimensional reduction.Comment: 25 pages, 37 EPS figure
An application of the variational analysis to calculate the meson spectral functions
We present a new method to calculate meson spectral functions (SPFs) on the
lattice based on a variational method. Because, on a finite volume lattice, the
meson SPFs have discrete spectra only, a suitable way to extract such discrete
signals is needed. Using a variational method, we can calculate several
discrete quantities such as the position and the area of spectral peaks for
low-lying states. Moreover data accuracy can be improved by increasing the
number of basis functions. In this report, we first confirm our method in the
free quark case and show that our method works well. Then, we apply the method
to a quenched lattice QCD simulation and calculate the charmonium SPFs for S
and P-waves at zero temperature. Our results for the ground state are well
consistent with the position and the area of the lowest peaks of charmonium
SPFs calculated by the conventional maximum entropy method. For first excited
states, the signals may be reliablly extracted with our method because the
charmonium mass converges to a value close to the experimental one when the
number of basis functions is increased. We also investigate the SPFs for S-wave
charmonia at below and above . Our results suggest that and
may survive up to 1.4.Comment: 7 Pages, 6 figures, talk presented at the XXVIII International
Symposium on Lattice Field Theory, June 14-19 2010, Villasimius, Ital
Equation of state in (2+1)-flavor QCD at physical point with improved Wilson fermion action using gradient flow
We study the energy-momentum tensor and the equation of state as well as the
chiral condensate in (2+1)-flavor QCD at the physical point applying the method
of Makino and Suzuki based on the gradient flow. We adopt a nonperturbatively
O(a)-improved Wilson quark action and the renormalization group-improved
Iwasaki gauge action. At Lattice 2016, we have presented our preliminary
results of our study in (2+1)-flavor QCD at a heavy u, d quark mass point. We
now extend the study to the physical point and perform finite-temperature
simulations in the range T \simeq 155--544 MeV (Nt = 4--14 including odd Nt's)
at a \simeq 0.09 fm. We show our final results of the heavy QCD study and
present some preliminary results obtained at the physical point so far.Comment: 8 pages, 15 figures, talk presented at the 35th International
Symposium on Lattice Field Theory (LATTICE 2017), 18-24 June 2017, Granada,
Spai
EOS in 2+1 flavor QCD with improved Wilson quarks by the fixed-scale approach
We present the status of our study on the equation of state in 2+1 flavor QCD
with non-perturbatively improved Wilson quarks coupled with the RG improved
glue. We apply the T-integration method to non-perturbatively calculate the
equation of state by the fixed-scale approach.Comment: 7 pages, 7 figures, talk presented at the XXVIII International
Symposium on Lattice Field Theory, June 14-19 2010, Villasimius, Ital
The order of the deconfinement phase transition in a heavy quark mass region
We study the quark mass dependence of the QCD phase transition by an
effective potential defined through the distribution function of observables.
As a test of the method, we study the first order deconfinement phase
transition in the heavy quark mass limit and its fate at lighter quark masses.
We confirm that the distribution function for the plaquette has two peaks
indicating that the phase transition is of first order in the heavy quark
limit. We then study the quark mass dependence of the distribution function by
a reweighting method combined with the hopping parameter expansion. We find
that the first order transition turns into a crossover as the quark mass
decreases. We determine the critical point for the cases of =1, 2, 3 and
2+1. We find that the probability distribution function provides us with a
powerful tool to study the order of transitions.Comment: 7 pages, 7 figure, Talk presented at the XXVIII International
Symposium on Lattice Field Theory, Lattice2010, Villasimius, Italy, June 201
Equation of state at finite density in two-flavor QCD with improved Wilson quarks
We study the equation of state in two-flavor QCD at finite temperature and
density. Simulations are made with the RG-improved gluon action and the
clover-improved Wilson quark action. Along the lines of constant physics for
and 0.80, we compute the derivatives of the quark
determinant with respect to the quark chemical potential up to the
fourth order at . We adopt several improvement techniques in the
evaluation. We study thermodynamic quantities and quark number susceptibilities
at finite using these derivatives. We find enhancement of the quark
number susceptibility at finite , in accordance with previous
observations using staggered-type quarks. This suggests the existence of a
nearby critical point.Comment: 7 pages, 16 figures, presented at the XXVI International Symposium on
Lattice Field Theory (LATTICE 2008), July 14-19, 2008, Williamsburg,
Virginia, US
Scaling behavior of chiral phase transition in two-flavor QCD with improved Wilson quarks at finite density
We study scaling behavior of a chiral order parameter performing a simulation
of two-flavor QCD with improved Wilson quarks. It has been shown that the
scaling behavior of the chiral order parameter defined by a Ward-Takahashi
identity agrees with the scaling function of the three-dimensional O(4) spin
model at zero chemical potential. We extend the scaling study to finite density
QCD. Calculating derivatives of the chiral order parameter with respect to the
chemical potential in two-flavor QCD, the scaling property of chiral phase
transition is discussed in the low density region. We moreover calculate the
curvature of the phase boundary of the chirl phase transition in the
temperature and chemical potential plane assuming the O(4) scaling relation.Comment: 7 pages, 6 figures, poster presented at the XXVIII International
Symposium on Lattice Field Theory, June 14-19 2010, Villasimius, Ital