475 research outputs found
Equation of state in 2+1 flavor QCD with improved Wilson quarks by the fixed scale approach
We study the equation of state in 2+1 flavor QCD with nonperturbatively
improved Wilson quarks coupled with the RG-improved Iwasaki glue. We apply the
-integration method to nonperturbatively calculate the equation of state by
the fixed-scale approach. With the fixed-scale approach, we can purely vary the
temperature on a line of constant physics without changing the system size and
renormalization constants. Unlike the conventional fixed- approach, it is
easy to keep scaling violations small at low temperature in the fixed scale
approach. We study 2+1 flavor QCD at light quark mass corresponding to
, while the strange quark mass is chosen around the
physical point. Although the light quark masses are heavier than the physical
values yet, our equation of state is roughly consistent with recent results
with highly improved staggered quarks at large .Comment: 14 pages, 12 figures, v2: Table I and Figure 3 are corrected,
reference updated. Main discussions and conclusions are unchanged, v3:
version to appear in PRD, v4: reference adde
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
Application of fixed scale approach to static quark free energies in quenched and 2+1 flavor lattice QCD with improved Wilson quark action
Free energies between static quarks and Debye screening masses in the
quark-gluon plasma are studied on the basis of Polyakov-line correlations in
lattice simulations of 2+1 flavors QCD with the renormalization-group improved
gluon action and the -improved Wilson quark action. We perform
simulations at (0.74) for light (strange) flavors
with lattice sizes of with --12. We adopt the
fixed-scale approach, where temperature can be varied without changing the
spatial volume and renormalization factor. We find that, at short distance, the
free energies of static quarks in color-singlet channel converge to the
static-quark potential evaluated from the Wilson-loop at zero-temperature, in
accordance with the expected insensitivity of short distance physics to the
temperature. At long distance, the free energies of static quarks approach to
twice the single-quark free energies, implying that the interaction between
static quarks is fully screened. The screening properties can be well described
by the screened Coulomb form with appropriate Casimir factor at high
temperature. We also discuss a limitation of the fixed-scale approach at high
temperature.Comment: 16 pages, 14 figure
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
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
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
- …