4,960 research outputs found
The Density of States Method at Finite Chemical Potential
We study the density of states method to explore the phase diagram of the
chiral transition on the temperature and quark chemical potential plane. Four
quark flavors are used in the analysis. Though the method is quite expensive
small lattices show an indication for a triple-point connecting three different
phases on the phase diagram.Comment: 5 pages, 6 figures, talk given at 'Extreme QCD', August 2-5 2005,
Swansea, Wales, U
QCD phase diagram and charge fluctuations
We discuss the phase structure and fluctuations of conserved charges in two
flavor QCD. The importance of the density fluctuations to probe the existence
of the critical end point is summarized. The role of these fluctuations to
identify the first order phase transition in the presence of spinodal phase
separation is also discussed.Comment: 8 pages, 8 figures, plenary talk given at the 19th International
Conference on Ultrarelativistic Nucleus-Nucleus Collisions: Quark Matter 2006
(QM 2006), Shanghai, China, 14-20 Nov 200
Complex Langevin dynamics for dynamical QCD at nonzero chemical potential: a comparison with multi-parameter reweighting
We study lattice QCD at non-vanishing chemical potential using the complex
Langevin equation. We compare the results with multi-parameter reweighting both
from and phase quenched ensembles. We find a good agreement for lattice
spacings below 0.15 fm. On coarser lattices the complex Langevin
approach breaks down. Four flavors of staggered fermions are used on
and 8 lattices. For one ensemble we also use two flavors to investigate the
effects of rooting.Comment: 10 pages, 11 figures, PRD version, minor change
Two flavor color superconductivity in nonlocal chiral quark models
We study the competence between chiral symmetry restoration and two flavor
color superconductivity (2SC) using a relativistic quark model with covariant
nonlocal interactions. We consider two different nonlocal regulators: a
Gaussian regulator and a Lorentzian regulator. We find that although the phase
diagrams are qualitative similar to those obtained using models with local
interactions, in our case the superconducting gaps at medium values of the
chemical potential are larger. Consequently, we obtain that in that region the
critical temperatures for the disappearance of the 2SC phase might be of the
order of 100-120 MeV. We also find that for ratios of the quark-quark and
quark-antiquark couplings somewhat above the standard value 3/4, the end point
and triple point in the phase diagram meet and a phase where both the
chiral and diquark condensates are non-negligible appears.Comment: 15 pages incl. 5 Postscript figure
New results and perspectives on R_{AA} measurements below 20 GeV CM-energy at fixed target machines
Transverse momentum spectra of pi^{+/-} at midrapidity are measured at high
p_T in p+p and p+Pb collisions at 158 GeV/nucleon beam energy by the NA49
experiment. This study is complementary to our previous results on the same
spectra from Pb+Pb collisions. The nuclear modification factors R_{A+A/p+p},
R_{p+A/p+p} and R_{A+A/p+A} as a function of p_T are extracted and compared to
RHIC measurements, thus providing insight into the energy dependence of nuclear
modification. The modification factor R_{A+A/p+A} proved to be consistent with
our previous results on the central to peripheral modification factor R_{CP}.
The limitation of our current p_T range is discussed and planned future
upgrades are outlined. Some aspects of the FAIR-CBM experiment are also
presented as a natural future continuation of the measurements at very high
p_T.Comment: Proceedings of Quark Matter 200
SU(3) sextet model with Wilson fermions
We investigate the spectrum and IR properties of the SU(3) "sextet" model
with two Dirac fermions in the two-index symmetric representation via lattice
simulations. This model is a prime candidate for a realization of Walking
Technicolor, which features a minimal matter content and it is expected to be
inside or very close to the lower boundary of the conformal window. We use the
Wilson discretization for the fermions and map the phase structure of the
lattice model. We study several spectral and gradient flow observables both in
the bulk and the weak coupling phases. While in the bulk phase we find clear
signs of chiral symmetry breaking, in the weak coupling phase there is no clear
indication for it, and instead the chiral limit of the model seems compatible
with an IR-conformal behavior.Comment: 32 pages, many figure
EoS of finite density QCD with Wilson fermions by Multi-Parameter Reweighting and Taylor expansion
The equation of state (EoS), quark number density and susceptibility at
nonzero quark chemical potential are studied in lattice QCD simulations
with a clover-improved Wilson fermion of 2-flavors and RG-improved gauge
action. To access nonzero , we employ two methods : a multi-parameter
reweighting (MPR) in and and Taylor expansion in . The use
of a reduction formula for the Wilson fermion determinant enables to study the
reweighting factor in MPR explicitly and heigher-order coefficients in Taylor
expansion free from errors of noise method, although calculations are limited
to small lattice size. As a consequence, we can study the reliability of the
thermodynamical quantities through the consistency of the two methods, each of
which has different origin of the application limit.
The thermodynamical quantities are obtained from simulations on a lattice with an intermediate quark mass(. The MPR
and Taylor expansion are consistent for the EoS and number density up to
and for the number susceptibility up to . This
implies within a given statistics that the overlap problem for the MPR and
truncation error for the Taylor expansion method are negligible in these
regions.
In order to make MPR methods work, the fluctuation of the reweighting factor
should be small. We derive the equation of the reweighting line where the
fluctuation is small, and show that the equation of the reweighting line is
consistent with the fluctuation minimum condition.Comment: 20 pages, 11 figures. Accepted to JHEP. Discussions are added.
Figures for Taylor coefficients (Fig. 7) are modifie
QCD finite T transition -- Comparison between Wilson and staggered results
A quantitative comparison between the finite temperature behaviour of the
staggered and Wilson fermion formulations are performed. The comparison is
based on a physical quantity that is expected to be quite sensitive to the
fermionic features of the action. For that purpose we use the height of the
peak for , where is the quark number susceptibility.Comment: 6 pages. Talk presented at Lattice 200
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
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