851 research outputs found
Perturbative Thermodynamics of Lattice QCD with Chiral-Invariant Four-Fermion Interactions
Lattice QCD with additional chiral-invariant four-fermion interactions is
studied at nonzero temperature. Staggered Kogut-Susskind quarks are used. The
four-fermion interactions are implemented by introducing bosonic auxiliary
fields. A mean field treatment of the auxiliary fields is used to calculate the
model's asymptotic scale parameter and perturbative thermodynamics, including
the one-loop gluonic contributions to the energy, entropy, and pressure. In
this approach the calculations reduce to those of ordinary lattice QCD with
massive quarks. Hence, the previous calculations of these quantities in lattice
QCD using massless quarks are generalized to the massive case.Comment: 22 pages, RevTeX, 8 EPS figures, uses epsf.sty and feynmf.st
A Family of Equations of State Based on Lattice QCD: Impact on Flow in Ultrarelativistic Heavy-Ion Collisions
We construct a family of equations of state within a quasiparticle model by
relating pressure, energy density, baryon density and susceptibilities adjusted
to first-principles lattice QCD calculations. The relation between pressure and
energy density from lattice QCD is surprisingly insensitive to details of the
simulations. Effects from different lattice actions, quark masses and lattice
spacings used in the simulations show up mostly in the quark-hadron phase
transition region which we bridge over by a set of interpolations to a hadron
resonance gas equation of state. Within our optimized quasiparticle model we
then examine the equation of state along isentropic expansion trajectories at
small net baryon densities, as relevant for experiments and hydrodynamic
simulations at RHIC and LHC energies. We illustrate its impact on azimuthal
flow anisotropies and transverse momentum spectra of various hadron species
A Note on Asymptotic Freedom at High Temperatures
This short note considers, within the external field approach outlined in
hep-ph/0202026, the role of the lowest lying gluon Landau mode in QCD in the
high temperature limit. Its influence on a temperature- and field-dependent
running coupling constant is examined. The thermal imaginary part of the mode
is temperature-independent in our approach and exactly cancels the well-known
zero temperature imaginary part, thus rendering the Savvidy vacuum stable.
Combining the real part of the mode with the contributions from the higher
lying Landau modes and the vacuum contribution, a field-independent coupling
alpha_s(T) is obtained. It can be interpreted as the ordinary zero temperature
running coupling constant with average thermal momenta \approx 2pi T for
gluons and \approx pi T for quarks.Comment: 4 pages; minor changes, version to appear in Phys. Rev.
Thermodynamics of Two Flavor QCD to Sixth Order in Quark Chemical Potential
We present results of a simulation of 2-flavor QCD on a 4x16^3 lattice using
p4-improved staggered fermions with bare quark mass m/T=0.4. Derivatives of the
thermodynamic grand canonical partition function Z(V,T,mu_u,mu_d) with respect
to chemical potentials mu_(u,d) for different quark flavors are calculated up
to sixth order, enabling estimates of the pressure and the quark number density
as well as the chiral condensate and various susceptibilities as functions of
mu_q = (mu_u + mu_d)/2 via Taylor series expansion. Furthermore, we analyze
baryon as well as isospin fluctuations and discuss the relation between the
radius of convergence of the Taylor series and the chiral critical point in the
QCD phase diagram. We argue that bulk thermodynamic observables do not, at
present, provide direct evidence for the existence of a chiral critical point
in the QCD phase diagram. Results are compared to high temperature perturbation
theory as well as a hadron resonance gas model.Comment: 38 pages, 30 encapsulated postscript figures, typo corrected, 1
footnote adde
The beta function and equation of state for QCD with two flavors of quarks
We measure the pressure and energy density of two flavor QCD in a wide range
of quark masses and temperatures. The pressure is obtained from an integral
over the average plaquette or psi-bar-psi. We measure the QCD beta function,
including the anomalous dimension of the quark mass, in new Monte Carlo
simulations and from results in the literature. We use it to find the
interaction measure, E-3p, yielding non-perturbative values for both the energy
density E and the pressure p. uuencoded compressed PostScript file Revised
version should work on more PostScript printers.Comment: 24 page
Transverse Pressure and Strangeness Dynamics in Relativistic Heavy Ion Reactions
Transverse hadron spectra from proton-proton, proton-nucleus and
nucleus-nucleus collisions from 2 AGeV to 21.3 ATeV are investigated within two
independent transport approaches (HSD and UrQMD). For central Au+Au (Pb+Pb)
collisions at energies above 5 AGeV, the measured
transverse mass spectra have a larger inverse slope parameter than expected
from the default calculations. The additional pressure - as suggested by
lattice QCD calculations at finite quark chemical potential and
temperature - might be generated by strong interactions in the early
pre-hadronic/partonic phase of central Au+Au (Pb+Pb) collisions. This is
supported by a non-monotonic energy dependence of in the present
transport model.Comment: Proceedings of Strange Quark Matter 200
An Experimental Overview of Results Presented at SQM 2006
I have been asked to give an critical overview on the experimental results
shown in the conference with a emphasis of what has been learned and the
challenges that are ahead in trying to understand the physics of the strongly
interacting quark-gluon plasma. I will not try to summarize all of the results
presented, rather I will concentrate primarily on RHIC data from this
conference. Throughout this summary, I will periodically review some of the
previous results for those not familiar with the present state of the field.Comment: 15 pages, 12 Figure
The QCD equation of state for two flavours at non-zero chemical potential
We present results of a simulation of 2 flavour QCD on a
lattice using p4-improved staggered fermions with bare quark mass .
Derivatives of the thermodynamic grand canonical partition function
with respect to chemical potentials for
different quark flavours are calculated up to sixth order, enabling estimates
of the pressure and the quark number density as well as the chiral condensate
and various susceptibilities as functions of via Taylor series
expansion. Results are compared to high temperature perturbation theory as well
as a hadron resonance gas model. We also analyze baryon as well as isospin
fluctuations and discuss the relation to the chiral critical point in the QCD
phase diagram. We moreover discuss the dependence of the heavy quark free
energy on the chemical potential.Comment: 4 pages, 7 figures, talk presented at Quark Matter 2005, Budapes
News from Lattice QCD on Heavy Quark Potentials and Spectral Functions of Heavy Quark States
We discuss recent lattice results on in-medium properties of hadrons and
focus on thermal properties of heavy quark bound states. We will clarify the
relation between heavy quark free energies and potentials used to analyze the
melting of heavy quark bound states. Furthermore, we present calculations of
meson spectral functions which indicate that the charmonium ground states,
J/psi and eta_c, persist in the quark gluon plasma as well defined resonances
with no significant change of their zero temperature masses at least up to T ~
1.5 T_c. We also briefly comment on the current status of lattice calculations
at non-vanishing baryon number density.Comment: Plenary talk at the 17th International Conference on Ultra
Relativistic Nucleus-Nucleus Collisions (Quark Matter 2004), Oakland,
California, 11-17 Jan 2004. Submitted to J.Phys.
Lattice calculations of meson correlators and spectral functions at finite temperature
I review recent progress in relating meson spectral function to imaginary
time correlation function at finite temperature calculated on isotropic as well
as on anisotropic lattices. Special attention is payed for the lattice
artifacts present in calculation of meson spectral functions. Results in the
case of light quarks as well as heavy quarks are reviewed which indicate in
particular that even in the chiral limit meson spectral functions have
non-trivial structure and the ground state quarkonia survive up to temperature
1.5T_cComment: Invited plenary talk presented at SQM03 (Atlantic Beach, March 12-17,
2003), 10 pages LaTeX, uses iopams.sty, iopart.cl
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