35 research outputs found
In Medium Hadron Properties
We discuss modifications of hadron properties in the heat bath extracted from
Euclidian correlation functions and spectral functions r econstructed with the
Maximum Entropy Method. To investigate the cut-off dependencies we perform
simulation on various lattice sizes and present the result of an analytic
calculation of the mesonic spectral functions in the infinite temperature
limit.Comment: Contribution to the Conference on Strong and Electroweak Matter
(SEWM2002),Heidelberg, October 2-5 2002, 5 pages, 8 figure
Common features of deconfining and chiral critical points in QCD and the three state Potts model in an external field
In the presented study we investigated the second order endpoints of the
lines of first order phase transitions which emerge for the QCD in the heavy
and light quark mass regime and for the three-dimensional three state Potts
model with an external field. We located the endpoints with Binder cumulants
and constructed the energy-like and ordering field like observables. The joint
probability distributions of these scaling fields and the values of the Binder
cumulant confirm that all three endpoints belong to the universality class of
the 3-dimensional Ising model.Comment: Based on a poster presented by S.Stickan at the CCP2001 Aachen,4
pages,6 figures, to be published in computer physics communicatio
A Lattice Calculation of Thermal Dilepton Rates
Using clover improved Wilson fermions we calculate thermal vector meson
correlation functions above the deconfinement phase transition of quenched QCD.
At temperatures 1.5 Tc and 3Tc they are found to differ by less than 15% from
that of a freely propagating quark anti-quark pair. This puts severe
constraints on the dilepton production rate and in particular rules out a
strong divergence of the dilepton rate at low energies. The vector spectral
function, which has been reconstructed using the Maximum Entropy Method, yields
an enhancement of the dilepton rate over the Born rate of at most a factor two
in the energy interval 4 < E/T < 8 and suggests that the spectrum is cut-off at
low energies by a thermal mass threshold of about (2-3)T.Comment: 9 pages, LaTeX2e File, 5 EPS files; minor corrections, modified error
bins in Fig.2
QCD Thermodynamics with 2 and 3 Quark Flavors
We discuss the flavor dependence of the pressure and critical temperature
calculated in QCD with 2, 2+1 and 3 flavors using improved gauge and staggered
fermion actions on lattices with temporal extent Nt=4. For T > 2 Tc we find
that bulk thermodynamics of QCD with 2 light and a heavier strange quark is
well described by 3-flavor QCD while the transition temperature is closer to
that of 2-flavor QCD. Furthermore, we present evidence that the chiral critical
point of 3-flavor QCD, i.e. the second order endpoint of the line of first
order chiral phase transitions, belongs to the universality class of the 3d
Ising model.Comment: 6 pages, LaTeX2e File, 7 EPS-figures, presented at SEWM 2000,
Marseille, June 13-17th, 200
Hadron correlators, spectral functions and thermal dilepton rates from lattice QCD
We discuss information on thermal modifications of hadron properties which
can be extracted from the structure of Euclidean correlation functions of
hadronic currents as well as more direct information obtained through the
reconstruction of the spectral functions based on the Maximum Entropy Method.Comment: 4 pages, latex2e, 5 EPS-files, invited contribution to the 16th Int.
Conf. on Ultra-Relativistic Nucleus-Nucleus Collisions, Nantes, France, 18 -
24 July, 200
Lattice calculation of medium effects at short and long distances
We investigate medium effects in QCD like chromoelectric screening and
quasi-particle mass generation by calculating the heavy quark potential as well
as the temporal quark and gluon Coulomb gauge propagators in quenched
approximation.Comment: To appear in proceedings of Quark Matter 2001, 4 pages LaTeX, uses
espcrc1.st
Free Meson Spectral Functions on the Lattice
We present results from an analytic calculation of thermal meson spectral
functions in the infinite temperature (free field) limit. We compare spectral
functions for various lattice fermion formulations used at present in studies
of in-medium properties of hadrons based on the maximum entropy method (MEM).
In particular, we will present a new calculation of spectral functions
performed with extended quark sources.Comment: 3 pages, Lattice2003(nonzero
Meson Spectral Functions at finite Temperature
The Maximum Entropy Method provides a Bayesian approach to reconstruct the
spectral functions from discrete points in Euclidean time. The applicability of
the approach at finite temperature is probed with the thermal meson correlation
function. Furthermore the influence of fuzzing/smearing techniques on the
spectral shape is investigated. We present first results for meson spectral
functions at several temperatures below and above . The correlation
functions were obtained from quenched calculations with Clover fermions on
large isotropic lattices of the size . We compare the
resulting pole masses with the ones obtained from standard 2-exponential fits
of spatial and temporal correlation functions at finite temperature and in the
vacuum. The deviation of the meson spectral functions from free spectral
functions is examined above the critical temperature.Comment: Lattice2001(hightemp), 3 pages, 6 figure
Flavor and Quark Mass Dependence of QCD Thermodynamics
We calculate the transition temperature in 2 and 3-flavor QCD using improved
gauge and staggered fermion actions on lattices with temporal extent Nt=4. We
find Tc=173(8)MeV and 154(8)MeV for nf=2 and 3, respectively. In the case of
3-flavor QCD we present evidence that the chiral critical point, i.e. the
second order endpoint of the line of first order chiral phase transitions,
belongs to the universality class of the 3d Ising model.Comment: Talk given at Lattice 2000 (Finite Temperature), 4 pages, 6
EPS-figure