13 research outputs found
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: The Numerical Study ofStrongly Interacting Matter under Extreme Conditions
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
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
Infinite temperature limit of meson spectral functions calculated on the lattice
We analyze the cut-off dependence of mesonic spectral functions calculated at
finite temperature on Euclidean lattices with finite temporal extent. In the
infinite temperature limit we present analytic results for lattice spectral
functions calculated with standard Wilson fermions as well as a truncated
perfect action. We explicitly determine the influence of `Wilson doublers' on
the high momentum structure of the mesonic spectral functions and show that
this cut-off effect is strongly suppressed when using an improved fermion
action.Comment: 25 pages, 8 figure
The Instanton Molecule Liquid and "Sticky Molasses" Above T_c
The main objective of this work is to explore the evolution in the structure
of the quark-antiquark bound states in going down in the chirally restored
phase from the so-called "zero binding points" T_zb to the QCD critical
temperature T_c at which the Nambu-Goldstone and Wigner-Weyl modes meet. In
doing this, we adopt the idea recently introduced by Shuryak and Zahed for
charmed , light-quark mesons and
gluons that at T_zb, the quark-antiquark scattering length goes through
infinity at which conformal invariance is restored, thereby transforming the
matter into a near perfect fluid behaving hydrodynamically, as found at RHIC.
We show that the binding of these states is accomplished by the combination of
(i) the color Coulomb interaction, (ii) the relativistic effects, and (iii) the
interaction induced by the instanton-anti-instanton molecules. The spin-spin
forces turned out to be small. While near T_zb all mesons are large-size
nonrelativistic objects bound by Coulomb attraction, near T_c they get much
more tightly bound, with many-body collective interactions becoming important
and making the and masses approach zero (in the chiral limit).
The wave function at the origin grows strongly with binding, and the near-local
four-Fermi interactions induced by the instanton molecules play an increasingly
more important role as the temperature moves downward toward T_c.Comment: Contribution to QM2004 proceedings, 4 page
QCD Thermodynamics: The Numerical Study of Strongly Interacting Matter under Extreme Conditions
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