49 research outputs found
Gluon Condensate and Non-Perturbative Quark-Photon Vertex
We evaluate the quark-photon vertex non-perturbatively taking into account
the gluon condensate at finite temperature. This vertex is related to the
previously derived effective quark propagator by a QED like Ward-Takahashi
identity. The importance of the effective vertex for the dilepton production
rate from a quark-gluon plasma is stressed.Comment: 9 pages including two figure
Quark Propagation in a Quark-Gluon Plasma with Gluon Condensate
We present a calculation of the thermal quark propagator taking the gluon
condensate above the critical temperature into account. The quark dispersion
relation following from this propagator, describing two massive modes, is
discussed.Comment: 11 pages, REVTEX, 2 PostScript figures, revised version accepted for
publication in Phys. Lett.
Hard photon production rate of a quark-gluon plasma at finite quark chemical potential
We compute the photon production rate of a quark-gluon plasma (QGP) at finite
quark chemical potential using the Braaten-Pisarski method, thus
continuing the work of Kapusta, Lichard, and Seibert who did the calculation
for .Comment: 9 pages, revtex, no figures, error in soft part corrected, figures
available at ftp://theorie.physik.uni-giessen.de/usr/users/ftp/photon
Quark Dispersion Relation and Dilepton Production in the Quark-Gluon Plasma
Under very general assumptions we show that the quark dispersion relation in
the quark-gluon plasma is given by two collective branches, of which one has a
minimum at a non-vanishing momentum. This general feature of the quark
dispersion relation leads to structures (van Hove singularities, gaps) in the
low mass dilepton production rate, which might provide a unique signature for
the quark-gluon plasma formation in relativistic heavy ion collisions.Comment: 6 pages, Revtex, 2 PostScript figures, revised version to be
published in Phys. Rev. Let
Hard Loop Approach to Anisotropic Systems
Anisotropic systems of quarks and gluons, which at least for sufficiently
short space-time intervals can be treated as homogeneous and static, are
considered. The gluon polarization tensor of such a system is explicitly
computed within the semiclassical kinetic and Hard Loop diagrammatic theories.
The equivalence of the two approaches is demonstrated. The quark self energy is
computed as well, and finally, the dispersion relations of quarks and gluons in
the anisotropic medium are discussed.Comment: 10 pages, revised to appear in Phys. Rev.
Can Van Hove singularities be observed in relativistic heavy-ion collisions ?
Based on general arguments the in-medium quark propagator in a quark-gluon
plasma leads to a quark dispersion relation consisting of two branches, of
which one exhibits a minimum at some finite momentum. This results in a
vanishing group velocity for collective quark modes. Important quantities such
as the production rate of low mass lepton pairs and mesonic correlators depend
inversely on this group velocity. Therefore these quantities, which follow from
self energy diagrams containing a quark loop, are strongly affected by Van Hove
singularities (peaks and gaps). If these sharp structures could be observed in
relativistic heavy-ion collisions it would reveal the physical picture of the
QGP as a gas of quasiparticles.Comment: 12 pages including nine figures and style files, invited talk given
at the ICPAQGP-2001, November 26-30, 2001, Jaipur, Indi
Chiral Susceptibility in Hard Thermal Loop Approximation
The static and dynamic chiral susceptibilities in the quark-gluon plasma are
calculated within the lowest order perturbative QCD at finite temperature and
the Hard Thermal Loop resummation technique using an effective quark
propagator. After regularisation of ultraviolet divergences, the Hard Thermal
Loop results are compared to QCD lattice simulations.Comment: 12 pages, 4 figures, revised version, to be published in Phys. Rev.
Damping Rate of a Scalar Particle in Hot Scalar QED
In contrast to the damping of partons in a quark-gluon plasma, the damping of
a scalar particle in a hot scalar QED plasma can be calculated to leading order
for the whole momentum range using the Braaten-Pisarski method. In this way the
evolution of the logarithmic infrared singularity caused by the exchange of a
transverse photon from soft to hard momenta can be studied.Comment: 10 pages, uuencoded postscript file with 6 figure
Photon Emission from a Parton Gas at Chemical Non-Equilibrium
We compute the hard photon production rate of a chemically non-equilibrated
quark-gluon plasma. We assume that the plasma is already thermally
equilibrated, i.~e. describable by a temperature, but with a phase-space
distribution that deviates from the Fermi/Bose distribution by a time dependent
factor (fugacity). The photon spectrum is obtained by integrating the photon
rate over the space-time evolution of the quark-gluon plasma. Some consequences
for ultrarelativistic heavy ion collisions are discussed.Comment: 17 pages, uuencoded Postscript file, figures include