66 research outputs found
Damping Rate of a Hard Photon in a Relativistic Plasma
The damping rate of a hard photon in a hot relativistic QED and QCD plasma is
calculated using the resummation technique by Braaten and Pisarski.Comment: 4 pages, REVTeX, 2 figures (not included), UGI-MT-94-0
Damping Rate of a Yukawa Fermion at Finite Temperature
The damping of a massless fermion coupled to a massless scalar particle at
finite temperature is considered using the Braaten-Pisarski resummation
technique. First the hard thermal loop diagrams of this theory are extracted
and effective Green's functions are constructed. Using these effective Green's
functions the damping rate of a soft Yukawa fermion is calculated. This rate
provides the most simple example for the damping of a soft particle. To leading
order it is proportional to , whereas the one of a hard fermion is of
higher order.Comment: 5 pages, REVTEX, postscript figures appended, UGI-94-0
Phenomenology of Jet Quenching in Heavy Ion Collisions
We derive an analytical expression for the quenching factor in the strong
quenching limit where the spectrum of hard partons is dominated by
surface emission. We explore the phenomenological consequences of different
scaling laws for the energy loss and calculate the additional suppression of
the away-side jet.Comment: Substantially modified manuscrip
QCD Perturbation Theory at Finite Temperature/Density and its Application
In order to describe properties of an equilibrated quark-gluon plasma, QCD at
finite temperature (and density) has to be considered. Besides lattice
calculations, which can be applied only to static quantities at zero density,
perturbative QCD has been used. At finite temperature, however, serious
problems such as infrared divergent and gauge dependent results have been
encountered. These difficulties can be (partially) avoided if one starts from
effective Green functions constructed by resumming a certain class of diagrams
(hard thermal loops). Within the last few years this improved perturbation
theory (Braaten-Pisarski method) turned out to be a powerful tool for computing
interesting quantities of the quark-gluon plasma phase. In the present talk a
basic introduction to the Braaten-Pisarski method is provided and its
applications and limits are reviewed. In particular, damping rates, the energy
loss of energetic partons, thermalization times, the viscosity of the
quark-gluon plasma, and the production of photons and dileptons are discussed.Comment: 12 pages, LaTeX (style file included), 9 PostScript figures, to be
published in Proc. Quark Matter'97 (Tsukuba
Time-resolved cathodoluminescence of InGaAs/AlGaAs tetrahedral pyramidal quantum structures
An original time resolved cathodoluminescence set up has been used to investigate the optical properties and the carrier transport in quantum structures located in InGaAs/AlGaAs tetrahedral pyramids. An InGaAs quantum dot formed just below the top of the pyramid is connected to four types of low-dimensional barriers: InGaAs quantum wires on the edges of the pyramid, InGaAs quantum wells on the (111)A facets and segregated AlGaAs vertical quantum wire and AlGaAs vertical quantum wells formed at the centre and at the pyramid edges. Experiments were performed at a temperature of 92K, an accelerating voltage of 10kV and a beam probe current of 10pA. The cathodoluminescence spectrum shows five luminescence peaks. Rise and decay times for the different emission wavelengths provide a clear confirmation of the peak attribution (previously done with other techniques) to the different nanostructures grown in a pyramid. Moreover, experimental results suggest a scenario where carriers diffuse from the lateral quantum structures towards the central structures (the InGaAs quantum dot and the segregated AlGaAs vertical quantum wire) via the InGaAs quantum wires on the edges of the pyramid. According to this hypothesis, we have modeled the carrier diffusion along these quantum wires. An ambipolar carrier mobility of 1400cm2/V s allows to obtain a good fit to all temporal dependence
Finite Temperature Meson Correlation Functions in HTL Approximation
We calculate temporal correlators and their spectral functions with meson
quantum numbers in the deconfined phase of QCD using the hard thermal loop
(HTL) approximation for the quark propagator. Although this approach does not
result in a complete next-to-leading order perturbative calculation it takes
into account important medium effects such as thermal quark masses and Landau
damping in the quark-gluon plasma. We show that both effects lead to competing
modifications of the free mesonic correlation functions. We find that
correlators in scalar channels are only moderately influenced by the HTL medium
effects, while the HTL-vertex corrections lead to divergent vector correlators.Comment: 14 pages, LaTeX2e File, 8 EPS-files, minor changes in abstract and
text, to appear in Phys. Lett.
Energy Loss of a Heavy Fermion in an Anisotropic QED Plasma
We compute the leading-order collisional energy loss of a heavy fermion
propagating in a QED plasma with an electron distribution function which is
anisotropic in momentum space. We show that in the presence of such
anisotropies there can be a significant directional dependence of the heavy
fermion energy loss with the effect being quite large for highly-relativistic
velocities. We also repeat the analysis of the isotropic case more carefully
and show that the final result depends on the intermediate scale used to
separate hard and soft contributions to the energy loss. We then show that the
canonical isotropic result is obtained in the weak-coupling limit. For
intermediate-coupling we use the residual scale dependence as a measure of our
theoretical uncertainty. We also discuss complications which could arise due to
the presence of unstable soft photonic modes and demonstrate that the
calculation of the energy loss is safe.Comment: 19 pages, 18 figures. v2 - Correction to normalization of numerical
results; some figures modified as a result; discussion of role of unstable
modes added along with two new figure
Is \lq\lq Heavy Quark Damping Rate Puzzle'' in Hot QCD Really the Puzzle?
Within the framework of perturbative resummation scheme of Pisarski and
Braaten, the decay- or damping-rate of a moving heavy quark (muon) to leading
order in weak coupling in hot QCD (QED) is examined. Although, as is well
known, the conventionally-defined damping rate diverges logarithmically at the
infrared limit, shown is that no such divergence appears in the physically
measurable decay rate. The cancellation occurs between the contribution from
the \lq\lq real'' decay diagram and the contribution from the diagrams with
\lq\lq thermal radiative correction''.Comment: 13pages, OCU-PHYS-15
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.
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