89 research outputs found
Parton Energy Loss in Two-Stream Plasma System
The energy loss of a fast parton scattering elastically in a weakly coupled
quark-gluon plasma is formulated as an initial value problem. The approach is
designed to study an unstable plasma, but it also reproduces the well known
result of energy loss in an equilibrium plasma. A two-stream system, which is
unstable due to longitudinal chromoelectric modes, is discussed here some
detail. In particular, a strong time and directional dependence of the energy
loss is demonstrated.Comment: 6 pages; presented by K. Deja at the conference Strangeness in Quark
Matter, Cracow, Poland, September 18-24, 201
Influence of statistical fluctuations on ratios in relativistic heavy ion collisions
The influence of pure statistical fluctuations on ratio is
investigated in an event-by-event way. Poisson and the modified negative
binomial distributions are used as the multiplicity distributions since they
both have statistical background. It is shown that the distributions of the
ratio in these cases are Gaussian, and the mean and relative variance are given
analytically.Comment: 6 pages in RevTeX, 3 eps figures include
Hydrodynamic transport functions from quantum kinetic theory
Starting from the quantum kinetic field theory [E. Calzetta and B. L. Hu,
Phys. Rev. D37, 2878 (1988)] constructed from the closed-time-path (CTP),
two-particle-irreducible (2PI) effective action we show how to compute from
first principles the shear and bulk viscosity functions in the
hydrodynamic-thermodynamic regime. For a real scalar field with self-interaction we need to include 4 loop graphs in the equation of
motion. This work provides a microscopic field-theoretical basis to the
``effective kinetic theory'' proposed by Jeon and Yaffe [S. Jeon and L. G.
Yaffe, Phys. Rev. D53, 5799 (1996)], while our result for the bulk viscosity
reproduces their expression derived from linear response theory and the
imaginary-time formalism of thermal field theory. Though unavoidably involved
in calculations of this sort, we feel that the approach using fundamental
quantum kinetic field theory is conceptually clearer and methodically simpler
than the effective kinetic theory approach, as the success of the latter
requires clever rendition of diagrammatic resummations which is neither
straightforward nor failsafe. Moreover, the method based on the CTP-2PI
effective action illustrated here for a scalar field can be formulated entirely
in terms of functional integral quantization, which makes it an appealing
method for a first-principles calculation of transport functions of a thermal
non-abelian gauge theory, e.g., QCD quark-gluon plasma produced from heavy ion
collisions.Comment: 25 pages revtex, 11 postscript figures. Final version accepted for
publicatio
Fluctuations driven isotropization of the quark-gluon plasma in heavy ion collisions
Averaged over ensemble of initial conditions kinetic transport equations of
weakly coupled systems of quarks and gluons are derived. These equations
account for the correlators of fluctuations of particles and classical gluon
fields. The isotropization of particle momenta by field fluctuations at the
early prethermal stage of matter evolution in ultrarelativistic heavy ion
collisions is discussed. Our results can be useful for understanding under what
conditions isotropization of the quark-gluon plasma in ultrarelativistic heavy
ion collisions can be reached within phenomenologically observed time scales.Comment: 16 pages, misprints corrected, to be published in Phys. Rev.
In-medium relativistic kinetic theory and nucleon-meson systems
Within the model of coupled nucleon-meson systems, a
generalized relativistic Lenard--Balescu--equation is presented resulting from
a relativistic random phase approximation (RRPA). This provides a systematic
derivation of relativistic transport equations in the frame of nonequilibrium
Green's function technique including medium effects as well as flucuation
effects. It contains all possible processes due to one meson exchange and
special attention is kept to the off--shell character of the particles. As a
new feature of many particle effects, processes are possible which can be
interpreted as particle creation and annihilation due to in-medium one meson
exchange. In-medium cross sections are obtained from the generalized derivation
of collision integrals, which possess complete crossing symmetries.Comment: See nucl-th/9310032 for revised version which the authors
incompetently resubmitted rather than correctly replacing thi
Stochastic dynamics of correlations in quantum field theory: From Schwinger-Dyson to Boltzmann-Langevin equation
The aim of this paper is two-fold: in probing the statistical mechanical
properties of interacting quantum fields, and in providing a field theoretical
justification for a stochastic source term in the Boltzmann equation. We start
with the formulation of quantum field theory in terms of the Schwinger - Dyson
equations for the correlation functions, which we describe by a
closed-time-path master () effective action. When the hierarchy
is truncated, one obtains the ordinary closed-system of correlation functions
up to a certain order, and from the nPI effective action, a set of
time-reversal invariant equations of motion. But when the effect of the higher
order correlation functions is included (through e.g., causal factorization--
molecular chaos -- conditions, which we call 'slaving'), in the form of a
correlation noise, the dynamics of the lower order correlations shows
dissipative features, as familiar in the field-theory version of Boltzmann
equation. We show that fluctuation-dissipation relations exist for such
effectively open systems, and use them to show that such a stochastic term,
which explicitly introduces quantum fluctuations on the lower order correlation
functions, necessarily accompanies the dissipative term, thus leading to a
Boltzmann-Langevin equation which depicts both the dissipative and stochastic
dynamics of correlation functions in quantum field theory.Comment: LATEX, 30 pages, no figure
The problem of nonlinear Landau damping in quark-gluon plasma
On the basis of the semiclassical equations for quark-gluon plasma (QGP) and
Yang-Mills equation, the generalized kinetic equation for waves with regard to
its interaction is obtained. The physical mechanisms defining nonlinear
scattering of a plasmon by QGP particles are analysed. The problem on a
connection of nonlinear Landau damping rate of longitudinal oscillation with
damping rate, obtained on the basis of hard thermal loops approximation, is
considered.Comment: 33 page
Antideuteron and deuteron production in mid-central Pb+Pb collisions at 158 GeV
Production of deuterons and antideuterons was studied by the NA49 experiment
in the 23.5% most central Pb+Pb collisions at the top SPS energy of
=17.3 GeV. Invariant yields for and were measured
as a function of centrality in the center-of-mass rapidity range .
Results for together with previously published
measurements are discussed in the context of the coalescence model. The
coalescence parameters were deduced as a function of transverse momentum
and collision centrality.Comment: 9 figure
System-size and centrality dependence of charged kaon and pion production in nucleus-nucleus collisions at 40A GeV and158A GeV beam energy
Measurements of charged pion and kaon production are presented in centrality
selected Pb+Pb collisions at 40A GeV and 158A GeV beam energy as well as in
semi-central C+C and Si+Si interactions at 40A GeV. Transverse mass spectra,
rapidity spectra and total yields are determined as a function of centrality.
The system-size and centrality dependence of relative strangeness production in
nucleus-nucleus collisions at 40A GeV and 158A GeV beam energy are derived from
the data presented here and published data for C+C and Si+Si collisions at 158A
GeV beam energy. At both energies a steep increase with centrality is observed
for small systems followed by a weak rise or even saturation for higher
centralities. This behavior is compared to calculations using transport models
(UrQMD and HSD), a percolation model and the core-corona approach.Comment: 32 pages, 14 figures, 4 tables, typo table II correcte
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