3,712 research outputs found
Collisional Energy Loss of Fast Charged Particles in Relativistic Plasmas
Following an argument by Kirzhnits we rederive an exact expression for the
energy loss of a fast charged particle in a relativistic plasma using the
quantum field theoretical language. We compare this result to perturbative
calculations of the collisional energy loss of an energetic electron or muon in
an electron-positron plasma and of an energetic parton in the quark-gluon
plasma.Comment: 9 pages, LATEX, 2 PostScript figure
Constraint Correlation Dynamics of SU(N) Gauge Theories
A constraint correlation dynamics up to 4-point Green functions is proposed
for SU(N) gauge theories which reduces the N-body quantum field problem to the
two-body level. The resulting set of nonlinear coupled equations fulfills all
conservation laws including fermion number, linear and angular momenta as well
as the total energy. Apart from the conservation laws in the space-time degrees
of freedom the Gauss law is conserved as a quantum expectation value
identically for all times. The same holds for the Ward identities as generated
by commutators of Gauss operators. The constraint dynamical equations are
highly non-perturbative and thus applicable also in the strong coupling regime,
as e.g. low-energy QCD problems.Comment: 26 pages, LATEX, UGI-94-0
Ward Identities in Non-equilibrium QED
We verify the QED Ward identity for the two- and three -point functions at
non-equilibrium in the HTL limit. We use the Keldysh formalism of real time
finite temperature field theory. We obtain an identity of the same form as the
Ward identity for a set of one loop self-energy and one loop three-point vertex
diagrams which are constructed from HTL effective propagators and vertices.Comment: 19 pages, RevTex, 4 PostScript figures, revised version to be
published in Phys. Rev.
Autowaves in a dc complex plasma confined behind a de Laval nozzle
Experiments to explore stability conditions and topology of a dense
microparticle cloud supported against gravity by a gas flow were carried out.
By using a nozzle shaped glass insert within the glass tube of a dc discharge
plasma chamber a weakly ionized gas flow through a de Laval nozzle was
produced. The experiments were performed using neon gas at a pressure of 100 Pa
and melamine-formaldehyde particles with a diameter of 3.43 {\mu}m. The
capturing and stable global confining of the particles behind the nozzle in the
plasma were demonstrated. The particles inside the cloud behaved as a single
convection cell inhomogeneously structured along the nozzle axis in a tube-like
manner. The pulsed acceleration localized in the very head of the cloud
mediated by collective plasma-particle interactions and the resulting wave
pattern were studied in detail.Comment: 6 pages, 4 figure
The Quark-Gluon-Plasma Liquid
The quark-gluon plasma close to the critical temperature is a strongly
interacting system. Using strongly coupled, classical, non-relativistic plasmas
as an analogy, we argue that the quark-gluon plasma is in the liquid phase.
This allows to understand experimental observations in ultrarelativistic
heavy-ion collisions and to interpret lattice QCD results. It also supports the
indications of the presence of a strongly coupled QGP in ultrarelativistic
heavy-ion collisions.Comment: 8 pages, 2 figures, final version, to bepublished in J. Phys.
decays from photoproduction of -mesons off protons
A study of the partial-wave content of the
reaction in the fourth resonance region is presented, which has been prompted
by new measurements of polarization observables for that process. Using the
Bonn-Gatchina partial-wave formalism, the incorporation of new data indicates
that the , , , and are
the most significant contributors to the photoproduction process. New results
for the branching ratios of the decays of these more prominent resonances to
final states are provided; such branches have not been indicated
in the most recent edition of the Review of Particle Properties. Based on the
analysis performed here, predictions for the helicity asymmetry for the
reaction are presented.Comment: 7 pages, 5 figures, 3 table
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
Decay of a Yukawa fermion at finite temperature and applications to leptogenesis
We calculate the decay rate of a Yukawa fermion in a thermal bath using
finite temperature cutting rules and effective Green's functions according to
the hard thermal loop resummation technique. We apply this result to the decay
of a heavy Majorana neutrino in leptogenesis. Compared to the usual approach
where thermal masses are inserted into the kinematics of final states, we find
that deviations arise through two different leptonic dispersion relations. The
decay rate differs from the usual approach by more than one order of magnitude
in the temperature range which is interesting for the weak washout regime. We
discuss how to arrive at consistent finite temperature treatments of
leptogenesis.Comment: 16 pages, 5 figure
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