165 research outputs found
Relativistic Quantum Transport Theory
Relativistic quantum transport theory has begun to play an important role in
the space-time description of matter under extreme conditions of high energy
density in out-of-equilibrium situations. The following introductory lectures
on some of its basic concepts and methods comprise the sections: 1.
Introduction; 2. Aims of transport theory (classical); 3. Quantum mechanical
distribution functions - the density matrix and the Wigner function; 4.
Transport theory for quantum fields; 5. Particle production by classical
fields; 6. Fluid dynamics of relativistic quantum dust.Comment: Lectures presented at PASI "New States of Matter in Hadronic
Interactions", Campos do Jordao, Brazil, Jan.7-18, 2002. - 19 pages; LaTe
Time without time: a stochastic clock model
We study a classical reparametrization-invariant system, in which ``time'' is
not a priori defined. It consists of a nonrelativistic particle moving in five
dimensions, two of which are compactified to form a torus. There, assuming a
suitable potential, the internal motion is ergodic or more strongly irregular.
We consider quasi-local observables which measure the system's ``change'' in a
coarse-grained way. Based on this, we construct a statistical timelike
parameter, particularly with the help of maximum entropy method and Fisher-Rao
information metric. The emergent reparametrization-invariant ``time'' does not
run smoothly but is simply related to the proper time on the average. For
sufficiently low energy, the external motion is then described by a unitary
quantum mechanical evolution in accordance with the Schr\"odinger equation.Comment: 18 pages; LaTeX. 4 (.ps) plus 2 (.gif) figure file
Collective Modes in Neutrino `Beam' Electron-Positron Plasma Interactions
We derive semiclassical neutrino-electron transport equations in the
collisionless (Vlasov) limit from the coupled Dirac equations, incorporating
the charged and neutral weak current-current as well as electromagnetic
interactions. A corresponding linear response theory is derived. In particular,
we calculate the response functions for a variety of beam-plasma geometries,
which are of interest in a supernova scenario. We apply this to the study of
plasmons and to a new class of collective {\it pharon} resonance modes, which
are characterized by . We find that the growth rates of the
unstable modes correspond to a strongly temperature ()
and linearly momentum dependent e-folding length of about km under
typical conditions for Type II supernovae. This appears to rule out such
long-wavelength collective modes as an efficient means of depositing neutrino
energy into the plasma sphere.Comment: 27 pages; LaTex. Replaced by published version. - Appendix about
neutrino Wigner functions added and main text correspondingly revised.
Conclusions unchange
The Functional Derivation of Master Equations
Master equations describe the quantum dynamics of open systems interacting
with an environment. They play an increasingly important role in understanding
the emergence of semiclassical behavior and the generation of entropy, both
being related to quantum decoherence. Presently we derive the exact master
equation for a homogeneous scalar Higgs or inflaton like field coupled to an
environment field represented by an infinite set of harmonic oscillators. Our
aim is to demonstrate a derivation directly from the path integral
representation of the density matrix propagator. Applications and
generalizations of this result are discussed.Comment: 10 pages; LaTex. - Contribution to the workshop Hadron Physics VI,
March 1998, Florianopolis (Brazil); proceedings, E. Ferreira et al., eds.
(World Scientific). Replaced by slightly modified published versio
Kinetic equation for gluons at the early stage
We derive the kinetic equation for pure gluon QCD plasma in a general way,
applying the background field method. We show that the quantum kinetic equation
contains a term as in the classical case, that describes a color charge
precession of partons moving in the gauge field. We emphasize that this new
term is necessary for the gauge covariance of the resulting equation.Comment: 6 pages, no figure, to appear in the proceedings of the 6th
international conference on strange quarks in matter, Frankfurt, Germany,
25-29 september 200
Equal-Time Hierarchies in Quantum Transport Theory
We investigate in the equal-time formalism the derivation and truncation of
infinite hierarchies of equations of motion for the energy moments of the
covariant Wigner function. From these hierarchies we then extract kinetic
equations for the physical distribution functions which are related to
low-order energy moments, and show how to determine the higher order moments in
terms of these lowest order ones. We apply the general formalism to scalar and
spinor QED with classical background fields and compare with the results
derived from the three-dimensional Wigner transformation method.Comment: 44 pages, no figure
- …