220 research outputs found
Dissipative Time Evolution of Observables in Non-equilibrium Statistical Quantum Systems
We discuss differential-- versus integral--equation based methods describing
out--of thermal equilibrium systems and emphasize the importance of a well
defined reduction to statistical observables. Applying the projection operator
approach, we investigate on the time evolution of expectation values of linear
and quadratic polynomials in position and momentum for a statistical anharmonic
oscillator with quartic potential. Based on the exact integro-differential
equations of motion, we study the first and naive second order approximation
which breaks down at secular time-scales. A method is proposed to improve the
expansion by a non--perturbative resummation of all quadratic operator
correlators consistent with energy conservation for all times. Motion cannot be
described by an effective Hamiltonian local in time reflecting non-unitarity of
the dissipative entropy generating evolution. We numerically integrate the
consistently improved equations of motion for large times. We relate entropy to
the uncertainty product, both being expressible in terms of the observables
under consideration.Comment: 20 pages, 6 Figure
Effects of weak self-interactions in a relativistic plasma on cosmological perturbations
The exact solutions for linear cosmological perturbations which have been
obtained for collisionless relativistic matter within thermal field theory are
extended to a self-interacting case. The two-loop contributions of scalar
theory to the thermal graviton self-energy are evaluated, which
give the corrections in the perturbation equations. The changes
are found to be perturbative on scales comparable to or larger than the Hubble
horizon, but the determination of the large-time damping behavior of subhorizon
perturbations requires a resummation of thermally induced masses.Comment: 11 pages, REVTEX, 4 postscript figures included by epsf.sty -
expanded version (more details on the resummation of thermal masses which is
required for the late-time damping behaviour
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