14,378 research outputs found
Fluctuation, dissipation, and thermalization in non-equilibrium AdS_5 black hole geometries
We give a simple recipe for computing dissipation and fluctuations
(commutator and anti-commutator correlation functions) for non-equilibrium
black hole geometries. The recipe formulates Hawking radiation as an initial
value problem, and is suitable for numerical work. We show how to package the
fluctuation and dissipation near the event horizon into correlators on the
stretched horizon. These horizon correlators determine the bulk and boundary
field theory correlation functions. In addition, the horizon correlators are
the components of a horizon effective action which provides a quantum
generalization of the membrane paradigm. In equilibrium, the analysis
reproduces previous results on the Brownian motion of a heavy quark. Out of
equilibrium, Wigner transforms of commutator and anti-commutator correlation
functions obey a fluctuation-dissipation relation at high frequency.Comment: 28 pages, 6 figure
Time dependent diffusion in a disordered medium with partially absorbing walls: A perturbative approach
We present an analytical study of the time dependent diffusion coefficient in
a dilute suspension of spheres with partially absorbing boundary condition.
Following Kirkpatrick (J. Chem. Phys. 76, 4255) we obtain a perturbative
expansion for the time dependent particle density using volume fraction of
spheres as an expansion parameter. The exact single particle -operator for
partially absorbing boundary condition is used to obtain a closed form
time-dependent diffusion coefficient accurate to first order in the
volume fraction . Short and long time limits of are checked against
the known short-time results for partially or fully absorbing boundary
conditions and long-time results for reflecting boundary conditions. For fully
absorbing boundary condition the long time diffusion coefficient is found to be
, to the first order of
perturbation theory. Here is small but non-zero, the diffusion
coefficient in the absence of spheres, and the radius of the spheres. The
validity of this perturbative result is discussed
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