164 research outputs found
Propagation of Partially Coherent Photons in an Ultra-Intense Radiation Gas
The scattering of photons off photons at the one-loop level is investigated.
We give a short review of the weak field limit, as given by the first order
term in the series expansion of the Heisenberg-Euler Lagrangian. The dispersion
relation for a photon in a radiation gas is presented. Based on this, a wave
kinetic equation and a set of fluid equations is formulated. These equations
describe the interaction between a partially coherent electromagnetic pulse and
an intense radiation gas. The implications of the results are discussed.Comment: 10 pages, 1 figure, revtex
Radiation dominated particle and plasma dynamics
We consider the general problem of charged particle motion in a strong
electromagnetic field of arbitrary configuration and find a universal
behaviour: for sufficiently high field strengths, the radiation losses lead to
a general tendency of the charge to move along the direction that locally
yields zero lateral acceleration. The relativistic motion along such a
direction results in no radiation losses, according to both classical and
quantum descriptions of radiation reaction. We show that such a radiation-free
direction (RFD) exists at each point of an arbitrary electromagnetic field,
while the time-scale of approaching this direction decreases with the increase
of field strength. Thus, in the case of a sufficiently strong electromagnetic
field, at each point of space, the charges mainly move and form currents along
local RFD, while the deviation of their motion from RFD can be calculated in
order to account for their incoherent emission. This forms a general
description of particle, and therefore plasma, dynamics in strong
electromagnetic fields, the latter can be generated by state-of-the-art lasers
or in astrophysical environments
Scalar Perturbations in Two-Temperature Cosmological Plasmas
We study the properties of density perturbations of a two-component plasma
with a temperature difference on a homogeneous and isotropic background. For
this purpose we extend the general relativistic gauge invariant covariant (GIC)
perturbation theory to include a multi-fluid with a particular equations of
state (ideal gas) and imperfect fluid terms due to the relative energy flux
between the two species. We derive closed sets of GIC vector and subsequently
scalar evolution equations. We then investigate solutions in different regimes
of interest. In particular, we study long wavelength and arbitrary wavelength
Langmuir and ion-acoustic perturbations. The harmonic oscillations are
superposed on a Jeans type instability. We find a generalised Jeans criterion
for collapse in a two-temperature plasma, which states that the species with
the largest sound velocity determines the Jeans wavelength. Furthermore, we
find that within the limit for gravitational collapse, initial perturbations in
either the total density or charge density lead to a growth in the initial
temperature difference. These results are relevant for the basic understanding
of the evolution of inhomogeneities in cosmological models.Comment: 9 pages. Accepted for publication in MNRAS, 5 April 2006 (submitted
20 Januari 2006
Rotating matter in general relativity -- stationary state I
Stationary rotating matter configurations in general relativity are
considered. A formalism for general stationary space times is developed.
Axisymmetric systems are discussed by the use of a nonholonomic and nonrigid
frame in the three-space of the time-like Killing trajectories. Two symmetric
and trace-free tensors are constructed. They characterize a class of matter
states in which both the interior Schwarzschild and the Kerr solution are
contained. Consistency relations for this class of perfect fluids are derived.
Incompressible fluids characterized by these tensors are investigated, and one
differentially rotating solution is found.Comment: 25 pages, REVTe
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