2,041 research outputs found
On the contribution of exchange interactions to the Vlasov equation
Exchange effects play an important role in determining the equilibrium
properties of dense matter systems, as well as for magnetic phenomena. There
exists an extensive literature concerning, e.g., the effects of exchange
interactions on the equation of state of dense matter. Here, a generalization
of the Vlasov equation to include exchange effects is presented allowing for
electromagnetic mean fields, thus incorporating some of the dynamic effects due
to the exchange interactions. Treating the exchange term perturbatively, the
correction to classical Langmuir waves in plasmas is found, and the results are
compared with previous work. It is noted that the relative importance of
exchange effects scales similarly with density and temperature as particle
dispersive effects, but that the overall magnitude is sensitive to the details
of the specific problem. The implications of our results are discussed.Comment: 9 page
Graviton mediated photon-photon scattering in general relativity
In this paper we consider photon-photon scattering due to self-induced
gravitational perturbations on a Minkowski background. We focus on four-wave
interaction between plane waves with weakly space and time dependent
amplitudes, since interaction involving a fewer number of waves is excluded by
energy-momentum conservation. The Einstein-Maxwell system is solved
perturbatively to third order in the field amplitudes and the coupling
coefficients are found for arbitrary polarizations in the center of mass
system. Comparisons with calculations based on quantum field theoretical
methods are made, and the small discrepances are explained.Comment: 5 pages, 3 figure
Circularly polarized waves in a plasma with vacuum polarization effects
The theory for large amplitude circularly polarized waves propagating along
an external magnetic field is extended in order to include also vacuum
polarization effects. A general dispersion relation, which unites previous
results, is derived.Comment: 5 pages (To appear in Physics of Plasmas
Effects of high energy photon emissions in laser generated ultra-relativistic plasmas: real-time synchrotron simulations
We model the emission of high energy photons due to relativistic charged
particle motion in intense laser-plasma interactions. This is done within a
particle-in-cell code, for which high frequency radiation normally cannot be
resolved due to finite time steps and grid size. A simple expression for the
synchrotron radiation spectra is used together with a Monte-Carlo method for
the emittance. We extend previous work by allowing for arbitrary fields,
considering the particles to be in instantaneous circular motion due to an
effective magnetic field. Furthermore we implement noise reduction techniques
and present validity estimates of the method. Finally, we perform a rigorous
comparison to the mechanism of radiation reaction, and find the emitted energy
to be in excellent agreement with the losses calculated using radiation
reaction
A phonon laser in ultra-cold matter
We show the possible excitation of a phonon laser instability in an
ultra-cold atomic gas confined in a magneto-optical trap. Such an effect
results from a negative Landau damping of the collective density perturbations
in the gas, leading to the coherent emission of phonons. This laser instability
can be driven by a blue-detuned laser superimposed to the usual red-detuning
laser beams which usually provide the cooling mechanism. Threshold conditions,
instability growth rates and saturation levels are derived. This work
generalizes, on theoretical grounds, the recent results obtained with single
ion phonon laser, to an ultra-cold atomic gas, where real phonons can be
excited. Future phonon lasers could thus adequately be called phasers.Comment: 4 pages, submitted to PR
Spin induced nonlinearities in the electron MHD regime
We consider the influence of the electron spin on the nonlinear propagation
of whistler waves. For this purpose a recently developed electron two-fluid
model, where the spin up- and down populations are treated as different fluids,
is adapted to the electron MHD regime. We then derive a nonlinear Schrodinger
equation for whistler waves, and compare the coefficients of nonlinearity with
and without spin effects. The relative importance of spin effects depend on the
plasma density and temperature as well as the external magnetic field strength
and the wave frequency. The significance of our results to various plasmas are
discussed.Comment: 5 page
Gravitational and magnetosonic waves in gamma-ray bursts
One of the possible sources of gamma-ray bursts are merging, compact
neutronstar binaries. More than 90% of the binding energy of such a binary is
released in the form of gravitational waves (GWs) in the last few seconds of
the spiral-in phase before the formation of a black hole. In this article we
investigate whether a fraction of this GW-energy is transferred to
magnetohydrodynamic waves in the magnetized plasma wind around the binary.
Using the 3+1 orthonormal tedrad formalism, we study the propagation of a
monochromatic, plane fronted, linearly polarized GW perpendicular to the
ambient magnetic field in an ultra-relativistic wind, first in the comoving and
then in the observer frame. A closed set of general relativistic
magnetohydrodynamic equations is derived in the form of conservation laws for
electric charge, matter energy, momentum and magnetic energy densities. We
linearize these equations under the action of a monochromatic GW, which acts as
a driver and find that fast magneto-acoustic waves grow, with amplitudes
proportional to the GW amplitude and frequency and the strength of the
background magnetic field.Comment: Accepted for publication in Astronomy & Astrophysics (A&A). 7 pages,
1 figur
Short wavelength quantum electrodynamical correction to cold plasma-wave propagation
The effect of short wavelength quantum electrodynamic (QED) correction on
plasma-wave propagation is investigated. The effect on plasma oscillations and
on electromagnetic waves in an unmagnetized as well as a magnetized plasma is
investigated. The effects of the short wavelength QED corrections are most
significant for plasma oscillations and for extraordinary modes. In particular,
the QED correction allow plasma oscillations to propagate, and the
extra-ordinary mode looses its stop band. The significance of our results is
discussed.Comment: 12 pages, 5 figure
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