12,959 research outputs found
Damping of electromagnetic waves due to electron-positron pair production
The problem of the backreaction during the process of electron-positron pair
production by a circularly polarized electromagnetic wave propagating in a
plasma is investigated. A model based on the relativistic Boltzmann-Vlasov
equation with a source term corresponding to the Schwinger formula for the pair
creation rate is used. The damping of the wave, the nonlinear up-shift of its
frequency due to the plasma density increase and the effect of the damping on
the wave polarization and on the background plasma acceleration are
investigated as a function of the wave amplitude.Comment: 11 pages, 5 figures; revtex
Pair Production Beyond the Schwinger Formula in Time-Dependent Electric Fields
We investigate electron-positron pair production in pulse-shaped electric
background fields using a non-Markovian quantum kinetic equation. We identify a
pulse-length range for subcritical fields still in the nonperturbative regime
where the number of produced pairs significantly exceeds that of a naive
expectation based on the Schwinger formula. From a conceptual viewpoint, we
find a remarkable quantitative agreement between the (real-time) quantum
kinetic approach and the (imaginary-time) effective action approach.Comment: 5 pages, 3 figures. Typos corrected and references added, PRD Versio
Dynamically assisted Schwinger mechanism
We study electron-positron pair creation {from} the Dirac vacuum induced by a
strong and slowly varying electric field (Schwinger effect) which is
superimposed by a weak and rapidly changing electromagnetic field (dynamical
pair creation). In the sub-critical regime where both mechanisms separately are
strongly suppressed, their combined impact yields a pair creation rate which is
{dramatically} enhanced. Intuitively speaking, the strong electric field lowers
the threshold for dynamical particle creation -- or, alternatively, the fast
electromagnetic field generates additional seeds for the Schwinger mechanism.
These findings could be relevant for planned ultra-high intensity lasers.Comment: 4 pages, 2 figure
Phase transition for the frog model
We study a system of simple random walks on graphs, known as frog model. This
model can be described as follows: There are active and sleeping particles
living on some graph G. Each active particle performs a simple random walk with
discrete time and at each moment it may disappear with probability 1-p. When an
active particle hits a sleeping particle, the latter becomes active. Phase
transition results and asymptotic values for critical parameters are presented
for Z^d and regular trees
Population synthesis of DA white dwarfs: constraints on soft X-ray spectra evolution
Extending the population synthesis method to isolated young cooling white
dwarfs we are able to confront our model assumptions with observations made in
ROSAT All-Sky Survey (Fleming et al., 1996). This allows us to check model
parameters such as evolution of spectra and separation of heavy elements in DA
WD envelopes. It seems like X-ray spectrum temperature of these objects is
given by the formula T_{X-ray} = min(T_eff, T_max). We have obtained DA WD's
birth rate and upper limit of the X-ray spectrum temperature: DA birth rate in cubic parsec per year and T_max = 41000 K. These values
are in good correspondence with values obtained by other authors (Liebert et
al., 2004; Wolff et al., 1996). From this fact we also conclude that our
population synthesis method is applicable to the population of close-by
isolated cooling white dwarfs as well as to the population of the isolated
cooling neutron stars.Comment: 4 pages, 3 figures, conference "European White Dwarf Workshop, 2010",
Tubingen, German
The Determination of the `Diffusion Coefficients' and the Stellar Wind Velocities for X-Ray Binaries
The distribution of neutron stars (NS's) is determined by stationary solution
of the Fokker-Planck equation. In this work using the observed period changes
for four systems: Vela X-1, GX 301-2, Her X-1 and Cen X-3 we determined D, the
'diffusion coefficient',-parameter from the Fokker-Planck equation. Using
strong dependence of D on the velocity for Vela X-1 and GX 301-2, systems
accreting from a stellar wind, we determined the stellar wind velocity. For
different assumptions for a turbulent velocity we obtained . It is in good agreement with the stellar wind velocity determined by
other methods. We also determined the specific characteristic time scales for
the 'diffusion processes' in X-ray pulsars. It is of order of 200 sec for
wind-fed pulsars and 1000-10000 sec for the disk accreting systems.Comment: 8 pages, Latex, no figures, accepted for publication to Astronomical
and Astrophysical Transactions (1995). Admin note 20Feb2000: original
(broken) version now paper.tex.orig in source; fixed version with two bad
equations set in verbatim used for PS, paper.tex in sourc
Quantum simulator for the Schwinger effect with atoms in bi-chromatic optical lattices
Ultra-cold atoms in specifically designed optical lattices can be used to
mimic the many-particle Hamiltonian describing electrons and positrons in an
external electric field. This facilitates the experimental simulation of (so
far unobserved) fundamental quantum phenomena such as the Schwinger effect,
i.e., spontaneous electron-positron pair creation out of the vacuum by a strong
electric field.Comment: 4 pages, 2 figures; minor corrections and improvements in text and in
figures; references adde
Momentum dependence in the dynamically assisted Sauter-Schwinger effect
Recently it has been found that the superposition of a strong and slow
electric field with a weaker and faster pulse can significantly enhance the
probability for non-perturbative electron-positron pair creation out of the
vacuum -- the dynamically assisted Sauter-Schwinger effect. Via the WKB method,
we estimate the momentum dependence of the pair creation probability and
compare it to existing numerical results. Besides the theoretical interest, a
better understanding of this pair creation mechanism should be helpful for the
planned experiments aiming at its detection.Comment: 4 pages RevTeX, 1 figur
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