25 research outputs found
Anisotropy of Electrons Accelerated by a High-Intensity Laser Pulse
We describe a realistic model for a focused high-intensity laser pulse in
three dimensions. Relativistic dynamics of an electron submitted to such pulse
is described by equations of motion with ponderomotive potential depending on a
single free parameter in the problem, which we refer to as the "asymmetry
parameter". It is shown that the asymmetry parameter can be chosen to provide
quantitative agreement of the developed theory with experimental results of
Malka et al. [Phys. Rev. Lett. 78, 3314 (1997)] who detected angular asymmetry
in the spatial pattern of electrons accelerated in vacuum by a high-intensity
laser pulse
Unruh quantization in presence of a condensate
We have shown that the Unruh quantization scheme can be realized in Minkowski
spacetime in the presence of Bose-Einstein condensate containing infinite
average number of particles in the zero boost mode and located basically inside
the light cone. Unlike the case of an empty Minkowski spacetime the condensate
provides the boundary conditions necessary for the Fulling quantization of the
part of the field restricted only to the Rindler wedge of Minkowski spacetime.Comment: 4 page
Generation of harmonics by a focused laser beam in vacuum
Generation of odd harmonics by a super strong focused laser beam in vacuum is
considered. The process occurs due to the plural light-by-light scattering
effect. In the leading order of perturbation theory, generation of th
harmonic is described by a loop diagram with external incoming, and
two outgoing legs. A frequency of the beam is assumed to be much smaller than
the Compton frequency, so that the approximation of a constant uniform
electromagnetic field is valid locally. Analytical expressions for angular
distribution of generated photons, as well as for their total emission rate are
obtained in the leading order of perturbation theory. Influence of higher-order
diagrams is studied numerically using the formalism of Intense Field QED. It is
shown that the process may become observable for the beam intensity of the
order of .Comment: 4 pages, 3 figures. Added comparison with the probability of SHG in
the crossed beam setup, several abridgments mad
An example of a uniformly accelerated particle detector with non-Unruh response
We propose a scalar background in Minkowski spacetime imparting constant
proper acceleration to a classical particle. In contrast to the case of a
constant electric field the proposed scalar potential does not create
particle-antiparticle pairs. Therefore an elementary particle accelerated by
such field is a more appropriate candidate for an "Unruh-detector" than a
particle moving in a constant electric field. We show that the proposed
detector does not reveal the universal thermal response of the Unruh type.Comment: 12 pages, 1 figur
"Shaking" of an atom in a non-stationary cavity
We consider an atom interacting with a quantized electromagnetic field inside
a cavity with variable parameters. The atom in the ground state located in the
initially empty cavity can be excited by variation of cavity parameters. We
have discovered two mechanisms of atomic excitation. The first arises due to
the interaction of the atom with the non-stationary electromagnetic field
created by modulation of cavity parameters. If the characteristic time of
variation of cavity parameters is of the order of the atomic transition time,
the processes of photon creation and atomic excitation are going on
simultaneously and hence excitation of the atom cannot be reduced to trivial
absorption of the photons produced by the dynamical Casimir effect. The second
mechanism is "shaking" of the atom due to fast modulation of its ground state
Lamb shift which takes place as a result of fast variation of cavity arameters.
The last mechanism has no connection with the vacuum dynamical Casimir effect.
Moreover, it opens a new channel of photon creation in the non-stationary
cavity. Nevertheless, the process of photon creation is altered by the presence
of the atom in the cavity, even if one disregards the existence of the new
channel. In particular, it removes the restriction for creation of only even
number of photons and also changes the expectation value for the number of
created photons. Our consideration is based on a simple model of a two-level
atom interacting with a single mode of the cavity field. Qualitatively our
results are valid for a real atom in a physical cavity.Comment: 12 pages,4 *.eps figures, this version is identical to the one to be
published in Physics Letters A (in print
On "Schwinger Mechanism for Gluon Pair Production in the Presence of Arbitrary Time Dependent Chromo-Electric Field"
Recently the paper "Schwinger Mechanism for Gluon Pair Production in the
Presence of Arbitrary Time Dependent Chromo-Electric Field" by G. C. Nayak was
published [Eur. Phys. J. C 59, 715 (2009); arXiv:0708.2430]. Its aim is to
obtain an exact expression for the probability of non-perturbative gluon pair
production per unit time per unit volume and per unit transverse momentum in an
arbitrary time-dependent chromo-electric background field. We believe that the
obtained expression is open to question. We demonstrate its inconsistency on
some well-known examples. We think that this is a consequence of using the
so-called "shift theorem" [arXiv:hep-th/0609192] in deriving the expression for
the probability. We make some critical comments on the theorem and its
applicability to the problem in question.Comment: 4 page
Probing vacuum birefringence by phase-contrast Fourier imaging under fields of high-intensity lasers
In vacuum high-intensity lasers can cause photon-photon interaction via the
process of virtual vacuum polarization which may be measured by the phase
velocity shift of photons across intense fields. In the optical frequency
domain, the photon-photon interaction is polarization-mediated described by the
Euler-Heisenberg effective action. This theory predicts the vacuum
birefringence or polarization dependence of the phase velocity shift arising
from nonlinear properties in quantum electrodynamics (QED). We suggest a method
to measure the vacuum birefringence under intense optical laser fields based on
the absolute phase velocity shift by phase-contrast Fourier imaging. The method
may serve for observing effects even beyond the QED vacuum polarization.Comment: 14 pages, 9 figures. Accepted by Applied Physics
Quantum field aspect of Unruh problem
It is shown using both conventional and algebraic approach to quantum field
theory that it is impossible to perform quantization on Unruh modes in
Minkowski spacetime. Such quantization implies setting boundary condition for
the quantum field operator which changes topological properties and symmetry
group of spacetime and leads to field theory in two disconnected left and right
Rindler spacetimes. It means that "Unruh effect" does not exist.Comment: LaTeX, 13 pages, 1 figur
Vacuum instability in external fields
We study particles creation in arbitrary space-time dimensions by external
electric fields, in particular, by fields, which are acting for a finite time.
The time and dimensional analysis of the vacuum instability is presented. It is
shown that the distributions of particles created by quasiconstant electric
fields can be written in a form which has a thermal character and seems to be
universal. Its application, for example, to the particles creation in external
constant gravitational field reproduces the Hawking temperature exactly.Comment: 36 pages, LaTe
The quantum vacuum at the foundations of classical electrodynamics
In the classical theory of electromagnetism, the permittivity and the
permeability of free space are constants whose magnitudes do not seem to
possess any deeper physical meaning. By replacing the free space of classical
physics with the quantum notion of the vacuum, we speculate that the values of
the aforementioned constants could arise from the polarization and
magnetization of virtual pairs in vacuum. A classical dispersion model with
parameters determined by quantum and particle physics is employed to estimate
their values. We find the correct orders of magnitude. Additionally, our simple
assumptions yield an independent estimate for the number of charged elementary
particles based on the known values of the permittivity and the permeability,
and for the volume of a virtual pair. Such interpretation would provide an
intriguing connection between the celebrated theory of classical
electromagnetism and the quantum theory in the weak field limit.Comment: Accepted in Applied Physics B: Special Issue for the 50 years of the
laser. Comments are welcome