93 research outputs found
Photon propagation in slowly varying electromagnetic fields
We study the effective theory of soft photons in slowly varying
electromagnetic background fields at one-loop order in QED. This is of
relevance for the study of all-optical signatures of quantum vacuum
nonlinearity in realistic electromagnetic background fields as provided by
high-intensity lasers. The central result derived in this article is a new
analytical expression for the photon polarization tensor in two linearly
polarized counter-propagating pulsed Gaussian laser beams. As we treat the peak
field strengths of both laser beams as free parameters this field configuration
can be considered as interpolating between the limiting cases of a purely
right- or left-moving laser beam (if one of the peak field strengths is set to
zero) and the standing-wave type scenario with two counter-propagating beams of
equal strength.Comment: 6 pages, 1 figure; contribution to the Workshop Proceedings of the
International Workshop SFP-2016: Strong Field Problems in Quantum Theory,
Tomsk, Russia, June 6-12, 201
The photon polarization tensor in a homogeneous magnetic or electric field
We revisit the photon polarization tensor in a homogeneous external magnetic
or electric field. The starting point of our considerations is the momentum
space representation of the one-loop photon polarization tensor in the presence
of a homogeneous electromagnetic field, known in terms of a double parameter
integral. Our focus is on explicit analytical insights for both on- and
off-the-light-cone dynamics in a wide range of well-specified physical
parameter regimes, ranging from the perturbative to the manifestly
nonperturbative strong field regime. The basic ideas underlying
well-established approximations to the photon polarization tensor are carefully
examined and critically reviewed. In particular, we systematically keep track
of all contributions, both the ones to be neglected and those to be taken into
account explicitly, to all orders. This allows us to study their ranges of
applicability in a much more systematic and rigorous way. We point out the
limitations of such approximations and manage to go beyond at several
instances.Comment: 43 pages, 2 figures; two misprints in Eqs. (118) and (142) corrected
(a factor 2^(-2/3) was missing
Quark-antiquark static energy from a restricted Fourier transform
We provide a fully analytical determination of the perturbative
quark-antiquark static energy in position space as defined by a restricted
Fourier transformation from momentum to position space. Such a determination is
complicated by the fact that the static energy genuinely decomposes into a
strictly perturbative part (made up of contributions , with
) which is conventionally evaluated in momentum space, and a
so-called ultrasoft part (including terms ,
with and ) which, conversely, is naturally evaluated
in position space. Our approach facilitates the explicit determination of the
static energy in position space at the accuracy with which the perturbative
potential in momentum space is known, i.e., presently up to order .Comment: 16 pages, 6 figures; some clarifications added, matches journal
versio
Probing vacuum birefringence using x-ray free electron and optical high-intensity lasers
Vacuum birefringence is one of the most striking predictions of strong field
quantum electrodynamics: Probe photons traversing a strong field region can
indirectly sense the applied "pump" electromagnetic field via quantum
fluctuations of virtual charged particles which couple to both pump and probe
fields. This coupling is sensitive to the field alignment and can effectively
result in two different indices of refraction for the probe photon polarization
modes giving rise to a birefringence phenomenon. In this article we perform a
dedicated theoretical analysis of the proposed discovery experiment of vacuum
birefringence at a x-ray free electron laser/optical high-intensity laser
facility. Describing both pump and probe laser pulses realistically in terms of
their macroscopic electromagnetic fields, we go beyond previous analyses by
accounting for various effects not considered before in this context. Our study
facilitates stringent quantitative predictions and optimizations of the signal
in an actual experiment.Comment: 23 pages, 4 figure
Photon propagation in slowly varying inhomogeneous electromagnetic fields
Starting from the Heisenberg-Euler effective Lagrangian, we determine the
photon current and photon polarization tensor in inhomogeneous, slowly varying
electromagnetic fields. To this end, we consider background field
configurations varying in both space and time, paying special attention to the
tensor structure. As a main result, we obtain compact analytical expressions
for the photon polarization tensor in realistic Gaussian laser pulses, as
generated in the focal spots of high-intensity lasers. These expressions are of
utmost importance for the investigation of quantum vacuum nonlinearities in
realistic high-intensity laser experiments.Comment: 15 pages, 1 figure; some clarifications added, matches journal
versio
Probing vacuum polarization effects with high-intensity lasers
These notes provide a pedagogical introduction to the theoretical study of vacuum
polarization effects in strong electromagnetic fields as provided by state-of-the-art high-intensity lasers.
Quantum vacuum fluctuations give rise to effective couplings between electromagnetic fields, thereby
supplementing Maxwell’s linear theory of classical electrodynamics with nonlinearities. Resorting to a
simplified laser pulse model, allowing for explicit analytical insights, we demonstrate how to efficiently
analyze all-optical signatures of these effective interactions in high-intensity laser experiments. Moreover,
we highlight several key features relevant for the accurate planning and quantitative theoretical analysis
of quantum vacuum nonlinearities in the collision of high-intensity laser pulses
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