9 research outputs found
All Stable Characteristic Classes of Homological Vector Fields
An odd vector field on a supermanifold is called homological, if
. The operator of Lie derivative makes the algebra of smooth
tensor fields on into a differential tensor algebra. In this paper, we give
a complete classification of certain invariants of homological vector fields
called characteristic classes. These take values in the cohomology of the
operator and are represented by -invariant tensors made up of the
homological vector field and a symmetric connection on by means of tensor
operations.Comment: 17 pages, references and comments adde
Photon polarization tensor in circularly polarized Hermite- and Laguerre-Gaussian beams
We derive analytical expressions for the photon polarization tensor in
circularly polarized Hermite- and Laguerre-Gaussian beams, complementing the
corresponding results for linearly polarized beams obtained recently. As they
are based upon a locally constant field approximation of the one-loop
Heisenberg-Euler effective Lagrangian for quantum electrodynamics (QED) in
constant fields, our results are generically limited to slowly varying
electromagnetic fields, varying on spatial (temporal) scales much larger than
the Compton wavelength (time) of the electron.Comment: 6 pages; Contribution to the LPHYS'17 Conference Proceeding
X-ray photon scattering at a focused high-intensity laser pulse
We study x-ray photon scattering in the head-on collision of an XFEL pulse
and a focused high-intensity laser pulse, described as paraxial
Laguerre-Gaussian beam of arbitrary mode composition. For adequately chosen
relative orientations of the polarization vectors of the colliding laser
fields, this gives rise to a vacuum birefringence effect manifesting itself in
polarization flipped signal photons. Throughout this article the XFEL is
assumed to be mildly focused to a waist larger than that of the high-intensity
laser beam. As previously demonstrated for the special case of a fundamental
paraxial Gaussian beam, this scenario is generically accompanied by a
scattering phenomenon of x-ray energy signal photons outside the forward cone
of the XFEL beam, potentially assisting the detection of the effect in
experiment. Here, we study the fate of the x-ray scattering signal under
exemplary deformations of the transverse focus profile of the high-intensity
pump.Comment: 21 pages, 3 figure
Photon polarization tensor in pulsed Hermite- and Laguerre-Gaussian beams
In this article, we provide analytical expressions for the photon
polarization tensor in pulsed Hermite- and Laguerre-Gaussian laser beams. Our
results are based on a locally constant field approximation of the one-loop
Heisenberg-Euler effective Lagrangian for quantum electrodynamics. Hence, by
construction they are limited to slowly varying electromagnetic fields, varying
on spatial and temporal scales significantly larger than the Compton
wavelength/time of the electron. The latter criterion is fulfilled by all laser
beams currently available in the laboratory. Our findings will, e.g., be
relevant for the study of vacuum birefringence experienced by probe photons
brought into collision with a high-intensity laser pulse which can be
represented as a superposition of either Hermite- or Laguerre-Gaussian modes.Comment: 18 pages, 1 figur
Enhancing quantum vacuum signatures with tailored laser beams
We demonstrate that tailored laser beams provide a powerful means to make
quantum vacuum signatures in strong electromagnetic fields accessible in
experiment. Typical scenarios aiming at the detection of quantum vacuum
nonlinearities at the high-intensity frontier envision the collision of focused
laser pulses. The effective interaction of the driving fields mediated by
vacuum fluctuations gives rise to signal photons encoding the signature of
quantum vacuum nonlinearity. Isolating a small number of signal photons from
the large background of the driving laser photons poses a major experimental
challenge. The main idea of the present work is to modify the far-field
properties of a driving laser beam to exhibit a field-free hole in its center,
thereby allowing for an essentially background free measurement of the signal
scattered in the forward direction. Our explicit construction makes use of a
peculiar far-field/focus duality.Comment: 5 pages, 3 figures; presentation improved, matches PRD versio