24 research outputs found
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
Master formulas for photon amplitudes in a combined constant and plane-wave background field
The worldline formalism has previously been used for deriving compact master
formulas for the QED - photon amplitudes in vacuum, in a constant field and
in a plane-wave field. Here we carry this program one step further by deriving
master formulas for the scalar and spinor QED -photon amplitudes in the
background of the "parallel" special case of a combined constant and plane-wave
field.Comment: 20 pages, no figures, typo in eq. (58) correcte
Stimulated photon emission from the vacuum
We study the effect of stimulated photon emission from the vacuum in strong
space-time-dependent electromagnetic fields. We emphasize the viewpoint that
the vacuum subjected to macroscopic electromagnetic fields with at least one
nonzero electromagnetic field invariant, as, e.g., attainable by superimposing
two laser beams, can represent a source term for outgoing photons. We believe
that this view is particularly intuitive and allows for a straightforward and
intuitive study of optical signatures of quantum vacuum nonlinearity in
realistic experiments involving the collision of high-intensity laser pulses,
and exemplify this view for the vacuum subjected to a strong standing
electromagnetic wave as generated in the focal spot of two counterpropagating,
linearly polarized, high-intensity laser pulses. Focusing on a comparably
simple electromagnetic field profile, which should nevertheless capture the
essential features of the electromagnetic fields generated in the focal spots
of real high-intensity laser beams, we provide estimates for emission
characteristics and the numbers of emitted photons attainable with present and
near future high-intensity laser facilities.Comment: 19 pages, 4 figures. Numerical results corrected: The peak electric
field E is given by \sqrt{2*I}, with mean intensity I. Accounting for the
factor of 2 missed previously, the experimental predictions \sim E^3 are
increased by a factor of
Neutrino interactions with a weak slowly varying electromagnetic field
We derive the effective action for processes involving two neutrinos and two
photons at energies much below the electron mass. We discuss several
applications in which one or both photons are replaced by external fields. In
particular, Cherenkov radiation and neutrino pair production in weak external
fields are investigated for massive Dirac neutrinos.Comment: 7 pages, no figure
Assisted neutrino pair production in combined external fields
Neutrino--antineutrino () pair production is one of the main
processes responsible for the energy loss of stars. Apart from the collision of
two () or three ()
real photons, photon decay and photon collisions in the presence of nuclear
Coulomb fields or external magnetic fields have been considered previously.
Here, we study the low-energy photon decay into a pair of neutrino and
antineutrino in the presence of a combined homogeneous magnetic field and the
Coulomb field of a nucleus with charge number .Comment: 6 pages, 2 figure
Polarized positron beams via intense two-color laser pulses
Generation of ultrarelativistic polarized positrons during interaction of an
ultrarelativistic electron beam with a counterpropagating two-color petawatt
laser pulse is investigated theoretically. Our Monte Carlo simulation based on
a semi-classical model, incorporates photon emissions and pair productions,
using spin-resolved quantum probabilities in the local constant field
approximation, and describes the polarization of electrons and positrons for
the pair production and photon emission processes, as well as the classical
spin precession in-between. The main reason of the polarization is shown to be
the spin-asymmetry of the pair production process in strong external fields,
combined with the asymmetry of the two-color laser field. Employing a feasible
scenario, we show that highly polarized positron beams, with a polarization
degree of , can be produced in a femtosecond time scale,
with a small angular divergence, mrad, and high density cm. The laser-driven positron source, along with laser
wakefield acceleration, may pave the way to small scale facilities for high
energy physics studies
Single-shot determination of spin-polarization for ultrarelativistic electron beams via nonlinear Compton scattering
Impacts of spin-polarization of an ultrarelativistic electron beam head-on
colliding with a strong laser pulse on emitted photon spectra and electron
dynamics have been investigated in the quantum radiation regime. We simulate
photon emissions quantum mechanically and electron dynamics semiclassically via
taking spin-resolved radiation probabilities in the local constant field
approximation. A small ellipticity of the laser field brings about an asymmetry
in angle-resolved photon spectrum, which sensitively relies on the polarization
of the electron beam. The asymmetry is particularly significant in high-energy
photon spectra, and is employed for the polarization detection of a high-energy
electron beam with extraordinary precision, e.g., better than 0.3\% for a
few-GeV electron beam at a density of the scale of cm with
currently available strong laser fields. This method demonstrates for the first
time a way of single-shot determination of polarization for ultrarelativistic
electron beams via nonlinear Compton scattering. A similar method based on the
asymmetry in the electron momentum distribution after the interaction due to
spin-dependent radiation reaction is proposed as well
Ultrarelativistic polarized positron jets via collision of electron and ultraintense laser beams
Relativistic spin-polarized positron beams are indispensable for future
electron-positron colliders to test modern high-energy physics theory with high
precision. However, present techniques require very large scale facilities for
those experiments.
We put forward a novel efficient way for generating ultrarelativistic
polarized positron beams employing currently available laser fields. For this
purpose the generation of polarized positrons via multiphoton Breit-Wheeler
pair production and the associated spin dynamics in single-shot interaction of
an ultraintense laser pulse with an ultrarelativistic electron beam is
investigated in the quantum radiation-dominated regime. A specifically tailored
small ellipticity of the laser field is shown to promote splitting of the
polarized particles along the minor axis of laser polarization into two
oppositely polarized beams. In spite of radiative de-polarization, a dense
positron beam with up to about 90\% polarization can be generated in tens of
femtoseconds. The method may eventually usher high-energy physics studies into
smaller-scale laser laboratories