317 research outputs found
Optical depth for VHE gamma-rays from distant sources from a generic EBL density
Very-high-energy (VHE; E>100GeV) gamma-rays from distant sources suffer
attenuation through pair-production with low energy photons from the diffuse
extragalactic photon fields in the ultraviolet (UV) to far-infrared (FIR)
(commonly referred to as Extragalactic Background Light; EBL). When modeling
the intrinsic spectra of the VHE gamma-ray sources it is crucial to correctly
account for the attenuation. Unfortunately, direct measurements of the EBL are
difficult and the knowledge about the EBL over certain wavelength ranges is
poor. To calculate the EBL attenuation usually predictions from theoretical
models are used. Recently, the limits on the EBL from direct and indirect
methods have narrowed down the possible EBL range and many of the previous
models are in conflict with these limits. We propose a new generic EBL density
(not a complete model), which is in compliance with the new EBL limits. EBL
evolution with redshift is included in the calculation in a very simple but
effective ad-hoc way. Properties of this generic EBL are discussed.Comment: Proceedings of the workshop 'High Energy Phenomena in Relativistic
Outflows' (HEPRO), Dublin, 24-28 September 200
Infra-red divergences in plane wave backgrounds
We show that the emission of soft photons via nonlinear Compton scattering in
a pulsed plane wave (laser field) is in general infra-red divergent. We give
examples of both soft and soft-collinear divergences, and we pay particular
attention to the case of crossed fields in both classical and quantum theories.Comment: 15 pages, 7 figure
Vector boson in constant electromagnetic field
The propagator and complete sets of in- and out-solutions of wave equation,
together with Bogoliubov coefficients, relating these solutions, are obtained
for vector -boson (with gyromagnetic ratio ) in a constant
electromagnetic field. When only electric field is present the Bogoliubov
coefficients are independent of boson polarization and are the same as for
scalar boson. When both electric and magnetic fields are present and collinear,
the Bogoliubov coefficients for states with boson spin perpendicular to the
field are again the same as in scalar case. For spin along (against) the
magnetic field the Bogoliubov coefficients and the contributions to the
imaginary part of the Lagrange function in one loop approximation are obtained
from corresponding expressions for scalar case by substitution
. For gyromagnetic ratio the vector boson interaction
with constant electromagnetic field is described by the functions, which can be
expected by comparing wave functions for scalar and Dirac particle in constant
electromagnetic field.Comment: 20 pages, LATEX2e, no figure
Signatures of High-Intensity Compton Scattering
We review known and discuss new signatures of high-intensity Compton
scattering assuming a scenario where a high-power laser is brought into
collision with an electron beam. At high intensities one expects to see a
substantial red-shift of the usual kinematic Compton edge of the photon
spectrum caused by the large, intensity dependent, effective mass of the
electrons within the laser beam. Emission rates acquire their global maximum at
this edge while neighbouring smaller peaks signal higher harmonics. In
addition, we find that the notion of the centre-of-mass frame for a given
harmonic becomes intensity dependent. Tuning the intensity then effectively
amounts to changing the frame of reference, going continuously from inverse to
ordinary Compton scattering with the centre-of-mass kinematics defining the
transition point between the two.Comment: 25 pages, 16 .eps figure
Consistency restrictions on maximal electric field strength in QFT
QFT with an external background can be considered as a consistent model only
if backreaction is relatively small with respect to the background. To find the
corresponding consistency restrictions on an external electric field and its
duration in QED and QCD, we analyze the mean energy density of quantized fields
for an arbitrary constant electric field E, acting during a large but finite
time T. Using the corresponding asymptotics with respect to the dimensionless
parameter , one can see that the leading contributions to the energy are
due to the creation of paticles by the electric field. Assuming that these
contributions are small in comparison with the energy density of the electric
background, we establish the above-mentioned restrictions, which determine, in
fact, the time scales from above of depletion of an electric field due to the
backreactionComment: 7 pages; version accepted for publication in Phys. Rev. Lett.; added
one ref. and some comment
The probability distribution of the number of electron-positron pairs produced in a uniform electric field
The probability-generating function of the number of electron-positron pairs
produced in a uniform electric field is constructed. The mean and variance of
the numbers of pairs are calculated, and analytical expressions for the
probability of low numbers of electron-positron pairs are given. A recursive
formula is derived for evaluating the probability of any number of pairs. In
electric fields of supercritical strength |eE| > \pi m^2/ \ln 2, where e is the
electron charge, E is the electric field, and m is the electron mass, a
branch-point singularity of the probability-generating function penetrates the
unit circle |z| = 1, which leads to the asymptotic divergence of the cumulative
probability. This divergence indicates a failure of the continuum limit
approximation. In the continuum limit and for any field strength, the positive
definiteness of the probability is violated in the tail of the distribution.
Analyticity, convergence, and positive definiteness are restored upon the
summation over discrete levels of electrons in the normalization volume.
Numerical examples illustrating the field strength dependence of the asymptotic
behavior of the probability distribution are presented.Comment: 7 pages, REVTeX, 4 figures; new references added; a short version of
this e-print has appeared in PR
Dirac fermions in strong electric field and quantum transport in graphene
Our previous results on the nonperturbative calculations of the mean current
and of the energy-momentum tensor in QED with the T-constant electric field are
generalized to arbitrary dimensions. The renormalized mean values are found;
the vacuum polarization and particle creation contributions to these mean
values are isolated in the large T-limit, the vacuum polarization contributions
being related to the one-loop effective Euler-Heisenberg Lagrangian.
Peculiarities in odd dimensions are considered in detail. We adapt general
results obtained in 2+1 dimensions to the conditions which are realized in the
Dirac model for graphene. We study the quantum electronic and energy transport
in the graphene at low carrier density and low temperatures when quantum
interference effects are important. Our description of the quantum transport in
the graphene is based on the so-called generalized Furry picture in QED where
the strong external field is taken into account nonperturbatively; this
approach is not restricted to a semiclassical approximation for carriers and
does not use any statistical assumtions inherent in the Boltzmann transport
theory. In addition, we consider the evolution of the mean electromagnetic
field in the graphene, taking into account the backreaction of the matter field
to the applied external field. We find solutions of the corresponding
Dirac-Maxwell set of equations and with their help we calculate the effective
mean electromagnetic field and effective mean values of the current and the
energy-momentum tensor. The nonlinear and linear I-V characteristics
experimentally observed in both low and high mobility graphene samples is quite
well explained in the framework of the proposed approach, their peculiarities
being essentially due to the carrier creation from the vacuum by the applied
electric field.Comment: 24 pages, 1 figure; version accepted for publication in Physical
Review D., some comments adde
Production of high energy particles in laser and Coulomb fields and e^+e^- antenna
A strong laser field and the Coulomb field of a nucleus can produce
e^{+}e^{-} pairs. It is shown for the first time that there is a large
probability that electrons and positrons created in this process collide after
one or several oscillations of the laser field. These collisions can take place
at high energy resulting in several phenomena. The quasielastic collision
e^{+}e^{-} -> e^{+}e^{-} allows acceleration of leptons in the laser field to
higher energies. The inelastic collisions allow production of high energy
photons e^{+}e^{-}-> 2 gamma and muons, e^{+}e^{-} -> mu^{+}mu^{-}. The yield
of high-energy photons and muons produced via this mechanism exceeds
exponentially their production through conventional direct creation in laser
and Coulomb fields. A relation of the phenomena considered with the
antenna-mechanism of multiphoton absorption in atoms is discussed.Comment: 4 page
Black hole collapse simulated by vacuum fluctuations with a moving semi-transparent mirror
Creation of scalar massless particles in two-dimensional Minkowski
space-time--as predicted by the dynamical Casimir effect--is studied for the
case of a semitransparent mirror initially at rest, then accelerating for some
finite time, along a trajectory that simulates a black hole collapse (defined
by Walker, and Carlitz and Willey), and finally moving with constant velocity.
When the reflection and transmission coefficients are those in the model
proposed by Barton, Calogeracos, and Nicolaevici [r(w)=-i\alpha/(\w+i\alpha)
and s(w)=\w/(\w+i\alpha), with ], the Bogoliubov coefficients
on the back side of the mirror can be computed exactly. This allows us to prove
that, when is very large (case of an ideal, perfectly reflecting
mirror) a thermal emission of scalar massless particles obeying Bose-Einstein
statistics is radiated from the mirror (a black body radiation), in accordance
with results previously obtained in the literature. However, when is
finite (semitransparent mirror, a physically realistic situation) the striking
result is obtained that the thermal emission of scalar massless particles obeys
Fermi-Dirac statistics. We also show here that the reverse change of statistics
takes place in a bidimensional fermionic model for massless particles, namely
that the Fermi-Dirac statistics for the completely reflecting situation will
turn into the Bose-Einstein statistics for a partially reflecting, physical
mirror.Comment: 13 pages, no figures, version to appear in Physical Review
Radiating electron source generation in ultraintense laser-foil interactions
A radiating electron source is shown to be created by a laser pulse (with intensity of 10^23 W/cm^2 and duration equal to 30 fs) interacting with a near-critical density plasma. It is shown that the back radiation reaction resulting from high energy synchrotron radiation tends to counteract the action of the ponderomotive force. This enhances the collective dynamics of the radiating electrons in the highest field areas, resulting in the production of a compact radiation source (containing 80% of the synchrotron radiation emission), with an energy on the order of tens of MeV over the laser pulse duration. These phenomena are investigated using a QED-particle-in-cell code, and compared with a kinetic model accounting for the radiation reaction force in the electron distribution function. The results shed new light on electron-photon sources at ultra-high laser intensities and could be tested on future laser facilities
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