3,014 research outputs found
Ultrarelativistic quasiclassical wave functions in strong laser and atomic fields
The problem of an ultrarelativistic charge in the presence of an atomic and a
plane-wave field is investigated in the quasiclassical regime by including
exactly the effects of both background fields. Starting from the quasiclassical
Green's function obtained in [Phys. Lett. B \textbf{717}, 224 (2012)], the
corresponding in- and out-wave functions are derived in the experimentally
relevant case of the particle initially counterpropagating with respect to the
plane wave. The knowledge of these electron wave functions opens the
possibility of investigating a variety of problems in strong-field QED, where
both the atomic field and the laser field are strong enough to be taken into
account exactly from the beginning in the calculations.Comment: 24 pages, no figure
Investigation of classical radiation reaction with aligned crystals
Classical radiation reaction is the effect of the electromagnetic field
emitted by an accelerated electric charge on the motion of the charge itself.
The self-consistent underlying classical equation of motion including
radiation-reaction effects, the Landau-Lifshitz equation, has never been tested
experimentally, in spite of the first theoretical treatments of radiation
reaction having been developed more than a century ago. Here we show that
classical radiation reaction effects, in particular those due to the near
electromagnetic field, as predicted by the Landau-Lifshitz equation, can be
measured in principle using presently available facilities, in the energy
emission spectrum of electrons crossing a
- thick diamond crystal in the axial channeling regime. Our
theoretical results indicate the feasibility of the suggested setup, e.g., at
the CERN Secondary Beam Areas (SBA) beamlines.Comment: 8 pages, 5 figure
Study of symmetry in F(R) theory of gravity
An action in which the Ricci scalar is nonminimally coupled with a scalar
field and contains higher order curvature invariant terms carries a conserved
current under certain conditions that decouples geometric part from the scalar
field. The conserved current relates the pair of arbitrary coupling parameters
and with the gravitational field variable, where
is the Brans-Dicke coupling parameter. The existence of such
conserved current may be helpful to sketch the cosmological evolution from its
early age till date in a single frame.Comment: 6 page
Effect of a strong laser field on photoproduction by relativistic nuclei
We study the influence of a strong laser field on the Bethe-Heitler
photoproduction process by a relativistic nucleus. The laser field propagates
in the same direction as the incoming high-energy photon and it is taken into
account exactly in the calculations. Two cases are considered in detail. In the
first case, the energy of the incoming photon in the nucleus rest frame is much
larger than the electron's rest energy. The presence of the laser field may
significantly suppress the photoproduction rate at soon available values of
laser parameters. In the second case, the energy of the incoming photon in the
rest frame of the nucleus is less than and close to the electron-positron pair
production threshold. The presence of the laser field allows for the pair
production process and the obtained electron-positron rate is much larger than
in the presence of only the laser and the nuclear field. In both cases we have
observed a strong dependence of the rate on the mutual polarization of the
laser field and of the high-energy photon and the most favorable configuration
is with laser field and high-energy photon linearly polarized in the same
direction. The effects discussed are in principle measurable with presently
available proton accelerators and laser systems.Comment: 21 pages, 4 figure
Angular distribution of high-energy photoproduction close to the end of spectrum
We consider the differential cross section of electron-positron pair
production by a high-energy photon in a strong Coulomb field close to the end
of the electron or positron spectrum. When the momentum transfer largely
exceeds the electron mass, the cross section is obtained analytically in a
compact form. Coulomb corrections essentially modify the cross section even for
moderate values of the nuclear charge number . In the same kinematical
region, the angular distribution for bound-free pair production,
bremsstrahlung, and photorecombination is also obtained.Comment: 12 pages, 4 figure
Pair production in a strong slowly varying magnetic field: the effect of a background gravitational field
The production probability of an pair in the presence of a strong,
uniform and slowly varying magnetic field is calculated by taking into account
the presence of a background gravitational field. The curvature of the
spacetime metric induced by the gravitational field not only changes the
transition probabilities calculated in the Minkowski spacetime but also primes
transitions that are strictly forbidden in absence of the gravitational field.Comment: 56 pages, no figure
Coulomb-Blockade directional coupler
A tunable directional coupler based on Coulomb Blockade effect is presented.
Two electron waveguides are coupled by a quantum dot to an injector waveguide.
Electron confinement is obtained by surface Schottky gates on single
GaAs/AlGaAs heterojunction. Magneto-electrical measurements down to 350 mK are
presented and large transconductance oscillations are reported on both outputs
up to 4.2 K. Experimental results are interpreted in terms of Coulomb Blockade
effect and the relevance of the present design strategy for the implementation
of an electronic multiplexer is underlined.Comment: 4 pages, 4 figures, to be published in Applied Physics Letter
Apparatus for timeâresolved measurements of acoustic birefringence in particle dispersions
An apparatus for timeâresolved measurements of the birefringence induced in a particle suspension by an acoustic wave pulse is described. Efficient acoustic coupling is obtained by operating near the transducer resonant frequency and by matching the acoustic impedances of the cell constituents. An almostâoverdamped acoustic configuration can alternatively be employed whenever a faster response is needed. Careful design of the optical setup and of the detection unit minimize diffraction and stressâbirefringence parasitic effects and yields a good responsivity at fairly low acoustic intensities. A test of the apparatus on a colloidal suspension of PTFE rodlike particles is presented and discussed
Energy transfer in nonlinear network models of proteins
We investigate how nonlinearity and topological disorder affect the energy
relaxation of local kicks in coarse-grained network models of proteins. We find
that nonlinearity promotes long-range, coherent transfer of substantial energy
to specific, functional sites, while depressing transfer to generic locations.
Remarkably, transfer can be mediated by the self-localization of discrete
breathers at distant locations from the kick, acting as efficient
energy-accumulating centers.Comment: 4 pages, 3 figure
Nonlinear double Compton scattering in the full quantum regime
A detailed analysis of the process of two photon emission by an electron
scattered from a high-intensity laser pulse is presented. The calculations are
performed in the framework of strong-field QED and include exactly the presence
of the laser field, described as a plane wave. We investigate the full quantum
regime of interaction, where photon recoil plays an essential role in the
emission process, and substantially alters the emitted photon spectra as
compared to those in previously-studied regimes. We provide a semiclassical
explanation for such differences, based on the possibility of assigning a
trajectory to the electron in the laser field before and after each quantum
photon emission. Our numerical results indicate the feasibility of
investigating experimentally the full quantum regime of nonlinear double
Compton scattering with already available plasma-based electron accelerator and
laser technology.Comment: 5 pages, 3 figure
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