14,036 research outputs found
On the problem of relativistic particles motion in strong magnetic field and dense matter
We consider a problem of electron motion in different media and magnetic
field. It is shown that in case of nonmoving medium and constant homogenious
magnetic field the electron energies are quantized. We also discuss the general
problem of eigenvectors and eigenvalues of a given class of Hamiltonians. We
examine obtained exact solutions for the particular case of the electron motion
in a rotating neutron star with account for matter and magnetic field effects.
We argue that all of these considerations can be usefull for astrophysical
applications
Polarization of the electron and positron produced in combined Coulomb and strong laser fields
The process of production in the superposition of a Coulomb and a
strong laser field is considered. The pair production rate integrated over the
momentum and summed over the spin projections of one of the particles is
derived exactly in the parameters of the laser field and in the Born
approximation with respect to the Coulomb field. The case of a monochromatic
circularly polarized laser field is considered in detail. A very compact
analytical expression of the pair production rate and its dependence on the
polarization of one of the created particles is obtained in the quasiclassical
approximation for the experimentally relevant case of an undercritical laser
field. As a result, the polarization of the created electron (positron) is
derived.Comment: 16 pages, no figure
Hyperbolic carbon nanoforest for phase matching of ordinary and backward electromagnetic waves: second harmonic generation
We show that deliberately engineered dispersive metamaterial slab can enable
the co-existence and phase matching of contra-propagating ordinary fundamental
and extraordinary backward second harmonic surface electromagnetic modes.
Energy flux and phase velocity are contra-directed in the backward waves which
is the phenomenon that gives rise to unique nonlinear optical propagation
processes. We show that frequencies, phase, and group velocities, as well as
nanowaveguide losses inherent to the electromagnetic modes supported by such
metamaterial, can be tailored to maximize conversion of frequencies and to
reverse propagation direction of the generated wave. Such a possibility, which
is of paramount importance for nonlinear photonics, is proved with a numerical
model of the hyperbolic metamaterial made of carbon nanotubes standing on the
metal surface. Extraordinary properties of the backward-wave second harmonic
generation in the reflection direction and of the corresponding frequency
doubling metareflector in the THz are investigated with a focus on the pulsed
regime.Comment: 6 pages, 5 figures. arXiv admin note: text overlap with
arXiv:1602.0249
Pair Production Beyond the Schwinger Formula in Time-Dependent Electric Fields
We investigate electron-positron pair production in pulse-shaped electric
background fields using a non-Markovian quantum kinetic equation. We identify a
pulse-length range for subcritical fields still in the nonperturbative regime
where the number of produced pairs significantly exceeds that of a naive
expectation based on the Schwinger formula. From a conceptual viewpoint, we
find a remarkable quantitative agreement between the (real-time) quantum
kinetic approach and the (imaginary-time) effective action approach.Comment: 5 pages, 3 figures. Typos corrected and references added, PRD Versio
Practical analytical solutions for benchmarking of 2-D and 3-D geodynamic Stokes problems with variable viscosity
Geodynamic modeling is often related with challenging computations
involving solution of the Stokes and continuity equations under
the condition of highly variable viscosity. Based on a new analytical
approach we have developed particular analytical solutions for 2-D and
3-D incompressible Stokes flows with both linearly and exponentially
variable viscosity. We demonstrate how these particular solutions
can be converted into 2-D and 3-D test problems suitable for
benchmarking numerical codes aimed at modeling various mantle
convection and lithospheric dynamics problems. The Main advantage of
this new generalized approach is that a large variety of benchmark
solutions can be generated, including relatively complex cases with
open model boundaries, non-vertical gravity and variable gradients
of the viscosity and density fields, which are not parallel to the Cartesian
axes. Examples of respective 2-D and 3-D MatLab codes are provided
with this paper
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