144 research outputs found
Self-amplified Emission of Cherenkov Radiation from a Relativistic Particle Inside Layered Dielectric-filled Waveguide
It is shown that in some special cases the Cherenkov radiation from a charged
particle moving along the axis of cylindrical waveguide filled with a
semi-infinite material consisting of dielectric plates alternated with vacuum
gaps is many times stronger than that in the waveguide filled with
semi-infinite solid dielectric without vacuum gaps.Comment: 1 page, abstract submitted to 4th International Conference
"Channeling 2010", Ferrara, Italy, October 3-8, 201
On the theory of coherent pair production in crystals in presence of acoustic waves
The influence of hypersonic waves excited in a single crystal is investigated
on the process of electron-positron pair creation by high-energy photons. The
coherent part of the corresponding differential cross-section is derived as a
function of the amplitude and wave number of the hypersound. The values of the
parameters are specified for which the latter affects remarkably on the pair
creation cross-section. It is shown that under certain conditions the presence
of hypersonic waves can result in enhancement of the process cross-section.Comment: 10 pages, 3 EPS figure
Radiation from a charged particle-in-flight from a laminated medium to vacuum
The radiation from a charged particle-in-flight from a semi-infinite
laminated medium to vacuum and back,- from vacuum to the laminated medium, has
been investigated. Expressions for the spectral-angular distribution of
radiation energy in vacuum (at large distances from the boundary of laminated
medium) were obtained for both the cases with no limitations on the amplitude
and variation profile of the laminated medium permittivity. The results of
appropriate numerical calculations are presented and possible applications of
the obtained results are discussed.Comment: 8 pages, 6 figures, contribution to Proceedings of International
Symposium RREPS-2009, 07-11 September, 2009, Zvenigorod, Russi
Casimir densities for a spherical boundary in de Sitter spacetime
Two-point functions, mean-squared fluctuations, and the vacuum expectation
value of the energy-momentum tensor operator are investigated for a massive
scalar field with an arbitrary curvature coupling parameter, subject to a
spherical boundary in the background of de Sitter spacetime. The field is
prepared in the Bunch-Davies vacuum state and is constrained to satisfy Robin
boundary conditions on the sphere. Both the interior and exterior regions are
considered. For the calculation in the interior region, a mode-summation method
is employed, supplemented with a variant of the generalized Abel-Plana formula.
This allows us to explicitly extract the contributions to the expectation
values which come from de Sitter spacetime without boundaries. We show that the
vacuum energy-momentum tensor is non-diagonal with the off-diagonal component
corresponding to the energy flux along the radial direction. With dependence on
the boundary condition and the mass of the field, this flux can be either
positive or negative. Several limiting cases of interest are then studied. In
terms of the curvature coupling parameter and the mass of the field, two very
different regimes are realized, which exhibit monotonic and oscillatory
behavior of the vacuum expectation values, respectively, far from the sphere.
The decay of the boundary induced expectation values at large distances from
the sphere is shown to be power-law (monotonic or oscillating), independent of
the value of the field mass.Comment: 32 pages, 4 figures, new paragraph about generalizations, discussion
and references added, accepted for publication in Phys. Rev.
Self-amplified Cherenkov radiation from a relativistic electron in a waveguide partially filled with a laminated material
The radiation from a relativistic electron uniformly moving along the axis of
cylindrical waveguide filled with laminated material of finite length is
investigated. Expressions for the spectral distribution of radiation passing
throw the transverse section of waveguide at large distances from the laminated
material are derived with no limitations on the amplitude and variation profile
of the layered medium permittivity and permeability. Numerical results for
layered material consisting of dielectric plates alternated with vacuum gaps
are given. It is shown that at a special choice of problem parameters,
Cherenkov radiation generated by the relativistic electron inside the plates is
self-amplified. The visual explanation of this effect is given and a possible
application is discussed.Comment: 8 pages, 4 figures,1 table, the paper is accepted for publication in
the Journal of Physics: Conference Serie
Radiation from a charge circulating inside a waveguide with dielectric filling
The emitted power of the radiation from a charged particle moving uniformly
on a circle inside a cylindrical waveguide is considered. The expressions for
the energy flux of the radiation passing through the waveguide cross-section
are derived for both TE and TM waves. The results of the numerical evaluation
are presented for the number of emitted quanta depending on the waveguide
radius, the radius of the charge rotation orbit and dielectric permittivity of
the filling medium. These results are compared with the corresponding
quantities for the synchrotron radiation in a homogeneous medium.Comment: 10 pages, Latex, four EPS figure
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