107 research outputs found

### Self-force of a point charge in the space-time of a symmetric wormhole

We consider the self-energy and the self-force for an electrically charged
particle at rest in the wormhole space-time. We develop general approach and
apply it to two specific profiles of the wormhole throat with singular and with
smooth curvature. The self-force for these two profiles is found in manifest
form; it is an attractive force. We also find an expression for the self-force
in the case of arbitrary symmetric throat profile. Far from the throat the
self-force is always attractive.Comment: 18 pages, 3 figures Comments: corrected pdf, enlarged pape

### Ground State Energy of Massive Scalar Field Inside a Spherical Region in the Global Monopole Background

Using the zeta function regularization method we calculate the ground state
energy of scalar massive field inside a spherical region in the space-time of a
point-like global monopole. Two cases are investigated: (i) We calculate the
Casimir energy inside a sphere of radius $R$ and make an analytical analysis
about it. We observe that this energy may be positive or negative depending on
metric coefficient $\alpha$ and non-conformal coupling $\xi$. In the limit
$R\to\infty$ we found a zero result. (ii) In the second model we surround the
monopole by additional sphere of radius $r_0<R$ and consider scalar field
confined in the region between these two spheres. In the latter, the ground
state energy presents an additional contribution due to boundary at $r_0$ which
is divergent for small radius. Additional comments about renormalization are
considered.Comment: 30 pages and 2 figures. LATEX fil

### Casimir effect for a collection of parallel conducting surfaces

Â© 2015, Pleiades Publishing, Ltd. We consider the Casimir energy for a system of conducting parallel planes with constant surface conductance and obtain a general expression for the Casimir energy of the systems of two, three, and four planes. For equal separations between the planes, the energy is inversely proportional to the cubed distance between the planes and for low conductance is independent of the Planck constant and the speed of light. For a system of ideally conducting planes, the Casimir energy is the sum of the Casimir energies of pairs of adjacent planes

### Electromagnetic field near cosmic string

The retarded Green function of the electromagnetic field in spacetime of a
straight thin cosmic string is found. It splits into a geodesic part
(corresponding to the propagation along null rays) and to the field scattered
on the string. With help of the Green function the electric and magnetic fields
of simple sources are constructed. It is shown that these sources are
influenced by the cosmic string through a self-interaction with their field.
The distant field of static sources is studied and it is found that it has a
different multipole structure than in Minkowski spacetime. On the other hand,
the string suppresses the electric and magnetic field of distant sources--the
field is expelled from regions near the string.Comment: 12 pages, 8 figures (low-resolution figures; for the version with
high-resolution figures see http://utf.mff.cuni.cz/~krtous/papers/), v2: two
references added, typos correcte

### Self-energy and Self-force in the Space-time of a Thick Cosmic String

We calculate the self-energy and self-force for an electrically charged
particle at rest in the background of Gott-Hiscock cosmic string space-time. We
found the general expression for the self-energy which is expressed in terms of
the $S$ matrix of the scattering problem. The self-energy continuously falls
down outward from the string's center with maximum at the origin of the string.
The self-force is repulsive for an arbitrary position of the particle. It tends
to zero in the string's center and also far from the string and it has a
maximum value at the string's surface. The plots of the numerical calculations
of the self-energy and self-force are shown.Comment: 15 pages, 4 Postscript figures, ReVTe

### Dynamic tsallis entropy for simple model systems

In this paper we consider the dynamic Tsallis entropy and employ it for four model systems: (i) the motion of Brownian oscillator, (ii) the motion of Brownian oscillator with noise, (iii) the fluctuation of particle density in hydrodynamics limit as well as in (iv) ideal gas. We show that the small value of parameter non-extensivity 0 < q < 1 acts as a non-linear magnifier for small values of the entropy. The frequency spectra become more sharp and it is possible to extract useful information in the case of noise. We show that the ideal gas remains non-Markovian for arbitrary values of q

### The Casimir effect for planar layered system

Â© 2016 World Scientific Publishing Company. We consider the Casimir energy and force for stack of the N conductive planes at zero temperature. The Casimir-Polder force for an atom near this stack is calculated, too. We derive general expressions and make analysis for the case of ideal metal. In all considered cases the finite conductivity plays important role for the Casimir effect

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