597 research outputs found
Vacuum Polarization of a Massless Scalar Field in the Background of a Global Monopole with Finite Core
In this paper we analyze the vacuum polarization effects of a massless scalar
field in the background of a global monopole considering a inner structure to
it. Specifically we investigate the effect of its structure on the vacuum
expectation value of the square of the field operator, ,
admitting a non-minimal coupling between the field with the geometry: $\xi
{\cal{R}}\hat{\Phi}^2$. Also we calculate the corrections on the vacuum
expectation value of the energy-momentum tensor, , due to
the inner structure of the monopole. In order to develop these analysis, we
calculate the Euclidean Green function associated with the system for points in
the region outside the core. As we shall see, for specific value of the
coupling parameter , the corrections caused by the inner structure of the
monopole can provide relevant contributions on these vacuum polarizations.Comment: Accepted for publication in Classical and Quantum Gravity. Added
references. 22 pages, 1 figur
Lateral projection as a possible explanation of the nontrivial boundary dependence of the Casimir force
We find the lateral projection of the Casimir force for a configuration of a
sphere above a corrugated plate. This force tends to change the sphere position
in the direction of a nearest corrugation maximum. The probability distribution
describing different positions of a sphere above a corrugated plate is
suggested which is fitted well with experimental data demonstrating the
nontrivial boundary dependence of the Casimir force.Comment: 5 pages, 1 figur
New features of the thermal Casimir force at small separations
The difference of the thermal Casimir forces at different temperatures
between real metals is shown to increase with a decrease of the separation
distance. This opens new opportunities for the demonstration of the thermal
dependence of the Casimir force. Both configurations of two parallel plates and
a sphere above a plate are considered. Different approaches to the theoretical
description of the thermal Casimir force are shown to lead to different
measurable predictions.Comment: 5 pages, 3 figures, to appear in Phys. Rev. Let
Higher order conductivity corrections to the Casimir force
The finite conductivity corrections to the Casimir force in two
configurations are calculated in the third and fourth orders in relative
penetration depth of electromagnetic zero oscillations into the metal. The
obtained analytical perturbation results are compared with recent computations.
Applications to the modern experiments are discussed.Comment: 15 pages, 4 figure
Application of Wavelet Transform and Artificial Neural Network to Extract Power Quality Information from Voltage Oscillographic Signals in Electric Power Systems
Impact of surface imperfections on the Casimir force for lenses of centimeter-size curvature radii
The impact of imperfections, which are always present on surfaces of lenses
with centimeter-size curvature radii, on the Casimir force in the lens-plate
geometry is investigated. It is shown that the commonly used formulation of the
proximity force approximation is inapplicable for spherical lenses with surface
imperfections, such as bubbles and pits. More general expressions for the
Casimir force are derived that take surface imperfections into account. Using
these expressions we show that surface imperfections can both increase and
decrease the magnitude of the Casimir force up to a few tens of percent when
compared with the case of a perfectly spherical lens. We demonstrate that the
Casimir force between a perfectly spherical lens and a plate described by the
Drude model can be made approximately equal to the force between a sphere with
some surface imperfection and a plate described by the plasma model, and vice
versa. In the case of a metallic sphere and semiconductor plate, approximately
the same Casimir forces are obtained for four different descriptions of charge
carriers in the semiconductor if appropriate surface imperfections on the lens
surface are present. The conclusion is made that there is a fundamental problem
in the interpretation of measurement data for the Casimir force, obtained by
using spherical lenses of centimeter-size radii, and their comparison with
theory.Comment: 28 pages, 7 figures, 1 table. To appear in Phys. Rev.
Gravitating Magnetic Monopole in the Global Monopole Spacetime
In this paper we study the regular self-gravitating 't Hooft-Polyakov
magnetic monopole in a global monopole spacetime. We show that for the large
distance, the structure of the manifold corresponds to the
Reissner-Nordstr\"{o}m spacetime with a solid angle deficit factor. Although we
analyze static and spherically symmetric solutions, it is not possible to solve
analytically the system of coupled differential equations and only numerical
evaluations can provide detailed information about the behavior of this system
at the neighborhood of the defect's core. So, for this reason we solve
numerically the set of differential equations for the metric tensor and for the
matter fields for different values of the Higgs field vacuum expectation value,
, and the self-coupling constant, .Comment: 26 pages, 6 figures, LaTex forma
Casimir and van der Waals force between two plates or a sphere (lens) above a plate made of real metals
The Casimir and van der Waals forces acting between two metallic plates or a
sphere (lens) above a plate are calculated accounting for the finite
conductivity of the metals. The simple formalism of surface modes is briefly
presented which allows the possibility to obtain the generalization of Lifshitz
results for the case of two semi-spaces covered by the thin layers. Additional
clarifications of the regularization procedure provides the means to obtain
reliable results not only for the force but also for the energy density. This,
in turn, leads to the value of the force for the configuration of a sphere
(lens) above a plate both of which are covered by additional layers. The
Casimir interaction between Al and Au test bodies is recalculated using the
optical tabulated data for the complex refractive index of these metals. The
computations turn out to be in agreement with the perturbation theory up to the
fourth order in relative penetration depth of electromagnetic zero point
oscillations into the metal. The disagreements between the results recently
presented in the literature are resolved. The Casimir force between Al bodies
covered by the thin Au layers is computed and the possibility to neglect
spatial dispersion effects is discussed as a function the layer thickness. The
van der Waals force is calculated including the transition region to the
Casimir force. The pure non-retarded van der Waals force law between Al and Au
bodies is shown to be restricted to a very narrow distance interval from 0.5 nm
to (2--4) nm. New, more exact, values of the Hamaker constant for Al and Au are
determined.Comment: 5 figure
Temperature correction to the Casimir force in cryogenic range and anomalous skin effect
Temperature correction to the Casimir force is considered for real metals at
low temperatures. With the temperature decrease the mean free path for
electrons becomes larger than the field penetration depth. In this condition
description of metals with the impedance of anomalous skin effect is shown to
be more appropriate than with the permittivity. The effect is crucial for the
temperature correction. It is demonstrated that in the zero frequency limit the
reflection coefficients should coincide with those of ideal metal if we demand
the entropy to be zero at T=0. All the other prescriptions discussed in the
literature for the term in the Lifshitz formula give negative entropy. It
is shown that the temperature correction in the region of anomalous skin effect
is not suppressed as it happens in the plasma model. This correction will be
important in the future cryogenic measurements of the Casimir force.Comment: 12 pages, 2 figures, to be published in Phys. Rev.
Thermal correction to the Casimir force, radiative heat transfer, and an experiment
The low-temperature asymptotic expressions for the Casimir interaction
between two real metals described by Leontovich surface impedance are obtained
in the framework of thermal quantum field theory. It is shown that the Casimir
entropy computed using the impedance of infrared optics vanishes in the limit
of zero temperature. By contrast, the Casimir entropy computed using the
impedance of the Drude model attains at zero temperature a positive value which
depends on the parameters of a system, i.e., the Nernst heat theorem is
violated. Thus, the impedance of infrared optics withstands the thermodynamic
test, whereas the impedance of the Drude model does not. We also perform a
phenomenological analysis of the thermal Casimir force and of the radiative
heat transfer through a vacuum gap between real metal plates. The
characterization of a metal by means of the Leontovich impedance of the Drude
model is shown to be inconsistent with experiment at separations of a few
hundred nanometers. A modification of the impedance of infrared optics is
suggested taking into account relaxation processes. The power of radiative heat
transfer predicted from this impedance is several times less than previous
predictions due to different contributions from the transverse electric
evanescent waves. The physical meaning of low frequencies in the Lifshitz
formula is discussed. It is concluded that new measurements of radiative heat
transfer are required to find out the adequate description of a metal in the
theory of electromagnetic fluctuations.Comment: 19 pages, 4 figures. svjour.cls is used, to appear in Eur. Phys. J.
- …