101 research outputs found
The electromagnetic field near a dielectric half-space
We compute the expectations of the squares of the electric and magnetic
fields in the vacuum region outside a half-space filled with a uniform
non-dispersive dielectric. This gives predictions for the Casimir-Polder force
on an atom in the `retarded' regime near a dielectric. We also find a positive
energy density due to the electromagnetic field. This would lead, in the case
of two parallel dielectric half-spaces, to a positive, separation-independent
contribution to the energy density, besides the negative, separation-dependent
Casimir energy. Rough estimates suggest that for a very wide range of cases,
perhaps including all realizable ones, the total energy density between the
half-spaces is positive.Comment: Latex2e, IOP macros, 15 pages, 2 eps figure
On the importance of testing gravity at distances less than 1cm
If the mechanism responsible for the smallness of the vacuum energy is
consistent with local quantum field theory, general arguments suggest the
existence of at least one unobserved scalar particle with Compton wavelength
bounded from below by one tenth of a millimeter. We show that this bound is
saturated if vacuum energy is a substantial component of the energy density of
the universe. Therefore, the success of cosmological models with a significant
vacuum energy component suggests the existence of new macroscopic forces with
range in the sub-millimeter region. There are virtually no experimental
constraints on the existence of quanta with this range of interaction.Comment: 9 pages TeX, 2 eps figures, uses mtexsis.tex and epsf.tex. Entry in
1996 Gravity Research Foundation essay competition. To be published in the
Journal of General Relativity and Gravitatio
How Multivalency controls Ionic Criticality
To understand how multivalency influences the reduced critical temperatures,
Tce (z), and densities, roce (z), of z : 1 ionic fluids, we study equisized
hard-sphere models with z = 1-3. Following Debye, Hueckel and Bjerrum,
association into ion clusters is treated with, also, ionic solvation and
excluded volume. In good accord with simulations but contradicting
integral-equation and field theories, Tce falls when z increases while roce
rises steeply: that 80-90% of the ions are bound in clusters near T_c serves to
explain these trends. For z \neq 1 interphase Galvani potentials arise and are
evaluated.Comment: 4 pages, 4 figure
Spectral representation of the Casimir Force Between a Sphere and a Substrate
We calculate the Casimir force in the non-retarded limit between a spherical
nanoparticle and a substrate, and we found that high-multipolar contributions
are very important when the sphere is very close to the substrate. We show that
the highly inhomegenous electromagnetic field induced by the presence of the
substrate, can enhance the Casimir force by orders of magnitude, compared with
the classical dipolar approximation.Comment: 5 page + 4 figures. Submitted to Phys. Rev. Let
Effects related to spacetime foam in particle physics
It is found that the existence of spacetime foam leads to a situation in
which the number of fundamental quantum bosonic fields is a variable quantity.
The general aspects of an exact theory that allows for a variable number of
fields are discussed, and the simplest observable effects generated by the foam
are estimated. It is shown that in the absence of processes related to
variations in the topology of space, the concept of an effective field can be
reintroduced and standard field theory can be restored. However, in the
complete theory the ground state is characterized by a nonvanishing particle
number density. From the effective-field standpoint, such particles are "dark".
It is assumed that they comprise dark matter of the universe. The properties of
this dark matter are discussed, and so is the possibility of measuring the
quantum fluctuation in the field potentials.Comment: 18 pages, minor corrections added to the published varian
Casimir Energy for Spherical boundaries
Calculations of the Casimir energy for spherical geometries which are based
on integrations of the stress tensor are critically examined. It is shown that
despite their apparent agreement with numerical results obtained from mode
summation methods, they contain a number of serious errors. Specifically, these
include (1) an improper application of the stress tensor to spherical
boundaries, (2) the neglect of pole terms in contour integrations, and (3) the
imposition of inappropriate boundary conditions upon the relevant propagators.
A calculation which is based on the stress tensor and which avoids such
problems is shown to be possible. It is, however, equivalent to the mode
summation method and does not therefore constitute an independent calculation
of the Casimir energy.Comment: Revtex, 7 pages, Appendix added providing details of failure of
stress tensor metho
Matter-field theory of the Casimir force
A matter-field theory of the Casimir force is formulated in which the
electromagnetic field and collective modes of dielectric media are treated on
an equal footing. In our theory, the Casimir force is attributed to zero-point
energies of the combined matter-field modes. We analyze why some of the
existing theories favor the interpretation of the Casimir force as originating
from zero-point energies of the electromagnetic field and others from those of
the matter.Comment: 12pages, 1 Postscript 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
Repulsive Casimir forces
We discuss repulsive Casimir forces between dielectric materials with non
trivial magnetic susceptibility. It is shown that considerations based on naive
pair-wise summation of Van der Waals and Casimir Polder forces may not only
give an incorrect estimate of the magnitude of the total Casimir force, but
even the wrong sign of the force when materials with high dielectric and
magnetic response are involved. Indeed repulsive Casimir forces may be found in
a large range of parameters, and we suggest that the effect may be realized in
known materials. The phenomenon of repulsive Casimir forces may be of
importance both for experimental study and for nanomachinery applications
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