3,214 research outputs found
Can the QCD Effective Charge Be Symmetrical in the Euclidean and the Minkowskian Regions?
We study a possible symmetrical behavior of the effective charges defined in
the Euclidean and Minkowskian regions and prove that such symmetry is
inconsistent with the causality principle.Comment: 5 pages, REVTe
Green's Dyadic Approach of the Self-Stress on a Dielectric-Diamagnetic Cylinder with Non-Uniform Speed of Light
We present a Green's dyadic formulation to calculate the Casimir energy for a
dielectric-diamagnetic cylinder with the speed of light differing on the inside
and outside. Although the result is in general divergent, special cases are
meaningful. It is pointed out how the self-stress on a purely dielectric
cylinder vanishes through second order in the deviation of the permittivity
from its vacuum value, in agreement with the result calculated from the sum of
van der Waals forces.Comment: 8 pages, submitted to proceedings of QFEXT0
Mode-by-mode summation for the zero point electromagnetic energy of an infinite cylinder
Using the mode-by-mode summation technique the zero point energy of the
electromagnetic field is calculated for the boundary conditions given on the
surface of an infinite solid cylinder. It is assumed that the dielectric and
magnetic characteristics of the material which makes up the cylinder
and of that which makes up the surroundings obey the relation . With this
assumption all the divergences cancel. The divergences are regulated by making
use of zeta function techniques. Numerical calculations are carried out for a
dilute dielectric cylinder and for a perfectly conducting cylindrical shell.
The Casimir energy in the first case vanishes, and in the second is in complete
agreement with that obtained by DeRaad and Milton who employed a Green's
function technique with an ultraviolet regulator.Comment: REVTeX, 16 pages, no figures and tables; transcription error in
previous version corrected, giving a zero Casimir energy for a tenuous
cylinde
The Casimir Problem of Spherical Dielectrics: Quantum Statistical and Field Theoretical Approaches
The Casimir free energy for a system of two dielectric concentric nonmagnetic
spherical bodies is calculated with use of a quantum statistical mechanical
method, at arbitrary temperature. By means of this rather novel method, which
turns out to be quite powerful (we have shown this to be true in other
situations also), we consider first an explicit evaluation of the free energy
for the static case, corresponding to zero Matsubara frequency ().
Thereafter, the time-dependent case is examined. For comparison we consider the
calculation of the free energy with use of the more commonly known field
theoretical method, assuming for simplicity metallic boundary surfaces.Comment: 31 pages, LaTeX, one new reference; version to appear in Phys. Rev.
Stress-Energy Tensor Induced by Bulk Dirac Spinor in Randall-Sundrum Model
Motivated by the possible extension into a supersymmetric Randall-Sundrum
(RS) model, we investigate the properties of the vacuum expectation value (VEV)
of the stress-energy tensor for a quantized bulk Dirac spinor field in the RS
geometry and compare it with that for a real scalar field. This is carried out
via the Green function method based on first principles without invoking the
degeneracy factor, whose validity in a warp geometry is a priori unassured. In
addition, we investigate the local behavior of the Casimir energy near the two
branes. One salient feature we found is that the surface divergences near the
two branes have opposite signs. We argue that this is a generic feature of the
fermionic Casimir energy density due to its parity transformation in the fifth
dimension. Furthermore, we investigate the self-consistency of the RS metric
under the quantum correction due to the stress-energy tensor. It is shown that
the VEV of the stress-energy tensor and the classical one become comparable
near the visible brane if k ~ M ~ M_Pl (the requirement of no hierarchy
problem), where k is the curvature of the RS warped geometry and M the
5-dimensional Planck mass. In that case the self-consistency of RS model that
includes bulk fields is in doubt. If, however, k <~ M, then an approximate
self-consistency of the RS-type metric may still be satisfied.Comment: 7 pages with 2 figure
Casimir energy of a dilute dielectric ball in the mode summation method
In the --approximation the Casimir energy of a
dilute dielectric ball is derived using a simple and clear method of the mode
summation. The addition theorem for the Bessel functions enables one to present
in a closed form the sum over the angular momentum before the integration over
the imaginary frequencies. The linear in contribution
into the vacuum energy is removed by an appropriate subtraction. The role of
the contact terms used in other approaches to this problem is elucidated.Comment: 14 pages, REVTeX, no figures, no tables; presentation is made better,
new references are adde
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