233 research outputs found
Zeta-function approach to Casimir energy with singular potentials
In the framework of zeta-function approach the Casimir energy for three
simple model system: single delta potential, step function potential and three
delta potentials is analyzed. It is shown that the energy contains
contributions which are peculiar to the potentials. It is suggested to
renormalize the energy using the condition that the energy of infinitely
separated potentials is zero which corresponds to subtraction all terms of
asymptotic expansion of zeta-function. The energy obtained in this way obeys
all physically reasonable conditions. It is finite in the Dirichlet limit and
it may be attractive or repulsive depending on the strength of potential. The
effective action is calculated and it is shown that the surface contribution
appears. The renormalization of the effective action is discussed.Comment: 17 pages, 2 figures, added reference, address correcte
Gravitational particle production in braneworld cosmology
Gravitational particle production in time variable metric of an expanding
universe is efficient only when the Hubble parameter is not too small in
comparison with the particle mass. In standard cosmology, the huge value of the
Planck mass makes the mechanism phenomenologically irrelevant. On the
other hand, in braneworld cosmology the expansion rate of the early universe
can be much faster and many weakly interacting particles can be abundantly
created. Cosmological implications are discussed.Comment: 4 pages, 1 figure, v3 with new definition of and minor text
modification
Thermodynamics via Creation from Nothing: Limiting the Cosmological Constant Landscape
The creation of a quantum Universe is described by a {\em density matrix}
which yields an ensemble of universes with the cosmological constant limited to
a bounded range . The
domain is ruled out by a cosmological bootstrap
requirement (the self-consistent back reaction of hot matter). The upper cutoff
results from the quantum effects of vacuum energy and the conformal anomaly
mediated by a special ghost-avoidance renormalization. The cutoff establishes a new quantum scale -- the accumulation point of an infinite
sequence of garland-type instantons. The dependence of the cosmological
constant range on particle phenomenology suggests a possible dynamical
selection mechanism for the landscape of string vacua.Comment: RevTex, 4 pages, 4 figure
Attractive Casimir Forces in a Closed Geometry
We study the Casimir force acting on a conducting piston with arbitrary cross
section. We find the exact solution for a rectangular cross section and the
first three terms in the asymptotic expansion for small height to width ratio
when the cross section is arbitrary. Though weakened by the presence of the
walls, the Casimir force turns out to be always attractive. Claims of repulsive
Casimir forces for related configurations, like the cube, are invalidated by
cutoff dependence.Comment: An updated version to coincide with the one published December 2005
in PRL. 4 pages, 2 figure
Particle creation in a toroidal universe
We calculate the particle production rate in an expanding universe with a
three-torus topology. We discuss also the complete evolution of the size of
such a universe. The energy density of particles created through the nonzero
modes is computed for selected masses. The unique contribution of the zero mode
and its properties are also analyzed.Comment: 9 pages, 11 figure
Casimir force on a piston
We consider a massless scalar field obeying Dirichlet boundary conditions on
the walls of a two-dimensional L x b rectangular box, divided by a movable
partition (piston) into two compartments of dimensions a x b and (L-a) x b. We
compute the Casimir force on the piston in the limit L -> infinity. Regardless
of the value of a/b, the piston is attracted to the nearest end of the box.
Asymptotic expressions for the Casimir force on the piston are derived for a <<
b and a >> b.Comment: 10 pages, 1 figure. Final version, accepted for publication in Phys.
Rev.
Casimir interaction of two plates inside a cylinder
The new exact formulas for the attractive Casimir force acting on each of the
two identical perfectly conducting plates moving freely inside an infinite
perfectly conducting cylinder with the same cross section are derived at zero
and finite temperatures by making use of the zeta function technique. The long
and short distance behaviour of the plates' free energy is investigated.Comment: 14 pages, 1 figure, latex2
Strain-Compensated AlInGaAs-GaAsP Superlattices for Highly-Polarized Electron Emission
Spin-polarized electron emission from the first superlattice photocathodes
developed with strain compensation is investigated. An opposite strain in the
quantum well and barrier layers is complished using an InAlGaAs/GaAsP
superlattice structure. The measured values of maximum polarization and quantum
yield for the structure with a 0.18 um-thick working layer are close to the
best results reported for any strained superlattice photocathode structure,
demonstrating the high potential of strain compensation for future photocathode
applications. An analysis of the photoemission spectra is used to estimate the
parameters responsible for the polarization losses.Comment: 10 pages, 2 figure
CFT driven cosmology and the DGP/CFT correspondence
We present a dual 5D braneworld picture of a recently suggested model for a
microcanonical description of a 4D cosmology driven by a conformal field theory
with a large number of quantum fields. The 5D side of the duality relation is
represented by a generalized brane induced gravity model in a Schwarzschild-de
Sitter bulk. The values of the bulk cosmological and the induced 4D
cosmological constants are determined by requiring the absence of conical
singularity at the de Sitter horizon of the Euclidean Schwarzschild-de Sitter
bulk. Those values belong to the vicinity of the upper bound of a range of
admissible values for the cosmological constant. This upper bound is enforced
by the 4D CFT and coincides with the natural gravitational cutoff in a theory
with many quantum species. The resulting DGP/CFT duality suggests the
possibility of a new type of {\em background independent} correspondence. A
mechanism for inverting the sign of the effective cosmological constant is
found, which might reconcile a negative value of the primordial cosmological
constant compatible with supersymmetry with the one required by inflationary
cosmology.Comment: LaTeX, 23 pages, 3 figure
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