1,515 research outputs found

### Casimir force for cosmological domain walls

We calculate the vacuum fluctuations that may affect the evolution of
cosmological domain walls. Considering domain walls, which are classically
stable and have interaction with a scalar field, we show that explicit symmetry
violation in the interaction may cause quantum bias that can solve the
cosmological domain wall problem.Comment: 15 pages, 2figure

### Casimir force driven ratchets

We explore the non-linear dynamics of two parallel periodically patterned
metal surfaces that are coupled by the zero-point fluctuations of the
electromagnetic field between them. The resulting Casimir force generates for
asymmetric patterns with a time-periodically driven surface-to-surface distance
a ratchet effect, allowing for directed lateral motion of the surfaces in
sizeable parameter ranges. It is crucial to take into account inertia effects
and hence chaotic dynamics which are described by Langevin dynamics. Multiple
velocity reversals occur as a function of driving, mean surface distance, and
effective damping. These transport properties are shown to be stable against
weak ambient noise.Comment: 4 pages, 3 figure

### The Fundamental Commutator For Massless Particles

It is discussed that the usual Heisenberg commutation relation (CR) is not a
proper relation for massless particles and then an alternative is obtained. The
canonical quantization of the free electromagnetic(EM)fields based on the field
theoretical generalization of this alternative is carried out. Without imposing
the normal ordering condition,the vacuum energy is automatically zero.This can
be considered as a solution to the EM fields vacuum catastrophe and a step
toward managing the cosmologial constant problem at least for the EM fields
contribution to the state of vacuum.Comment: 12 pages,no figures,To appear in Mod.Phys.Ltt.

### What is the Temperature Dependence of the Casimir Force between Real Metals?

The situation with the temperature corrections to the Casimir force between
real metals of finite conductivity is reported. It is shown that the plasma
dielectric function is well adapted to the Lifshitz formula and leads to
reasonable results for real conductors. The Drude dielectric function which
describes media with dissipation is found not to belong to the application
range of the Lifshitz formula at nonzero temperature. For Drude metals the
special modification of the zero-frequency term of this formula is suggested.
The contradictory results on the subject in recent literature are analysed and
explained.Comment: 10 pages, 1 figure, Contribution to the 5th Workshop on Quantum Field
Theory under the Influence of External Conditions, Leipzig, Germany, 10-14
Sep 200

### Casimir potential of a compact object enclosed by a spherical cavity

We study the electromagnetic Casimir interaction of a compact object
contained inside a closed cavity of another compact object. We express the
interaction energy in terms of the objects' scattering matrices and translation
matrices that relate the coordinate systems appropriate to each object. When
the enclosing object is an otherwise empty metallic spherical shell, much
larger than the internal object, and the two are sufficiently separated, the
Casimir force can be expressed in terms of the static electric and magnetic
multipole polarizabilities of the internal object, which is analogous to the
Casimir-Polder result. Although it is not a simple power law, the dependence of
the force on the separation of the object from the containing sphere is a
universal function of its displacement from the center of the sphere,
independent of other details of the object's electromagnetic response.
Furthermore, we compute the exact Casimir force between two metallic spheres
contained one inside the other at arbitrary separations. Finally, we combine
our results with earlier work on the Casimir force between two spheres to
obtain data on the leading order correction to the Proximity Force
Approximation for two metallic spheres both outside and within one another.Comment: 12 pages, 6 figure

### Casimir Energy and Entropy between perfect metal Spheres

We calculate the Casimir energy and entropy for two perfect metal spheres in
the large and short separation limit. We obtain nonmonotonic behavior of the
Helmholtz free energy with separation and temperature, leading to parameter
ranges with negative entropy, and also nonmonotonic behavior of the entropy
with temperature and with the separation between the spheres. The appearance of
this anomalous behavior of the entropy is discussed as well as its
thermodynamic consequences.Comment: 10 pages and 8 figures. Accepted for publication in the Proceedings
of the tenth conference on Quantum Field Theory under the influence of
external conditions - QFEXT'1

### Worldline algorithms for Casimir configurations

We present improved worldline numerical algorithms for high-precision
calculations of Casimir interaction energies induced by scalar-field
fluctuations with Dirichlet boundary conditions for various Casimir geometries.
Significant reduction of numerical cost is gained by exploiting the symmetries
of the worldline ensemble in combination with those of the configurations. This
facilitates high-precision calculations on standard PCs or small clusters. We
illustrate our strategies using the experimentally most relevant sphere-plate
and cylinder-plate configuration. We compute Casimir curvature effects for a
wide parameter range, revealing the tight validity bounds of the commonly used
proximity force approximation (PFA). We conclude that data analysis of future
experiments aiming at a precision of 0.1% must no longer be based on the PFA.
Revisiting the parallel-plate configuration, we find a mapping between the
D-dimensional Casimir energy and properties of a random-chain polymer ensemble.Comment: 23 pages, 9 figure

### The Zeta Function Method and the Harmonic Oscillator Propagator

We show how the pre-exponential factor of the Feynman propagator for the
harmonic oscillator can be computed by the generalized $\zeta$-function method.
Besides, we establish a direct equivalence between this method and Schwinger's
propertime method.Comment: 12 latex pages, no figure

### Tunable Casimir repulsion with three dimensional topological insulators

In this Letter, we show that switching between repulsive and attractive
Casimir forces by means of external tunable parameters could be realized with
two topological insulator plates. We find two regimes where a repulsive
(attractive) force is found at small (large) distances between the plates,
canceling out at a critical distance. For a frequency range where the effective
electromagnetic action is valid, this distance appears at length scales
corresponding to $1-\epsilon(\omega) (2/\pi)\alpha\theta$.Comment: 9 pages, 5 figures, published version with auxiliary material.
Featured in Physical Review Focu

### Measurement of thermal conductance of silicon nanowires at low temperature

We have performed thermal conductance measurements on individual single
crystalline silicon suspended nanowires. The nanowires (130 nm thick and 200 nm
wide) are fabricated by e-beam lithography and suspended between two separated
pads on Silicon On Insulator (SOI) substrate. We measure the thermal
conductance of the phonon wave guide by the 3 method. The cross-section
of the nanowire approaches the dominant phonon wavelength in silicon which is
of the order of 100 nm at 1K. Above 1.3K the conductance behaves as T3, but a
deviation is measured at the lowest temperature which can be attributed to the
reduced geometry

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