6,631 research outputs found
Casimir effect of electromagnetic field in Randall-Sundrum spacetime
We study the finite temperature Casimir effect on a pair of parallel
perfectly conducting plates in Randall-Sundrum model without using scalar field
analogy. Two different ways of interpreting perfectly conducting conditions are
discussed. The conventional way that uses perfectly conducting condition
induced from 5D leads to three discrete mode corrections. This is very
different from the result obtained from imposing 4D perfectly conducting
conditions on the 4D massless and massive vector fields obtained by decomposing
the 5D electromagnetic field. The latter only contains two discrete mode
corrections, but it has a continuum mode correction that depends on the
thicknesses of the plates. It is shown that under both boundary conditions, the
corrections to the Casimir force make the Casimir force more attractive. The
correction under 4D perfectly conducting condition is always smaller than the
correction under the 5D induced perfectly conducting condition. These
statements are true at any temperature.Comment: 20 pages, 4 figure
Casimir effect of electromagnetic field in D-dimensional spherically symmetric cavities
Eigenmodes of electromagnetic field with perfectly conducting or infinitely
permeable conditions on the boundary of a D-dimensional spherically symmetric
cavity is derived explicitly. It is shown that there are (D-2) polarizations
for TE modes and one polarization for TM modes, giving rise to a total of (D-1)
polarizations. In case of a D-dimensional ball, the eigenfrequencies of
electromagnetic field with perfectly conducting boundary condition coincides
with the eigenfrequencies of gauge one-forms with relative boundary condition;
whereas the eigenfrequencies of electromagnetic field with infinitely permeable
boundary condition coincides with the eigenfrequencies of gauge one-forms with
absolute boundary condition. Casimir energy for a D-dimensional spherical shell
configuration is computed using both cut-off regularization and zeta
regularization. For a double spherical shell configuration, it is shown that
the Casimir energy can be written as a sum of the single spherical shell
contributions and an interacting term, and the latter is free of divergence.
The interacting term always gives rise to an attractive force between the two
spherical shells. Its leading term is the Casimir force acting between two
parallel plates of the same area, as expected by proximity force approximation.Comment: 28 page
Mode summation approach to Casimir effect between two objects
In this paper, we explore the TGTG formula from the perspective of mode
summation approach. Both scalar fields and electromagnetic fields are
considered. In this approach, one has to first solve the equation of motion to
find a wave basis for each object. The two T's in the TGTG formula are
T-matrices representing the Lippmann-Schwinger T-operators, one for each of the
objects. The two G's in the TGTG formula are the translation matrices, relating
the wave basis of an object to the wave basis of the other object. After
discussing the general theory, we apply the prescription to derive the explicit
formulas for the Casimir energies for the sphere-sphere, sphere-plane,
cylinder-cylinder and cylinder-plane interactions. First the T-matrices for a
plane, a sphere and a cylinder are derived for the following cases: the object
is imposed with general Robin boundary conditions; the object is
semitransparent; and the object is magnetodielectric. Then the operator
approach is used to derive the translation matrices. From these, the explicit
TGTG formula for each of the scenarios can be written down. Besides summarizing
all the TGTG formulas that have been derived so far, we also provide the TGTG
formulas for some scenarios that have not been considered before.Comment: 42 page
Dirac semimetal in three dimensions
In a Dirac semimetal, the conduction and valence bands contact only at
discrete (Dirac) points in the Brillouin zone (BZ) and disperse linearly in all
directions around these critical points. Including spin, the low energy
effective theory around each critical point is a four band Dirac Hamiltonian.
In two dimensions (2D), this situation is realized in graphene without
spin-orbit coupling. 3D Dirac points are predicted to exist at the phase
transition between a topological and a normal insulator in the presence of
inversion symmetry. Here we show that 3D Dirac points can also be protected by
crystallographic symmetries in particular space-groups and enumerate the
criteria necessary to identify these groups. This reveals the possibility of 3D
analogs to graphene. We provide a systematic approach for identifying such
materials and present ab initio calculations of metastable \beta-cristobalite
BiO_2 which exhibits Dirac points at the three symmetry related X points of the
BZ.Comment: 6 pages, 4 figure
Non-Singularity of the Exact Two-Dimensional String Black Hole
We study the global structure of the exact two-dimensional space-time which
emerges from string theory. Previous work has shown that in the semi-classical
limit, this is a black hole similar to the Schwarzschild solution. However, we
find that in the exact case, a new Euclidean region appears "between" the
singularity and black hole interior. However the boundary between the
Lorentzian and Euclidean regions is a coordinate singularity, which turns out
to be a surface of time reflection symmetry in an extended space-time. Thus
strings having fallen through the black hole horizon would eventually emerge
through another one into a new asymptotically flat region. The maximally
extended space-time consists of an infinite number of universes connected by
wormholes. There are no singularities present in this geometry. We also
calculate the mass and temperature associated with the space-time.Comment: 9 pages, latex, DAMTP R93/
Recommended from our members
Defining user perception of distributed multimedia quality
This article presents the results of a study that explored the human side of the multimedia experience. We propose a model that assesses quality variation from three distinct levels: the network, the media and the content levels; and from two views: the technical and the user perspective. By facilitating parameter variation at each of the quality levels and from each of the perspectives, we were able to examine their impact on user quality perception. Results show that a significant reduction in frame rate does not proportionally reduce the user's understanding of the presentation independent of technical parameters, that multimedia content type significantly impacts user information assimilation, user level of enjoyment, and user perception of quality, and that the device display type impacts user information assimilation and user perception of quality. Finally, to ensure the transfer of information, low-level abstraction (network-level) parameters, such as delay and jitter, should be adapted; to maintain the user's level of enjoyment, high-level abstraction quality parameters (content-level), such as the appropriate use of display screens, should be adapted
It is all in the looks: A rapid field-based visual assessment tool for evaluating the spawning likelihood of the Asian green mussel, Perna viridis (Linnaeus, 1758)
Numerous interceptions of Perna viridis on vessels entering Western Australian waters prompted the development of a rapid field-based assessment technique for determining reproductive status and hence spawning likelihood of P. viridis. The visual assessment tool and spawning likelihood matrix were developed using correlations between laboratory-based assessments of P. viridis size, colour and egg size in combination with field-based validations from mussels collected on vessels in Western Australian waters. The spawning likelihood matrix provides an immediate indicator of whether the mussel is low, medium or high likelihood of spawning. Mussels were recorded initiating gonad tissue development from approximately 6.5 mm in length, with the mean size of mature animals 59.6 mm. There was a positive correlation between mussel size and stage of reproductive development. Gonad colour, however, appeared to be a more accurate indicator of gonad maturity than mussel size. Female mussels showed a decrease in gonad colour intensity following spawning. Mussels that scored 1 for colour (potential score 1–3) generally had a low proportion of mature eggs (< 70 % mature eggs). Over 60% of the mussels with a colour score of 2 contained 70–100% mature eggs, indicating the capacity for further spawning. Mussels were assigned an overall spawning likelihood score (through the spawning likelihood matrix) based on the proportion of the visceral mass occupied by gonad tissues (% gonad cover, value from 1–3) and overall colour of gonads (value from 1–3). The spawning likelihood score was significantly related to the percentage of mature eggs present, and hence the spawning potential of the mussel. The matrix provides an immediate indicator of the risk of spawning posed by the sample. As such, it is expected that application of the matrix in situ would enable the potential likelihood posed by P. viridis translocated on vessels to be determined quickly and efficiently
- …