465 research outputs found
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
ImmigraciĂł a Ponent. Resultats d'una evoluciĂł
El treball analitza l’evoluciĂł de la darrera onada migratòria, la seva composiciĂł i la seva distribuciĂł en el territori i entre els nuclis municipals. Agafar l’à mbit de Ponent permet escapar a una escala comarcal i comparar una realitat mĂ©s diversa que ofereix una perspectiva mĂ©s Ă mplia. L’assentament de poblaciĂł nouvinguda i l’alteraciĂł d’alguns parĂ metres demogrĂ fics han transformat algunes localitats de Ponent i mostren una tendència cap al procĂ©s d’urbanitzaciĂł d’unes comarques tradicionalment rurals. L’anĂ lisi es realitza, principalment, a partir de les dades obtingudes de l’INE i de l’IDESCAT i d’entrevistes realitzades a persones amb responsabilitats tècniques i polĂtiques de les administracion
Surface Divergences and Boundary Energies in the Casimir Effect
Although Casimir, or quantum vacuum, forces between distinct bodies, or
self-stresses of individual bodies, have been calculated by a variety of
different methods since 1948, they have always been plagued by divergences.
Some of these divergences are associated with the volume, and so may be more or
less unambiguously removed, while other divergences are associated with the
surface. The interpretation of these has been quite controversial. Particularly
mysterious is the contradiction between finite total self-energies and surface
divergences in the local energy density. In this paper we clarify the role of
surface divergences.Comment: 8 pages, 1 figure, submitted to proceedings of QFEXT0
Casimir self-energy of a \delta-\delta' sphere
We extend previous work on the vacuum energy of a massless scalar field in
the presence of singular potentials. We consider a single sphere denoted by the
so-called "delta-delta prime" interaction. Contrary to the Dirac delta
potential, we find a nontrivial one-parameter family of potentials such that
the regularization procedure gives an unambiguous result for the Casimir
self-energy. The procedure employed is based on the zeta function
regularization and the cancellation of the heat kernel coefficient a_2. The
results obtained are in agreement with particular cases, such as the Dirac
delta or Robin and Dirichlet boundary conditions
Searching for a C-function on the three-dimensional sphere
We present a detailed analytic study on the three-dimensional sphere of the most popular candidates for C-functions, both for Dirac and scalar free massive fields. We discuss to which extent the effective action, the RĂ©nyi entanglement entropy and the renormalized entanglement entropy fulfill the conditions expected from C-functions. In view of the absence of a good candidate in the case of the scalar field, we introduce a new candidate, which we call the modified effective action, and analyze its pros and cons.Instituto de FĂsica La Plat
Topological entropy and renormalization group flow in 3-dimensional spherical spaces
We analyze the renormalization group (RG) flow of the temperature independent term of the entropy in the high temperature limit ß/a « 1 of a massive field theory in 3-dimensional spherical spaces, M 3, with constant curvature 6/a 2. For masses lower than 2p/ß , this term can be identified with the free energy of the same theory on M 3 considered as a 3-dimensional Euclidean space-time. The non-extensive part of this free energy, S hol, is generated by the holonomy of the spatial metric connection. We show that for homogeneous spherical spaces the holonomy entropy S hol decreases monotonically when the RG scale flows to the infrared. At the conformal fixed points the values of the holonomy entropy do coincide with the genuine topological entropies recently introduced. The monotonic behavior of the RG flow leads to an inequality between the topological entropies of the conformal field theories connected by such flow, i.e. S top UV¿>¿S top IR . From a 3-dimensional viewpoint the same term arises in the 3-dimensional Euclidean effective action and has the same monotonic behavior under the RG group flow. We conjecture that such monotonic behavior is generic, which would give rise to a 3-dimensional generalization of the c-theorem, along the lines of the 2-dimensional c-theorem and the 4-dimensional a-theorem. The conjecture is related to recent formulations of the F-theorem. In particular, the holonomy entropy on lens spaces is directly related to the topological Rényi entanglement entropy on disks of 2-dimensional flat spaces
Non-contact gears: II. Casimir torque between concentric corrugated cylinders for the scalar case
The Casimir interaction between two concentric corrugated cylinders provides
the mechanism for non-contact gears. To this end, we calculate the Casimir
torque between two such cylinders, described by -potentials, which
interact through a scalar field. We derive analytic expressions for the Casimir
torque for the case when the corrugation amplitudes are small in comparison to
the corrugation wavelengths. We derive explicit results for the Dirichlet case,
and exact results for the weak coupling limit, in the leading order. The
results for the corrugated cylinders approach the corresponding expressions for
the case of corrugated parallel plates in the limit of large radii of cylinders
(relative to the difference in their radii) while keeping the corrugation
wavelength fixed.Comment: 9 pages, 3 figures, references correcte
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