6,356 research outputs found
Black Hole entropy in D=2+1 dimensions from extended Chern-Simons term in a gravitational background
We study the contribution to entropy of Black Holes in D=2+1 dimensions from
an extension of the Chern Simons theory including higher derivative in a curved
space-time.Comment: 8 pages, AMSte
An alternative calculation of the Casimir energy for kappa-deformed electrodynamics
A simple, but effcient way of calculating regularized Casimir energies
suitable for non-trivial frequency spectra is briefly described and applied to
the case of a kappa-deformed scalar field theory. The results are consistent
with the ones obtained by other means.Comment: Four pages, latex file. Submitted for the Proceedings of the XXIV
Brazilian National Meeting on Particles and Fields held in Caxambu MG,
Brazil, September 30 -- October 4, 200
Non-Abelian Magnetic Monopoles in a Background of Gravitation with Fermions
The purpose of this paper is to study static solution configuration which describes the magnetic monopoles in a scenary where the gravitation is coupled with Higgs, Yang-Mills and fermions. We are looking for analysis of the energy functional and Bogomol'nyi equations. The Einstein equations now take into consideration the fermions' contribution for energy-momentum tensor. The interesting aspect here is to verify that the fermion field gives a contribution for non abelian magnetic field and for potential which minimise the energy functional
G\"{o}del Type solution with rotation, expansion and closed time-like curves
We propose a time-varying parameter for G\"{o}del metric
and an energy momentum tensor corresponding to this geometry is found. To
satisfy covariance arguments time-varying gravitational and cosmological term
are introduced. The ``Einstein's equation'' for this special evolution for the
Universe are written down where expansion, rotation and closed time-like curves
appear as a combination between standard model, G\"{o}del and steady state
properties are obtained.Comment: 10 pages, AMSte
Black Hole Entropy in 1+1 Dimensions from a Quasi-Chern Simons term in a Gravitational Background
We introduce a 'quasi-topological` term [1] in D=1+1 dimensions and the entropy for black holes is calculated [2]. The source of entropy in this case is justified by a non-null stress-energy tensor
Analysis of Maxwell Equations in a Gravitational Field
In a gravitational field, we analyze the Maxwell equations, the correponding
electromagnetic wave and continuity equations. A particular solution for
parellel electric and magnetic fields in a gravitational background is
presented. These solutions also satisfy the free-wave equations and the
phenomenology suggested by plasma physics.Comment: 10 pages, AMSte
Some Comments of Vlasov-Liouville Equation and its Relation with Gravitational Field
We discuss here the possibility to write the Liouville-Vlasov equation for
the Wigner-function of a spinor field coupled to a gauge field with field
strength tensor in a curved space-time versus a local Lorentz
manifold (introduction of local Lorentz coordinates) with an appropriate
definition of a covariant derivative carried out using a spin connection
.Comment: 11 pages, AMSte
Some Comments on Wheeler De Witt Equation for Gravitational Collapse and the Problem of Time
We write the Hamiltonian for a gravitational spherically symmetric scalar
field collapse with massive scalar field source, and we discuss the application
of Wheeler De Witt equation as well as the appearence of time in this context.
Using an Ansatz for Wheeler De Witt equation, solutions are discussed including
the appearence of time evolution.Comment: 9 pages, AMSte
Molding the flow of light with a magnetic field: plasmonic cloaking and directional scattering
We investigate electromagnetic scattering and plasmonic cloaking in a system
composed by a dielectric cylinder coated with a magneto-optical shell. In the
long-wavelength limit we demonstrate that the application of an external
magnetic field can not only switch on and off the cloaking mechanism but also
mitigate losses, as the absorption cross-section is shown to be minimal
precisely at the cloaking operation frequency band. We also show that the
angular distribution of the scattered radiation can be effectively controlled
by applying an external magnetic field, allowing for a swift change in the
scattering pattern. By demonstrating that these results are feasible with
realistic, existing magneto-optical materials, such as graphene epitaxially
grown on SiC, we suggest that magnetic fields could be used as an effective,
versatile external agent to tune plasmonic cloaks and to dynamically control
electromagnetic scattering in an unprecedented way, we hope that these results
may find use in disruptive photonic technologies.Comment: 7 pages, 8 figure
Tuning plasmonic cloaks with an external magnetic field
We propose a mechanism to actively tune the operation of plasmonic cloaks
with an external magnetic field by investigating electromagnetic scattering by
a dielectric cylinder coated with a magneto-optical shell. In the long
wavelength limit we show that the presence of an external magnetic field may
drastically reduce the scattering cross-section at all observation angles. We
demonstrate that the application of external magnetic fields can modify the
operation wavelength without the need of changing material and/or geometrical
parameters. We also show that applied magnetic fields can reversibly switch on
and off the cloak operation. These results, which could be achieved for
existing magneto-optical materials, are shown to be robust to material losses,
so that they may pave the way for developing actively tunable, versatile
plasmonic cloaks.Comment: 5 pages and 4 figures Figure 4 has been remad
- …