427 research outputs found
Sistema de controle de horas extras.
Editores técnicos: Joseani Mesquita Antunes, Ana Lídia Variani Bonato, Márcia Barrocas Moreira Pimentel
Evolving Lorentzian wormholes supported by phantom matter with constant state parameters
In this paper we study the possibility of sustaining an evolving wormhole via
exotic matter made out of phantom energy. We show that this exotic source can
support the existence of evolving wormhole spacetimes. Explicitly, a family of
evolving Lorentzian wormholes conformally related to another family of
zero-tidal force static wormhole geometries is found in Einstein gravity.
Contrary to the standard wormhole approach, where first a convenient geometry
is fixed and then the matter distribution is derived, we follow the
conventional approach for finding solutions in theoretical cosmology. We derive
an analytical evolving wormhole geometry by supposing that the radial tension
(which is negative to the radial pressure) and the pressure measured in the
tangential directions have barotropic equations of state with constant state
parameters. At spatial infinity this evolving wormhole, supported by this
anisotropic matter, is asymptotically flat, and its slices constant are
spaces of constant curvature. During its evolution the shape of the wormhole
expands with constant velocity, i.e without acceleration or deceleration, since
the scale factor has strictly a linear evolution.Comment: 9 pages, 2 figures, Accepted for publication in Phys. Rev.
Coulomb's law modification in nonlinear and in noncommutative electrodynamics
We study the lowest-order modifications of the static potential for
Born-Infeld electrodynamics and for the -expanded version of the
noncommutative U(1) gauge theory, within the framework of the gauge-invariant
but path-dependent variables formalism. The calculation shows a long-range
correction (-type) to the Coulomb potential in Born-Infeld
electrodynamics. However, the Coulomb nature of the potential (to order )
is preserved in noncommutative electrodynamics.Comment: 14 pages, 1 figur
Verificação, avaliação e processamento das informações do programa de melhoramento de trigo para acesso e consulta por meio de bancos de dados relacional e grafo.
Editores técnicos: Joseani Mesquita Antunes, Ana Lídia Variani Bonato, Márcia Barrocas Moreira Pimentel
n-Dimensional FLRW Quantum Cosmology
We introduce the formalism of quantum cosmology in a
Friedmann-Lema\^itre-Robertson-Walker (FLRW) universe of arbitrary dimension
filled with a perfect fluid with equation of state. First we
show that the Schutz formalism, developed in four dimensions, can be extended
to a n-dimensional universe. We compute the quantum representant of the scale
factor , in the Many-Worlds, as well as, in the de Broglie-Bohm
interpretation of quantum mechanics. We show that the singularities, which are
still present in the n-dimensional generalization of FLRW universe, are
excluded with the introduction of quantum theory. We quantize, via the de
Broglie-Bohm interpretation of quantum mechanics, the components of the Riemann
curvature tensor in a tetrad basis in a n-dimensional FLRW universe filled with
radiation (). We show that the quantized version of the
Ricci scalar are perfectly regular for all time . We also study the behavior
of the energy density and pressure and show that the ratio
tends to the classical value only for , showing that is
somewhat privileged among the other dimensions. Besides that, as ,
.Comment: 12 pages, revtex, minor modification
Quantum singularities in FRW universe revisited
The components of the Riemann tensor in the tetrad basis are quantized and,
through the Einstein equation, we find the local expectation value in the
ontological interpretation of quantum mechanics of the energy density and
pressure of a perfect fluid with equation of state in the
flat Friedmann-Robertson-Walker quantum cosmological model. The quantum
behavior of the equation of state and energy conditions are then studied and it
is shown that the later is violated since the singularity is removed with the
introduction of quantum cosmology, but in the classical limit both the equation
of state and the energy conditions behave as in the classical model. We also
calculate the expectation value of the scale factor for several wave packets in
the many-worlds interpretation in order to show the independence of the non
singular character of the quantum cosmological model with respect to the wave
packet representing the wave function of the Universe. It is also shown that,
with the introduction of non-normalizable wave packets, solutions of the
Wheeler-DeWitt equation, the singular character of the scale factor, can be
recovered in the ontological interpretation.Comment: 15 pages, revtex, accepted for publication in PR
Scattering map for two black holes
We study the motion of light in the gravitational field of two Schwarzschild
black holes, making the approximation that they are far apart, so that the
motion of light rays in the neighborhood of one black hole can be considered to
be the result of the action of each black hole separately. Using this
approximation, the dynamics is reduced to a 2-dimensional map, which we study
both numerically and analytically. The map is found to be chaotic, with a
fractal basin boundary separating the possible outcomes of the orbits (escape
or falling into one of the black holes). In the limit of large separation
distances, the basin boundary becomes a self-similar Cantor set, and we find
that the box-counting dimension decays slowly with the separation distance,
following a logarithmic decay law.Comment: 20 pages, 5 figures, uses REVTE
Chaos around a H\'enon-Heiles-inspired exact perturbation of a black hole
A solution of the Einstein's equations that represents the superposition of a
Schwarszchild black hole with both quadrupolar and octopolar terms describing a
halo is exhibited. We show that this solution, in the Newtonian limit, is an
analog to the well known H\'enon-Heiles potential. The integrability of orbits
of test particles moving around a black hole representing the galactic center
is studied and bounded zones of chaotic behavior are found.Comment: 7 pages Revte
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