7,471 research outputs found
Evolving wormhole geometries within nonlinear electrodynamics
In this work, we explore the possibility of evolving (2+1) and
(3+1)-dimensional wormhole spacetimes, conformally related to the respective
static geometries, within the context of nonlinear electrodynamics. For the
(3+1)-dimensional spacetime, it is found that the Einstein field equation
imposes a contracting wormhole solution and the obedience of the weak energy
condition. Nevertheless, in the presence of an electric field, the latter
presents a singularity at the throat, however, for a pure magnetic field the
solution is regular. For the (2+1)-dimensional case, it is also found that the
physical fields are singular at the throat. Thus, taking into account the
principle of finiteness, which states that a satisfactory theory should avoid
physical quantities becoming infinite, one may rule out evolving
(3+1)-dimensional wormhole solutions, in the presence of an electric field, and
the (2+1)-dimensional case coupled to nonlinear electrodynamics.Comment: 17 pages, 1 figure; to appear in Classical and Quantum Gravity. V2:
minor corrections, including a referenc
Deconvolving the information from an imperfect spherical gravitational wave antenna
We have studied the effects of imperfections in spherical gravitational wave
antenna on our ability to properly interpret the data it will produce. The
results of a numerical simulation are reported that quantitatively describe the
systematic errors resulting from imperfections in various components of the
antenna. In addition, the results of measurements on a room-temperature
prototype are presented that verify it is possible to accurately deconvolve the
data in practice.Comment: 5 pages, 2 figures, to be published in Europhysics Letter
A Chiellini type integrability condition for the generalized first kind Abel differential equation
The Chiellini integrability condition of the first order first kind Abel
equation is extended to the case of the general Abel
equation of the form , where
, and . In the case the generalized
Abel equations reduces to a Riccati type equation, for which a Chiellini type
integrability condition is obtained.Comment: 4 pages, no figure
Arbitrary scalar field and quintessence cosmological models
The mechanism of the initial inflationary scenario of the universe and of its
late-time acceleration can be described by assuming the existence of some
gravitationally coupled scalar fields , with the inflaton field
generating inflation and the quintessence field being responsible for the late
accelerated expansion. Various inflationary and late-time accelerated scenarios
are distinguished by the choice of an effective self-interaction potential
, which simulates a temporarily non-vanishing cosmological term. In
this work, we present a new formalism for the analysis of scalar fields in flat
isotropic and homogeneous cosmological models. The basic evolution equation of
the models can be reduced to a first order non-linear differential equation.
Approximate solutions of this equation can be constructed in the limiting cases
of the scalar field kinetic energy and potential energy dominance,
respectively, as well as in the intermediate regime. Moreover, we present
several new accelerating and decelerating exact cosmological solutions, based
on the exact integration of the basic evolution equation for scalar field
cosmologies. More specifically, exact solutions are obtained for exponential,
generalized cosine hyperbolic, and power law potentials, respectively.
Cosmological models with power law scalar field potentials are also analyzed in
detail.Comment: 22 pages, 4 figures; references added; major revision; accepted for
publication in EPJ
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