10,230 research outputs found
Oscillatons revisited
In this paper, we study some interesting properties of a spherically
symmetric oscillating soliton star made of a real time-dependent scalar field
which is called an oscillaton. The known final configuration of an oscillaton
consists of a stationary stage in which the scalar field and the metric
coefficients oscillate in time if the scalar potential is quadratic. The
differential equations that arise in the simplest approximation, that of
coherent scalar oscillations, are presented for a quadratic scalar potential.
This allows us to take a closer look at the interesting properties of these
oscillating objects. The leading terms of the solutions considering a quartic
and a cosh scalar potentials are worked in the so called stationary limit
procedure. This procedure reveals the form in which oscillatons and boson stars
may be related and useful information about oscillatons is obtained from the
known results of boson stars. Oscillatons could compete with boson stars as
interesting astrophysical objects, since they would be predicted by scalar
field dark matter models.Comment: 10 pages REVTeX, 10 eps figures. Updated files to match version
published in Classical and Quantum Gravit
On the Space Time of a Galaxy
We present an exact solution of the averaged Einstein's field equations in
the presence of two real scalar fields and a component of dust with spherical
symmetry. We suggest that the space-time found provides the characteristics
required by a galactic model that could explain the supermassive central object
and the dark matter halo at once, since one of the fields constitutes a central
oscillaton surrounded by the dust and the other scalar field distributes far
from the coordinate center and can be interpreted as a halo. We show the
behavior of the rotation curves all along the background. Thus, the solution
could be a first approximation of a ``long exposition photograph'' of a galaxy.Comment: 8 pages REVTeX, 11 eps figure
Generation of Closed Timelike Curves with Rotating Superconductors
The spacetime metric around a rotating SuperConductive Ring (SCR) is deduced
from the gravitomagnetic London moment in rotating superconductors. It is shown
that theoretically it is possible to generate Closed Timelike Curves (CTC) with
rotating SCRs. The possibility to use these CTC's to travel in time as
initially idealized by G\"{o}del is investigated. It is shown however, that
from a technology and experimental point of view these ideas are impossible to
implement in the present context.Comment: 9 pages. Submitted to Classical and Quantum Gravit
Erratum: Martins, M.S., et al. Wideband and wIde beam polyvinylidene difluoride (PVDF) acoustic transducer for broadband underwater. Sensors 2019, 19, 3991
The authors wish to make the following erratum to this paper [...].info:eu-repo/semantics/publishedVersio
Quintessence and Scalar Dark Matter in the Universe
Continuing with previous works, we present a cosmological model in which dark
matter and dark energy are modeled by scalar fields and ,
respectively, endowed with the scalar potentials and . This model contains 95% of
scalar field. We obtain that the scalar dark matter mass is The solution obtained allows us to recover the success of the
standard CDM. The implications on the formation of structure are reviewed. We
obtain that the minimal cutoff radio for this model is Comment: 4 pages REVTeX, 3 eps color figures. Minor changes and references
updated. To appear in Classical and Quantum Gravity as a Letter to the
Editor. More information at http://www.fis.cinvestav.mx/~siddh/PHI
Decoherence and the quantum-classical limit in the presence of chaos
We investigate how decoherence affects the short-time separation between
quantum and classical dynamics for classically chaotic systems, within the
framework of a specific model. For a wide range of parameters, the distance
between the corresponding phase-space distributions depends on a single
parameter that relates an effective Planck constant ,
the Lyapunov coeffficient, and the diffusion constant. This distance peaks at a
time that depends logarithmically on , in agreement with
previous estimations of the separation time for Hamiltonian systems. However,
for , the separation remains small, going down with , so the concept of separation time loses its meaning.Comment: 5 pages, 4 figures (in 6 postscript files) two of them are color
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