6,787 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
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
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
Scalar Field Dark Matter: head-on interaction between two structures
In this manuscript we track the evolution of a system consisting of two
self-gravitating virialized objects made of a scalar field in the newtonian
limit. The Schr\"odinger-Poisson system contains a potential with
self-interaction of the Gross-Pitaevskii type for Bose Condensates. Our results
indicate that solitonic behavior is allowed in the scalar field dark matter
model when the total energy of the system is positive, that is, the two blobs
pass through each other as should happen for solitons; on the other hand, there
is a true collision of the two blobs when the total energy is negative.Comment: 8 revtex pages, 11 eps figures. v2 matches the published version.
v2=v1+ref+minor_change
Scalar-Tensor theories from Plebanski gravity
We study a modification of the Plebanski action, which generically
corresponds to a bi-metric theory of gravity, and identify a subclass which is
equivalent to the Bergmann-Wagoner-Nordtvedt class of scalar-tensor theories.
In this manner, scalar-tensor theories are displayed as constrained BF
theories. We find that in this subclass, there is no need to impose reality of
the Urbantke metrics, as also the theory with real bivectors is a scalar-tensor
theory with a real Lorentzian metric. Furthermore, while under the former
reality conditions instabilities can arise from a wrong sign of the scalar mode
kinetic term, we show that such problems do not appear if the bivectors are
required to be real. Finally, we discuss how matter can be coupled to these
theories. The phenomenology of scalar field dark matter arises naturally within
this framework.Comment: 21 page
Quantum mechanical counterpart of nonlinear optics
Raman-type laser excitation of a trapped atom allows one to realize the
quantum mechanical counterpart of phenomena of nonlinear optics, such as
Kerr-type nonlinearities, parametric amplification, and multi-mode mixing.
Additionally, huge nonlinearities emerge from the interference of the atomic
wave function with the laser waves. They lead to a partitioning of the phase
space accompanied by a significantly different action of the time evolution in
neighboring phase-space zones. For example, a nonlinearly modified coherent
"displacement" of the motional quantum state may induce strong amplitude
squeezing and quantum interferences.Comment: 6 pages, 4 figures, to be published in Phys. Rev. A 55 (June
Spherical Scalar Field Halo in Galaxies
We study a spherically symmetric fluctuation of scalar dark matter in the
cosmos and show that it could be the dark matter in galaxies, provided that the
scalar field has an exponential potential whose overall sign is negative and
whose exponent is constrained observationally by the rotation velocities of
galaxies. The local space-time of the fluctuation contains a three dimensional
space-like hypersurface with surplus of angle.Comment: 5 REVTeX pages, no figures. Contains important suggestions provided
by the referee. Final version, to appear in Phys. Rev.
Quantum metrology at the Heisenberg limit with ion traps
Sub-Planck phase-space structures in the Wigner function of the motional
degree of freedom of a trapped ion can be used to perform weak force
measurements with Heisenberg-limited sensitivity. We propose methods to
engineer the Hamiltonian of the trapped ion to generate states with such small
scale structures, and we show how to use them in quantum metrology
applications.Comment: 10 pages, 6 figure
Quantum-state synthesis of multi-mode bosonic fields: Preparation of arbitrary states of 2-D vibrational motion of trapped ions
We present a universal algorithm for an efficient deterministic preparation
of an arbitrary two--mode bosonic state. In particular, we discuss in detail
preparation of entangled states of a two-dimensional vibrational motion of a
trapped ion via a sequence of laser stimulated Raman transitions. Our formalism
can be generalized for multi-mode bosonic fields. We examine stability of our
algorithm with respect to a technical noise.Comment: 8 pages, revtex, including 2 ps-figures, section about physical
implementation added, references updated, submitted to Phys. Rev. A, computer
program available at http://www.savba.sk/sav/inst/fyzi/qo
Scalar Field as Dark Matter in the Universe
We investigate the hypothesis that the scalar field is the dark matter and
the dark energy in the Cosmos, wich comprises about 95% of the matter of the
Universe. We show that this hypothesis explains quite well the recent
observations on type Ia supernovae.Comment: 4 pages REVTeX, 1 eps figure. Minor changes. To appear in Classical
and Quantum Gravit
- …