3,808 research outputs found
Vacuum entanglement enhancement by a weak gravitational field
Separate regions in space are generally entangled, even in the vacuum state.
It is known that this entanglement can be swapped to separated Unruh-DeWitt
detectors, i.e., that the vacuum can serve as a source of entanglement. Here,
we demonstrate that, in the presence of curvature, the amount of entanglement
that Unruh-DeWitt detectors can extract from the vacuum can be increased.Comment: 6 pages, 1 figur
Estimating the sensitivity of wide-parameter-space searches for gravitational-wave pulsars
This paper presents an in-depth study of how to estimate the sensitivity of
searches for gravitational-wave pulsars -- rapidly-rotating neutron stars which
emit quasi-sinusoidal gravitational waves. It is particularly concerned with
searches over a wide range of possible source parameters, such as searches over
the entire sky and broad frequency bands. Traditional approaches to estimating
the sensitivity of such searches use either computationally-expensive Monte
Carlo simulations, or analytic methods which sacrifice accuracy by making an
unphysical assumption about the population of sources being searched for. This
paper develops a new, analytic method of estimating search sensitivity which
does not rely upon this unphysical assumption. Unlike previous analytic
methods, the new method accurately predicts the sensitivity obtained using
Monte Carlo simulations, while avoiding their computational expense. The change
in estimated sensitivity due to properties of the search template bank, and the
geographic configuration of the gravitational wave detector network, are also
investigated.Comment: 16 figures, 2 tables, REVTeX 4.1; minor typos corrected from v2,
updated reference
Topological Reverberations in Flat Space-times
We study the role played by multiply-connectedness in the time evolution of
the energy E(t) of a radiating system that lies in static flat space-time
manifolds M_4 whose t=const spacelike sections M_3 are compact in at least one
spatial direction. The radiation reaction equation of the radiating source is
derived for the case where M_3 has any non-trivial flat topology, and an exact
solution is obtained. We also show that when the spacelike sections are
multiply-connected flat 3-manifolds the energy E(t) exhibits a reverberation
pattern with discontinuities in the derivative of E(t) and a set of relative
minima and maxima, followed by a growth of E(t). It emerges from this result
that the compactness in at least one spatial direction of Minkowski space-time
is sufficient to induce this type of topological reverberation, making clear
that our radiating system is topologically fragile. An explicit solution of the
radiation reaction equation for the case where M_3 = R^2 x S^1 is discussed,
and graphs which reveal how the energy varies with the time are presented and
analyzed.Comment: 16 pages, 4 figures, REVTEX; Added five references and inserted
clarifying details. Version to appear in Int. J. Mod. Phys. A (2000
A Quantum Cosmological Model With Static and Dynamic Wormholes
Quantization is performed of a Friedmann-Robertson-Walker universe filled
with a conformally invariant scalar field and a perfect fluid with equation of
state . A well-known discrete set of static quantum wormholes is
shown to exist for radiation (), and a novel continuous set is
found for cosmic strings (), the latter states having throat
radii of any size. In both cases wave-packet solutions to the Wheeler-DeWitt
equation are obtained with all the properties of evolving quantum wormholes. In
the case of a radiation fluid, a detailed analysis of the quantum dynamics is
made in the context of the Bohm-de Broglie interpretation. It is shown that a
repulsive quantum force inversely proportional to the cube of the scale factor
prevents singularities in the quantum domain. For the states considered, there
are no particle horizons either.Comment: LaTex file, 13 pages. To appear in General Relativity and Gravitatio
Troubles with quantum anistropic cosmological models: Loss of unitarity
The anisotropic Bianchi I cosmological model coupled with perfect fluid is
quantized in the minisuperspace. The perfect fluid is described by using the
Schutz formalism which allows to attribute dynamical degrees of freedom to
matter. A Schr\"odinger-type equation is obtained where the matter variables
play the role of time. However, the signature of the kinetic term is
hyperbolic. This Schr\"odinger-like equation is solved and a wave packet is
constructed. The norm of the resulting wave function comes out to be time
dependent, indicating the loss of unitarity in this model. The loss of
unitarity is due to the fact that the effective Hamiltonian is hermitian but
not self-adjoint. The expectation value and the bohmian trajectories are
evaluated leading to different cosmological scenarios, what is a consequence of
the absence of a unitary quantum structure. The consistency of this quantum
model is discussed as well as the generality of the absence of unitarity in
anisotropic quantum models.Comment: Latex file, 18 pages. To appear in General Relativity and Gravitatio
Dilaton Quantum Cosmology with a Schrodinger-like equation
A quantum cosmological model with radiation and a dilaton scalar field is
analysed. The Wheeler-deWitt equation in the mini-superspace induces a
Schr\"odinger equation, which can be solved. An explicit wavepacket is
constructed for a particular choice of the ordering factor. A consistent
solution is possible only when the scalar field is a phantom field. Moreover,
although the wavepacket is time dependent, a Bohmian analysis allows to extract
a bouncing behaviour for the scale factor.Comment: 14 pages, 3 figures in eps format. Minors corrections, new figure
Quantum cosmological perfect fluid models
Perfect fluid Friedmann-Robertson-Walker quantum cosmological models for an
arbitrary barotropic equation of state are constructed using
Schutz's variational formalism. In this approach the notion of time can be
recovered. By superposition of stationary states, finite-norm wave-packet
solutions to the Wheeler-DeWitt equation are found. The behaviour of the scale
factor is studied by applying the many-worlds and the ontological
interpretations of quantum mechanics. Singularity-free models are obtained for
.Comment: Latex file, 12 pages. New paragraphs in the Introduction and
Conclusion, and other minor corrections in the text and in some formulas.
Accepted for publication in General Relativity and Gravitatio
On the Solution to the "Frozen Star" Paradox, Nature of Astrophysical Black Holes, non-Existence of Gravitational Singularity in the Physical Universe and Applicability of the Birkhoff's Theorem
Oppenheimer and Snyder found in 1939 that gravitational collapse in vacuum
produces a "frozen star", i.e., the collapsing matter only asymptotically
approaches the gravitational radius (event horizon) of the mass, but never
crosses it within a finite time for an external observer. Based upon our recent
publication on the problem of gravitational collapse in the physical universe
for an external observer, the following results are reported here: (1) Matter
can indeed fall across the event horizon within a finite time and thus BHs,
rather than "frozen stars", are formed in gravitational collapse in the
physical universe. (2) Matter fallen into an astrophysical black hole can never
arrive at the exact center; the exact interior distribution of matter depends
upon the history of the collapse process. Therefore gravitational singularity
does not exist in the physical universe. (3) The metric at any radius is
determined by the global distribution of matter, i.e., not only by the matter
inside the given radius, even in a spherically symmetric and pressureless
gravitational system. This is qualitatively different from the Newtonian
gravity and the common (mis)understanding of the Birkhoff's Theorem. This
result does not contract the "Lemaitre-Tolman-Bondi" solution for an external
observer.Comment: 8 pages, 4 figures, invited plenary talk at "The first Galileo-Xu
Guangqi conference", Shanghai, China, 2009. To appear in International
Journal of Modern Physics D (2010
Strange matter in rotating compact stars
We have constructed equations of state involving various exotic forms of
matter with large strangeness fraction such as hyperon matter, Bose-Einstein
condensates of antikaons and strange quark matter. First order phase
transitions from hadronic to antikaon condensed and quark matter are considered
here. The hadronic phase is described by the relativistic field theoretical
model. Later those equations of state are exploited to investigate models of
uniformly rotating compact stars. The effect of rotation on the third family
branch for the equation of state involving only antikaon condensates is
investigated. We also discuss the back bending phenomenon due to a first order
phase transition from condensed to quark matter.Comment: 8 pages, 4 figures; Plenary talk delivered at Strangeness in Quark
Matter (SQM) 2004 held in Cape Town, South Africa from 15-20 September;
Accepted for publication in the proceedings in Journal of Physics
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