60 research outputs found
Classical and quantum spinor cosmology with signature change
We study the classical and quantum cosmology of a universe in which the
matter source is a massive Dirac spinor field and consider cases where such
fields are either free or self-interacting. We focus attention on the spatially
flat Robertson-Walker cosmology and classify the solutions of the
Einstein-Dirac system in the case of zero, negative and positive cosmological
constant . For , these solutions exhibit signature
transitions from a Euclidean to a Lorentzian domain. In the case of massless
spinor fields it is found that signature changing solutions do not exist when
the field is free while in the case of a self-interacting spinor field such
solutions may exist. The resulting quantum cosmology and the corresponding
Wheeler-DeWitt equation are also studied for both free and self interacting
spinor fields and closed form expressions for the wavefunction of the universe
are presented. These solutions suggest a quantization rule for the energy.Comment: 13 pages, 4 figure
Stabilization of test particles in Induced Matter Kaluza-Klein theory
The stability conditions for the motion of classical test particles in an -dimensional Induced Matter Kaluza-Klein theory is studied. We show that
stabilization requires a variance of the strong energy condition for the
induced matter to hold and that it is related to the hierarchy problem.
Stabilization of test particles in a FRW universe is also discussed.Comment: 15 pages, 1 figure, to appear in Class. Quantum Gra
On extra forces from large extra dimensions
The motion of a classical test particle moving on a 4-dimensional brane
embedded in an -dimensional bulk is studied in which the brane is allowed to
fluctuate along the extra dimensions. It is shown that these fluctuations
produce three different forces acting on the particle, all stemming from the
effects of extra dimensions. Interpretations are then offered to describe the
origin of these forces and a relationship between the 4 and -dimensional
mass of the particle is obtained by introducing charges associated with large
extra dimensions.Comment: 9 pages, no figuer
Compactification and signature transition in Kaluza-Klein spinor cosmology
We study the classical and quantum cosmology of a 4+1-dimensional space-time
with a non-zero cosmological constant coupled to a self interacting massive
spinor field. We consider a spatially flat Robertson-Walker universe with the
usual scale factor and an internal scale factor associated with
the extra dimension. For a free spinor field the resulting equations admit
exact solutions, whereas for a self interacting spinor field one should resort
to a numerical method for exhibiting their behavior. These solutions give rise
to a degenerate metric and exhibit signature transition from a Euclidean to a
Lorentzian domain. Such transitions suggest a compactification mechanism for
the internal and external scale factors such that in the
Lorentzian region. The corresponding quantum cosmology and the ensuing
Wheeler-DeWitt equation have exact solutions in the mini-superspace when the
spinor field is free, leading to wavepackets undergoing signature change. The
question of stabilization of the extra dimension is also discussed.Comment: 12 pages, 1 figure, to appear in Annals of Physic
Quantum Black Hole in the Generalized Uncertainty Principle Framework
In this paper we study the effects of the Generalized Uncertainty Principle
(GUP) on canonical quantum gravity of black holes. Through the use of modified
partition function that involves the effects of the GUP, we obtain the
thermodynamical properties of the Schwarzschild black hole. We also calculate
the Hawking temperature and entropy for the modification of the Schwarzschild
black hole in the presence of the GUP.Comment: 11 pages, no figures, to appear in Physical Review
Late time acceleration in a deformed phase space model of dilaton cosmology
The effects of noncommutativity on the phase space of a dilatonic
cosmological model is investigated. The existence of such noncommutativity
results in a deformed Poisson algebra between the minisuperspace variables and
their momenta conjugate. For an exponential dilaton potential, the exact
solutions in the commutative and noncommutative cases, are presented and
compared. We use these solutions to address the late time acceleration issue of
cosmic evolution.Comment: 10 pages, 2 figures, to appear in PLB, typos correcte
Signature Change in Noncommutative FRW Cosmology
The conditions for which the no boundary proposal may have a classical
realization of a continuous change of signature, are investigated for a
cosmological model described by FRW metric coupled with a self interacting
scalar field, having a noncommutative phase space of dynamical variables. The
model is then quantized and a good correspondence is shown between the
classical and quantum cosmology indicating that the noncommutativity does not
destruct the classical-quantum correspondence. It is also shown that the
quantum cosmology supports a signature transition where the bare cosmological
constant takes a vast continuous spectrum of negative values. The bounds of
bare cosmological constant are limited by the values of noncommutative
parameters. Moreover, it turns out that the physical parameters are constrained
by the noncommutativity parametres.Comment: 15 pages, 4 figures, Minor revision, references adde
Quantization of the interior Schwarzschild black hole
We study a Hamiltonian quantum formalism of a spherically symmetric
space-time which can be identified with the interior of a Schwarzschild black
hole. The phase space of this model is spanned by two dynamical variables and
their conjugate momenta. It is shown that the classical Lagrangian of the model
gives rise the interior metric of a Schwarzschild black hole. We also show that
the the mass of such a system is a Dirac observable and then by quantization of
the model by Wheeler-DeWitt approach and constructing suitable wave packets we
get the mass spectrum of the black hole.Comment: 12 pages, 1 figure, revised versio
Classical tests in brane gravity
The vacuum solutions in brane gravity differ from those in 4D by a number of
additional terms and reduce to the familiar Schwarzschild metric at small
distances. We study the possible roles that such terms may play in the
precession of planetary orbits, bending of light, radar retardation and the
anomaly in mean motion of test bodies. Using the available data from Solar
System experiments, we determine the range of the free parameters associated
with the linear term in the metric. The best results come from the anomalies in
the mean motion of planets. Such studies should shed some light on the origin
of dark energy via the solar system tests.Comment: 10 pages, no figures, to appear in CQ
Postoperative acute kidney injury in adult non-cardiac surgery:joint consensus report of the Acute Disease Quality Initiative and PeriOperative Quality Initiative
Postoperative acute kidney injury (PO-AKI) is a common complication of major surgery that is strongly associated with short-term surgical complications and long-term adverse outcomes, including increased risk of chronic kidney disease, cardiovascular events and death. Risk factors for PO-AKI include older age and comorbid diseases such as chronic kidney disease and diabetes mellitus. PO-AKI is best defined as AKI occurring within 7 days of an operative intervention using the Kidney Disease Improving Global Outcomes (KDIGO) definition of AKI; however, additional prognostic information may be gained from detailed clinical assessment and other diagnostic investigations in the form of a focused kidney health assessment (KHA). Prevention of PO-AKI is largely based on identification of high baseline risk, monitoring and reduction of nephrotoxic insults, whereas treatment involves the application of a bundle of interventions to avoid secondary kidney injury and mitigate the severity of AKI. As PO-AKI is strongly associated with long-term adverse outcomes, some form of follow-up KHA is essential; however, the form and location of this will be dictated by the nature and severity of the AKI. In this Consensus Statement, we provide graded recommendations for AKI after non-cardiac surgery and highlight priorities for future research
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