672 research outputs found
Integrable Multicomponent Perfect Fluid Multidimensional Cosmology II: Scalar Fields
We consider anisotropic cosmological models with an universe of dimension 4
or more, factorized into n>1 Ricci-flat spaces, containing an m-component
perfect fluid of m non-interacting homogeneous minimally coupled scalar fields
under special conditions. We describe the dynamics of the universe: It has a
Kasner-like behaviour near the singularity and isotropizes during the expansion
to infinity.
Some of the considered models are integrable, and classical as well as
quantum solutions are found. Some solutions produce inflation from "nothing".
There exist classical asymptotically anti-de Sitter wormholes, and quantum
wormholes with discrete spectrum.Comment: 28 pages, LaTeX, subm. to Gen. Rel. Gra
Cosmological solutions in multidimensional model with multiple exponential potential
A family of cosmological solutions with Ricci-flat spaces in the
theory with several scalar fields and multiple exponential potential is
obtained when coupling vectors in exponents obey certain relations. Two
subclasses of solutions with power-law and exponential behaviour of scale
factors are singled out. It is proved that power-law solutions may take place
only when coupling vectors are linearly independent and exponential dependence
occurs for linearly dependent set of coupling vectors. A subfamily of solutions
with accelerated expansion is singled out. A generalized isotropization
behaviours of certain classes of general solutions are found. In quantum case
exact solutions to Wheeler-DeWitt equation are obtained and special "ground
state" wave functions are considered.Comment: 22 pages, 1 figur
Stars in five dimensional Kaluza Klein gravity
In the five dimensional Kaluza Klein (KK) theory there is a well known class
of static and electromagnetic--free KK--equations characterized by a naked
singularity behavior, namely the Generalized Schwarzschild solution (GSS). We
present here a set of interior solutions of five dimensional KK--equations.
These equations have been numerically integrated to match the GSS in the
vacuum. The solutions are candidates to describe the possible interior perfect
fluid source of the exterior GSS metric and thus they can be models for stars
for static, neutral astrophysical objects in the ordinary (four dimensional)
spacetime.Comment: 15 pages, 8 figures. To be published in EPJ
Generalized uncertainty principle in Bianchi type I quantum cosmology
We study a quantum Bianchi type I model in which the dynamical variables of
the corresponding minisuperspace obey the generalized Heisenberg algebra. Such
a generalized uncertainty principle has its origin in the existence of a
minimal length suggested by quantum gravity and sting theory. We present
approximate analytical solutions to the corresponding Wheeler-DeWitt equation
in the limit where the scale factor of the universe is small and compare the
results with the standard commutative and noncommutative quantum cosmology.
Similarities and differences of these solutions are also discussed.Comment: 8 pages, 3 figures, to appear in PL
Renal insufficiency as a predictor of cardiovascular outcomes and mortality in elderly individuals
AbstractObjectivesThis study was designed to evaluate the relationship between elevated creatinine levels and cardiovascular events.BackgroundEnd-stage renal disease is associated with high cardiovascular morbidity and mortality. The association of mild to moderate renal insufficiency with cardiovascular outcomes remains unclear.MethodsWe analyzed data from the Cardiovascular Health Study, a prospective population-based study of subjects, aged >65 years, who had a serum creatinine measured at baseline (n = 5,808) and were followed for a median of 7.3 years. Proportional hazards models were used to examine the association of creatinine to all-cause mortality and incident cardiovascular mortality and morbidity. Renal insufficiency was defined as a creatinine level ≥1.5 mg/dl in men or ≥1.3 mg/dl in women.ResultsAn elevated creatinine level was present in 648 (11.2%) participants. Subjects with elevated creatinine had higher overall (76.7 vs. 29.5/1,000 years, p < 0.001) and cardiovascular (35.8 vs. 13.0/1,000 years, p < 0.001) mortality than those with normal creatinine levels. They were more likely to develop cardiovascular disease (54.0 vs. 31.8/1,000 years, p < 0.001), stroke (21.1 vs. 11.9/1,000 years, p < 0.001), congestive heart failure (38.7 vs. 17/1,000 years, p < 0.001), and symptomatic peripheral vascular disease (10.6 vs. 3.5/1,000 years, p < 0.001). After adjusting for cardiovascular risk factors and subclinical disease measures, elevated creatinine remained a significant predictor of all-cause and cardiovascular mortality, total cardiovascular disease (CVD), claudication, and congestive heart failure (CHF). A linear increase in risk was observed with increasing creatinine.ConclusionsElevated creatinine levels are common in older adults and are associated with increased risk of mortality, CVD, and CHF. The increased risk is apparent early in renal disease
Period-doubling bifurcation in strongly anisotropic Bianchi I quantum cosmology
We solve the Wheeler-DeWitt equation for the minisuperspace of a cosmological
model of Bianchi type I with a minimally coupled massive scalar field as
source by generalizing the calculation of Lukash and Schmidt [1]. Contrarily to
other approaches we allow strong anisotropy. Combining analytical and numerical
methods, we apply an adiabatic approximation for , and as new feature we
find a period-doubling bifurcation. This bifurcation takes place near the
cosmological quantum boundary, i.e., the boundary of the quasiclassical region
with oscillating -function where the WKB-approximation is good. The
numerical calculations suggest that such a notion of a ``cosmological quantum
boundary'' is well-defined, because sharply beyond that boundary, the
WKB-approximation is no more applicable at all. This result confirms the
adequateness of the introduction of a cosmological quantum boundary in quantum
cosmology.Comment: Latest update of the paper at
http://www.physik.fu-berlin.de/~mbach/publics.html#
Stabilization of internal spaces in multidimensional cosmology
Effective 4-dimensional theories are investigated which were obtained under
dimensional reduction of multidimensional cosmological models with a minimal
coupled scalar field as matter source. Conditions for the internal space
stabilization are considered and the possibility for inflation in the external
space is discussed. The electroweak as well as the Planck fundamental scale
approaches are investigated and compared with each other. It is shown that
there exists a rescaling for the effective cosmological constant as well as for
gravitational exciton masses in the different approaches.Comment: 12 pages, LaTeX2e, to appear in Phys.Rev.D, note adde
Multidimensional cosmological models: cosmological and astrophysical implications and constraints
We investigate four-dimensional effective theories which are obtained by
dimensional reduction of multidimensional cosmological models with factorizable
geometry and consider the interaction between conformal excitations of the
internal space (geometrical moduli excitations) and Abelian gauge fields. It is
assumed that the internal space background can be stabilized by minima of an
effective potential. The conformal excitations over such a background have the
form of massive scalar fields (gravitational excitons) propagating in the
external spacetime. We discuss cosmological and astrophysical implications of
the interaction between gravexcitons and four-dimensional photons as well as
constraints arising on multidimensional models of the type considered in our
paper. In particular, we show that due to the experimental bounds on the
variation of the fine structure constant, gravexcitons should decay before
nucleosynthesis starts. For a successful nucleosynthesis the masses of the
decaying gravexcitons should be m>10^4 GeV. Furthermore, we discuss the
possible contribution of gravexcitons to UHECR. It is shown that, at energies
of about 10^{20}eV, the decay length of gravexcitons with masses m>10^4 GeV is
very small, but that for m <10^2 GeV it becomes much larger than the
Greisen-Zatsepin-Kuzmin cut-off distance. Finally, we investigate the
possibility for gravexciton-photon oscillations in strong magnetic fields of
astrophysical objects. The corresponding estimates indicate that even the high
magnetic field strengths of magnetars are not sufficient for an efficient and
copious production of gravexcitons.Comment: 16 pages, LaTeX2e, minor changes, improved references, to appear in
PR
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