4,341 research outputs found
Dynamics of Massive Scalar Fields in dS Space and the dS/CFT Correspondence
Global geometric properties of dS space are presented explicitly in various
coordinates. A Robertson-Walker like metric is deduced, which is convenient to
be used in study of dynamics in dS space. Singularities of wavefunctions of
massive scalar fields at boundary are demonstrated. A bulk-boundary propagator
is constructed by making use of the solutions of equations of motion. The
dS/CFT correspondence and the Strominger's mass bound is shown.Comment: latex, 14 pages and 3 figure
Carmeli's accelerating universe is spatially flat without dark matter
Carmeli's 5D brane cosmology has been applied to the expanding accelerating
universe and it has been found that the distance redshift relation will fit the
data of the high-z supernova teams without the need for dark matter. Also the
vacuum energy contribution to gravity indicates that the universe is
asymptotically expanding towards a spatially flat state, where the total
mass/energy density tends to unity.Comment: 4 pages, 5 figures, accepted for publication in Int. J. Theor.
Physics, this paper is based on an invited talk at FFP6, Udine, Italy, Sept
200
Spintessence: a possible candidate as a driver of the late time cosmic acceleration
In this paper, it is shown completely analytically that a spintessence model
can very well serve the purpose of providing an early deceleration and the
present day acceleration.Comment: 5 pages, no figure. Accepted for publication in Astrophysics and
Space Scienc
Phantom Energy Accretion by Stringy Charged Black Hole
We investigate the dynamical behavior of phantom energy near stringy
magnetically charged black hole. For this purpose, we derive equations of
motion for steady-state spherically symmetric flow of phantom energy onto the
stringy magnetically charged black hole. It is found that phantom energy
accreting onto black hole decreases its mass. Further, the location of critical
points of accretion is explored, which yields mass to charge ratio. This ratio
implies that accretion process cannot transform a black hole into an extremal
black hole or a naked singularity, hence cosmic censorship hypothesis remains
valid here.Comment: 7 pages, no figur
Domain walls in Born-Infeld-dilaton background
We study the dynamics of domain walls in Einstein-Born-Infeld-dilaton theory.
Dilaton is non-trivially coupled with the Born-Infeld electromagnetic field. We
find three different types of solutions consistent with the dynamic domain
walls. For every case, the solutions have singularity. Further more, in these
backgrounds, we study the dynamics of domain walls. We qualitatively plot
various form of the bulk metrics and the potential encountered by the domain
walls. In many cases, depending upon the value of the parameters, the domain
walls show bouncing universe and also undergo inflationary phase followed by
standard decelerated expansion.Comment: 18 pages,6 figures,latex, References added, Some points clarifie
Cosmology with two compactification scales
We consider a (4+d)-dimensional spacetime broken up into a (4-n)-dimensional
Minkowski spacetime (where n goes from 1 to 3) and a compact (n+d)-dimensional
manifold. At the present time the n compactification radii are of the order of
the Universe size, while the other d compactification radii are of the order of
the Planck length.Comment: 16 pages, Latex2e, 7 figure
Why we need to see the dark matter to understand the dark energy
The cosmological concordance model contains two separate constituents which
interact only gravitationally with themselves and everything else, the dark
matter and the dark energy. In the standard dark energy models, the dark matter
makes up some 20% of the total energy budget today, while the dark energy is
responsible for about 75%. Here we show that these numbers are only robust for
specific dark energy models and that in general we cannot measure the abundance
of the dark constituents separately without making strong assumptions.Comment: 4 pages, to be published in the Journal of Physics: Conference Series
as a contribution to the 2007 Europhysics Conference on High Energy Physic
Curvature Dependence of Peaks in the Cosmic Microwave Background Distribution
The widely cited formula for the multipole
number of the first Doppler peak is not even a crude approximation in the case
of greatest current interest, in which the cosmic mass density is less than the
vacuum energy density. For instance, with fixed at 0.3, the position
of any Doppler peak varies as near .Comment: 7 pages, Late
Cosmological constant influence on cosmic string spacetime
We investigate the line element of spacetime around a linear cosmic string in
the presence of a cosmological constant. We obtain the metric and argue that it
should be discarded because of asymptotic considerations. Then a time dependent
and consistent form of the metric is obtained and its properties are discussed.Comment: 3 page
Reconstructing the Cosmic Equation of State from Supernova distances
Observations of high-redshift supernovae indicate that the universe is
accelerating. Here we present a {\em model-independent} method for estimating
the form of the potential of the scalar field driving this
acceleration, and the associated equation of state . Our method is
based on a versatile analytical form for the luminosity distance ,
optimized to fit observed distances to distant supernovae and differentiated to
yield and . Our results favor at the
present epoch, steadily increasing with redshift. A cosmological constant is
consistent with our results.Comment: 4 pages, 5 figures, uses RevTex. Minor typo's in equations (1) and
(10) correcte
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