3,491 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
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
Discovery of a Supernova Explosion at Half the Age of the Universe and its Cosmological Implications
The ultimate fate of the universe, infinite expansion or a big crunch, can be
determined by measuring the redshifts, apparent brightnesses, and intrinsic
luminosities of very distant supernovae. Recent developments have provided
tools that make such a program practicable: (1) Studies of relatively nearby
Type Ia supernovae (SNe Ia) have shown that their intrinsic luminosities can be
accurately determined; (2) New research techniques have made it possible to
schedule the discovery and follow-up observations of distant supernovae,
producing well over 50 very distant (z = 0.3 -- 0.7) SNe Ia to date. These
distant supernovae provide a record of changes in the expansion rate over the
past several billion years. By making precise measurements of supernovae at
still greater distances, and thus extending this expansion history back far
enough in time, we can distinguish the slowing caused by the gravitational
attraction of the universe's mass density Omega_M from the effect of a possibly
inflationary pressure caused by a cosmological constant Lambda. We report here
the first such measurements, with our discovery of a Type Ia supernova (SN
1997ap) at z = 0.83. Measurements at the Keck II 10-m telescope make this the
most distant spectroscopically confirmed supernova. Over two months of
photometry of SN 1997ap with the Hubble Space Telescope and ground-based
telescopes, when combined with previous measurements of nearer SNe Ia, suggests
that we may live in a low mass-density universe. Further supernovae at
comparable distances are currently scheduled for ground and space-based
observations.Comment: 12 pages and 4 figures (figure 4 is repeated in color and black and
white) Nature, scheduled for publication in the 1 January, 1998 issue. Also
available at http://www-supernova.lbl.go
de Sitter black hole with a conformally coupled scalar field in four dimensions
A four-dimensional black hole solution of the Einstein equations with a
positive cosmological constant, coupled to a conformal scalar field, is given.
There is a curvature singularity at the origin, and scalar field diverges
inside the event horizon. The electrically charged solution, which has a fixed
charge-to-mass ratio is also found. The quartic self-interacting coupling
becomes bounded in terms of Newton's and the cosmological constants.Comment: 5 pages, no figures, CECS style, energy conditions are discussed and
some references were added. To appear in Phys. Rev.
The Genesis of Cosmological Tracker Fields
The role of the quintessence field as a probable candidate for the repulsive
dark energy, the conditions for tracking and the requisites for tracker fields
are examined. The concept of `integrated tracking' is introduced and a new
criterion for the existence of tracker potentials is derived assuming monotonic
increase in the scalar energy density parameter \Omega_\phi with the evolution
of the universe as suggested by the astrophysical constraints. It provides a
technique to investigate generic potentials of the tracker fields. The general
properties of the tracker fields are discussed and their behaviour with respect
to tracking parameter \epsilon is analyzed. It is shown that the tracker fields
around the limiting value \epsilon \simeq \frac 23 give the best fit with the
observational constraints.Comment: 8 pages, Latex file, 1 figure, comments adde
Optimal Supernova Search Strategies
Recent use of Type Ia supernovae to measure acceleration of the universe has
motivated questions regarding their optimal use to constrain cosmological
parameters Omega_M, Omega_{\Lambda} and w_Q. In this work we address the
question: what is the optimal distribution of supernovae in redshift in order
to best constrain the cosmological parameters? The solution to this problem is
not only of theoretical interest, but can be useful in planning supernova
searches. Using the Fisher matrix formalism we show that the error ellipsoid
corresponding to N parameters (for N=1, 2, 3) has the smallest volume if the
supernovae are located at N discrete redshifts, with equal number of supernovae
at each redshift and with one redshift always being the maximum one probed.
Including marginalization over the ``nuisance parameter'' M changes this result
only trivially.Comment: 12 pages, 6 eps figures. To appear in Proceedings of "Sources and
Detection of Dark Matter/Energy in the Universe", Marina Del Rey, Feb. 200
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
Phantom Accretion onto the Schwarzschild de-Sitter Black Hole
We deal with phantom energy accretion onto the Schwarzschild de-Sitter black
hole. The energy flux conservation, relativistic Bernoulli equation and mass
flux conservation equation are formulated to discuss the phantom accretion. We
discuss the conditions for critical accretion. It is found that mass of the
black hole decreases due to phantom accretion. There exist two critical points
which lie in the exterior of horizons (black hole and cosmological horizons).
The results for the phantom energy accretion onto the Schwarzschild black hole
can be recovered by taking .Comment: 9 pages, no figur
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