3,412 research outputs found
Opportunities for future supernova studies of cosmic acceleration
We investigate the potential of a future supernova dataset, as might be
obtained by the proposed SNAP satellite, to discriminate among different ``dark
energy'' theories that describe an accelerating Universe. We find that many
such models can be distinguished with a fit to the effective
pressure-to-density ratio, , of this energy. More models can be
distinguished when the effective slope, , of a changing is also fit,
but only if our knowledge of the current mass density, , is improved.
We investigate the use of ``fitting functions'' to interpret luminosity
distance data from supernova searches, and argue in favor of a particular
preferred method, which we use in our analysis.Comment: Four pages including figures. Final published version. No significant
changes from v
Cosmological constant and gravitational theory on D-brane
In a toy model we derive the gravitational equation on a self-gravitating
curved D-brane. The effective theory on the brane is drastically changed from
the ordinal Einstein equation. The net cosmological constant on the brane
depends on a tuning between the brane tension and the brane charges. Moreover,
non-zero matter stress tensor exists if the net cosmological constant is not
zero. This fact indicates a direct connection between matters on the brane and
the dark energy.Comment: 6 pages, minor corrections, accepted for publication in Physical
Review
f(T) modified teleparallel gravity models as an alternative for holographic and new agegraphic dark energy models
In the present work, we reconstruct different f(T)-gravity models
corresponding to the original and entropy-corrected version of the holographic
and new agegraphic dark energy models. We also obtain the equation of state
parameters of the corresponding f(T)-gravity models. We conclude that the
holographic and new agegraphic f(T)-gravity models behave like phantom or
quintessence model. Whereas in the entropy-corrected models, the equation of
state parameter can justify the transition from the quintessence state to the
phantom regime as indicated by the recent observations.Comment: 22 pages, 8 figures, the preprint has been improved considerabl
The influence of quintessence on the motion of a binary system in cosmology
We employ the metric of Schwarzschild space surrounded by quintessential
matter to study the trajectories of test masses on the motion of a binary
system. The results, which are obtained through the gradually approximate
approach, can be used to search for dark energy via the difference of the
azimuth angle of the pericenter. The classification of the motion is discussed.Comment: 7 pages, 1 figur
Gamma-ray burst contributions to constraining the evolution of dark energy
We explore the gamma-ray bursts' (GRBs') contributions in constraining the
dark energy equation of state (EOS) at high () and at middle
redshifts () and estimate how many GRBs are needed to get
substantial constraints at high redshifts. We estimate the constraints with
mock GRBs and mock type Ia supernovae (SNe Ia) for comparisons. When
constraining the dark energy EOS in a certain redshift range, we allow the dark
energy EOS parameter to vary only in that redshift bin and fix EOS parameters
elsewhere to -1. We find that it is difficult to constrain the dark energy EOS
beyond the redshifts of SNe Ia with GRBs unless some new luminosity relations
for GRBs with smaller scatters are discovered. However, at middle redshifts,
GRBs have comparable contributions with SNe Ia in constraining the dark energy
EOS.Comment: 3 pages, 5 figures. Published in Astronomy and Astrophysics.
Corrected referenc
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
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
Scalar-Tensor Gravity and Quintessence
Scalar fields with inverse power-law effective potentials may provide a
negative pressure component to the energy density of the universe today, as
required by cosmological observations. In order to be cosmologically relevant
today, the scalar field should have a mass
, thus potentially inducing sizable
violations of the equivalence principle and space-time variations of the
coupling constants. Scalar-tensor theories of gravity provide a framework for
accommodating phenomenologically acceptable ultra-light scalar fields. We
discuss non-minimally coupled scalar-tensor theories in which the scalar-matter
coupling is a dynamical quantity. Two attractor mechanisms are operative at the
same time: one towards the tracker solution, which accounts for the accelerated
expansion of the Universe, and one towards general relativity, which makes the
ultra-light scalar field phenomenologically safe today. As in usual
tracker-field models, the late-time behavior is largely independent on the
initial conditions. Strong distortions in the cosmic microwave background
anisotropy spectra as well as in the matter power spectrum are expected.Comment: 5 pages, 4 figure
High-redshift objects and the generalized Chaplygin gas
Motivated by recent developments in particle physics and cosmology, there has
been growing interest in an unified description of dark matter and dark energy
scenarios. In this paper we explore observational constraints from age
estimates of high- objects on cosmological models dominated by an exotic
fluid with equation of state (the so-called generalized
Chaplygin gas) which has the interesting feature of interpolating between
non-relativistic matter and negative-pressure dark energy regimes. As a general
result we find that, if the age estimates of these objects are correct, they
impose very restrictive limits on some of these scenarios.Comment: 5 pages, 3 figures, to appear in Phys. Rev.
K-essential Phantom Energy: Doomsday around the Corner? Revisited
We generalize some of those results reported by Gonz\'{a}lez-D\'{i}az by
further tuning the parameter () which is closely related to the
canonical kinetic term in -essence formalism. The scale factor could
be negative and decreasing within a specific range of (, : the equation-of-state parameter) during the initial
evolutional period.Comment: 1 Figure, 6 page
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