3,452 research outputs found
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
The Nearby Supernova Factory
The Nearby Supernova Factory (SNfactory) is an ambitious project to find and
study in detail approximately 300 nearby Type Ia supernovae (SNe~Ia) at
redshifts 0.03<z<0.08. This program will provide an exceptional data set of
well-studied SNe in the nearby smooth Hubble flow that can be used as
calibration for the current and future programs designed to use SNe to measure
the cosmological parameters. The first key ingredient for this program is a
reliable supply of Hubble-flow SNe systematically discovered in unprecedented
numbers using the same techniques as those used in distant SNe searches. In
2002, 35 SNe were found using our test-bed pipeline for automated SN search and
discovery. The pipeline uses images from the asteroid search conducted by the
Near Earth Asteroid Tracking group at JPL. Improvements in our subtraction
techniques and analysis have allowed us to increase our effective SN discovery
rate to ~12 SNe/month in 2003.Comment: 7 pages, 3 figures to be published in New Astronomy Review
Modified Chaplygin Gas and Constraints on its B parameter from CDM and UDME Cosmological models
We study Modified Chaplygin Gas (MCG) as a candidate for dark energy and
predict the values of parameters of the gas for a physically viable
cosmological model. The equation of state of MCG () involves three parameters: , and . The
permitted values of these parameters are determined with the help of
dimensionless age parameter () and Data. Specifically we
study the allowed ranges of values of B parameter in terms of and
( is defined in terms of the constants in the theory). We
explore the constraints of the parameters in Cold Dark Matter(CDM) model and
UDME(Unified Dark Matter Energy) model respectively.Comment: 5 pages, 10 fig
A late time acceleration of the universe with two scalar fields : many possibilities
In the present work, an attempt has been made to explain the recent cosmic
acceleration with two mutually interacting scalar fields, one being the
Brans-Dicke scalar field and the other a quintessence scalar field. Conditions
have been derived for which the quintessence scalar field has an early
oscillation and it grows during a later time to govern the dynamics of the
universe.Comment: 8 pages, no figures. Accepted for publication in Mod. Phys. Lett.
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
Can luminosity distance measurements probe the equation of state of dark energy
Distance measurements to Type Ia supernovae (SNe Ia) at cosmological
distances indicate that the Universe is accelerating and that a large fraction
of the critical energy density exists in a component with negative pressure.
Various hypotheses on the nature of this ``dark energy'' can be tested via
their prediction for the equation of state of this component. If the dark
energy is due to a scalar field, its equation of state will in general vary
with time and is related to the potential of the field. We review the intrinsic
degeneracies of luminosity distance measurements and compute the expected
accuracies that can be obtained for the equation of state parameter from a
realistic high statistic SNe Ia experiment.Comment: 12 pages, 3 Postscript figures, use epsfig, amssymb, amsmath.
Submitted to Physics Letters.
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
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