3,579 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
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
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
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
Some Dynamical Effects of the Cosmological Constant
Newton's law gets modified in the presence of a cosmological constant by a
small repulsive term (antigarvity) that is proportional to the distance.
Assuming a value of the cosmological constant consistent with the recent SnIa
data () we investigate the significance of this
term on various astrophysical scales. We find that on galactic scales or
smaller (less than a few tens of kpc) the dynamical effects of the vacuum
energy are negligible by several orders of magnitude. On scales of 1Mpc or
larger however we find that vacuum energy can significantly affect the
dynamics. For example we show that the velocity data in the Local Group of
galaxies correspond to galactic masses increased by 35% in the presence of
vacuum energy. The effect is even more important on larger low density systems
like clusters of galaxies or superclusters.Comment: 5 two column pages, 2 figure
From the elasticity theory to cosmology and vice versa
The paper shows how a generalization of the elasticity theory to four
dimensions and to space-time allows for a consistent description of the
homogeneous and isotropic universe, including the accelerated expansion. The
analogy is manifested by the inclusion in the traditional Lagrangian of general
relativity of an additional term accounting for the strain induced in the
manifold (i.e. in space-time) by the curvature, be it induced by the presence
of a texture defect or by a matter/energy distribution. The additional term is
sufficient to account for various observed features of the universe and to give
a simple interpretation for the so called dark energy. Then, we show how the
same approach can be adopted back in three dimensions to obtain the equilibrium
configuration of a given solid subject to strain induced by defects or applied
forces. Finally, it is shown how concepts coming from the familiar elasticity
theory can inspire new approaches to cosmology and in return how methods
appropriated to General Relativity can be applied back to classical problems of
elastic deformations in three dimensions.Comment: 11 pages, 3 figure
Positive Selection and Horizontal Gene Transfer in the Genome of a Male-Killing Wolbachia
Wolbachia are a genus of widespread bacterial endosymbionts in which some strains can hijack or manipulate arthropod host reproduction. Male killing is one such manipulation in which these maternally transmitted bacteria benefit surviving daughters in part by removing competition with the sons for scarce resources. Despite previous findings of interesting genome features of microbial sex ratio distorters, the population genomics of male-killers remain largely uncharacterized. Here, we uncover several unique features of the genome and population genomics of four Arizonan populations of a male-killing Wolbachia strain, wInn, that infects mushroom-feeding Drosophila innubila. We first compared the wInn genome with other closely related Wolbachia genomes of Drosophila hosts in terms of genome content and confirm that the wInn genome is largely similar in overall gene content to the wMel strain infecting D. melanogaster. However, it also contains many unique genes and repetitive genetic elements that indicate lateral gene transfers between wInn and non-Drosophila eukaryotes. We also find that, in line with literature precedent, genes in the Wolbachia prophage and Octomom regions are under positive selection. Of all the genes under positive selection, many also show evidence of recent horizontal transfer among Wolbachia symbiont genomes. These dynamics of selection and horizontal gene transfer across the genomes of several Wolbachia strains and diverse host species may be important underlying factors in Wolbachia’s success as a male-killer of divergent host species
Cosmological constant, renormalization group and Planck scale physics
Starting from generic quantum effects at the Planck scale M_P, we find that
the renormalization group running of the cosmological constant (CC) at low
energies is possible if there is a smooth decoupling of all massive particles
from M_P to the mass of the lightest neutrino. We discuss the theoretical
implications of this running for the ``old'' and ``new'' cosmological constant
problems. Interestingly enough, the CC running implies a strong relationship
between quantum field theory and cosmology, which should be observable in the
near future in experiments such as SNAP through the measurement of a cubic
redshift dependence of the CC.Comment: LaTeX, 6 pages, no figures. Talk presented at IRGA 2003:
Renormalization Group and Anomalies in Gravitation and Cosmology, Ouro Preto,
Brazil, 16-23 March, 200
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