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The geology and mineral resources of Medina County
University of Texas bulletin ; no. 1860 : Oct. 25, 1918UT Librarie
Cosmic string parameter constraints and model analysis using small scale Cosmic Microwave Background data
We present a significant update of the constraints on the Abelian Higgs
cosmic string tension by cosmic microwave background (CMB) data, enabled both
by the use of new high-resolution CMB data from suborbital experiments as well
as the latest results of the WMAP satellite, and by improved predictions for
the impact of Abelian Higgs cosmic strings on the CMB power spectra. The new
cosmic string spectra (presented in a previous work) were improved especially
for small angular scales, through the use of larger Abelian Higgs string
simulations and careful extrapolation. If Abelian Higgs strings are present
then we find improved bounds on their contribution to the CMB anisotropies,
f10< 0.095, and on their tension, G\mu< 0.57 x 10^-6, both at 95% confidence
level using WMAP7 data; and f10 < 0.048 and G\mu < 0.42 x 10^-6 using all the
CMB data. We also find that using all the CMB data, a scale invariant initial
perturbation spectrum, ns=1, is now disfavoured at 2.4\sigma\ even if strings
are present. A Bayesian model selection analysis no longer indicates a
preference for strings.Comment: 8 pages, 3 figures; Minor corrections, matches published versio
Statistical methods in cosmology
The advent of large data-set in cosmology has meant that in the past 10 or 20
years our knowledge and understanding of the Universe has changed not only
quantitatively but also, and most importantly, qualitatively. Cosmologists rely
on data where a host of useful information is enclosed, but is encoded in a
non-trivial way. The challenges in extracting this information must be overcome
to make the most of a large experimental effort. Even after having converged to
a standard cosmological model (the LCDM model) we should keep in mind that this
model is described by 10 or more physical parameters and if we want to study
deviations from it, the number of parameters is even larger. Dealing with such
a high dimensional parameter space and finding parameters constraints is a
challenge on itself. Cosmologists want to be able to compare and combine
different data sets both for testing for possible disagreements (which could
indicate new physics) and for improving parameter determinations. Finally,
cosmologists in many cases want to find out, before actually doing the
experiment, how much one would be able to learn from it. For all these reasons,
sophisiticated statistical techniques are being employed in cosmology, and it
has become crucial to know some statistical background to understand recent
literature in the field. I will introduce some statistical tools that any
cosmologist should know about in order to be able to understand recently
published results from the analysis of cosmological data sets. I will not
present a complete and rigorous introduction to statistics as there are several
good books which are reported in the references. The reader should refer to
those.Comment: 31, pages, 6 figures, notes from 2nd Trans-Regio Winter school in
Passo del Tonale. To appear in Lectures Notes in Physics, "Lectures on
cosmology: Accelerated expansion of the universe" Feb 201
Cosmological scaling solutions in generalised Gauss-Bonnet gravity theories
The conditions for the existence and stability of cosmological power-law
scaling solutions are established when the Einstein-Hilbert action is modified
by the inclusion of a function of the Gauss-Bonnet curvature invariant. The
general form of the action that leads to such solutions is determined for the
case where the universe is sourced by a barotropic perfect fluid. It is shown
by employing an equivalence between the Gauss-Bonnet action and a scalar-tensor
theory of gravity that the cosmological field equations can be written as a
plane autonomous system. It is found that stable scaling solutions exist when
the parameters of the model take appropriate values.Comment: 10 pages and 5 figure
Cosmology With Non-Minimally Coupled K-Field
We consider non-minimally coupled (with gravity) scalar field with
non-canonical kinetic energy. The form of the kinetic term is of
Dirac-Born-Infeld (DBI) form.We study the early evolution of the universe when
it is sourced only by the k-field, as well as late time evolution when both the
matter and k-field are present. For the k-field, we have considered constant
potential as well as potential inspired from Boundary String Field Theory
(B-SFT). We show that it is possible to have inflationary solution in early
time as well as late time accelerating phase. The solutions also exhibit
attractor property in a sense that it does not depend on the initial conditions
for a certain values of the parameters.Comment: 10 pages, Revtex style, 14 eps figures, to appear in General
Relativity and Gravitatio
Deviation From \Lambda CDM With Cosmic Strings Networks
In this work, we consider a network of cosmic strings to explain possible
deviation from \Lambda CDM behaviour. We use different observational data to
constrain the model and show that a small but non zero contribution from the
string network is allowed by the observational data which can result in a
reasonable departure from \Lambda CDM evolution. But by calculating the
Bayesian Evidence, we show that the present data still strongly favour the
concordance \Lambda CDM model irrespective of the choice of the prior.Comment: 15 Pages, Latex Style, 4 eps figures, Revised Version, Accepted for
publication in European Physical Journal
Constraints on accelerating universe using ESSENCE and Gold supernovae data combined with other cosmological probes
We use recently observed data: the 192 ESSENCE type Ia supernovae (SNe Ia),
the 182 Gold SNe Ia, the 3-year WMAP, the SDSS baryon acoustic peak, the X-ray
gas mass fraction in clusters and the observational data to constrain
models of the accelerating universe. Combining the 192 ESSENCE data with the
observational data to constrain a parameterized deceleration parameter,
we obtain the best fit values of transition redshift and current deceleration
parameter , .
Furthermore, using CDM model and two model-independent equation of
state of dark energy, we find that the combined constraint from the 192 ESSENCE
data and other four cosmological observations gives smaller values of
and , but a larger value of than the combined
constraint from the 182 Gold data with other four observations. Finally,
according to the Akaike information criterion it is shown that the recently
observed data equally supports three dark energy models: CDM,
and .Comment: 18 pages, 8 figure
Asymptotic behavior of w in general quintom model
For the quintom models with arbitrary potential , the
asymptotic value of equation of state parameter w is obtained by a new method.
In this method, w of stable attractors are calculated by using the ratio (d ln
V)/(d ln a) in asymptotic region. All the known results, have been obtained by
other methods, are reproduced by this method as specific examples.Comment: 8 pages, one example is added, accepted for publication in Gen. Rel.
Gra
Transition from decelerated to accelerated cosmic expansion in braneworld universes
Braneworld theory provides a natural setting to treat, at a classical level,
the cosmological effects of vacuum energy. Non-static extra dimensions can
generally lead to a variable vacuum energy, which in turn may explain the
present accelerated cosmic expansion. We concentrate our attention in models
where the vacuum energy decreases as an inverse power law of the scale factor.
These models agree with the observed accelerating universe, while fitting
simultaneously the observational data for the density and deceleration
parameter. The redshift at which the vacuum energy can start to dominate
depends on the mass density of ordinary matter. For Omega = 0.3, the transition
from decelerated to accelerated cosmic expansion occurs at z approx 0.48 +/-
0.20, which is compatible with SNe data. We set a lower bound on the
deceleration parameter today, namely q > - 1 + 3 Omega/2, i.e., q > - 0.55 for
Omega = 0.3. The future evolution of the universe crucially depends on the time
when vacuum starts to dominate over ordinary matter. If it dominates only
recently, at an epoch z < 0.64, then the universe is accelerating today and
will continue that way forever. If vacuum dominates earlier, at z > 0.64, then
the deceleration comes back and the universe recollapses at some point in the
distant future. In the first case, quintessence and Cardassian expansion can be
formally interpreted as the low energy limit of our model, although they are
entirely different in philosophy. In the second case there is no correspondence
between these models and ours.Comment: In V2 typos are corrected and one reference is added for section 1.
To appear in General Relativity and Gravitatio
Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter
The Bianchi type III dark energy models with constant deceleration parameter
are investigated. The equation of state parameter is found to be time
dependent and its existing range for this model is consistent with the recent
observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy
clustering statistics. The physical aspect of the dark energy models are
discussed.Comment: 12 pages, 2 figures, Accepted version of IJT
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