53 research outputs found
Acceleration of the universe: a reconstruction of the effective equation of state
The present work is based upon a parametric reconstruction of the effective
or total equation of state in a model for the universe with accelerated
expansion. The constraints on the model parameters are obtained by maximum
likelihood analysis using the supernova distance modulus data, observational
Hubble data, baryon acoustic oscillation data and cosmic microwave background
shift parameter data. For statistical comparison, the same analysis has also
been carried out for the wCDM dark energy model. Different model selection
criteria (Akaike information criterion (AIC)) and (Bayesian Information
Criterion (BIC)) give the clear indication that the reconstructed model is well
consistent with the wCDM model. Then both the models (w_{eff}(z) model and wCDM
model) have also been presented through (q_0 ,j_0 ) parameter space. Tighter
constraint on the present values of dark energy equation of state parameter
(w_{DE}(z = 0)) and cosmological jerk (j_0) have been achieved for the
reconstructed model.Comment: 11 pages, 8 figure
A parametric reconstruction of the cosmological jerk from diverse observational data sets
A parametric reconstruction of the jerk parameter, the third order derivative
of the scale factor expressed in a dimensionless way, has been discussed.
Observational constraints on the model parameters have been obtained by Maximum
Likelihood Analysis of the models using Supernova Distance Modulus data (SNe),
Observational Hubble Data (OHD), Baryon Acoustic Oscillation (BAO) data and CMB
shift parameter data (CMBShift). The present value of the jerk parameter has
been kept open to start with, but the plots of various cosmological parameter
like deceleration parameter , jerk parameter , dark energy equation
of state parameter indicate that the reconstructed models are very
close to a CDM model with a slight inclination towards a non-phantom
behaviour of the evolution.Comment: 12 pages, 44 figures; Accepted for publication in Phys. Rev.
A Reconstruction of Quintessence Dark Energy
With a parametric form of the equation of state parameter of dark energy, a
quintessence potential has been reconstructed. The potential is found to be a
generalization of a double exponential potential. The constraints on the
parameters are obtained by maximum likelihood analysis using observational
Hubble data, type Ia supernova data, baryon acoustic oscillation data and the
CMB shift parameter data. Th emodel shows preference towards the phantom
behaviour of dark energy
Acceleration of the Universe in f(R) Gravity Models
A general formalism for the investigation of the late time dynamics of the
universe for any analytic f(R) gravity model, along with a cold dark matter,
has been discussed in the present work. The formalism is then elucidated with
two examples. The values of the parameters of the models are chosen in such a
way that they are consistent with the basic observational requirement.Comment: 6 pages; 5 figures. To appear in Astrophysics and Space Scienc
Reconstructing late-time cosmology with kinematical models
The present work is based on the reconstruction of late-time cosmological
dynamics using purely kinematical models. The models are constructed from
different parameterizations of the deceleration parameter. The models are
confronted with cosmological observations which are completely independent of
any fiducial assumption about the background cosmological model. Different
kinematical parameters, namely the present Hubble parameter, present value of
the deceleration parameter and the redshift of transition from decelerated to
accelerated phase of expansion are constrained by Markov Chanin Monte Charlo
(MCMC) analysis using the observation data sets. The evolution of different
cosmological quantities are studied for the present models. The evolution of
linear matter density contrast has been studied for the present kinematical
models and the result is compared with the standard cosmological constant dark
energy scenario. The thermodynamic nature of the universe has also been
emphasized in the present context.Comment: 12 pages, 9 figure
Spherical collapse in DGP braneworld cosmology
The DGP (Dvali, Gabadaze and Porrati) braneworld cosmology gives an
alternative to dark energy. In DGP cosmology the alleged cosmic acceleration is
generated by the modification of gravity theory. Nonlinear evolution of matter
density contrast in DGP braneworld cosmology is studied in the present work.
The semi-analytic approach of spherical collapse of matter overdensity is
adopted in the present context to study the nonliner evolution. Further, the
number count of galaxy clusters along the redshift is studied for the DGP
cosmology using Press-Schechter and Sheth-Tormen mass function formalisms. It
is observed that for same values of cosmological parameters, the DGP model
enhances the number of galaxy cluster compared to the standard CDM
scenario.Comment: 14 pages, 6 figures. arXiv admin note: text overlap with
arXiv:2008.0379
Spherical collapse in a dark energy model with reconstructed effective equation of state
The present work deals with the study of spherical collapse of matter density
contrast in a latetime cosmological model with a reconstructed effective
equation of state. The linear and nonlinear evolution of matter density
contrast are studied. The variation of the critical density at collapse of the
spherical overdense region along redshift are also investigate. Further the
number count of collapsed object or the dark matter halos, equivalent to the
number count of galaxy clusters, are also studied. Two different halo mass
function formulations, namely the Press-Schechter mass function and the
Sheth-Tormen mass function, are adopetd to study the cluster number count along
the redshift. Similar analysis is also carried out for wCDM dark energy model
to have a direct comparison with the reconstructed effective equation of state
model. These two models are highly degenerate at the background and linear
level of matter perturbation. But the nonlinear evolution of matter overdensity
breaks the degeneracy. The reconstructed effective equation of state model
shows a substantial suppression in the cluster number count compared to wCDM
for redshift z > 0.5, and for z < 0.5, the number count is slightly higher than
that of wCDM.Comment: 12 pages, 5 figure
Clustering of dark matter in interacting tachyon dark energy with CDM background
One of the non-canonical descriptions of scalar field dark energy is the
tachyon. The present work is devoted to study the dynamics of dark matter
overdensity in a conformally coupled tachyon field dark energy model. The model
is tuned to mimic the CDM cosmology at background level. The
semi-analytic spherical collapse model of dark matter overdensity is adopted to
study the nonlinear evolution. The effects of non-minimal coupling in the
energy budget on the clustering of dark matter is investigated. It is observed
that the growth rate of matter overdensity is higher in presence of the
non-minimal coupling. The critical density at collapse is suppressed in case of
interaction. Further the number counts of dark matter halos or galaxy clusters
along redshift are studied using the Press-Schechter and Sheth- Tormen halo
mass functions. Suppression in the number of dark matter halos is observed when
the interaction is allowed. A comparison of cluster number count in the present
model and CDM is carried out. The present model allowing the
interaction produces much lower number of galaxy clusters compared to
CDM, but without interaction the cluster number count is slightly
higher than CDM cluster count.Comment: 15 pages, 6 figure
Astronomical bounds on a cosmological model allowing a general interaction in the dark sector
Non-gravitational interaction between two barotropic dark fluids, namely the
pressureless dust and the dark energy in a spatially flat
Friedmann-Lema\^{i}tre-Robertson-Walker model has been discussed. It is shown
that for the interactions which are linear in terms the energy densities of the
dark components and their first order derivatives, the net energy density is
governed by a second order differential equation with constant coefficients.
Taking a generalized interaction, which includes a number of already known
interactions as special cases, the dynamics of the universe is described for
three types of the dark energy equation of state, namely that of interacting
quintessence, interacting vacuum energy density and interacting phantom. The
models have been constrained using the standard cosmological probes, Supernovae
type Ia data from joint light curve analysis and the observational Hubble
parameter data. Two geometric tests, the cosmographic studies and the
diagnostic have been invoked so as to ascertain the behaviour of the present
model vis-a-vis the -cold dark matter model. We further discussed the
interacting scenarios taking into account the thermodynamic considerations.Comment: 20 pages; 4 tables; 14 figures; Published version in MNRA
Assessment of the cosmic distance duality relation using Gaussian Process
Two types of distance measurement are important in cosmological observations,
the angular diameter distance and the luminosity distance . In the
present work, we carried out an assessment of the theoretical relation between
these two distance measurements, namely the cosmic distance duality relation,
from type Ia supernovae (SN-Ia) data, the Cosmic Chronometer (CC) Hubble
parameter data, and baryon acoustic oscillation (BAO) data using Gaussian
Process. The luminosity distance curve and the angular diameter distance curve
are extracted from the SN-Ia data and the combination of BAO and CC data
respectively using the Gaussian Process. The distance duality relation is
checked by a non-parametric reconstruction using the reconstructed , ,
and the volume-averaged distance . We compare the results obtained for
different choices of the covariance function employed in the Gaussian Process.
It is observed that the theoretical distance duality relation is in well
agreement with the present analysis in 2 for the overlapping redshift
domain of the reconstruction.Comment: 10 pages, 8 sets of figures, accepted for publication in MNRA
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