35 research outputs found

### Dark Energy and the Statistical Study of the Observed Image Separations of the Multiply Imaged Systems in the CLASS Statistical Sample

The present day observations favour a universe which is flat, accelerated and
composed of $\sim 1/3$ matter (baryonic + dark) and $\sim 2/3$ of a negative
pressure component, usually referred to as dark energy or quintessence. The
Cosmic Lens All Sky Survey (CLASS), the largest radio-selected galactic mass
scale gravitational lens search project to date, has resulted in the largest
sample suitable for statistical analyses. In the work presented here, we
exploit observed image separations of the multiply imaged lensed radio sources
in the sample. We use two different tests: (1) image separation distribution
function $n(\Delta\theta)$ of the lensed radio sources and (2)
{\dtheta}_{\mathrm{pred}} vs {\dtheta}_{\mathrm{obs}} as observational
tools to constrain the cosmological parameters $w$ and \Om. The results are
in concordance with the bounds imposed by other cosmological tests.Comment: 20 pages latex; Modified " Results and Discussion " section, new
references adde

### Linear Coasting in Cosmology and SNe Ia

A strictly linear evolution of the cosmological expansion scale factor is a
characteristic feature in several classes of alternative gravity theories as
also in the standard (big-bang) model with specially chosen equations of state
of matter. Such an evolution has no free parameters as far as the classical
cosmological tests are concerned and should therefore be easily falsifiable. In
this article we demonstrate how such models present very good fits to the
current supernovae 1a data. We discuss the overall viability of such models.Comment: 12 latex 2e pages including 5 ps figures. More references and
Figuresinclude

### Delicate f(R) gravity models with disappearing cosmological constant and observational constraints on the model parameters

We study the $f(R)$ theory of gravity using metric approach. In particular we
investigate the recently proposed model by Hu-Sawicki, Appleby $-$ Battye and
Starobinsky. In this model, the cosmological constant is zero in flat space
time. The model passes both the Solar system and the laboratory tests. But the
model parameters need to be fine tuned to avoid the finite time singularity
recently pointed in the literature. We check the concordance of this model with
the $H(z)$ and baryon acoustic oscillation data. We find that the model
resembles the $\Lambda$CDM at high redshift. However, for some parameter values
there are variations in the expansion history of the universe at low redshift.Comment: 16 pages and 9 figures, typos corrected, few references and minor
clarifications added, revised version to appera in PR

### Gravitational lensing constraint on the cosmic equation of state

Recent redshift-distance measurements of Type Ia supernovae (SNe Ia) at
cosmological distances suggest that two-third of the energy density of the
universe is dominated by dark energy component with an effective negative
pressure. This dark energy component is described by the equation of state
$p_{x} = w \rho_{x}$ $(w \geq -1)$. We use gravitational lensing statistics to
constrain the equation of state of this dark energy. We use $n(\Delta\theta)$,
image separation distribution function of lensed quasars, as a tool to probe
$w$. We find that for the observed range of $\Omega_m \sim 0.2 - 0.4$, $w$
should lie between $-0.8 \leq w \leq -0.4$ in order to have five lensed quasars
in a sample of 867 optical quasars. This limit is highly sensitive to lens and
Schechter parameters and evolution of galaxies.Comment: Modified results and inclusion of calculations with new set of
parameter

### Cosmological Constraints on a Power Law Universe

Linearly coasting cosmology is comfortably concordant with a host of
cosmological observations. It is surprisingly an excellent fit to SNe Ia
observations and constraints arising from age of old quasars. In this article
we highlight the overall viability of an open linear coasting cosmological
model.The model is consistent with the latest SNe Ia ``gold'' sample and
accommodates a very old high-redshift quasar, which the standard cold-dark
model fails to do.Comment: 10 pages, 2 figure

### Variable Chaplygin Gas: Constraints from CMBR and SNe Ia

We constrain the parameters of the variable Chaplygin gas model, using the
location of peaks of the CMBR spectrum and SNe Ia ``gold '' data set. Equation
of state of the model is $P=-A(a)/\rho$, where $A(a)=A_0 a^{-n}$ is a positive
function of the cosmological scale factor $a$, $A_0$ and $n$ being constants.
The variable Chaplygin gas interpolates from dust-dominated era to quintessence
dominated era. The model is found to be compatible with current type Ia
Supernovae data and location of first peak if the values of $\Omega_m$ and $n$
lie in the interval $[0.017,~0.117]$ and $[-1.3,~2.6]$ respectively.Comment: 9 pages,4 figure