Shobhit Mahajan

Probing large distance higher dimensional gravity from lensing data

Abstract The modifications induced in the standard weak-lensing formula if Newtonian gravity differs from inverse square law at large distances are studied. The possibility of putting bounds on the mass of gravitons from lensing data is explored. A bound on graviton mass, estimated to be about 100 Mpc −1 is obtained from analysis of some recent data on gravitational lensing.

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 ~ 1/3 matter (baryonic + dark) and ~ 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 analysis. 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(Δθ) of the lensed radio sources and (2) Δθpred versus Δθobs as observational tools to constrain the cosmological parameters w and Ωm. The results are in concordance with the bounds imposed by other cosmological tests.

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 px = wρx (w ≥ - 1). We use gravitational lensing statistics to constrain the equation of state of this dark energy. We use n(Δθ), the image separation distribution function of lensed quasars, as a tool to probe w. We find that for the observed range of Ωm ~ 0.2–0.4, w should lie between -0.8 ≤ w ≤ -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 the evolution of galaxies.

CONSTRAINT ON THE COSMOLOGICAL CONSTANT FROM GRAVITATIONAL LENSING IN AN EVOLUTIONARY MODEL OF GALAXIES

We study the effect of the cosmological constant on the statistical properties of gravitational lenses in flat cosmologies (Ω0+λ0=1). It is shown that some of the lens observables are strongly affected by the cosmological constant, especially in a low-density universe, and its existence might be inferred by a statistical study of the lenses. In particular, the optical depth of the lens distribution may be used best for this purpose without depending much on the lens model. We calculate the optical depth (probability of a beam encountering a lens event) for a source in a new picture of galaxy evolution based on number evolution in addition to pure luminosity evolution. It seem that present-day galaxies result from the merging of a large number of building blocks. We have tried to put a limit on the cosmological constant in this new picture of galaxy evolution. This evolutionary model of galaxies permits a larger value of the cosmological constant.

Transition redshift: new constraints from parametric and nonparametric methods

In this paper, we use the Cosmokinematics approach to study the accelerated expansion of the Universe. This is a model independent approach and depends only on the assumption that the Universe is homogeneous and isotropic and is described by the FRW metric. We parametrize the deceleration parameter,

CONSTRAINTS ON GALAXY EVOLUTION THROUGH GRAVITATIONAL LENSING STATISTICS

q(z)

Constraining cosmic curvature by using age of galaxies and gravitational lenses

, to constrain the transition redshift (

NUCLEOSYNTHESIS IN A UNIVERSE WITH A LINEARLY EVOLVING SCALE FACTOR

z_t

Probing the cosmic distance duality relation using time delay lenses

) at which the expansion of the Universe goes from a decelerating to an accelerating phase. We use three different parametrizations of

Revisiting the distance duality relation using a non-parametric regression method

q(z)