Somasri Sen

Late time acceleration in Brans-Dicke cosmology

In this work we investigate the possibility of having a late time accelerated phase of the universe, suggested by recent supernova observation, in the context of Brans-Dicke theory with a potential having a time dependent mass squared term which has recently become negative and a matter field. We find that while a perfect fluid (pressureless and with pressure) cannot support this acceleration, a fluid with dissipative pressure can drive this late time acceleration for a simple power-law expansion of the universe. We have also calculated some cosmological parameters in our model to match with observations.

SELF INTERACTING BRANS–DICKE COSMOLOGY AND QUINTESSENCE

Recent cosmological observations reveal that we are living in a flat accelerated expanding universe. In this work we have investigated the nature of the potential compatible with the power law expansion of the universe in a self interacting Brans–Dicke cosmology with a perfect fluid background and have analyzed whether this potential supports the accelerated expansion. It is found that positive power law potential is relevant in this scenario and can drive accelerated expansion for negative Brans–Dicke coupling parameter ω. The evolution of the density perturbation is also analyzed in this scenario and is seen that the model allows growing modes for negative ω.

Dissipative fluid in Brans-Dicke theory and late time acceleration

We investigate the possibility of having a late time accelerated expansion phase for the universe. We use a dissipative fluid in Brans-Dicke (BD) theory for this purpose. The model does not involve any potential for the BD scalar field. We obtain the best fit values for the different parameters in our model by comparing our model predictions with SNIa data and also with the data from the ultracompact radio sources.

Observational Constraints on Cardassian Expansion

In this work, we have studied the observational constraints on the Cardassian model for dark energy. We have compared the model with existing supernova data. The dependence of the locations of the cosmic microwave background radiation (CMBR) peaks on the parameters of the model have also been studied. We find, in particular, that observational data from Archeops for the location of the first peak and BOOMERANG for the location of the third peak, together with the supernova data, significantly constrain the parameter space.In this work, we have studied the observational constraints on the Cardassian Model for the dark energy. We have compared the model with existing Supernova data. The dependence of the location of the Cosmic Microwave Background Radiation (CMBR) peaks on the parameters of the model have also been studied. We find, in particular, that observational data arising from Archeops for the location of the first peak, BOOMERANG for the location of the third peak, together with the Supernova data, constrain significantly the parameter space.

COSMOLOGY IN SCALAR–TENSOR THEORY AND ASYMPTOTICALLY de SITTER UNIVERSE

We have investigated the cosmological scenarios with a four-dimensional effective action which is connected with multidimensional, supergravity and string theories. The solution for the scale factor is such that initially universe undergoes a decelerated expansion but in late times it enters into the accelerated expansion phase. In fact, it asymptotically becomes a de Sitter universe. The dilaton field in our model is a decreasing function of time and it becomes a constant in late time resulting the exit from the scalar–tensor theory to the standard Einsteins gravity. Also the dilaton field results in the existence of a positive cosmological constant in late times.We have investigated the cosmological scenarios with a four dimensional effective action which is connected with multidimensional, supergravity and string theories. The solution for the scale factor is such that initially universe undergoes a decelerated expansion but in late times it enters into the accelerated expansion phase. Infact, it asymptotically becomes a de-Sitter universe. The dilaton field in our model is a decreasing function of time and it becomes a constant in late time resulting the exit from the scalar tensor theory to the standard Einsteins gravity. Also the dilaton field results the existence of a positive cosmological constant in late times.

Cosmic microwave background constraints on interacting cosmological models

Non-canonical scaling of the form

The thawing dark energy dynamics: Can we detect it?

\rho_{x} \propto \rho_{m} a^{\xi}

Bulk antisymmetric tensor fields in a Randall-Sundrum model

, where

Randall-Sundrum scenario with bulk dilaton and torsion

\rho_{x}

WMAP constraints on Cardassian model

and