Souvik Ghose | Harish Chandra Research Institute (original) (raw)

Papers by Souvik Ghose

We study modified Chaplygin gas (MCG) as a candidate for dark energy and predict the values of pa... more We study modified Chaplygin gas (MCG) as a candidate for dark energy and predict the values of parameters of the gas for a physically viable cosmological model. The equation of state of MCG (p = Bρ − A ρ α) involves three parameters: B, A and α. The permitted values of these parameters are determined with the help of a dimensionless age parameter (H 0 t 0) and H (z) − z data. Specifically, we study the allowed ranges of values of the B parameter in terms of α and A s (A s is defined in terms of the parameters in the theory). We explore the constraints of the parameters in the cold dark matter and unified dark matter energy models, respectively.

We obtain cosmological solutions which admit emergent universe (EU) scenario in the framework of ... more We obtain cosmological solutions which admit emergent universe (EU) scenario in the framework of Einstein Gauss-Bonnet (GB) gravity coupled with a dilaton field in 4-dimensions. The coupling parameter of the GB terms and the dilaton in the theory are determined for obtaining an EU scenario. The corresponding dilaton potential which admits such scenario is determined. It is found that the GB terms coupled with a dilaton field plays an important role in describing the dynamics of the evolution of the early as well as the late universe. We note an interesting case where the GB term dominates initially in the asymptotic past regime, subsequently it decreases and thereafter its contribution in determining the dynamics of the evolution dominates once again. We note that the Einstein's static universe solution permitted here is unstable which the asymptotic EU might follow. We also compare our EU model with supernova data.

Rényi Holographic Dark Energy (RHDE) Models have been studied in different dimensions considering... more Rényi Holographic Dark Energy (RHDE) Models have been studied in different dimensions considering a flat FRW metric and subsequently exploring the nature of evolution of different cosmological parameters. It is seen that the number of dimensions affect the evolution of the cosmological parameters and the transition of the universe from decelerating to accelerating phase. The statefinder diagnostics have been performed and it is seen that the model corresponds to the ΛCDM model for the present and future universe.

A specific class of singularity-free cosmological model has recently been considered in light of ... more A specific class of singularity-free cosmological model has recently been considered in light of different observational data such as observed Hubble data, BAO data from luminous red galaxy survey by Slowan digital sky survey (SDSS) and CMB data from WMAP. However, it is observed that only 12-14 data points are used to study the viability of the model in late time. In this paper, we discuss the viability of all the models belonging to the same class of EU in light of union compilation data (SNIa) which consists of over a hundred data points, thus getting a more robust test for viability. More importantly, it is crucial that we can distinguish between the various models proposed in the class of solution obtained. We discuss here why with the present observational data it is difficult to distinguish between all of them. We show that the late-time behaviour of the model is typical to any asymptotically de Sitter model.

We investigate multidimensional universe with nonlinear scalar curvature terms to evaluate the pr... more We investigate multidimensional universe with nonlinear scalar curvature terms to evaluate the probability of creation of primordial black holes. For this we obtain Euclidean instanton solution in two different topologies: (a) S DÀ1-topology which does not accommodate primordial black holes and (b) S 1 Â S DÀ2-topology which accommodates a pair of black holes. The probability for quantum creation of an inflationary universe with a pair of black holes has been evaluated assuming a gravitational action which is described by a polynomial function of scalar curvature with or without a cosmological constant (Ã) using the framework of semiclassical approximation of Hartle-Hawking boundary conditions. We discuss here a class of new gravitational instantons solution in the R 4 theory which are relevant for cosmological model building.

We investigate holographic dark energy (HDE) correspondence of interacting Generalized Chaplygin ... more We investigate holographic dark energy (HDE) correspondence of interacting Generalized Chaplygin Gas (GCG) in the framework of compact Kaluza-Klein (KK) cosmology. The evolution of the modified HDE with corresponding equation of state is obtained here. Considering the present value of the density parameter a stable configuration is found which accommodates Dark Energy (DE). We note a connection between DE and Phantom fields. It reveals that the DE might have evolved from a Phantom state in the past.

A class of emergent universe models is studied in the light of recent observational data. Signifi... more A class of emergent universe models is studied in the light of recent observational data. Significant constraints on model parameters are obtained from these observations. The density parameter for a class of models is also evaluated. Some of the models are in accordance with recent observations. Others are not of interest, yielding unrealistic present-day values of the density parameter.

A specific class of flat Emergent Universe (EU) is considered and its viability is tested in view... more A specific class of flat Emergent Universe (EU) is considered and its viability is tested in view of the recent observations. Model parameters are constrained from Stern data for Hubble parameter and redshift [H(z) versus z] and from a model-independent measurement of BAO peak parameter. It is noted that a composition of exotic matter, dust and dark energy, capable of producing an EU, cannot be ruled out with present data. Evolution of other relevant cosmological parameters, viz. density parameter () and effective equation of state (EOS) parameter (ω eff), are also shown.

We study a composition of normal and exotic matter which is required for a flat emergent universe... more We study a composition of normal and exotic matter which is required for a flat emergent universe scenario permitted by the equation of state (EOS) (p = Aρ − Bρ 1/2) and predict the range of the permissible values for the parameters A and B to explore a physically viable cosmological model. The permitted values of the parameters are determined taking into account the H(z)− z data obtained from observations, a model-independent Baryon Acoustic Oscillation (BAO) peak parameter and cosmic microwave background shift parameter (WMAP7 data). It is found that although A can be very close to zero, most of the observations favours a small and negative A. As a consequence, the effective EOS parameter for this class of emergent universe solutions remains negative always. We also compared the magnitude [μ(z)] versus redshift (z) curve obtained in the model with that obtained from the union compilation data. According to our analysis the class of emergent universe solutions considered here is not ruled out by the observations.

We investigate both the interacting and non-interacting Reńyi Holographic Dark Energy (RHDE) mode... more We investigate both the interacting and non-interacting Reńyi Holographic Dark Energy (RHDE) models in DGP brane world framework. Cosmological parameters and their evolutions are probed to obtain realistic cosmological models. We note that both the models accommodate the present accelerating phase of expansion with the observed dark energy density. Classical stability of the cosmological model and Om-diagnostic are also studied to test the suitability of the cosmological models obtained in the presence of RHDE in DGP braneworld.

We discuss the consequences of Anderson-Vetharaniam-Stedman (AVS) synchronization gauge on the st... more We discuss the consequences of Anderson-Vetharaniam-Stedman (AVS) synchronization gauge on the standing wave formation. We found that although the position of the node (s) is gauge invariant and remain the same as in the standard case of the stationary wave formation following the Einstein synchronization, the anti-node (s) becomes a gauge dependent (conventional) element and the resulting wave travels between two nodes, contrary to the experimental observation. The experimental detection of standing wave substantiates that the one-way velocity is equal to the round-trip velocity implying the uniqueness of the Einstein synchronization convention.

We study cosmologies in modified theories of gravity considering Lagrangian density fðRÞ which is... more We study cosmologies in modified theories of gravity considering Lagrangian density fðRÞ which is a polynomial function of scalar curvature ðRÞ in the Einstein-Hilbert action in vacuum. The field equation obtained from the modified action corresponding to a Robertson-Walker metric is highly nonlinear and not simple enough to obtain analytic solution. Consequently we adopt a numerical technique to study the evolution of the Friedmann-Robertson-Walker universe. A number of evolutionary phases of the Universe including the present accelerating phase are found to exist in the higher derivative theories of gravity. The cosmological solutions obtained here are new and interesting. We study a modified theory of gravity as a toy model to explore the past and the present, and to predict the future evolution. It is found that all the models analyzed here can reproduce the current accelerating phase of expansion of the Universe. The duration of the present accelerating phase is found to depend on the coupling constants of the gravitational action. The physical importance of the coupling parameters considered in the action are also discussed.