arXiv subjects

Prabir Rudra

Publications and source records attributed to Prabir Rudra.

At least 55 records · Page 3Linked to original sources

arXiv2018

Vaidya Spacetime in Brans-Dicke Gravity's Rainbow

In this note we study an energy dependent deformation of a time dependent geometry in the background of Brans-Dicke gravity theory. The study is performed using the gravity's rainbow formalism. We compute the field equations in Brans-Dicke gravity's rainbow using Vaidya metric which is a time dependent geometry. We study a star collapsing under such conditions. Our prime objective is to determine the nature of singularity formed as a result of gravitational collapse and its strength. The idea is to test the validity of the cosmic censorship hypothesis for our model. We have also studied the effect of such a deformation on the thermalization process. In this regard we have calculated the important thermodynamical quantities such as thermalization temperature, Helmholtz free energy, specific heat and analyzed the behavior of such quantities.

gr-qc↗

arXiv2018

Time Dependent Geometry in Massive Gravity

In this paper, we will analyze a time dependent geometry in a massive theory of gravity. This will be done by analyzing Vaidya space-time in such a massive theory of gravity. As gravitational collapse is a time dependent system, we will analyze it using the Vaidya space-time in massive gravity. The Vainshtein and dRGT mechanisms are used to obtain a ghost free massive gravity, and construct such time dependent solutions. Singularities formed, their nature and strength will be studied in detail. We will also study the thermodynamical aspects of such a geometry by calculating the important thermodynamical quantities for such a system, and analyzing the thermodynamical behavior of such quantities.

physics.gen-ph↗

arXiv2018

Generalised teleparallel quintom dark energy non-minimally coupled with the scalar torsion and a boundary term

Within this work, we propose a new generalised quintom dark energy model in the teleparallel alternative of general relativity theory, by considering a non-minimal coupling between the scalar fields of a quintom model with the scalar torsion component $T$ and the boundary term $B$. In the teleparallel alternative of general relativity theory, the boundary term represents the divergence of the torsion vector, $B=2\nabla_μT^μ$, and is related to the Ricci scalar $R$ and the torsion scalar $T$, by the fundamental relation: $R=-T+B$. We have investigated the dynamical properties of the present quintom scenario in the teleparallel alternative of general relativity theory by performing a dynamical system analysis in the case of decomposable exponential potentials. The study analysed the structure of the phase space, revealing the fundamental dynamical effects of the scalar torsion and boundary couplings in the case of a more general quintom scenario. Additionally, a numerical approach to the model is presented to analyse the cosmological evolution of the system.

gr-qc↗

arXiv2018

Gravitational Baryogenesis in Ho$\check{r}$ava-Lifshitz gravity

In this work we intend to address the matter-antimatter asymmetry via the gravitational baryogenesis mechanism in the background of a quantum theory of gravity. We investigate this mechanism under the framework of Ho$\check{r}$ava-Lifshitz gravity. We will compute the baryon-to-entropy ratio in the chosen framework and investigate its physical viability against the observational bounds. We also conduct the above study for various sources of matter like scalar field and Chaplygin gas as specific examples. We speculate that quantum corrections from the background geometry will lead to interesting results.

gr-qc↗

arXiv2017

Vaidya Spacetime in Massive Gravity's Rainbow

In this paper, we will analyze the energy dependent deformation of massive gravity using the formalism of massive gravity's rainbow. So, we will use the Vainshtein mechanism and the dRGT mechanism for the energy dependent massive gravity, and thus analyze a ghost free theory of massive gravity's rainbow. We study the energy dependence of a time-dependent geometry, by analyzing the radiating Vaidya solution in this theory of massive gravity's rainbow. The energy dependent deformation of this Vaidya metric will be performed using suitable rainbow functions.

gr-qc↗

arXiv2016

Vaidya Spacetime for Galileon Gravity's Rainbow

In this paper, we analyze Vaidya spacetime with an energy dependent metric in Galileon gravity's rainbow. This will be done using the rainbow functions which are motivated from the results obtained in loop quantum gravity approach and non-commutative geometry. We will investigate the Gravitational collapse in this Galileon gravity's rainbow. We will discuss the behavior of singularities formed from the gravitational collapse in this rainbow deformed Galileon gravity.

gr-qc↗

arXiv2016

Reconstruction of f(R) gravity with ordinary and Entropy-corrected (m,n)-type Holographic dark energy model

In this assignment we will present a reconstruction scheme between f(R) gravity with ordinary and entropy corrected (m,n)-type holographic dark energy. The correspondence is established and expressions for the reconstructed f(R) models are determined. To study the evolution of the reconstructed models plots are generated. The stability of the calculated models are also investigated using the squared speed of sound in the background of the reconstructed gravities.

physics.gen-ph↗

arXiv2015

Study of Some Cosmological Parameters for Interacting New Holographic Dark Energy Model in f(T) Gravity

The present work is based on the idea of an interacting framework of new holographic dark energy with cold dark matter in the background of $f(T)$ gravity. Here, we have considered the flat modified Friedmann universe for $f(T)$ gravity which is filled with new Holographic dark energy and dark matter. We have derived some cosmological parameters like Deceleration parameter, EoS parameter, State-finder parameters, Cosmographic parameters, {\it Om} parameter and graphically investigated the nature of these parameters for the above mentioned interacting scenario. The results are found to be consistent with the accelerating universe. Also we have graphically investigated the trajectories in $ω$--$ ω'$ plane for different values of the interacting parameter and explored the freezing region and thawing region in $ω$--$ ω'$ plane. Finally, we have analyzed the stability of this model.

gr-qc↗

arXiv2015

Red-shift parametrizations of dark energy and observational constraint on their parameters: Galileon gravity as background

In this work, FRW universe filled with dark matter (perfect fluid with negligible pressure) along with dark energy in the background of Galileon gravity is considered. Four dark energy models with different EoS parametrizations have been employed namely, Linear, CPL, JBP and Logarithmic parametrizations. From Stern, Stern+BAO and Stern+BAO+CMB joint data analysis, we have obtained the bounds of the arbitrary parameters $ω_{0}$ and $ω_{1}$ by minimizing the $χ^{2}$ test. The best-fit values and bounds of the parameters are obtained at 66\%, 90\% and 99\% confidence levels which are shown by closed confidence contours in the figures. For the logarithmic model unbounded confidence contours are obtained and hence the model parameters could not be finitely constrained. The distance modulus $μ$(z) against redshift $z$ has also been plotted for our predicted theoretical models for the best fit values of the parameters and compared with the observed Union2 data sample and SNe Type Ia 292 data and we have shown that our predicted theoretical models permits the observational data sets. From the data fitting it is seen that at lower redshifts $(z<0.3)$ the SNe Type Ia 292 data gives a better fit with our theoretical models compared to the Union2 data sample. So, from the data analysis, SNe Type Ia 292 data is the more favoured data sample over its counterpart given the present choice of free parameters. From the study, it is also seen that the logarithmic parametrization model is less supported by the observational data. Finally we have generated the plot for the deceleration parameter against the redshift parameter for all the theoretical models and compared the results with the work of Farooq et al, 2013.

gr-qc↗

arXiv2015

Observational data fitting to constrain Variable Modified Chaplygin Gas in the background of Horava-Lifshitz Gravity

FRW universe in Horava-Lifshitz (HL) gravity model filled with a combination of dark matter and dark energy in the form of variable modified Chaplygin gas (VMCG) is considered. The permitted values of the VMCG parameters are determined by the recent astrophysical and cosmological observational data. Here we present the Hubble parameter in terms of the observable parameters $Ω_{dm0}$, $Ω_{vmcg0}$, $H_{0}$, redshift $z$ and other parameters like $α$, $A$, $γ$ and $n$. From Stern data set (12 points), we have obtained the bounds of the arbitrary parameters by minimizing the $χ^{2}$ test. The best-fit values of the parameters are obtained by 66\%, 90\% and 99\% confidence levels. Next due to joint analysis with BAO and CMB observations, we have also obtained the bounds of the parameters ($A,γ$) by fixing some other parameters $α$ and $n$. The best fit value of distance modulus $μ(z)$ is obtained for the VMCG model in HL gravity, and it is concluded that our model is perfectly consistent with the union2 sample data.

gr-qc↗

arXiv2015

Coincidence Problem in f(T) Gravity Models

In this assignment we try to probe the role played by torsion in the current scenario of coincidence and devise a set-up for its realization. In order to model the scenario, the energy arising from the torsion component is considered analogous to dark energy. An interaction between dark energy and dark matter is considered, which is by far the best possible tool to realize the coincidence. A set-up is designed and a constraint equation is obtained which screens the models of \textit{f(T)} gravity that can successfully accommodate the stationary scenario in its framework, from those which cannot. Due to the absence of a universally accepted interaction term introduced by a fundamental theory, the study is conducted over three different forms of chosen interaction terms. As an illustration two widely known models of \textit{f(T)} gravity are taken into consideration and used in the designed setup. The study reveals that the realization of the coincidence scenario as well as the role played by torsion in the current universe is a model dependent phenomenon. It is found that the first model showed a considerable departure from the stationary scenario. On the contrary the other four models are perfectly consistent with our setup and generated a satisfactory stationary scenario, thus showing their cosmological viability and their superiority over their counterparts. For the third model (exponential model) it was seen that the cosmological coincidence is realized only in the phantom regime. For the fourth (logarithmic model) and the fifth models, we see that the the stationary scenario is attained for negative interaction values. This shows that the direction of flow must be from dark energy to dark matter unlike the previous models. Under such circumstances the universe will return from the present energy dominated phase to a matter dominated phase.

gr-qc↗

arXiv2015

Does f(R,T) gravity admit a stationary scenario between dark energy and dark matter in its framework?

In this note we address the well-known cosmic coincidence problem in the framework of the \textit{f(R,T)} gravity. In order to achieve this, an interaction between dark energy and dark matter is considered. A constraint equation is obtained which filters the \textit{f(R,T)} models that produce a stationary scenario between dark energy and dark matter. Due to the absence of a universally accepted interaction term introduced by a fundamental theory, the study is conducted over three different forms of chosen interaction terms. As an illustration three widely known models of \textit{f(R,T)} gravity are taken into consideration and used in the setup designed to study the problem. The study reveals that, the realization of the coincidence scenario is almost impossible for the popular models of $f(R,T)$ gravity, thus proving to be a major setback for these models.

gr-qc↗

arXiv2014

Towards a possible solution for the coincidence problem: f(G) gravity as background

In this article we address the well-known cosmic coincidence problem in the framework of the f(G) gravity. In order to achieve this, an interaction between dark energy and dark matter is considered. A set-up is designed and a constraint equation is obtained which generates the f(G) models that do not suffer from the coincidence problem. Due to the absence of a universally accepted interaction term introduced by a fundamental theory, the study is conducted over three different forms of logically chosen interaction terms. To illustrate the set-up three widely known models of f(G) gravity are taken into consideration and the problem is studied under the designed set-up. The study reveals that the popular f(G) gravity models does not approve of a satisfactory solution of the long standing coincidence problem, thus proving to be a major setback for them as successful models of universe. Finally, two non-conventional models of f(G) gravity have been proposed and studied in the framework of the designed set-up. It is seen that a complete solution of the coincidence problem is achieved for these models. The study also reveals that the b-interaction term is much more preferable compared to the other interactions, due to its greater compliance with the recent observational data.

gr-qc↗

arXiv2014

Loop Quantum effects on Om-diagnostic and its Cosmological Implications

In this paper we study the Loop quantum effects on the \textit{Om} diagnostic and subsequently on the universe. We reconstruct the \textit{Om} diagnostic in the background of Loop quantum gravity and then study the behaviour of various Chaplygin gas dark energy models using the modified diagnostic in a comparative scenario. The trajectories discriminate the various dark energy models from each other both in the Einstein gravity as well as Loop quantum gravity. The Loop quantum effects are also clearly noticeable from the trajectories in past, present and future universe. We see that the Loop quantum deviations are highly pronounced in the early universe, but alleviates as we tend towards the present universe and continue to decay in future. Thus it puts a big question on the effectiveness and consequently the suitability of loop quantum cosmology to explain the future universe.

gr-qc↗

arXiv2014

Dynamical System Analysis of Modified Chaplygin Gas in Einstein-Aether Gravity

In this work we investigate the background dynamics when dark energy is coupled to dark matter with a suitable interaction in the universe described by Einstein-Aether gravity. Dark energy in the form of Modified Chaplygin gas is considered. A suitable interaction between dark energy and dark matter is considered in order to at least alleviate (if not solve) the cosmic coincidence problem. The dynamical system of equations is solved numerically and a stable scaling solution is obtained. A significant attempt towards the solution of the cosmic coincidence problem is taken. The statefinder parameters are also calculated to classify the dark energy models. Graphs and phase diagrams are drawn to study the variations of these parameters. It is also seen that the background dynamics of modified Chaplygin gas in Einstein-Aether gravity is completely consistent with the notion of an accelerated expansion in the late universe. Finally, it has been shown that the universe follows the power law form of expansion around the critical point.

physics.gen-ph↗

arXiv2014

Gravitational Collapse In Husain Space-time For Brans-Dicke Gravity Theory with Power-law Potential

The motive of this work is to study gravitational collapse in Husain space-time in Brans-Dicke gravity theory. Among many scalar-tensor theories of gravity, Brans-Dicke is the simplest and the impact of it can be regulated by two parameters associated with it, namely, the Brans-Dicke parameter, $ω$, and the potential-scalar field dependency parameter $n$ respectively. V. Husain's work on exact solution for null fluid collapse in 1996 has influenced many authors to follow his way to find the end-state of the homogeneous/in-homogeneous dust cloud. Vaidya's metric is used all over to follow the nature of future outgoing radial null geodesics. Detecting whether the central singularity is naked or wrapped by an event horizon, by the existence of future directed radial null geodesic emitted in past from the singularity is the basic objective. To point out the existence of positive trajectory tangent solution, both particular parametric cases(through tabular forms) and wide range contouring process have been applied. Precisely, perfect fluid's EoS satisfies a wide range of phenomena : from dust to exotic fluid like dark energy. We have used the EoS parameter $k$ to determine the end state of collapse in different cosmological era. Our main target is to check low $ω$ (more deviations from Einstein gravity-more Brans Dicke effect) and negative $k$ zones. This particularly throws light on the nature of the end-state of collapse in accelerated expansion in Brans Dicke gravity. It is seen that for positive values of EoS parameter $k$, the collapse results in a black hole, whereas for negative values of $k$, naked singularity is the only outcome. It is also to be noted that "low $ω$" leads to the possibility of getting more naked singularities even for a non-accelerating universe.

physics.gen-ph↗

arXiv2014

Study of Some Parameters of Modified Chaplygin Gas in Galileon Gravity Theory from Observational Perspective

We have assumed the FRW model of the universe in Galileon gravity, which is filled with dark matter and Modified Chaplygin gas (MCG) type dark energy. We present the Hubble parameter in terms of some unknown parameters and observational parameters with the redshift $z$. Some cosmological parameters are reconstructed and plots are generated to study the nature of the model and its viability. It is seen that the model is perfectly consistent with the present cosmic acceleration. From \textit{observed Hubble data (OHD) set or Stern data set} of 12 points, we have obtained the bounds of the arbitrary parameters ($A,B$) & ($A,C$) by minimizing the $χ^{2}$ test. Next due to joint analysis of \textit{Stern+BAO} and \textit{Stern+BAO+CMB} observations, we have also obtained the best fit values and the bounds of the parameters ($A,B$) & ($A,C$) by fixing some other parameters. The best-fit values and bounds of the parameters are obtained with 66%, 90% and 99% confidence levels for \textit{Stern, Stern+BAO and Stern+BAO+CMB} joint analysis. Next we have also taken type Ia supernovae data set (union 2 data set with 557 data points). The distance modulus $μ(z)$ against redshift $z$ for our theoretical MCG model in Galileon gravity have been tested for the best fit values of the parameters and the observed \textit{SNe Ia union 2 data} sample and from this, we have concluded that our model is in agreement with the union 2 sample data.

physics.gen-ph↗

arXiv2014

Gravitational Collapse With Dark Energy And Dark Matter In Hořava-Lifshitz Gravity

In this work, the collapsing process of a spherically symmetric star, made of dust cloud, is studied in Hořava Lifshitz gravity in the background of Chaplygin gas dark energy. Two different classes of Chaplygin gas, namely, New variable modified Chaplygin gas and generalized cosmic Chaplygin gas are considered for the collapse study. Graphs are drawn to characterize the nature and to determine the possible outcome of gravitational collapse. A comparative study is done between the collapsing process in the two different dark energy models. It is found that for open and closed universe, collapse proceeds with an increase in black hole mass, the only constraint being that, relatively smaller values of $Λ$ has to be considered in comparison to $λ$. But in case of flat universe, possibility of the star undergoing a collapse in highly unlikely. Moreover it is seen that the most favourable environment for collapse is achieved when a combination of dark energy and dark matter is considered, both in the presence and absence of interaction. Finally, it is to be seen that, contrary to our expectations, the presence of dark energy does not really hinder the collapsing process in case of Hořava-Lifshitz gravity.

physics.gen-ph↗