arXiv subjects

Chayan Ranjit

Publications and source records attributed to Chayan Ranjit.

At least 19 recordsLinked to original sources

arXiv2026

Cosmology of the interacting Tsallis holographic dark energy in $f(R,T)$ gravity framework

In this work, we have analyzed the cosmology of the Tsallis holographic dark energy (THDE), a particular case of Nojiri-Odintsov HDE proposed in [S. Nojiri and S. D. Odintsov, \textit{Gen. Relativ. Gravit.} \textbf{38} (2006), 1285; \textit{Eur. Phys. J. C} \textbf{77} (2017) 528], using Hubble's horizon cutoff in $f(R,T)=\mu R+\nu T$ model considering pressureless dark matter. We have examined the equation of state (EoS) parameters in this scenario. The deceleration parameter has been evaluated for this interacting model to justify the late-time acceleration of the expanding universe. We have also studied the cosmological consequences of Statefinder pair, $O_{m}(z)$ diagnostics, $r-q$ plane, and $w_{DE}-w^{'}_{DE}$ pair for interacting THDE in $f(R,T)=\mu R+\nu T$ model. We have also illustrated the cosmology of the interacting THDE using Hubble's horizon cutoff in $f(R,T)=R+\gamma R^2+\xi T$ model. The EoS parameter, deceleration parameter and Statefinder pair are studied in this interacting scenario. Attainment of $\Lambda$CDM fixed point has been observed for both models. We have also constrained model parameters based on observational data sets through the formalism of $\chi^{2}$ minimum test.

gr-qc↗

arXiv2025

A comprehensive analysis of Barrow holographic Chaplygin gas model reconstruction and its cosmological consequences

In the current study, we have reconstructed variable modified Chaplygin gas in the Barrow holographic dark energy framework motivated by many recent studies. We have validated the generalized second law of thermodynamics for the reconstructed model. The permissible values of the reconstructed model have been determined by the recent astrophysical and cosmological observational data. The Hubble parameter is presented in terms of the observable parameters and redshift $z$ and other model parameters. From the Stern data set and joint data set of Stern with BAO and CMB observations, the bounds of the model parameters $(B_{0}, \Omega_{bhd0})$ are obtained by the $\chi^{2}$ minimization procedure. The best-fit value of the distance modulus $\mu(z)$ against redshift $z$ is obtained for the reconstructed model and it is consistent with the SNe Ia union2 sample data.

gr-qc↗

arXiv2022

Cosmological effects on $f(\bar{R},\bar{T})$ gravity through a non-standard theory

This study aims to investigate the impact of dark energy in cosmological scenarios by exploiting $f(\bar{R},\bar{T})$ gravity within the framework of a {\it non-standard} theory, called {\it {\bf K-}essence} theory, where $\bar{R}$ represents the Ricci scalar and $\bar{T}$ denotes the trace of the energy-momentum tensor associated with the {\bf K-}essence geometry. The Dirac-Born-Infeld (DBI) non-standard Lagrangian has been employed to generate the emergent gravity metric $(\bar{G}_{\mu\nu})$ associated with the {\bf K-}essence. This metric is distinct from the usual gravitational metric $(g_{\mu\nu})$. It has been shown that under a flat FLRW background gravitational metric, the modified field equations and the Friedmann equations of the $f(\bar{R},\bar{T})$ gravity are distinct from the usual ones. In order to get the equation of state (EOS) parameter $\omega$, we have solved the Friedmann equations by taking into account the function $f(\bar{R},\bar{T})\equiv f(\bar{R})+\lambda \bar{T}$, where $\lambda$ represents a parameter within the model. We have found a relationship between $\omega$ and time for different kinds of $f(\bar{R})$ by treating the kinetic energy of the {\bf K-}essence scalar field ($\dot{\phi}^{2}$) as the dark energy density which fluctuates with time. Surprisingly, this result meets the condition of the restriction on $\dot{\phi}^{2}$. By presenting graphical representations of the EOS parameter with time, we show that our model is consistent with the data of $SNIa$+$BAO$+$H(z)$ within a certain temporal interval.

gr-qc↗

arXiv2021

Compact stellar models in modified gravity

In the present investigation compact stellar models are dealt with in the framework of the modified gravity theory, specifically of $f(\mathbb{T},\mathcal{T})$ type. We have considered that the compact objects are following a spherically symmetric static metric and obtained the Einstein field equations in the spacetime of $f(\mathbb{T},\mathcal{T})$. To make the Einstein equations solvable we employ the methodology of conformal Killing vectors. Thereafter by using the MIT bag equation of state to the compact stars, considering that the stars are formed by strange quark, we find the solutions set. The solutions are examined via several physical tastings which exhibit viability of the model.

gr-qc↗

arXiv2020

Constraints on Energy Momentum Squared Gravity from cosmic chronometers and Supernovae Type Ia data

In this work we perform an observational data analysis on the energy momentum squared gravity model. Possible solutions for matter density are obtained from the model and their cosmological implications are studied. Some recent observational data is used to constrain model parameters using statistical techniques. We have used the cosmic chronometer and SNe Type-Ia Riess (292) $H(z)-z$ data-sets in our study. Along with the data-sets we have also used baryon acoustic oscillation (BAO) peak parameter and cosmic microwave background (CMB) peak parameter to obtain bounds on the model parameters. Joint analysis of the data with the above mentioned parameters have been performed to obtain better results. For the statistical analysis we have used the minimization technique of the $\chi^{2}$ statistic. Using this tool we have constrained the free parameters of the model. Confidence contours have been generated for the predicted values of the free parameters at the $66\%$, $90\%$ and $99\%$ confidence levels. Finally we have compared our analysis with the union2 data sample presented by Amanullah et al.,2010 and the recently published Pantheon data sample. Finally a multi-component model is investigated by adding dust to a general cosmological fluid with equation of state $w=-1/3$. The density parameters were studied and their values were found to comply with the observational results.

gr-qc↗

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 $\omega $--$ \omega'$ plane for different values of the interacting parameter and explored the freezing region and thawing region in $\omega $--$ \omega'$ 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 $\omega_{0}$ and $\omega_{1}$ by minimizing the $\chi^{2}$ 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 $\mu$(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 $\Omega_{dm0}$, $\Omega_{vmcg0}$, $H_{0}$, redshift $z$ and other parameters like $\alpha$, $A$, $\gamma$ and $n$. From Stern data set (12 points), we have obtained the bounds of the arbitrary parameters by minimizing the $\chi^{2}$ 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 ($A,\gamma$) by fixing some other parameters $\alpha$ and $n$. The best fit value of distance modulus $\mu(z)$ 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↗

arXiv2014

Constraining Parameters of Generalized Cosmic Chaplygin Gas in Loop Quantum Cosmology

We have assumed the FRW universe in loop quantum cosmology (LQC) model filled with the dark matter and the Generalized Cosmic Chaplygin gas (GCCG) type dark energy where dark matter follows the linear equation of state. We present the Hubble parameter in terms of the observable parameters $Ω_{m0}$ and $H_{0}$ with the redshift $z$ and the other parameters like $A$, $B$, $w_{m}$, $ ω$ and $α$ which coming from our model. From Stern data set (12 points)\& SNe Type Ia 292 data (from \cite{Riess1,Riess2,Astier}) 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 Stern+BAO and Stern+BAO+CMB observations, we have also obtained the bounds of the parameters ($A,B$) by fixing some other parameters $α$, $w_{m}$ and $ω$. From the best fit values of the parameters, we have obtained the distance modulus $μ(z)$ for our theoretical GCCG model in LQC and from Supernovae Type Ia (union2 sample 552 data from [\cite{Amanullah}] \& Riess 292 data from [\cite{Riess1,Riess2,Astier}]), we have concluded that our model is in agreement with the Supernovae Type Ia sample data. In addition, we have investigated in details about the various types of Future Singularities that may be formed in this model and it is notable that our model is completely free from any types of future singularities.

physics.gen-ph↗

arXiv2014

Reconstruction of Einstein-Aether Gravity from other Modified Gravity Models

We briefly describe the modified Friedmann equations for Einstein-Aether gravity theory and we find the effective density and pressure. The purpose of our present work is to reconstruction of Einstein-Aether Gravity from other modified gravities like $f(T)$, $f(R)$, $f(G)$, $f(R,T)$ and $f(R,G)$ and check its viability. The scale factor is chosen in power law form. The free function $F(K)$ for Einstein-Aether gravity (where $K$ is proportional to $H^{2}$) have been found in terms for $K$ by the correspondence between Einstein-Aether gravity and other modified gravities and the nature of $F(K)$ vs $K$ have been shown graphically for every cases. Finally, we analyzed the stability of each reconstructed Einstein-Aether gravity model.

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

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 $\chi^{2}$ 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 $\mu(z)$ 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↗

arXiv2013

Observational Constraints of Modified Chaplygin Gas in RS II Brane

FRW universe in RS II braneworld model filled with a combination of dark matter and dark energy in the form of modified Chaplygin gas (MCG) is considered. It is known that the equation of state (EoS) for MCG is a three-variable equation determined by $A$, $\alpha$ and $B$. The permitted values of these parameters are determined by the recent astrophysical and cosmological observational data. Here we present the Hubble parameter in terms of the observable parameters $\Omega_{m0}$, $\Omega_{x0}$, $H_{0}$, redshift $z$ and other parameters like $A$, $B$, $C$ and $\alpha$. From Stern data set (12 points), we have obtained the bounds of the arbitrary parameters by minimizing the $\chi^{2}$ 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 ($B,C$) by fixing some other parameters $\alpha$ and $A$. The best fit value of distance modulus $\mu(z)$ is obtained for the MCG model in RS II brane, and it is concluded that our model is perfectly consistent with the union2 sample data.

physics.gen-ph↗

arXiv2013

Observational Study of Higher Dimensional Magnetic Universe in Non-linear Electrodynamics

In this work, we have considered the flat FRW model of the universe in $(n+2)$-dimensions filled with the dark matter and the magnetic field. We present the Hubble parameter in terms of the observable parameters $Ω_{m0}$ and $H_{0}$ with the redshift $z$ and the other parameters like $B_{0},ω, μ_{0},δ,n,w_{m}$. The natures of magnetic field $B$, deceleration parameter $q$ and $Om$ diagnostic have also been analyzed for accelerating expansion of the universe. 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. Now to find the bounds of the parameters ($B_{0},ω$) and to draw the statistical confidence contour, we fixed four parameters $μ_{0},δ,n,w_{m}$. Here the parameter $n$ determines the higher dimensions and we perform comparative study between three cases : 4D $(n=2)$, 5D $(n=3)$ and 6D $(n=4)$ respectively. Next due to joint analysis with BAO observation, we have also obtained the bounds of the parameters ($B_{0},ω$) by fixing other parameters $μ_{0},δ,n,w_{m}$ for 4D, 5D and 6D. The best fit of distance modulus for our theoretical model and the Supernova Type Ia Union2 sample are drawn for different dimensions.

physics.gen-ph↗

arXiv2013

How effective is new variable modified Chaplygin gas to play the role of dark energy- A dynamical system analysis in RS II Brane model

Motivated by some previous works of Rudra et al we set to explore the background dynamics when dark energy in the form of New Variable Modified Chaplygin gas is coupled to dark matter with a suitable interaction in the universe described by brane cosmology. The main idea is to find out the efficiency of New variable modified Chaplygin gas to play the role of DE. As a result we resort to the technique of comparison with standard dark energy models. Here the RSII brane model have been considered as the gravity theory. An interacting model is considered in order to search for a possible solution of the cosmic coincidence problem. A dynamical system analysis is performed because of the high complexity of the system . The statefinder parameters are also calculated to classify the dark energy model. Graphs and phase diagrams are drawn to study the variations of these parameters and get an insight into the effectiveness of the dark energy model. It is also seen that the background dynamics of New Variable Modified Chaplygin gas is consistent with the late cosmic acceleration. After performing an extensive mathematical analysis, we are able to constrain the parameters of new variable modified Chaplygin gas as $m<n$ to produce the best possible results. Future singularities are studied and it is found that the model has a tendency to result in such singularities unlike the case of generalized cosmic Chaplygin gas. Our investigation leads us to the fact that New Variable Modified Chaplygin gas is not as effective as other Chaplygin gas models to play the role of dark energy.

physics.gen-ph↗

arXiv2012

Observational Constraints of Homogeneous Higher Dimensional Cosmology with Modified Chaplygin Gas

In this work, we have considered the flat FRW model of the universe in $(n+2)$-dimensions filled with the dark matter (perfect fluid with negligible pressure) and the modified Chaplygin gas (MCG) type dark energy. We present the Hubble parameter in terms of the observable parameters $\Omega_{m0}$, $\Omega_{x0}$ and $H_{0}$ with the redshift $z$ and the other parameters like $A$, $B$, $C$, $n$ and $\alpha$. From Stern data set (12 points), we have obtained the bounds of the arbitrary parameters by minimizing the $\chi^{2}$ test. The best-fit values of the parameters are obtained by 66%, 90% and 99% confidence levels. Now to find the bounds of the parameters and to draw the statistical confidence contour, we first fixed three parameters $C, n, \alpha$ and then fixed the three parameters $A, n, \alpha$. In the first case we find the bounds of $(A, B)$ and draw the contour between them for 4D$(n=2)$, 5D$(n=3)$ and 6D$(n=4)$. In the second case we fixed three different values of A as 1, 1/3, -1/3 to find the bounds of $(B, C)$ and draw the contour between them. Here the parameter $n$ determines the higher dimensions and we perform comparative study between three cases : 4D $(n=2)$, 5D $(n=3)$ and 6D $(n=4)$ respectively. Next due to joint analysis with BAO observation, we have also obtained the bounds of the parameters ($A,B$) by fixing some other parameters $\alpha$ and $A$ for 4D, 5D and 6D.

physics.gen-ph↗

arXiv2012

Observational Constraints of Modified Chaplygin Gas in Loop Quantum Cosmology

We have considered the FRW universe in loop quantum cosmology (LQC) model filled with the dark matter (perfect fluid with negligible pressure) and the modified Chaplygin gas (MCG) type dark energy. We present the Hubble parameter in terms of the observable parameters $Ω_{m0}$, $Ω_{x0}$ and $H_{0}$ with the redshift $z$ and the other parameters like $A$, $B$, $C$ and $α$. 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 ($B,C$) by fixing some other parameters $α$ and $A$. From the best fit of distance modulus $μ(z)$ for our theoretical MCG model in LQC, we concluded that our model is in agreement with the union2 sample data.

physics.gen-ph↗

arXiv2012

Study of Tachyonic Field and its statefinder diagnostics in Various Scenarios of The Anisotropic Universe

In the present work, we have considered N-dimensional Einstein field equations in which 4-dimensional space-time is described by a FRW metric and that of the extra d-dimensions by an Euclidean metric. Considering the universe filled with tachyonic field we have reconstructed the potential $V(\phi)$ corresponding to the field reconstructions in an anisotropic universe under \emph{Emergent-Power law}, \emph{Emergent-Intermediate}, \emph{Emergent-Logamediate}and \emph{Logamediate-Intermediate} scenarios. The statefinder parameters have been investigated in all of the said scenarios.

gr-qc↗