arXiv subjects

Surajit Chattopadhyay

Publications and source records attributed to Surajit Chattopadhyay.

At least 73 records · Page 4Linked to original sources

arXiv2013

Stability of Non-asymptotically flat thin-shell wormholes in generalized dilaton-axion gravity

We construct a new type of thin-shell wormhole for non-asymptotically flat charged black holes in generalized dilaton-axion gravity inspired by low-energy string theory using cut-and-paste technique. We have shown that this thin shell wormhole is stable. The most striking feature of our model is that the total amount of exotic matter needed to support the wormhole can be reduced as desired with the suitable choice of the value of a parameter. Various other aspects of thin-shell wormhole are also analyzed.

gr-qc↗

arXiv2013

A reconstruction of modified holographic Ricci dark energy in $f(R,T)$ gravity

In this paper, we consider a recently proposed model of Dark Energy (DE) know as Modified Holographic Ricci DE (MHRDE) (which is function of the Hubble parameter and its first derivative with respect to the cosmic time $t$) in the light of the $f(R,T)$ model of modified gravity, considering the particular model $f(R,T) = μR + νT$, with $μ$ and $ν$ constants. The equation of state (EoS) parameter $ω_Λ$ approaches but never reaches the value -1, implying a quintessence-like behavior of the model. The deceleration parameter $q$ passes from decelerated to accelerated phase at a redshift of $z\approx 0.2$, showing also a small dependence from the values of the parameters considered. Thanks to the statefinder diagnostic analysis, we observed that the $Λ$CDM phase for the considered model is attainable. We observed that the fractional energy densities for DE and DM $Ω_Λ$ and $Ω_m$ have, respectively, an increasing and a decreasing pattern with the evolution of the universe, indicating an evolution from matter to DE dominated universe. Finally, studying the squared speed of the sound $v_s^2$ for our model, we found that is classically stable.

physics.gen-ph↗

arXiv2012

On the stability of the dark energy based on generalized uncertainty principle

The new agegraphic Dark Energy (NADE) model (based on generalized uncertainty principle) interacting with Dark Matter (DM) is considered in this study via power-law form of the scale factor $a(t)$. The equation of state (EoS) parameter $ω_{G}$ is observed to have a phantom-like behaviour. The stability of this model is investigated through the squared speed of sound $v_{s}^{2}$: it is found that $v_{s}^{2}$ always stays at negative level, which indicates instability of the considered model.

physics.gen-ph↗

arXiv2012

Generalized second law of thermodynamics in the emergent universe for some viable models of f(T) gravity

The present study is motivated by the study of reference [1], where the generalized second law of thermodynamics has been investigated for a flat FRW universe for two viable models of $f(T)$ gravity. In the present work, we have considered a non-flat universe and accordingly studied the behaviors of equation of state parameter and deceleration parameter. Subsequently, using the first law of thermodynamics we derived the expressions for the time derivative of the total entropy of a universe enveloped by apparent horizon. In the next phase, with the choice of scale factor pertaining to an emergent universe we have investigated the sign of the time derivatives of total entropy for three viable models of $f(T)$ gravity.

gr-qc↗

arXiv2012

Correspondence between $f(G)$ Gravity and Holographic Dark Energy via Power-law Solution

In this paper, we discuss cosmological application of holographic Dark Energy (HDE) in the framework of $f(G)$ modified gravity. For this purpose, we construct $f(G)$ model with the inclusion of HDE and a well-known power law form of the scale factor $a(t)$. The reconstructed $f(G)$ is found to satisfy a sufficient condition for a realistic modified gravity model. We find quintessence behavior of effective equation of state (EoS) parameter $ω_{DE}$ through energy conditions in this context. Also, we observe that the squared speed of sound $v_s^2$ remains negative which shows the instability of HDE $f(G)$ model.

physics.gen-ph↗

arXiv2012

Reconstruction of f(T) gravity from the Holographic dark energy

Among different candidates to play the role of Dark Energy (DE), modified gravity has emerged as offering a possible unification of Dark Matter (DM) and DE. The purpose of this work is to develop a reconstruction scheme for the modified gravity with $f(T)$ action using holographic energy density. In the framework of the said modified gravity we have considered the equation of state of the Holographic DE (HDE) density. Subsequently we have developed a reconstruction scheme for modified gravity with $f(T)$ action. Finally we have obtained a modified gravity action consistent with the HDE scenario.

physics.gen-ph↗

arXiv2012

Behaviour of interacting Ricci dark energy in logarithmic f(T) gravity

In the present work we have considered a modified gravity dubbed as "logarithmic $f(T)$ gravity" and investigated the behavior of Ricci dark energy interacting with pressureless dark matter. We have chosen the interaction term in the form $Q\propto Hδρ_{m}$ and investigated the behavior of the Hubble parameter $H$ as a function of the redshift $z$. For this reconstructed $H$ we have investigated the behavior of the density of the Ricci dark energy $ρ_{RDE}$ and density contribution due to torsion $ρ_{T}$. All of the said cosmological parameters are seen to have increasing behavior from higher to lower redshifts for all values of $c^{2}$ pertaining to the Ricci dark energy. Subsequently, we observed the equation of state parameter $w_{RDE}$ in this situation. The equation of state parameter is found to behave like phantom for all choices of $c^{2}$ in the Ricci dark energy.

physics.gen-ph↗

arXiv2012

A study on the interacting Ricci dark energy in $f(R,T)$ gravity

The present work reports study on the interacting Ricci dark energy in a modified gravity theory named $f(R,T)$ gravity. The specific model $f(R,T)=μR+νT$ (proposed by R. Myrzakulov, arXiv:1205.5266v2) is considered here. For this model we have observed a quintom-like behavior of the equation of state (EoS) parameter and a transition from matter dominated to dark energy density has been observed through fraction density evolution. The statefinder parameters reveal that the model interpolates between dust and $Λ$CDM phases of the universe.

physics.gen-ph↗

arXiv2012

The generalized second law of thermodynamics in f(R) gravity for various choices of scale factor

The present study is aimed at investigating the validity of the generalized second law (GSL) of thermodynamics in $f(\cal R)$ gravity. Choosing $f(\cal R)=R+ξR^μ+ζR^{-ν}$ [following Phys Rev D, 68, 123512 (2003)] we have computed the time derivatives of total entropy for various choices of scale factor pertaining to emergent, intermediate and logamediate scenarios of the universe. We have taken into account the radii of hubble, apparent, particle and event horizons while computing the time derivatives of entropy under various situations being considered. After analyzing through the plots of time derivative of total entropy against cosmic time it is observed that the derivative always stays at positive level that indicate the validity of GSL of thermodynamics in the $f(\cal R)$ gravity irrespective of the choices of scale factor and enveloping horizon.

physics.gen-ph↗

arXiv2012

Monthly sunspot number time series analysis and its modeling through autoregressive artificial neural network

This study reports a statistical analysis of monthly sunspot number time series and observes non homogeneity and asymmetry within it. Using Mann-Kendall test a linear trend is revealed. After identifying stationarity within the time series we generate autoregressive AR(p) and autoregressive moving average (ARMA(p,q)). Based on minimization of AIC we find 3 and 1 as the best values of p and q respectively. In the next phase, autoregressive neural network (AR-NN(3)) is generated by training a generalized feedforward neural network (GFNN). Assessing the model performances by means of Willmott's index of second order and coefficient of determination, the performance of AR-NN(3) is identified to be better than AR(3) and ARMA(3,1).

physics.gen-ph↗

arXiv2012

A study of generalized second law of thermodynamics in modified f(R) Horava-Lifshitz gravity

This work investigates the validity of the generalized second law of thermodynamics in modified f(R) Horava-Lifshitz gravity proposed by Chaichian et al (2010) [Class. Quantum Grav. 27 (2010) 185021], which is invariant under foliation-preserving diffeomorphisms. It has been observed that the equation of state parameter behaves like quintessence (w > -1). We study the thermodynamics of the apparent, event and particle horizons in this modified gravity. We observe that under this gravity, the time derivative of total entropy stays at positive level and hence the generalized second law is validated.

physics.gen-ph↗

arXiv2012

Interacting Ricci Dark Energy and its Statefinder Description

In this paper we have considered an interacting Ricci dark energy in flat FRW universe. We have reconstructed the Hubble's parameter under this interaction. Also, we have investigated the statefinder diagnostics. It has been revealed that the equation of state parameter behaves like quintessence in this interaction and from the statefinder diagnostics it has been concluded that the interacting Ricci dark energy interpolates between dust and $Λ$CDM stages of the universe.

gr-qc↗

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 $V(ϕ)$ 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↗

arXiv2012

Application of Principal Component Analysis in Machine-Part Cell Formation

The present paper applied Principal Component Analysis (PCA) for grouping of machines and parts so that the part families can be processed in the cells formed by those associated machines. An incidence matrix with binary entries has been chosen to apply this methodology. After performing the eigenanalysis of the principal component and observing the component loading plot of the principal components, the machine groups and part families have been identified and arranged to form machine-part cells. Later the same methodology has been extended and applied to nine other machine-part matrices collected from literature for the validation of the proposed methodology. The goodness of cell formation was compared using the grouping efficacy and the potential of eigenanalysis in cell formation has been established over the best available results using the various established methodologies. The result shows that in 70% of the problem there is increase in grouping efficacy and in 30% problem the performance measure of cell formation is as good as the best result from literature.

nlin.AO↗

arXiv2012

Generalized Second Law of Thermodynamics for FRW Cosmology with Power-Law Entropy Correction

In this work, we have considered the power law correction of entropy on the horizon. If the flat FRW Universe is filled with the n components fluid with interactions, the GSL of thermodynamics for apparent and event horizons have been investigated for equilibrium and non-equilibrium cases. If we consider a small perturbation around the de Sitter space-time, the general conditions of the validity of GSL have been found. Also if a phantom dominated Universe has a polelike type scale factor, the validity of GSL has also been analyzed. Further we have obtained constraints on the power-law parameter α in the phantom and quintessence dominated regimes. Finally we obtain conditions under which GSL breaks down in a cosmological background.

gr-qc↗

arXiv2011

Validity of Generalized Second Law of Thermodynamics in the Logamediate and Intermediate scenarios of the Universe

In this work, we have investigated the validity of the generalized second law of thermodynamics in logamediate and intermediate scenarios of the universe bounded by the Hubble, apparent, particle and event horizons using and without using first law of thermodynamics. We have observed that the GSL is valid for Hubble, apparent, particle and event horizons of the universe in the logamediate scenario of the universe using first law and without using first law. Similarly the GSL is valid for all horizons in the intermediate scenario of the universe using first law. Also in the intermediate scenario of the universe, the GSL is valid for Hubble, apparent and particle horizons but it breaks down whenever we consider the universe enveloped by the event horizon.

physics.gen-ph↗

arXiv2011

A Dark Energy Model with Generalized Uncertainty Principle in the Emergent, Intermediate and Logamediate Scenarios of the Universe

This work is motivated by the work of Kim et al (2008), which considered the equation of state parameter for the new agegraphic dark energy based on generalized uncertainty principle coexisting with dark matter without interaction. In this work, we have considered the same dark energy inter- acting with dark matter in emergent, intermediate and logamediate scenarios of the universe. Also, we have investigated the statefinder, kerk and lerk parameters in all three scenarios under this inter- action. The energy density and pressure for the new agegraphic dark energy based on generalized uncertainty principle have been calculated and their behaviors have been investigated. The evolu- tion of the equation of state parameter has been analyzed in the interacting and non-interacting situations in all the three scenarios. The graphical analysis shows that the dark energy behaves like quintessence era for logamediate expansion and phantom era for emergent and intermediate expansions of the universe.

gr-qc↗

arXiv2011

Fractional Action Cosmology: Some Dark Energy Models in Emergent, Logamediate and Intermediate Scenarios of the Universe

In the framework of Fractional Action Cosmology, we have reconstructed the scalar potentials and scalar fields, namely, quintessence, phantom, tachyon, k-essence, DBI-essence, Hessence, dilaton field and Yang-Mills field. To get more physical picture of the variation of the scalar field and potential with time, we express scale factor in emergent, logamediate and intermediate scenarios, under which the Universe expands differently.

physics.gen-ph↗