arXiv subjects

Ujjal Debnath

Publications and source records attributed to Ujjal Debnath.

At least 127 records · Page 7Linked to original sources

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

Statefinder Parameter for Varying G in Three Fluid System

In this work, we have considered variable G in flat FRW universe filled with the mixture of dark energy, dark matter and radiation. If there is no interaction between the three fluids, the deceleration parameter and statefinder parameters have been calculated in terms of dimensionless density parameters which can be fixed by observational data. Also the interaction between three fluids has been analyzed due to constant $G$. The statefinder parameters also calculated in two cases: pressure is constant and pressure is variable.

physics.gen-ph↗

arXiv2011

Brans-Dicke Theory in Anisotropic Model with Viscous Fluid

In this paper we have considered an anisotropic space-time model of the Universe in presence of Brans-Dicke (BD) scalar field $ϕ$, causal viscous fluid and barotropic fluid. We have shown that irrespective of fluid the causality theory provides late time acceleration of the Universe. If the deceleration occurs in radial direction and acceleration occurs in transverse direction then the anisotropic Universe will accelerate for a particular condition of the power law representation of the scale factors.

gr-qc↗

arXiv2011

The Effects of Tachyonic and Phantom Fields in the Intermediate and Logamediate Scenarios of the Anisotropic Universe

In this work, we have analyzed two scenarios namely, "intermediate" and "logamadiate" scenarios for closed, open and flat anisotropic universe in presence of phantom field, normal tachyonic field and phantom tachyonic field. We have assumed that there is no interaction between the above mentioned dark energy and dark matter. In these two types of the scenarios of the universe, the nature of the scalar fields and corresponding potentials have been investigated. In intermediate scenario, (i) the potential for normal tachyonic field decreases, (ii) the potentials for phantom tachyonic field and phantom field increase with the corresponding fields. Also in logamediate scenario, (i) the potential for normal tachyonic field increases, (ii) the potentials for phantom tachyonic field and phantom field decrease with the corresponding fields.

physics.gen-ph↗

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↗

arXiv2011

Dynamical System Analysis of Interacting Variable Modified Chaplygin Gas Model in FRW Universe

In this work, we have considered interacting dynamical model taking variable modified Chaplygin gas which plays as dark energy coupled to cold dark matter in the flat FRW universe. Since the nature of dark energy and dark matter is still unknown, it is possible to have interaction between them and we choose the interaction term in phenomenologically. We have converted all the equations in the dynamical system of equations by considering the dimensionless parameters and seen the evolution of the corresponding autonomous system. The feasible critical point has been found and for the stability of the dynamical system about the critical point, we linearize the governing equation around the critical point. We found that there exists a stable scaling (attractor) solution at late times of the Universe and found some physical range of $n$ and the interaction parameter $c$. We have shown that for our calculated physical range of the parameters, the Universe explores upto quintessence stage. The deceleration parameter, statefinder parameters, Hubble parameter and the scale factor have been calculated around the critical point. Finally some consequences around the critical point i.e., the distance measurement of the Universe like lookback time, luminosity distance, proper distance, angular diameter distance, comoving volume, distance modulus and probability of intersecting objects have been analyzed before and after the present age of the Universe.

physics.gen-ph↗

arXiv2011

Fractional Action Cosmology: Emergent, Logamediate, Intermediate, Power law Scenarios of the Universe and Generalized Second Law of Thermodynamics

In the framework of Fractional Action Cosmology (FAC), we study the generalized second law of thermodynamics for the Friedmann Universe enclosed by a boundary. We use the four well-known cosmic horizons as boundaries namely, apparent horizon, future event horizon, Hubble horizon and particle horizon. We construct the generalized second law (GSL) using and without using the first law of thermodynamics. To check the validity of GSL, we express the law in the form of four different scale factors namely emergent, logamediate, intermediate and power law. For Hubble, apparent and particle horizons, the GSL holds for emergent and logamediate expansions of the universe when we apply with and without using first law. For intermediate scenario, the GSL is valid for Hubble, apparent, particle horizons when we apply with and without first law. Also for intermediate scenario, the GSL is valid for event horizon when we apply first law but it breaks down without using first law. But for power law expansion, the GSL may be valid for some cases and breaks down otherwise.

physics.gen-ph↗

arXiv2011

Higher Dimensional Cosmology with Some Dark Energy Models in Emergent, Logamediate and Intermediate Scenarios of the Universe

We have considered N-dimensional Einstein field equations in which four-dimensional space-time is described by a FRW metric and that of extra dimensions by an Euclidean metric. We have chosen the exponential forms of scale factors a and d numbers of b in such a way that there is no singularity for evolution of the higher dimensional Universe. We have supposed that the Universe is filled with K-essence, Tachyonic, Normal Scalar Field and DBI-essence. Here we have found the nature of potential of different scalar field and graphically analyzed the potentials and the fields for three scenario namely Emergent Scenario, Logamediate Scenario and Intermediate Scenario. Also graphically we have depicted the geometrical parameters named statefinder parameters and slow-roll parameters in the higher dimensional cosmology with the above mentioned scenarios.

physics.gen-ph↗

arXiv2011

Role of Chameleon Field in presence of Variable Modified Chaplygin gas in Brans-Dicke Theory

In this work, we have considered FRW model of the universe for Brans-Dicke (BD) theory with BD scalar field as a Chameleon field. First we have transformed the field equations and conservation equation from Jordan's frame to Einstein's frame. We have shown in presence of variable modified Chaplygin gas, the potential function $V$ and another analytic function $f$ always increase with respect to BD-Chameleon scalar field $ϕ$.

physics.gen-ph↗

arXiv2011

Study of Thermodynamic Quantities in Generalized Gravity Theories

In this work, we have studied the thermodynamic quantities like temperature of the universe, heat capacity and squared speed of sound in generalized gravity theories like Brans-Dicke, Ho$\check{\text r}$ava-Lifshitz and $f(R)$ gravities. We have considered the universe filled with dark matter and dark energy. Also we have considered the equation of state parameters for open, closed and flat models. We have observed that in all cases the equation of state behaves like quintessence. The temperature and heat capacity of the universe are found to decrease with the expansion of the universe in all cases. In Brans-Dicke and $f(R)$ gravity theories the squared speed of sound is found to exhibit increasing behavior for open, closed and flat models and in Ho$\check{\text r}$ava-Lifshitz gravity theory it is found to exhibit decreasing behavior for open and closed models with the evolution of the universe. However, for flat universe, the squared speed of sound remains constant in Ho$\check{\text r}$ava-Lifshitz gravity.

gr-qc↗

arXiv2011

Natures of Statefinder Parameters and Om Diagnostic for Cardassian Universe in Horava-Lifshitz Gravity

In this work, we have considered Cardassian Universe in Horava-Lifshitz gravity. Four types of Cardassian Universe models i.e., polytropic/power law, modified polytropic, exponential and modified exponential models have been considered for accelerating models. The natures of statefinder parameters, deceleration parameter, Om diagnostic and EoS parameters have been investigated for all types of Cardassian models in Horava-Lifshitz gravity.

physics.gen-ph↗

arXiv2011

Role of generalized Ricci dark energy on Chameleon field in the emergent universe

In this paper, we have considered the generalized Ricci dark energy (GRDE) and generalized holographic dark energy (GHDE) in the scenario of emergent universe. Fractional energy density and deceleration parameters for GRDE were derived under emergent universe scenario. Also role of GRDE on the Chameleon field in the emergent universe scenario has been examined. Finally, the behaviours of the Chameleon scalar field $ϕ$, corresponding potential $V$ and associated function $f$ were investigated in presence of GRDE.

physics.gen-ph↗

arXiv2011

Statefinder Description in Generalized Holographic and Ricci Dark Energy Models

We have considered the generalized holographic and generalized Ricci dark energy models for acceleration of the universe. If the universe filled with only GHDE/GRDE the corresponding decel- eration parameter, EOS parameter and statefinder parameters have been calculated. Next we have considered that the mixture of GHDE/GRDE and dark matter in interacting and non-interacting situations. Also the mixture of GHDE/GRDE and generalized Chaplygin gas have been analyzed during evolution of the universe. The natures of above mentioned parameters have been investigated for interacting and non-interacting situations. Finally, it follows that the prescribed models derive the acceleration of the universe.

physics.gen-ph↗

arXiv2011

Study of Thermodynamics in Generalized Holographic and Ricci Dark Energy Models

We have considered the flat FRW model of the universe which is filled with the combination of dark matter and dark energy. Here we have considered two types of dark energy models: (i) Generalized holographic and (ii) generalized Ricci dark energies. The general descriptions of first law and generalized second law (GSL) of thermodynamics have studied on the apparent horizon, particle horizon and event horizon of the universe. We have shown that the first law and GSL are always valid on apparent horizon and first law can not be satisfied on the particle and event horizons in Einstein's gravity. These results are always true for any types of dark energy models i.e., these results do not depend on the dark energy models in Einstein's gravity. But the GSL completely depends on the choices of dark energy models in Einstein's gravity. Here we have discussed the validity of GSL in Generalized holographic and generalized Ricci dark energy models. On the particle horizon GSL may be satisfied but on the event horizon the GSL can not be satisfied for both the dark energy models. Also we have considered the Generalized holographic dark energy and generalized Ricci dark energy as the original holographic dark energy, so in this situation we have calculated the expression of the radius of the horizon $L$. On this horizon, we have shown that the first law can not be satisfied. Finally, on the horizon of radius $L$, we have found that the GSL can not be satisfied for both the dark energy models.

physics.gen-ph↗

arXiv2011

A Study of Generalized Second Law of Thermodynamics in Magnetic Universe in the light of Non-Linear Electrodynamics

In this work, we have considered the magnetic universe in non-linear electrodynamics. The Einstein's field equations for non-flat FRW model have been considered when the universe is filled with the matter and magnetic field only. We have discussed the validity of the generalized second law of thermodynamics of the magntic universe bounded by Hubble, apparent, particle and event horizons using Gibb's law and the first law of thermodynamics for interacting and non-interacting scenarios. It has been shown that the GSL is always satisfied for Hubble, apparent and particle horizons but for event horizon, the GSL is violated initially and satisfied at late stage of the universe.

gr-qc↗

arXiv2011

Correspondence between DBI-essence and Modified Chaplygin Gas and the Generalized Second Law of Thermodynamics

In this work, we have considered the DBI-essence dark energy model in FRW Universe. We have found the exact solutions of potential, warped brane tension and DBI scalar field. We also calculate the statefinder parameters for our model that make it distinguishable among numerous dark energy models. Moreover, we establish correspondence between DBI-essence and modified Chaplygin gas (MCG) and hence reconstruct the potential and warped brane tension. By this reconstruction, we observe that DBI scalar field and potential increase and warped brane tension decreases during evolution of the Universe. Finally, we investigate the validity of the generalized second law (GSL) of thermodynamics in the presence of DBI-essence and modified Chaplygin gas. It is observed that the GSL breaks down for DBI-essence model but GSL always satisfied for MCG model.

physics.gen-ph↗

arXiv2011

Dilaton Dark Energy Model in f(R), f(T) and Horava-Lifshitz Gravities

In this work, we have considered dilaton dark energy model in Weyl-scaled induced gravitational theory in presence of barotropic fluid. It is to be noted that the dilaton field behaves as a quintessence. Here we have discussed the role of dilaton dark energy in modified gravity theories namely, f(R); f(T) and Horava-Lifshitz gravities and analyzed the behaviour of the dilaton field and the corresponding potential in respect to these modified gravity theories instead of Einstein's gravity. In f(R) and f(T) gravities, we have considered some particular forms of f(R) and f(T) and we have shown that the potentials always increase with the dilaton fields. But in Horava-Lifshitz gravity, it has been seen that the potential always decreases as dilation field increases.

physics.gen-ph↗

arXiv2011

Entropy-Corrected New Agegraphic Dark Energy Model in Horava-Lifshitz Gravity

In this work, we have considered the entropy-corrected new agegraphic dark energy (ECNADE) model in Horava-Lifshitz gravity in FRW universe. We have discussed the correspondence between ECNADE and other dark energy models such as DBI-essence,Yang-Mills dark energy, Chameleon field, Non-linear electrodynamics field and hessence dark energy in the context of Horava-Lifshitz gravity and reconstructed the potentials and the dynamics of the scalar field theory which describe the ECNADE.

physics.gen-ph↗