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Anil Kumar Yadav

Publications and source records attributed to Anil Kumar Yadav.

70 records · Page 4Linked to original sources
arXiv2011

Some LRS Bianchi-I String Cosmological Models with Variable Deceleration Parameter

The present study deals with LRS Bianchi type I cosmological model representing massive string. The energy-momentum tensor for such string as formulated by Letelier (1983) is used to construct massive string cosmological models for which we assume that the shear scalar ($σ$) is proportional to the expansion scalar ($θ$). The study reveals that massive strings dominate the early Universe. The strings eventually disappear from the Universe for sufficiently large time, which is in agreement with the current astronomical observations. Some physical and geometrical behaviour of models are also discussed.

gr-qc↗
arXiv2011

Bulk Viscous LRS Biachi-I Universe with variable $G$ and decaying $Λ$

The present study deals with spatially homogeneous and totally anisotropic locally rotationally symmetric (LRS) Bianchi type I cosmological model with variable $G$ and $Λ$ in presence of imperfect fluid. To get the deterministic model of Universe, we assume that the expansion $(θ)$ in the model is proportional to shear $(σ)$. This condition leads to $A=\ell B^{n}$, where $A$,\;$B$ are metric potential. The cosmological constant $Λ$ is found to be decreasing function of time and it approaches a small positive value at late time which is supported by recent Supernovae Ia (SN Ia) observations. Also it is evident that the distance modulus curve of derived model matches with observations perfectly.

physics.gen-ph↗
arXiv2011

Some Anisotropic Dark Energy Models in Bianchi Type-V Space-time

The paper deals with Bianchi type V Universe, which has dynamical energy density. We consider Bianchi type V space-time, introducing three different skewness parameters along spatial directions to quantify the deviation of pressure from isotropy. To study the anisotropic nature of the dynamical dark energy, we assume that the skewness parameters are time dependent. It is found that the Universe achieves flatness in quintessence model. The physical behavior of the Universe has been discussed in detail.

physics.gen-ph↗
arXiv2011

Lyra's Cosmology of Massive String in Anisotropic Bianchi-II Space-time

The paper deals with a spatially homogeneous and totally anisotropic Bianchi II cosmological models representing massive strings in normal gauge for Lyra's manifold. The modified Einstein's field equations have been solved by applying variation law for Hubble's parameter. This law generates two type of solutions for average scale factor, one is of power law type and other is of exponential law type. The power law describes the dynamics of Universe from big bang to present epoch while exponential law seems reasonable to project dynamics of future Universe. It has been found that the displacement actor $(β)$ is a decreasing function of time and it approaches to small positive value at late time, which is collaborated with Halford (1970) as well as recent observations of SN Ia. The study reveals that massive strings dominate in early Universe and eventually disappear from Universe for sufficiently large time, which is in agreement with the current astronomical observations.

physics.gen-ph↗
arXiv2011

Generation of Bianchi Type V String Cosmological Models with Bulk Viscosity

Bianchi type V string cosmological models with bulk viscosity for massive string are investigated. The bulk viscosity is assumed to vary with time in such a manner that it is related to simple power function of the energy density. Using generation technique (Camci~et~al., 2001), it is shown that Einstein's field equations are solvable for any arbitrary cosmic scale function. Solution for particular form of cosmic scale functions are also obtained. It is found that solutions based on generation technique are relevant to the observational results. Some physical and geometrical aspect of the models are also discussed.

gr-qc↗
arXiv2011

LRS Bianchi Type-II Massive String Cosmological Models in General Relativity

The present study deals with locally rotationally symmetric (LRS) Bianchi type II cosmological models representing massive string. The energy-momentum tensor for such string as formulated by Letelier (1983) is used to construct massive string cosmological models for which we assume that the expansion ($θ$) in the models is proportional to the shear ($σ$). This condition leads to $A = B^{m}$, where A and B are the metric coefficients and m is constant. We have derived two types of models depending on different values of m i.e. for $m\neq \sqrt{2}$ and $m = \sqrt{2}$ respectively. For suitable choice of constant m (i.e. for $m = 1/2$), it is observed that in early stage of the evolution of the universe, the universe is dominated by strings in both cases. Our models are in accelerating phase which is consistent to the recent observations of type Is supernovae. Some physical and geometric behaviour of the models are also discussed.

physics.gen-ph↗
arXiv2011

Dissipative Future Universe without Big Rip

The present study deals with dissipative future universe without big rip in context of Eckart formalism. The generalized chaplygin gas, characterized by equation of state $p=-\frac{A}{ρ^\frac{1}α}$, has been considered as a model for dark energy due to its dark-energy-like evolution at late time. It is demonstrated that, if the cosmic dark energy behaves like a fluid with equation of state $p=ωρ$; $ω< -1$, as well as chaplygin gas simultaneously then the big rip problem does not arises and the scale factor is found to be regular for all time.

gr-qc↗
arXiv2010

Bianchi Type V String Cosmological Models in General Relativity

Bianchi type V string cosmological models in general relativity are investigated. To get the exact solution of Einstein's field equations, we have taken some scale transformations followed by Camci $\it et ~ al$ (2001). It is shown that Einstein's field equations are solvable for any arbitrary cosmic scale function. Solution for particular form of cosmic scale functions are also obtained. Some physical and geometrical aspects of the models are discussed.

gr-qc↗
arXiv2010

Some Bianchi Type-V Models of Accelerating Universe with Dark Energy

The paper deals with a spatially homogeneous and anisotropic universe filled with perfect fluid and dark energy components. The two sources are assumed to interact minimally together with a special law of variation for the average Hubble's parameter in order to solve the Einstein's field equations. The law yields two explicit forms of the scale factor governing the Bianchi-V space-time and constant values of deceleration parameter. The role of dark energy with variable equation of state parameter has been studied in detail in the evolution of Bianchi-V universe. It has been found that dark energy dominates the Universe at the present epoch, which is consistent with the observations. The Universe achieves flatness after the dominance of dark energy. The physical behavior of the Universe has been discussed in detail.

physics.gen-ph↗
arXiv2010

Bianchi Type III Anisotropic Dark Energy Models with Constant Deceleration Parameter

The Bianchi type III dark energy models with constant deceleration parameter are investigated. The equation of state parameter $ω$ is found to be time dependent and its existing range for this model is consistent with the recent observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy clustering statistics. The physical aspect of the dark energy models are discussed.

gr-qc↗
arXiv2010

Dark energy models with variable equation of state parameter

The dark energy models with variable equation of state parameter $ω$ is investigated by using law of variation of Hubble's parameter that yields the constant value of deceleration parameter. The equation of state parameter $ω$ is found to be time dependent and its existing range for this model is consistent with the recent observations of SN Ia data, SN Ia data (with CMBR anisotropy) and galaxy clustering statistics. The physical significance of the dark energy models has also been discussed.

gr-qc↗
arXiv2010

Bianchi Type I Anisotropic Universe without Big Smash Driven by Law of Variation of Hubble's Parameter

A spatially homogeneous and anisotropic Bianchi Type I universe has been studied with ω <-1 without Big Smash. It is demonstrated that if cosmic dark energy behaves like a fluid with equation of state p = ωρ (p and ρ being pressure and energy density respectively) as well as generalized chaplygin gas simultaneously, Big Rip or Big Smash problem does not arise even for equation of state parameter ω <-1 unlike other phantom models, here, the scale factor for Bianchi Type I universe is found regular for all time. The present model is derived by using law of variation of Hubble's parameter from Bianchi Type I space-time and also the effective role of GCG behaviour is discussed.

gr-qc↗
arXiv2010

Lyra's cosmology of inhomogeneous universe with electromagnetic field

The plane-symmetric inhomogeneous cosmological models of perfect fluid distribution with electro-magnetic field is obtained in the framework of Lyra's geometry. To get the deterministic solution, I have considered $ A=f(x)ν(t) $, $ B=g(x)μ(t) $ and $ C=h(x)μ(t) $, where A, B and C are metric coefficients. It has been found that the solutions generalize the solution obtained by Pradhan, Yadav and Singh (2007) and are consistent with the recent observations of type Ia supernovae. A detailed study of physical and kinematical properties of the models have been carried out.

gr-qc↗
arXiv2009

Thermodynamical Behaviour of Inhomogeneous Universe with Varying $Λ$ in Presence of Electromagnetic Field

Thermodynamical Behaviour of Inhomogeneous Universe with Varying $ Λ$ in Presence of Electromagnetic Field is obtained. $ F_{12} $ is the non-vanishing component of electromagnetic field tensor. To get a deterministic solution, it is assumed that the free gravitational field is Petrov type-II non-degenerate.The value of cosmological constant is found to be small and pasitive supported by recent results from the supernovae observations recently obtained by High-Z Supernovae Ia Team and Supernovae Cosmological Project. A relation between cosmological constant and thermodynamical quantities is established. Some physical and geometric properties of the model are also discussed.

gr-qc↗
arXiv2009

Bianchi Type V Matter Filled Universe with Varying Lambda Term in General Relativity

Bianchi type V matter filled universe with varying lambda in general relativity are investigated by using the law of variation for the generalized mean Hubble parameter. This yields the constant value of deceleration parameter and generates two types of solutions for the average scale factor one is of power law type and other is of exponential type. The cosmological constant is found to be a decreasing function of time, which is supported by results from recent type Ia supernovae observations. Also it has been found that cosmological constant affects entropy. Some physical and geometric behaviour of the models are discussed.

gr-qc↗