arXiv subjects

Anil Kumar Yadav

Publications and source records attributed to Anil Kumar Yadav.

At least 37 records · Page 2Linked to original sources

arXiv2021

Modeling of accelerating Universe with bulk viscous fluid in Bianchi V space-time

In this paper, we have investigated a bulk viscous anisotropic Universe and constrained its model parameters with recent $H(z)$ and Pantheon compilation data. Using cosmic chronometric technique, we estimate the present value of Hubble's constant as $H_{0} = 69.39 \pm 1.54~km~s^{-1}Mpc^{-1}$, $70.016 \pm 1.65~km~s^{-1}Mpc^{-1}$ and $69.36 \pm 1.42~km~s^{-1}Mpc^{-1}$ by bounding our derived model with recent $H(z)$ data, Pantheon and joint $H(z)$ and Pantheon data respectively. The present age of the Universe is specified as $t_0= 0.9796H_0^{-1}\sim 13.79$ Gyrs. The model favours a transitioning Universe with the transition red-shift as $z_{t} = 0.73$. We have reconstructed the jerk parameter using the observational data sets. From the analysis of the jerk parameter, it is observed that, our derived model shows a marginal departure from the concordance $Λ$CDM model.

gr-qc↗

arXiv2020

Note on Tsallis holographic dark energy in Brans-Dicke cosmology

In this comment, we have investigated that the power law variation of Brans-Dicke scalar field $(ϕ)$ with scale factor $(a)$ is not validated by field equations in general for the Universe filled with dark matter and Tsallis type holographic dark energy. However, for specific choice of free parameters $(ω= -\frac{3}{2}\;\; \&\;\; n = -1)$ which are differ from its values fixed in Ghaffari et al \textcolor{blue}{[Ghaffari et al. Euro. Phys. J. C \textbf{78}, 706 (2018)]} to describe various physical properties of the Universe in derived model, the power law variation of $ϕ$ with $a$ leads to consistent results. Further, we notice that the energy conservation law for Tsallis holographic dark energy in Brans-Dicke gravity does not hold.

physics.gen-ph↗

arXiv2020

Lyra's cosmology of homogeneous and isotropic universe in Brans-Dicke theory

In this paper, we investigate a scalar field Brans-Dicke cosmological model in Lyra's geometry which is based on the modifications in geometrical term as well as energy term of Einstein's field equations. We have examined the validity of proposed cosmological model on observational scale by performing statistical analysis from latest $H(z)$ and SN Ia observational data. We find that the estimated values of Hubble's constant and matter energy density parameter are in agreement with their corresponding values, obtained from recent observations of WMAP and Plank collaboration. We also derived deceleration parameter, age of the universe and jerk parameter in terms of red-shift and computed its present values. The dynamics of deceleration parameter in derived model of the universe shows a signature flipping from positive to negative value and also indicates that the present universe is in accelerating phase.

gr-qc↗

arXiv2020

Transitioning Universe with hybrid scalar field in Bianchi I space-time

In this paper we investigate a Bianchi type I transitioning Universe in Brans-Dicke theory. To get an explicit solution of the field equations, we assume scalar field as $ϕ= ϕ_{0}\left[t^αexp(βt)\right]^δ$ with $ϕ_{0}$, $α$, $β$ and $δ$ as constants. The values of $α$ and $β$ are obtained by probing the proposed model with recent observational Hubble data (OHD) points. The interacting and non-interacting scenarios between dark matter and dark energy of the derived Universe within the framework of Brans-Dicke gravity are investigated. The $om(z)$ analysis of the Universe in derived model shows that the Universe is filled with dynamical dark energy with its equation of state parameter $ω_{de} > -1$. Hence the Universe behaves like a quintessence model at present epoch. Some physical properties of the Universe are also discussed.

gr-qc↗

arXiv2020

Comment on Brans-Dicke Scalar Field Cosmological Model in Lyra's Geometry

In the present study, we comment on Brans-Dicke scalar field cosmological model in Lyra's geometry [Maurya \& Zia, Phys. Rev. D \textbf{100}, 023503 (2019)]. In this comment, we investigate that there is no acceleration in the model proposed by the authors of Phys. Rev. D \textbf{100}, 023503 (2019). Therefore, despite the claims to the contrary the Brans-Dicke Scalar Field Cosmological Model in Lyra's Geometry with high Brans-Dicke (BD) coupling parameter $ω$ and constant $β$ can not produce late time acceleration in the universe.

gr-qc↗

arXiv2020

An exact solution of the observable universe in Bianchi V space-time

In this paper we investigate an observable universe in Bianchi type V space-time by taking into account the cosmological constant as the source of energy. We have performed a $χ^{2}$ test to obtain the best fit values of the model parameters of the universe in the derived model. We have used two types of data sets, viz: i) 31 values of the Hubble parameter and ii) the 1048 Phanteon data set of various supernovae distance moduli and apparent magnitudes. From both the data sets, we have estimated the current values of the Hubble constant, density parameters $(Ω_{m})_{0}$ and $(Ω_Λ)_{0}$. The present value of deceleration parameter of the universe in derived model is obtained as $q_{0} = 0.59^{+0.04}_{-0.03}$ and $0.59^{+0.02}_{-0.03}$ in accordance with $H(z)$ and Pantheon data respectively. Also we observe that there is a signature flipping in the sign of deceleration parameter from positive to negative and transition red-shift exists. Thus, the universe in derived model represents a transitioning universe which is in accelerated phase of expansion at present epoch. We have estimated the current age of the universe $(t_{0})$ and present value of jerk parameter $(j_{0})$. Our obtained values of $t_{0}$ and $j_{0}$ are in good agreement with its values estimated by Plank collaborations and WMAP observations.

physics.gen-ph↗

arXiv2020

Plane symmetric cosmological models

In the present work, we execute the Lie symmetry analysis on the Einstein-Maxwell field equations in the plane symmetric spacetime. Under the background of the plane symmetric space-time we compute the Lie point symmetries, perform the similarity reductions and obtain exact solutions in connection to the evolutionary scenario of the universe. The special feature of the study is that it deals with the electromagnetic energy of the inhomogeneous universe through the non-vanishing component of electromagnetic field tensor $F_{12}$ and assumes that the free gravitational field is of Petrov type-II non-degenerate. We have found that the electromagnetic field tensor is positive and increasing function of time. To validate the solution set, we examine with detailed discussions several physical as well as geometrical features of a specific sub-case of the model.

physics.gen-ph↗

arXiv2020

Singularity-free nonexotic compact star in $f(R,T)$ gravity

In the present work, we have searched the existence of anisotropic and non-singular compact star in the $f(R,T)$ gravity by taking into account the non-exotic equation of state (EoS). In order to obtain the solutions of the matter content of compact object, we assume the well known barotropic form of EoS that yields the linear relation between pressures and energy density. We propose the existence of non-exotic compact star which shows the validation of energy conditions and stability with in the $f(R,T)$ extended theory of gravity perspective. The linear material correction in the extended theory the matter content of compact star remarkably able to satisfies energy condition. We discuss various physical features of compact star and show that proposed model of stellar object satisfies all regularity conditions and is stable as well as singularity-free.

gr-qc↗

arXiv2020

Power-law solution for homogeneous and isotropic universe in $f(R,T)$ gravity

In the present work, we search the simplest cosmological model in $f(R,T)$ gravity by considering its functional form $f(R,T) = R + ξR T$ with $ξ$ being positive constant. We have constructed the Einstein's field equation in $f(R,T)$ gravity for homogeneous and isotropic space time. The explicit solution of the constructed model is obtained by considering the scale factor as $a = αt^β$ with $α$ and $β$ being free parameters. The values of $α$ and $β$ are obtained by using Markov Chain Monte Carlo (MCMC) method to constraining the model under consideration with observational $H(z)$ data. Some physical and kinematic properties of the model are also discussed.

physics.gen-ph↗

arXiv2020

Constraining Bianchi type V universe with recent H(z) and BAO observations in Brans-Dicke theory of gravitation

In this paper, we investigate a transitioning model of Bianchi type V universe in Brans-Dicke theory of gravitation. The derived model not only validates Mach's principle but also describes the present acceleration of the universe. In this paper, our aim is to constrain an exact Bianchi type V universe in Brans - Dicke gravity. For this sake, firstly we obtain an exact solution of field equations in modified gravity and secondly constrain the model parameters by bounding the model with recent $H(z)$ and Baryon acoustic oscillations (BAO) observational data. The current phase of accelerated expansion of the universe is also described by the contribution coming from cosmological constant screened scalar field with deceleration parameter showing a transition redshift of about $z_{t} = 0.79$. Some physical properties of the universe are also discussed.

physics.gen-ph↗

arXiv2020

Existence of bulk viscous universe in $f(R,T)$ gravity and confrontation with observational data

In this paper we have investigated a bulk viscous universe in $f(R,T)$ gravity where $R$ and $T$ are the Ricci scalar and trace of energy momentum tensor respectively. We have obtained explicit solutions of field equations in modified gravity by considering the power law form of scale factor. The Hubble parameter and deceleration parameter are derived in terms of cosmic time and redshift both. We have estimated the present values of these parameters with observational Hubble data and SN Ia data sets. At 1$σ$ level, the estimated values of $q_{0}$ and $m$ are obtained as $q_{0}=-0.30 \pm 0.05$ \& $ m = 0.70 \pm 0.02 $ where $q_{0}$ is the present value of deceleration parameter and $m$ is the model parameter. The energy conditions and Om(z) analysis for the anisotropic LRS Bianchi type I model are also discussed.

physics.gen-ph↗

arXiv2019

Accelerating model of flat universe in $f(R,T)$ gravity

The $f(R,T)$ theory of gravitation is an extended theory of gravitation in which the gravitational action contains both the Ricci scalar $R$ and the trace of energy momentum tensor $T$ and hence the cosmological models based on $f(R,T)$ gravity are eligible to describing late time acceleration of present universe. In this paper, we investigate an accelerating model of flat universe with linearly varying deceleration parameter (LVDP). We apply the linearly time varying law for deceleration parameters that generates a model of transitioning universe from early decelerating phase to current accelerating phase. We carry out the state-finder and Om(z) analysis, and obtain that LVDP model have consistency with astrophysical observations. We also discuss profoundly the violation of energy-momentum conservation law in $f(R,T)$ gravity and dynamical behavior of the model.

physics.gen-ph↗

arXiv2019

Constraining An Exact Brans-Dicke gravity theory with Recent Observations

In this paper first we study Brans-Dicke equations with the cosmological constant to find an exact solution in the spatially flat Robertson-Walker metric. Then we use Observational Hubble data, the baryon acoustic oscillation distance ratio data as well as cosmic microwave background data from Planck to constrain parameters of the obtained Brans-Dicke model. To compare our results and find out the amount of deviation from general relativity, we also constrain concordance cosmological model using the same data. In our theoretical model the Brans-Dicke coupling constant is replaced by a , say new, parameter namely \textgravedbl scalar field density $Ω_ϕ$\textacutedbl. Therefore, as $Ω_ϕ\to 0$ which is equivalent to $ω\to \infty$ general relativity is recovered. In general, we found no significant deviation from general relativity. Our estimations show $Ω_ϕ=0.010^{+0.021}_{-0.012}$ which is equivalent to $ω>1560$ at $95\%$ confidence level. We also obtained constraint the rate of change of gravitational constant, $\dot{G}/G$, at present time as $1.150\times 10^{-13}yr^{-1}<\dot{G}/G<1.198\times 10^{-13}yr^{-1}$ (at $1σ$ error). The total variation of gravitational constant, since the epoch of recombination, is also constrained as $-0.0084<δG/G<-0.0082$ at $68\%$ confidence level.

gr-qc↗

arXiv2019

Viability of Bianchi type V Universe in $f(R,T)= f_{1}(R)+f_{2}(R)f_{3}(T)$ gravity

In this paper, we examine the viability of Bianchi type V universe in $f(R,T)$ theory of gravitation. To solve the field equations, we have considered the power law for scale factor and constructed a singular Lagrangian model which is based on the coupling between Ricci scalar R and trace of energy-momentum tensor T. We find the constraints on Hubble constant $H_{0}$ and free parameter $n$ with 46 observational Hubble dataset and obtain pretty satisfactory results. The physical features of the model and transitional behavior of equation of state (EOS) parameter are analyzed. We examine the nature of physical parameters and validity of energy conditions as well as stability condition. We also present the Om(z) and statefinder diagnostic analysis for the derived model.

physics.gen-ph↗

arXiv2019

Two Fluid Scenario in Bianchi Type-I Universe

In this paper, we study a Bianchi type -I model of universe filled with barotropic and dark energy(DE) type fluids. The present values of cosmological parameters such as Hubble constant $H_0$, barotropic, DE and anisotropy energy parameters $(Ω_{m})_0$, $(Ω_{de})_0$ and $(Ω_σ)_0 $ and Equation of State(EoS) parameter for DE ($ω_{de}$) are statistically estimated in two ways by taking 38 point data set of Hubble parameter H(z) and 581 point data set of distance modulus of supernovae in the range $0\leq z \leq 1.414$. It is found that the results agree with the Planck result [P.A.R. Ade, et al., Astron. Astrophys. 594 A14 (2016)] and more latest result obtained by Amirhashchi and Amirhashchi [H. Amirhashchi and S. Amirhashchi, arXiv:1811.05400v4 (2019)]. Various physical properties such as age of the universe, deceleration parameter etc have also been investigated.

gr-qc↗

arXiv2018

Similarity dark energy models in Bianchi type - I space-time

We investigate some new similarity inhomogeneous solutions of anisotropic dark energy and perfect fluid in Bianchi type-I space-time. Three different equation of state parameters along the spatial directions are introduced to quantify the deviation of pressure from isotropy. We consider the case when the dark energy is minimally coupled to the perfect fluid as well as direct interaction with it. The Lie symmetry generators that leave the equation invariant are identified and we generate an optimal system of one-dimensional subalgebras. Each element of the optimal system is used to reduce the partial differential equation to an ordinary differential equation which is further analyzed. We solve the Einstein field equations, described by a system of non-linear partial differential equations (NLPDEs), by using the Lie point symmetry analysis method. The geometrical and kinematical features of the models and the behavior of the anisotropy of dark energy, are examined in detail.

gr-qc↗

arXiv2018

Transitioning scenario of Bianchi-I universe within $f\left(R,T\right)$ formalism

In this paper, we report the existence of transitioning scenario of Bianchi type I universe in the context of $f\left(R,T\right)$ gravity with special case $f\left(R,T\right) = f_{1}(R) + f_{2}(R)f_{3}(T)$ and it's functional forms $f_{1}(R) = f_{2}(R) = R$ and $f_{3}(T) = αT$ with $α$ being constant. The exact solution of the Einstein's field equations are derived by using the generalized hybrid expansion law that yields the model of transitioning universe from early deceleration phase to current acceleration phase. Under this specification, we obtain the singular as well as non singular solution of Bianchi type I model depending upon the particular choice of the value of problem parameters. We also notice that the validation of weak energy condition and dominant energy condition and violation of strong energy condition occurs for these values of problem parameters. The deceleration parameter is found to be negative at present (z = 0) in the derived model which is supported by recent observations.

physics.gen-ph↗

arXiv2017

Invariant Bianchi type I models in $f\left(R,T\right)$ Gravity

In this paper, we search the existence of invariant solutions of Bianchi type I space-time in the context of $f\left(R,T\right)$ gravity. The exact solution of the Einstein's field equations are derived by using Lie point symmetry analysis method that yield two models of invariant universe for symmetries $X^{(1)}$ and $X^{(3)}$. The model with symmetries $X^{(1)}$ begins with big bang singularity while the model with symmetries $X^{(3)}$ does not favour the big bang singularity. Under this specification, we find out at set of singular and non singular solution of Bianchi type I model which present several other physically valid features within the framework of $f\left(R,T\right)$.

physics.gen-ph↗