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Some Magnetized Bulk Viscous String Cosmological Models in Cylindrically Symmetric Inhomogeneous Universe with Variable Λ-Term 被引量:1
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作者 anirudh pradhan 《Communications in Theoretical Physics》 SCIE CAS CSCD 2009年第2期367-374,共8页
Some cylindrically symmetric inhomogeneous viscous fluid string cosmological models with magnetic field and cosmological term A varying with time are investigated. To get the deterministic solution, it has been assume... Some cylindrically symmetric inhomogeneous viscous fluid string cosmological models with magnetic field and cosmological term A varying with time are investigated. To get the deterministic solution, it has been assumed that the expansion (θ) in the model is proportional to the eigen value σ^11 of the shear tensor σ^ij. The value of cosmological constant for the model is found to be small and positive, which is supported by the results from recent supernovae Ia observations. The effect of bulk viscosity is to produce a change in perfect fluid and hence exhibits essential influence on the character of the solution. The physical and geometric properties of the models are also discussed in presence and absence of magnetic field. 展开更多
关键词 STRING inhomogeneous universe cylindrical symmetry variable cosmological term bulk viscosity
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Stability of LRS Bianchi type-I cosmological models in f(R,T)-gravity
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作者 Umesh Kumar Sharma Rashid Zia +1 位作者 anirudh pradhan Aroon Beesham 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2019年第4期63-76,共14页
This paper examines the stability of the transition from the early decelerating stage of the Universe to the recent accelerating stage for the perfect fluid cosmological locally rotationally symmetric(LRS) Bianchi-I m... This paper examines the stability of the transition from the early decelerating stage of the Universe to the recent accelerating stage for the perfect fluid cosmological locally rotationally symmetric(LRS) Bianchi-I model in f(R, T) theory. To determine the solution of field equations, the idea of a timevarying deceleration parameter(DP) which yields a scale factor, for which the Universe attains a phase transition scenario and is consistent with recent cosmological observations, is used. The time-dependent DP yields a scale factor a=exp■, where β and k are respectively arbitrary and integration constants. By using the recent cons_traints(H_0 _= 73.8, and q_0 =-0.54) from Type Ia Supernova(SN Ia) data in combination with Baryonic Acoustic Oscillations(BAO) and Cosmic Microwave Background(CMB) observations(Giostri et al.), we obtain the values of β = 0.0062 and k = 0.000016 for which we have derived a cosmological model from the early decelerated phase to the present accelerating phase. By applying_ other r_ecent constraints(H_0 = 73.8, q_0 =-0.73) from SNe Ia Union data(Cunha), we obtain the values of β = 0.0036 and k = 0.000084 for which we have derived a cosmological model in the accelerating phase only. We have compared both models with experimental data. The stability of the background solution has been examined also for the metric perturbations alongside the properties of future singularities in a Universe ruled by dark energy with phantom type fluid. We demonstrate the presence of a stable fixed point with a condition of state ω <-1 and numerically affirm this is really a late-time attractor in the ghost overwhelmed Universe. Some physical and geometric properties of the model are found and examined. 展开更多
关键词 LRS Bianchi-I UNIVERSE Time-dependent DECELERATION parameter f(R T) GRAVITY theory Transit UNIVERSE
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Thick Domain Walls in Lyra Geometry with Bulk Viscosity
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作者 anirudh pradhan 《Communications in Theoretical Physics》 SCIE CAS CSCD 2009年第2期378-384,共7页
In this paper, we evaluate the general solutions for plane-symmetric thick domain walls in Lyra geometry in presence of bulk viscous fluid. Expressions for the energy density and pressure of domain walls are derived i... In this paper, we evaluate the general solutions for plane-symmetric thick domain walls in Lyra geometry in presence of bulk viscous fluid. Expressions for the energy density and pressure of domain walls are derived in both cases of uniform and time varying displacement field β. Some physical consequences of the models are also given. Finally, the geodesic equations and acceleration of the test particle are discussed. 展开更多
关键词 COSMOLOGY plane symmetric domain walls bulk viscous model Lyra geometry
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Anisotropic Bianchi Type-I Magnetized String Cosmological Models with Decaying Vacuum Energy Density A(t)
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作者 anirudh pradhan 《Communications in Theoretical Physics》 SCIE CAS CSCD 2011年第5期931-941,共11页
The present study deals with a spatially homogeneous and anisotropic Bianehi-I cosmological models representing massive strings with magnetic field and decaying vacuum energy density A. The energy-momentum tensor, as ... The present study deals with a spatially homogeneous and anisotropic Bianehi-I cosmological models representing massive strings with magnetic field and decaying vacuum energy density A. The energy-momentum tensor, as formulated by Letelier (1983), has been used to construct massive string cosmological models for which we assume the expansion scalar in the models is proportional to one of the components of shear tensor. The Einstein's field equations have been solved by applying a variation law for generalized Hubble's parameter in Bianchi-I space-time. The variation law for Hubble's parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential form. Using these two forms, Einstein's field equations are solved separately that correspond to expanding singular and non-singular models of the universe respectively. We have made a comparative study of accelerating and decelerating models in the presence of string scenario. The study reveals that massive strings dominate in the decelerating universe whereas strings dominate in the accelerating universe. The strings eventually disappear from the universe for sufficiently large times, which is in agreement with current astronomical observations. The cosmological constant A is found to be a positive decreasing function of time which is corroborated by results from recent supernovae Ia observations. The physical and geometric properties of the models have been also discussed in detail. 展开更多
关键词 cosmic strings Bianchi-I universe variable cosmological constant Hubble's parameter
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Massive String Cosmology in Bianchi Type Ⅲ Space-Time with Electromagnetic Field
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作者 anirudh pradhan Suman Lata H.Amirhashchi 《Communications in Theoretical Physics》 SCIE CAS CSCD 2010年第11期950-956,共7页
Exact solution of Einstein's field equations is obtained for massive string cosmological model of Bianchi III space-time using the technique given by Letelier (1983) in presence of perfect fluid and electromagnetic... Exact solution of Einstein's field equations is obtained for massive string cosmological model of Bianchi III space-time using the technique given by Letelier (1983) in presence of perfect fluid and electromagnetic field. To get the deterministic solution of the field equations the expansion 0 in the model is considered as proportional to the eigen value σ2^2of the shear tensor σi^j and also the fluid obeys the barotropic equation of state. It is observed that in early stage of the evolution of the universe string dominates over the particle whereas the universe is dominated by massive string at the late time. It is also observed that the string phase of the universe disappears in our model because particle density becomes negative. Some physical and geometric properties of the model are also discussed. 展开更多
关键词 massive string exact solution perfect fluid electromagnetic field
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Inhomogeneous Bulk Viscous Fluid Universe with Electromagnetic Field and Variable A-Term
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作者 anirudh pradhan Vandana Rai Kanti Jotania 《Communications in Theoretical Physics》 SCIE CAS CSCD 2008年第7期279-288,共10页
Cylindrically symmetric inhomogeneous cosmological model for bulk viscous fluid distribution with electro- magnetic field is obtained. The source of the magnetic field is due to an electric current produced along the ... Cylindrically symmetric inhomogeneous cosmological model for bulk viscous fluid distribution with electro- magnetic field is obtained. The source of the magnetic field is due to an electric current produced along the z-axis. F12 is the non-vanishing component of electromagnetic field tensor. To get the deterministic solution, it has been assumed that the expansion 0 in the model is proportional to the shear σ. The values of cosmological constant for these models are found to be small and positive at late time, which are consistent with the results from recent supernovae Ia observations. Physical and geometric aspects of the models are also discussed in presence and absence of magnetic field. 展开更多
关键词 COSMOLOGY variable cosmological term electromagnetic field inhomogeneous universe
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A Plane-Symmetric Inhomogeneous Cosmological Model of Perfect Fluid Distribution with Electromagnetic Field Ⅰ
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作者 anirudh pradhan Prashant KumarSingh Anil Kumar Yadav 《Communications in Theoretical Physics》 SCIE CAS CSCD 2010年第7期191-196,共6页
A plane-symmetric inhomogeneous cosmological model of perfect fluid distribution with electro-magnetic field is obtained. F12 is the non-vanishing component of electromagnetic field tensor. To get a deterministic solu... A plane-symmetric inhomogeneous cosmological model of perfect fluid distribution with electro-magnetic field is obtained. F12 is the non-vanishing component of electromagnetic field tensor. To get a deterministic solution, we assume the free gravitational field is Petrov type-Ⅱ non-degenerate. Some physical and geometric properties of the model are also discussed. 展开更多
关键词 COSMOLOGY electromagnetic field inhomogeneous solution
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An Interacting Two-Fluid Scenario for Dark Energy in an FRW Universe
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作者 Hassan Amirhashchi anirudh pradhan Bijan Saha 《Chinese Physics Letters》 SCIE CAS CSCD 2011年第3期248-251,共4页
We study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic Friedmann-Robertson-Walker(FRW)model filled with barotropic fluid and dark energy.To obtain the determinist... We study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic Friedmann-Robertson-Walker(FRW)model filled with barotropic fluid and dark energy.To obtain the deterministic solution we choose the scale factor a(t)=(√te^(t)),which yields a time-dependent deceleration parameter(DP).In doing so,we consider the case minimally coupled with dark energy to the perfect fluid as well as direct interaction with it. 展开更多
关键词 energy parameter FILLED
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Accelerating dark energy models with anisotropic fluid in Bianchi type Ⅵ_0 space-time
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作者 anirudh pradhan 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2013年第2期139-158,共20页
Motivated by the increasing evidence for the need of a geometry that re- sembles Bianchi morphology to explain the observed anisotropy in the WMAP data, we have discussed some features of Bianchi type VI0 universes in... Motivated by the increasing evidence for the need of a geometry that re- sembles Bianchi morphology to explain the observed anisotropy in the WMAP data, we have discussed some features of Bianchi type VI0 universes in the presence of a fluid that has an anisotropic equation of state (EoS) parameter in general relativity. We present two accelerating dark energy (DE) models with an anisotropic fluid in Bianchi type VI0 space-time. To ensure a deterministic solution, we choose the scale factor a(t) = √tnet, which yields a time-dependent deceleration parameter, representing a class of models which generate a transition of the universe from the early decelerating phase to the recent accelerating phase. Under suitable conditions, the anisotropic mod- els approach an isotropic scenario. The EoS for DE co is found to be time-dependent and its existing range for derived models is in good agreement with data from recent observations of type Ia supernovae (SNe Ia) (Knop et al. 2003), SNe Ia data com- bined with cosmic microwave background (CMB) anisotropy and galaxy clustering statistics (Tegmark et al. 2004a), as well as the latest combination of cosmological datasets coming from CMB anisotropies, luminosity distances of high redshift SNe Ia and galaxy clustering. For different values of n, we can generate a class of physically viable DE models. The cosmological constant A is found to be a positive decreasing function of time and it approaches a small positive value at late time (i.e. the present epoch), which is corroborated by results from recent SN Ia observations. We also ob- serve that our solutions are stable. The physical and geometric aspects of both models are also discussed in detail. 展开更多
关键词 cosmological models -- dark energy -- variable EoS parameter
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Interacting two-fluid viscous dark energy models in a non-flat universe
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作者 Hassan Amirhashchi anirudh pradhan Hishamuddin Zainuddin 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2013年第2期129-138,共10页
We study the evolution of the dark energy parameter within the scope of a spatially non-fiat and isotropic Friedmann-Robertson-Walker model filled with barotropic fluid and bulk viscous stresses. We have obtained cosm... We study the evolution of the dark energy parameter within the scope of a spatially non-fiat and isotropic Friedmann-Robertson-Walker model filled with barotropic fluid and bulk viscous stresses. We have obtained cosmological solutions that do not have a Big Rip singularity, and concluded that in both non-interacting and interacting cases the non-fiat open Universe crosses the phantom region. We find that during the evolution of the Universe, the equation of state for dark energy ωD changes from ωDeff 〉 - 1 to ωDeff 〈 - 1, which is consistent with recent observations. 展开更多
关键词 cosmology: theory -- dark energy -- viscous fluid
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Charged quark stars in f(R,T)gravity 被引量:1
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作者 Juan M.Z.Pretel Takol Tangphati +1 位作者 Ayan Banerjee anirudh pradhan 《Chinese Physics C》 SCIE CAS CSCD 2022年第11期308-317,共10页
Recent advances in nuclear theory and new astrophysical observations have led to the need for specific theoretical models applicable to dense-matter physics phenomena.Quantum chromodynamics(QCD)predicts the existence ... Recent advances in nuclear theory and new astrophysical observations have led to the need for specific theoretical models applicable to dense-matter physics phenomena.Quantum chromodynamics(QCD)predicts the existence of non-nucleonic degrees of freedom at high densities in neutron-star matter,such as quark matter.Within a confining quark matter model,which consists of homogeneous,neutral 3-flavor interacting quark matter with O(m_(s)^(4))corrections,we examine the structure of compact stars composed of a charged perfect fluid in the context of f(R,T)gravity.The system of differential equations describing the structure of charged compact stars has been derived and numerically solved for a gravity model with f(R,T)=R+2βT.For simplicity,we assumed that the charge density is proportional to the energy density,namely,ρ_(ch)=αρ.It is demonstrated that the matter-geometry coupling constant β and charge parameter α affect the total gravitational mass and the radius of the star. 展开更多
关键词 charged stars f(R T)gravity
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