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Anisotropic Bianchi Type-I Magnetized String Cosmological Models with Decaying Vacuum Energy Density A(t)

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Communications in Theoretical Physics 2011年第5期55卷 931-941页

作者： anirudh pradhan Department of Mathematics Hindu Post-graduate College

The present study deals with a spatially homogeneous and anisotropic Bianchi-Ⅰ cosmological modelsrepresenting massive strings with magnetic field and decaying vacuum energy density *** energy-momentum tensor,as formulated by Letelier(1983),has been used to construct massive string cosmological models for which we assume theexpansion scalar in the models is proportional to one of the components of shear *** Einstein’s field equationshave been solved by applying a variation law for generalized Hubble’s parameter in Bianchi-Ⅰ *** variationlaw for Hubble’s parameter generates two types of solutions for the average scale factor,one is of power-law type andother is of the exponential *** these two forms,Einstein’s field equations are solved separately that correspondto expanding singular and non-singular models of the universe *** have made a comparative study ofaccelerating and decelerating models in the presence of string *** study reveals that massive strings dominatein the decelerating universe whereas strings dominate in the accelerating *** strings eventually disappear fromthe universe for sufficiently large times,which is in agreement with current astronomical *** cosmologicalconstant A is found to be a positive decreasing function of time which is corroborated by results from recent supernovaela *** physical and geometric properties of the models have been also discussed in detail.

关键词：宇宙学模型能量密度各向异性真空爱因斯坦场方程哈勃望远镜衰减磁化

Some Magnetized Bulk Viscous String Cosmological Models in Cylindrically Symmetric Inhomogeneous Universe with Variable Λ-Term

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Communications in Theoretical Physics 2009年第2期51卷 367-374页

作者： anirudh pradhan Department of Mathematics Hindu Post-graduate College

某圆柱体的联盟者对称不同类粘滞液体绳有磁场并且宇宙论的术语 Λ 与时间变化的宇宙论的模型被调查。得到确定的解决方案，在模型的扩大(θ) 与 shear 张肌 σ11 成正比，这被假定 > j i 。为模型的宇宙论的常数的价值被发现小、积... 详细信息

某圆柱体的联盟者对称不同类粘滞液体绳有磁场并且宇宙论的术语 Λ 与时间变化的宇宙论的模型被调查。得到确定的解决方案，在模型的扩大(θ) 与 shear 张肌 σ11 成正比，这被假定 > j i 。为模型的宇宙论的常数的价值被发现小、积极，它被结果从最近的 supernovae Ia 观察支持。体积粘性的效果是在答案的特性上的完美的液体和因此展览必需品影响生产一个变化。模型的物理、几何的性质也在磁场的存在和缺席被讨论。

关键词：宇宙模型粘性流体非均匀柱对称字符串磁化中期时间变化

Thick Domain Walls in Lyra Geometry with Bulk Viscosity

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Communications in Theoretical Physics 2009年第2期51卷 378-384页

作者： anirudh pradhan Department of Mathematics Hindu Post-graduate College

在这篇论文，我们在体积的存在在天琴座几何学为飞机对称的厚领域墙评估一般答案粘滞液体。为精力密度和域墙的压力的表达式在制服和时间变化排水量域 β 的两个盒子中被导出。模型的一些物理后果也被给。最后，测试粒子的测地学的方程... 详细信息

在这篇论文，我们在体积的存在在天琴座几何学为飞机对称的厚领域墙评估一般答案粘滞液体。为精力密度和域墙的压力的表达式在制服和时间变化排水量域 β 的两个盒子中被导出。模型的一些物理后果也被给。最后，测试粒子的测地学的方程和加速被讨论。

关键词：天琴座体粘滞系数畴壁几何粘性流体能量密度时间变化测量方程

Accelerating dark energy models with anisotropic fluid in Bianchi type Ⅵ_0 space-time

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Research in Astronomy and Astrophysics 2013年第2期13卷 139-158页

作者： anirudh pradhan Department of Mathematics Hindu Post-graduate College

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.

关键词： cosmological models -- dark energy -- variable EoS parameter

Bianchi Type-Ⅲ String Cosmological Models with Time Dependent Bulk Viscosity

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Chinese Physics Letters 2007年第2期24卷 585-588页

作者： BALI Raj pradhan anirudh Department of Mathematics University of Rajasthan Jaipur-302 004 India Department'of Mathematics Hindu Post-Graduate College Zamania-232 331 Ghazipur India

Bianchi type-Ⅲ string cosmological models with bulk viscous fluid for massive string are investigated. To obtain the determinate model of the universe, we assume that the coeffcient of bulk viscosity ξ is inversely proportional to the expansion θ in the model and expansion θ in the model is proportional to the shear g. This leads to B =lC^n, where l and n are constants. Behaviour of the model in the presence and absence of bulk viscosity is discussed. The physical implications of the models are also discussed in detail.

关键词： Cosmological Dependent

An Interacting Two-Fluid Scenario for Dark Energy in an FRW Universe

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Chinese Physics Letters 2011年第3期28卷 248-251页

作者： Hassan Amirhashchi anirudh pradhan Bijan Saha Department of Physics Islamic Azad UniversityMahshahr BranchMahshahrIran Department of Mathematics Hindu Post-Graduate CollegeZamania-232331GhazipurIndia Laboratory of Information Technologies Joint Institute for Nuclear Research141980 DubnaRussia

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 *** 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.

关键词： energy parameter filled

Inhomogeneous Bulk Viscous Fluid Universe with Electromagnetic Field and Variable A-Term

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Communications in Theoretical Physics 2008年第7期50卷 279-288页

作者： anirudh pradhan Vandana Rai Kanti Jotania Department of Mathematics Hindu Post-graduate CollegeZamania-232 331GhazipurIndia Department of Mathematics Post-graduate CollegeGhazipur-233 001India Department of Physics Faculty of ScienceThe M.S.University of BarodaVadodara-390 002India

Cylindrically symmetric inhomogeneoas cosmological model for bulk viscous fluid distribution with electro-magnetic field is *** source of the magnetic field is due to an electric current produced along the z-axis.F_(12) isthe non-vanishing component of electromagnetic field *** get the deterministic solution,it has been assumed thatthe expansion θ in the model is proportional to the shear σ.The values of cosmological constant for these models arefound to be small and positive at late time,which are consistent with the results from recent supernovae Ia *** and geometric aspects of the models are also discussed in presence and absence of magnetic field.

关键词：宇宙论爆炸事件可变理论电磁域不均匀性

Bianchi .Type-I Massive String Magnetized Barotropic Perfect Fluid Cosmological Model in General Relativity

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Chinese Physics Letters 2007年第8期24卷 2455-2458页

作者： BALI Raj PAREEK Umesh Kumar pradhan anirudh Department of Mathematics University of Rajasthan Jaipur-302 004 India Department of Mathematics Jaipur Engineering College and Research Centre Jaipur-303 905 India Department of Mathematics Hindu Post-graduate College Zamania-232 331 Chazipur India

Bianchi type-I massive string cosmological model with magnetic field of barotropic perfect fluid distribution through the techniques used by Latelier and Stachel is investigated. To obtain the deterministic model of the universe, it is assumed that the universe is filled with barotropic perfect fluid distribution. The magnetic field is due to electric current produced Mong the x-axis with infinite electrical conduictivity. The behaviour of the model in the presence and absence of magnetic field together with other physical aspects is further discussed.

关键词： coated conductor buffer layer self-epitaxy CeO2

Interacting two-fluid viscous dark energy models in a non-flat universe

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Research in Astronomy and Astrophysics 2013年第2期13卷 129-138页

作者： Hassan Amirhashchi anirudh pradhan Hishamuddin Zainuddin Young Researchers Club Mahshahr BranchIslamic Azad University Department of Mathematics Hindu Post-graduate College Laboratory of Computational Sciences and Mathematical Physics Institute for Mathematical ResearchUniversity Putra Malaysia

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.

关键词： cosmology: theory -- dark energy -- viscous fluid