scholarly journals Bianchi Type—IX Barotropic Fluid Model with Time-Dependent Displacement Vector in Lyra Geometry

2012 ◽  
Vol 2012 ◽  
pp. 1-9
Author(s):  
Raj Bali ◽  
Rajendra Vadhwani ◽  
Jagdish Prasad Dhanka
Keyword(s):  
Bianchi Type ◽  
Deterministic Model ◽  
Displacement Vector ◽  
Fluid Model ◽  
Cosmic Time ◽  
Big Bang ◽  
Lyra Geometry ◽  
Barotropic Fluid ◽  
Frame Work ◽  
The Universe

Bianchi Type IX barotropic fluid cosmological model in the frame work of Lyra geometry is investigated. To get the deterministic model of the universe, it is assumed that shear () is proportional to expansion (). This leads to , where and are metric potentials and is a constant. To get the results in terms of cosmic time , we have also considered a special case (dust filled universe) and . We find that the model starts with a big bang initially and the displacement vector () is initially large but decreases due to lapse of time. The models and have point-type singularity at and , respectively. The physical and geometrical aspects of the models are also discussed.

BIANCHI TYPE-I STRING DUST COSMOLOGICAL MODELS IN LYRA GEOMETRY

2010 ◽  
Vol 25 (15) ◽  
pp. 3043-3054 ◽  
Author(s):  
RAJ BALI ◽  
LOKESH KUMAR GUPTA
Keyword(s):  
Bianchi Type ◽  
Deterministic Model ◽  
Cosmic Time ◽  
Lyra Geometry ◽  
Cosmological Models ◽  
Type I ◽  
Bianchi Type I ◽  
Tensor Formula ◽  
The Universe ◽  
Special Case

Bianchi type-I string cosmological models with time dependent gauge function (β) within the framework of Lyra geometry is presented. To get the deterministic model of the universe, we assume that the eigenvalue [Formula: see text] of shear tensor [Formula: see text] is proportional to the expansion (θ). This leads to A = (BC)nwhere A, B, C are metric potential and n is a constant. The physical and geometrical aspects of the model are discussed in detail. In a special case, the behavior of the model in terms of cosmic time t for [Formula: see text] is also discussed.

Scenario of two-fluid dark energy models in Bianchi type-III Universe

2018 ◽  
Vol 15 (11) ◽  
pp. 1850189 ◽  
Author(s):  
Rishi Kumar Tiwari ◽  
Aroonkumar Beesham ◽  
Bhupendra Kumar Shukla
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Bianchi Type ◽  
Cosmological Parameters ◽  
Cosmic Time ◽  
Physical Parameters ◽  
Field Equations ◽  
Barotropic Fluid ◽  
Type Iii ◽  
The Universe

In this paper, we have analyzed the equation of state parameter for dark energy in the spatially homogeneous and anisotropic Bianchi type-III spacetime filled with a barotropic fluid and dark energy by considering a variable deceleration parameter. To solve the Einstein field equations, we assume that the expansion scalar is proportional to the shear scalar. We find that during the evolution of the Universe, the equation of state and the cosmological parameters are positive decreasing functions of cosmic time [Formula: see text]. Also, we discuss the physical parameters, as well as the jerk and cosmic span parameters, which predict that the Universe in this model approaches the [Formula: see text]CDM model at late times.

TILTED BIANCHI TYPE-V BAROTROPIC FLUID COSMOLOGICAL MODELS WITH VARIABLE BULK VISCOSITY IN GENERAL RELATIVITY

2011 ◽  
Vol 26 (24) ◽  
pp. 4299-4310
Author(s):  
RAJ BALI ◽  
PRAMILA KUMAWAT ◽  
SHALINI SHARMA
Keyword(s):  
General Relativity ◽  
Heat Conduction ◽  
Bulk Viscosity ◽  
Bianchi Type ◽  
Deterministic Model ◽  
Cosmological Models ◽  
Barotropic Fluid ◽  
Type V ◽  
The Universe ◽  
Bianchi Type V

Tilted Bianchi type-V barotropic fluid cosmological models with heat conduction and variable bulk viscosity is investigated. To get the deterministic model of the universe, we have assumed two conditions: (i) A = (BC)nand (ii) ζθ = const where A, B, C are metric potentials, n is a constant, ζ the coefficient of bulk viscosity, θ the expansion in the model. The behavior of the model in presence and absence of bulk viscosity and singularities in the model are discussed. Some thermodynamic relations and physical aspects of the model related to the observation on the present day universe are also discussed.

Locally rotationally symmetric (LRS) Bianchi type II string dust viscous fluid cosmological models in Lyra geometry

2014 ◽  
Vol 92 (12) ◽  
pp. 1714-1719 ◽  
Author(s):  
Raj Bali ◽  
Mahesh Kumar Yadav ◽  
Lokesh Kumar Gupta
Keyword(s):  
Cosmological Model ◽  
Viscous Fluid ◽  
Bulk Viscosity ◽  
Bianchi Type ◽  
Displacement Vector ◽  
Lyra Geometry ◽  
Type Ii ◽  
Locally Rotationally Symmetric ◽  
Rotationally Symmetric ◽  
The Universe

In the present study, a locally rotationally symmetric Bianchi type II string dust cosmological model with varying bulk viscosity in the framework of Lyra geometry is investigated. To get the deterministic solution, we have assumed that shear (σ) is proportional to the expansion (θ) and ζθ = constant, where ζ is the coefficient of bulk viscosity. The ansatz ζθ = constant, was found to coincide with the occurrence of Little Rip (LR) cosmology using Friedmann–Robertson–Walker metric (Breviket al. Phys. Rev. D, 84, 103508-1-6 (2011)). The model describes the pre-inflationary stage of the universe. The presence of viscosity leads to inflationary-like solutions. Anisotropy is maintained because of the presence of strings. The presence of bulk viscosity prevents the matter density from vanishing. In a special case, the model represents the isotropy of the universe. The universe passes through a decelerating stage to an accelerating phase, which is in agreement with Ries et al.’s (Astrophys. J. 607, 665 (2004). doi:10.1086/383612 ) type Ia supernovae astronomical observations. The displacement vector (β) of Lyra geometry is a decreasing function of time analogous to the cosmological constant (Λ) of general relativity. We have attempted to explore the possibility of constructing a string dust viscous fluid cosmological model in Bianchi type II space–time with displacement vector (β) in Lyra geometry using the geometric condition that shear is proportional to expansion.

BIANCHI TYPE I MAGNETIZED DUST FILLED UNIVERSE IN LYRA GEOMETRY

2010 ◽  
Vol 25 (25) ◽  
pp. 4839-4848 ◽  
Author(s):  
RAJ BALI ◽  
NARESH K. CHANDNANI ◽  
JAGDISH PRASAD DHANKA
Keyword(s):  
Magnetic Field ◽  
Bianchi Type ◽  
Deterministic Model ◽  
Lyra Geometry ◽  
Type I ◽  
Astronomical Observations ◽  
Bianchi Type I ◽  
Tensor Formula ◽  
The Universe ◽  
Shear Tensor

Bianchi Type I dust filled universe in the frameworks of Lyra geometry in the presence of magnetic field is investigated. To get the deterministic model of the universe, we have also assumed that the eigenvalue [Formula: see text] of shear tensor [Formula: see text] is proportional to the expansion (θ) in the model. This leads to A = (BC)nwhere A, B and C are metric potentials and n is a constant. The physical and geometrical aspects of the model related with astronomical observations are also discussed.

scholarly journals Mixed fluid cosmological model in f(R, T) gravity

2020 ◽  
Vol 98 (11) ◽  
pp. 1015-1022 ◽  
Author(s):  
Parbati Sahoo ◽  
Barkha Taori ◽  
K.L. Mahanta
Keyword(s):  
Cosmological Model ◽  
Bianchi Type ◽  
Type I ◽  
Time Varying ◽  
Eos Parameter ◽  
Barotropic Fluid ◽  
Rotationally Symmetric ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Mixed Fluid

We construct a locally rotationally symmetric (LRS) Bianchi type-I cosmological model in f(R, T) theory of gravity when the source of gravitation is a mixture of barotropic fluid and dark energy (DE) by employing a time-varying deceleration parameter. We observe through the behavior of the state finder parameters (r, s) that our model begins from the Einstein static era and goes to ΛCDM era. The equation of state (EOS) parameter (ωd) for DE varies from the phantom (ω < –1) phase to quintessence (ω > –1) phase, which is consistent with observational results. It is found that the discussed model can reproduce the current accelerating phase of the expansion of the universe.

Homothetic vector fields in a specially homogenous Bianchi type-I cosmological model in Lyra geometry

2015 ◽  
Vol 93 (11) ◽  
pp. 1397-1401 ◽  
Author(s):  
A.S. Alofi ◽  
Ragab M. Gad
Keyword(s):  
Cosmological Model ◽  
Riemannian Geometry ◽  
Vector Fields ◽  
Bianchi Type ◽  
Displacement Vector ◽  
Lyra Geometry ◽  
Type I ◽  
Bianchi Type I ◽  
Homothetic Vector ◽  
Vector Formula

In this paper, homothetic vector fields of a spatially homogenous Bianchi type-I cosmological model have been evaluated based on Lyra geometry. Further, we investigate the equation of state in cases when a displacement vector [Formula: see text] is a function of t and when it is constant. We give a comparison between the obtained results, using Lyra geometry, and those obtained previously in the context of general relativity, based on Riemannian geometry.

Alternative cosmological theories

2019 ◽  
pp. 119-161
Author(s):  
Helge Kragh
Keyword(s):  
Standard Model ◽  
Cosmic Time ◽  
Big Bang ◽  
Field Equations ◽  
Static Universe ◽  
The Standard Model ◽  
Scientific Nature ◽  
Big Bang Model ◽  
The Universe ◽  
Alternative Theories

Since about 1970 the broadly accepted theory of the universe has been the standard hot big-bang model. However, there is and has always been alternative theories which challenge one or more features of the standard model or, more radically, question the scientific nature of cosmology. Is the universe governed by Einstein’s field equations? Is it really in a state of expansion? Did it begin with a big bang? The chapter discusses various alternative or heterodox theories in the period from about 1930 to 1980, among them the idea of a static universe and the conception that our universe evolves cyclically in infinite cosmic time. While some of these theories have been abandoned long ago, others still live on and are cultivated by a minority of cosmologists and other scientists.

Homothetic vector field in plane symmetric Bianchi type-I cosmological model in Lyra geometry

2014 ◽  
Vol 29 (22) ◽  
pp. 1450116 ◽  
Author(s):  
Ragab M. Gad ◽  
A. S. Alofi
Keyword(s):  
General Relativity ◽  
Vector Field ◽  
Riemannian Geometry ◽  
Bianchi Type ◽  
Displacement Vector ◽  
Lyra Geometry ◽  
Type I ◽  
Bianchi Type I ◽  
Plane Symmetric ◽  
Homothetic Vector

In this paper, we obtain a homothetic vector field of a plane symmetric Bianchi type-I spacetime based on Lyra geometry. We discuss the cases when the displacement vector is function of t and when it is constant. We investigate the equation of state in both two cases. A comparison between the obtained results, using Lyra geometry, and that have obtained previously in the context of General Relativity (GR), based on Riemannian geometry, will be given.

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