STRING COSMOLOGIES IN HIGHER DIMENSIONS

1993 ◽  
Vol 02 (01) ◽  
pp. 105-112 ◽  
Author(s):  
S. CHATTERJEE ◽  
N. BANERJEE ◽  
B. BHUI
Keyword(s):  
Equation Of State ◽  
Energy Density ◽  
Cosmological Model ◽  
Exact Solutions ◽  
Source Term ◽  
Bianchi Type ◽  
Dynamical Behavior ◽  
Higher Dimensions ◽  
Type I ◽  
Multidimensional Models

We extend to higher dimensions an earlier work of Letelier where a Bianchi type I cosmological model with massive strings as source term is studied. Exact solutions are obtained assuming either an equation of state between the energy density and tension density of the string or an explicit form of one of the metric coefficients. The dynamical behavior of the models is studied and a comparison is made with the analogous four-dimensional case where it is interestingly observed that the string dominated phase lasts a longer period in multidimensional models compared to its four-dimensional analogs. The Kantowski-Sachs type of metric is also briefly discussed.

scholarly journals Locally rotationally symmetric Bianchi type I massive string cosmological model with vacuum energy density and magnetic field in general relativity

2016 ◽  
Vol 94 (3) ◽  
pp. 267-270
Author(s):  
Raj Bali ◽  
Swati Singh
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Cosmological Model ◽  
Vacuum Energy ◽  
Bianchi Type ◽  
Vacuum Energy Density ◽  
Type I ◽  
Massive String ◽  
Total Energy Density ◽  
Rotationally Symmetric

A locally rotationally symmetric (LRS) Bianchi type I massive string cosmological model with vacuum energy density (Λ) and magnetic field is investigated. To get a deterministic model of the universe, we assume that shear (σ) is proportional to expansion (θ) and Λ ∼ 1/R2 as considered by Chen and Wu (Phys. Rev. D, 41, 695 (1990)) where R is a scale factor. We find that the total energy density (ρ), the particle density ρp decreases with time. The strong energy conditions as given by Hawking and Ellis (The large scale structure of space–time. Cambridge University Press, Cambridge, UK. p. 88. (1974)) are satisfied. The vacuum energy density decreases with time, which matches with astronomical observation. The model in general represents anisotropic space–time because of the presence of strings. The total energy density and string tension density decrease because of the presence of a magnetic field. Both the models have point-type singularities at T = 0 and τ = 0, respectively. The other physical aspects of the models are also discussed.

scholarly journals Dynamics of Bulk Viscous String Cosmological Model in f(R,G) Theory of Gravity

2021 ◽  
Vol 4 (4) ◽  
pp. 89-97
Author(s):  
Kailas R. Borgade ◽  
S. R. Bhoyar ◽  
Vineeta Basotia
Keyword(s):  
Cosmological Model ◽  
Exact Solutions ◽  
Bianchi Type ◽  
The Self ◽  
Alternative Theory ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Bulk Viscous ◽  
Theory Of Gravity

Existing investigations dedicated to the self-propelling investigation of dynamics of bulk viscous string in LRS Bianchi type-I cosmological model within the circumstance of alternative theory of gravity with Langrangian be the impulsive perform of Ricci scalar R and Gouss-Bonnet invariant G , say f(R,G) gravity. Exact solutions of the field equations correspond to special law of variation which provides singular model. Also some physical and kinematical aspects and its behavior with the present day universe of the cosmological model have been discussed.

scholarly journals Bianchi type-III cosmological model with quadratic EoS in Lyra geometry

2018 ◽  
Vol 15 (11) ◽  
pp. 1850194 ◽  
Author(s):  
Mahbubur Rahman Mollah ◽  
Kangujam Priyokumar Singh ◽  
Pheiroijam Suranjoy Singh
Keyword(s):  
Equation Of State ◽  
Cosmological Model ◽  
Exact Solutions ◽  
Bianchi Type ◽  
Lyra Geometry ◽  
Quadratic Equation ◽  
Anisotropic Space ◽  
Field Equations ◽  
Type Iii ◽  
Quadratic Equation Of State

The paper deals with the investigation of a homogeneous and anisotropic space-time described by Bianchi type-III metric with perfect fluid in Lyra geometry setting. Exact solutions of Einstein’s field equations have been obtained under the assumption of quadratic equation of state (EoS) of the form [Formula: see text], where [Formula: see text] is a constant and strictly [Formula: see text]. The physical and geometrical aspects are also examined in detail.

scholarly journals Classical Bianchi Type I Cosmology in K-Essence Theory

2014 ◽  
Vol 2014 ◽  
pp. 1-11 ◽  
Author(s):  
J. Socorro ◽  
Luis O. Pimentel ◽  
Abraham Espinoza-García
Keyword(s):  
Cosmological Model ◽  
Cosmological Constant ◽  
Exact Solutions ◽  
Bianchi Type ◽  
Friedmann Equation ◽  
Matter Content ◽  
Type I ◽  
Bianchi Type I ◽  
Bianchi I ◽  
The Universe

We use one of the simplest forms of the K-essence theory and we apply it to the classical anisotropic Bianchi type I cosmological model, with a barotropic perfect fluid (p=γρ) modeling the usual matter content and with cosmological constantΛ. Classical exact solutions for anyγ≠1andΛ=0are found in closed form, whereas solutions forΛ≠0are found for particular values in the barotropic parameter. We present the possible isotropization of the cosmological model Bianchi I using the ratio between the anisotropic parameters and the volume of the universe. We also include a qualitative analysis of the analog of the Friedmann equation.

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