scholarly journals Viscous Bianchi Type I Universe with Stiff Matter and Decaying Vacuum Energy Density

2012 ◽  
Vol 2012 ◽  
pp. 1-11 ◽  
Author(s):  
Raj Bali ◽  
Pratibha Singh ◽  
J. P. Singh
Keyword(s):  
Bulk Viscosity ◽  
Bianchi Type ◽  
Cosmological Term ◽  
Vacuum Energy Density ◽  
Late Time ◽  
Type I ◽  
Stiff Matter ◽  
Bianchi Type I ◽  
Initial Epoch ◽  
Bianchi Type I Universe

We examine homogeneous and anisotropic Bianchi type I cosmological model with viscous stiff matter and time-varying cosmological term which scales with Hubble parameter H. The resulting model approaches isotropy. The cosmological term relaxes to a genuine cosmological constant, and the model in the absence of bulk viscosity tends to a deSitter universe asymptotically. Our scenario presents an initial epoch with decelerating expansion followed by late-time acceleration consistent with observations. Bulk viscosity advances the accelerating phase in the model and prevents the matter density to vanish for large times.

scholarly journals BIANCHI TYPE I UNIVERSE WITH VISCOUS FLUID

2005 ◽  
Vol 20 (28) ◽  
pp. 2127-2143 ◽  
Author(s):  
BIJAN SAHA
Keyword(s):  
Viscous Fluid ◽  
Bulk Viscosity ◽  
Bianchi Type ◽  
Anisotropic Universe ◽  
Type I ◽  
Cosmological Singularity ◽  
Bianchi Type I ◽  
Bianchi Type I Universe ◽  
Ending Process

We study the evolution of a homogeneous, anisotropic Universe given by a Bianchi type-I cosmological model filled with viscous fluid, in the presence of a cosmological constant Λ. The role of viscous fluid and Λ term in the evolution the BI spacetime is studied. Though the viscosity cannot remove the cosmological singularity, it plays a crucial part in the formation of a qualitatively new behavior of the solutions near singularity. It is shown that the introduction of the Λ term can be handy in the elimination of the cosmological singularity. In particular, in case of a bulk viscosity, a negative Λ provides a never-ending process of evolution, whereas, for some positive values of Λ and the bulk viscosity being inverse proportional to the expansion, the BI Universe admits a singularity-free oscillatory mode of expansion. In case of a constant bulk viscosity and share viscosity being proportional to expansion, the model allows both non-periodic and inflationary expansion independent to the sign of Λ term.

AN LRS BIANCHI TYPE-I COSMOLOGICAL MODEL WITH TIME-DEPENDENT Λ TERM

2007 ◽  
Vol 16 (04) ◽  
pp. 745-754 ◽  
Author(s):  
J. P. SINGH ◽  
R. K. TIWARI
Keyword(s):  
Cosmological Model ◽  
Bianchi Type ◽  
Large Fraction ◽  
Cosmological Term ◽  
Type I ◽  
De Sitter ◽  
Stiff Matter ◽  
Bianchi Type I ◽  
Rotationally Symmetric ◽  
De Sitter Universe

In this paper, we investigate locally rotationally symmetric (LRS) Bianchi type-I cosmological model containing stiff matter with a cosmological term proportional to the Hubble parameter. This variation law for vacuum density has recently been proposed by Schützhold on the basis of quantum field estimations in the curved and expanding background. The model obtained approaches isotropy. The cosmological term tends asymptotically to a genuine cosmological constant and the model tends to a de Sitter universe. We obtain that the present universe is accelerating with a large fraction of cosmological density in the form of cosmological term. Taking matter density equal to half of the vacuum density, as suggested by observation, we obtain a universe age given by Ht = 0.55 and a decelerating parameter equal to 2σ2/3H2.

LRS Bianchi type I stiff fluid inflationary universe with variable bulk viscosity

2014 ◽  
Vol 92 (5) ◽  
pp. 365-369 ◽  
Author(s):  
Raj Bali ◽  
Swati Singh
Keyword(s):  
Bulk Viscosity ◽  
Bianchi Type ◽  
Energy Conditions ◽  
Anisotropic Universe ◽  
Inflationary Universe ◽  
Late Time ◽  
Type I ◽  
Stiff Fluid ◽  
Bianchi Type I ◽  
Special Case

Stiff fluid inflationary cosmological model with variable bulk viscosity in the frame work of locally rotationally symmetric (LRS) Bianchi type I space–time, is investigated. To get the deterministic solution, we have also assumed that σ is proportional to θ and ζθ = constant = α where σ is shear, θ the expansion, and ζ the coefficient of bulk viscosity. The ansatz ζθ = constant, was found to connect with the occurrence of Little Rip cosmology using Friedmann–Robertson–Walker metric given by Brevik et al. (Phys. Rev. D, 84, 103508 (2011)). We find that the model has constant expansion but represents accelerating phase. The model in general represents an anisotropic universe but in special case, it leads to an isotropic one. The spatial volume increases exponentially with time representing the inflationary scenario. The presence of bulk viscosity tends to increase the inflationary phase. Also, the model leads to the de Sitter model in a special case. The presence of bulk viscosity prevents the matter density to vanish at late time. The energy conditions as given by Kolassis et al. (Classical Quantum Gravity, 5, 1129 (1988)). Chatterjee and Banerjee (Gen. Relativ. Gravitation, 36, 303 (2004)) are also discussed. We find that the energy conditions are satisfied for stiff fluid inflationary universe with variable bulk viscosity.

Perfect fluid Bianchi type-I cosmological models with time-dependent cosmological term Λ

2018 ◽  
Vol 15 (08) ◽  
pp. 1850132
Author(s):  
J. P. Singh ◽  
Prashant S. Baghel ◽  
Abhay Singh
Keyword(s):  
Perfect Fluid ◽  
Bianchi Type ◽  
Cosmological Term ◽  
Cosmological Models ◽  
Time Dependent ◽  
Late Time ◽  
Type I ◽  
Field Equations ◽  
Vacuum Decay ◽  
Bianchi Type I

We present perfect fluid Bianchi type-I cosmological models with time-dependent cosmological term [Formula: see text]. Exact solutions of the Einstein’s field equations are presented via a suitable functional form for Hubble parameter [Formula: see text], which yields a model of the universe that represents initially decelerating and late-time accelerating expansion. We discuss, in the context of some vacuum decay laws, cosmological implications of the corresponding solutions. The physical and geometrical features of the models are also discussed.

Energy–momentum distributions of Ruban universe in general relativity and teleparallel gravity

2019 ◽  
Vol 34 (03n04) ◽  
pp. 1950011 ◽  
Author(s):  
C. Aktaş
Keyword(s):  
General Relativity ◽  
Bianchi Type ◽  
Teleparallel Gravity ◽  
Type I ◽  
Universe Model ◽  
Zero Energy ◽  
Bianchi Type I ◽  
Momentum Distributions ◽  
Bianchi Type I Universe

In this study, we obtain Einstein, Bergmann–Thomson (BT), Landau–Lifshitz (LL), Møller, Papapetrou (PP) and Tolman energy–momentum (EM) distributions for Ruban universe model in general relativity (GR) and teleparallel gravity (TG). We obtain same results for Einstein, Bergmann–Thomson and Landau–Lifshitz energy–momentum distributions in GR and TG. Also, we get same results for Einstein and Tolman energy–momentum distributions in GR. The Møller energy–momentum results are different in GR and TG. Also, using Ruban universe model, we obtain LRS Bianchi type I solutions and we get zero energy–momentum results for this universe model in GR and TG. These results of LRS Bianchi type I universe model agree with Aygün et al., Taşer et al., Doğru et al., Banerjee–Sen, Tryon and Xulu in different gravitation theories.

Sign in / Sign up

Export Citation Format

Share Document