scholarly journals ON THE ROLE OF VISCOSITY IN EARLY COSMOLOGY

2008 ◽  
Vol 23 (08) ◽  
pp. 1248-1252
Author(s):  
NAKIA CARLEVARO ◽  
GIOVANNI MONTANI
Keyword(s):  
Energy Density ◽  
Power Law ◽  
Bulk Viscosity ◽  
Viscosity Coefficient ◽  
Hydrodynamic Equations ◽  
Restricted Domain ◽  
Asymptotic Approach ◽  
Cosmological Singularity ◽  
Second Order In Time

We present a discussion of the effects induced by bulk viscosity on the very early Universe stability. The viscosity coefficient is assumed to be related to the energy density ρ via a power-law of the form ζ = ζ0ρs (where ζ0, s = const.) and the behavior of the density contrast in analyzed. In particular, we study both Einstein and hydrodynamic equations up to first and second order in time in the so-called quasi-isotropic collapsing picture near the cosmological singularity. As a result, we get a power-law solution existing only in correspondence to a restricted domain of ζ0. The particular case of pure isotropic FRW dynamics is then analyzed and we show how the asymptotic approach to the initial singularity admits an unstable collapsing picture.

scholarly journals STUDY OF THE QUASI-ISOTROPIC SOLUTION NEAR THE COSMOLOGICAL SINGULARITY IN THE PRESENCE OF BULK VISCOSITY

2008 ◽  
Vol 17 (06) ◽  
pp. 881-896 ◽  
Author(s):  
NAKIA CARLEVARO ◽  
GIOVANNI MONTANI
Keyword(s):  
Power Law ◽  
Bulk Viscosity ◽  
Dynamical Behavior ◽  
Viscosity Coefficient ◽  
Viscous Effects ◽  
Isotropic Universe ◽  
Cosmological Singularity ◽  
Isotropic Solution ◽  
Second Order In Time ◽  
The Universe

We analyze the dynamical behavior of a quasi-isotropic universe in the presence of a cosmological fluid endowed with bulk viscosity. We express the viscosity coefficient as a power law of the fluid energy density: ζ = ζ0∊s. Then we fix s = 1/2 as the only case in which viscosity plays a significant role in the singularity physics but does not dominate the universe dynamics (as required by its microscopic perturbative origin). The parameter ζ0is left free to define the intensity of the viscous effects.In spirit of the work by Lifshitz and Khalatnikov on the quasi-isotropic solution, we analyze both Einstein and hydrodynamic equations up to first and second order in time. As a result, we get a power law solution existing only in correspondence to a restricted domain of ζ0.

HIGHER DIMENSIONAL COSMOLOGICAL MODEL IN LYRA GEOMETRY: REVISITED

2003 ◽  
Vol 12 (05) ◽  
pp. 853-860 ◽  
Author(s):  
G. P. SINGH ◽  
S. KOTAMBKAR ◽  
ANIRUDH PRADHAN
Keyword(s):  
Cosmological Model ◽  
Power Law ◽  
Bulk Viscosity ◽  
Research Work ◽  
Lyra Geometry ◽  
Universe Model ◽  
Higher Dimensional ◽  
Empty Universe ◽  
Kaluza Klein

In this paper we have revisited the research work of Rahman and Bera22on Kaluza–Klein cosmological model within the framework of Lyra Geometry. It has been shown that the empty universe model yields a power law relation without any assumption. The role of bulk viscosity on five-dimensional cosmological model is discussed. The physical behaviour of the models is examined in all cases.

scholarly journals Stability Analysis of Bulk Viscous Cosmology

2018 ◽  
Vol 168 ◽  
pp. 08006 ◽  
Author(s):  
M. Sharif ◽  
Saadia Mumtaz
Keyword(s):  
Power Law ◽  
Bulk Viscosity ◽  
Viscosity Coefficient ◽  
Study Phase ◽  
Universe Model ◽  
Power Law Model ◽  
Frw Universe ◽  
Dimensionless Variables ◽  
The Stability ◽  
Bulk Viscosity Coefficient

In this paper, we study phase space analysis of FRW universe model by taking a power-law model for bulk viscosity coefficient. An autonomous system of equations is developed by defining normalized dimensionless variables. We find corresponding critical points for di.erent values of the parameters to investigate stability of the system. It is found that the presence of power-law model of bulk viscosity appears as an e.ective ingredient to enhance the stability of the respective universe model.

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.

scholarly journals REFLECTIONS ON THE HYPERBOLIC PLANE

2013 ◽  
Vol 22 (14) ◽  
pp. 1350085
Author(s):  
ORCHIDEA MARIA LECIAN
Keyword(s):  
Physical Interpretation ◽  
Hyperbolic Plane ◽  
Einstein Equations ◽  
Billiard Table ◽  
Billiard Ball ◽  
Cosmological Singularity ◽  
Triangular Domain ◽  
Quantum Properties ◽  
Poincaré Return Map

The most general solution to the Einstein equations in 4 = 3 + 1 dimensions in the asymptotic limit close to the cosmological singularity under the BKL (Belinskii–Khalatnikov–Lifshitz) hypothesis can be visualized by the behavior of a billiard ball in a triangular domain on the Upper Poincaré Half Plane (UPHP). The billiard system (named "big billiard") can be schematized by dividing the successions of trajectories according to Poincaré return map on the sides of the billiard table, according to the paradigms implemented by the BKL investigation and by the CB–LKSKS (Chernoff–Barrow–Lifshitz–Khalatnikov–Sinai–Khanin–Shchur) one. Different maps are obtained, according to different symmetry-quotienting mechanisms used to analyze the dynamics. In the inhomogeneous case, new structures have been uncovered, such that, in this framework, the billiard table (named "small billiard") consists of 1/6 of the previous one. The connections between the symmetry-quotienting mechanisms are further investigated on the UPHP. The relation between the complete billiard and the small billiard are also further explained according to the role of Weyl reflections. The quantum properties of the system are sketched as well, and the physical interpretation of the wave function is further developed. In particular, a physical interpretation for the symmetry-quotienting maps is proposed.

scholarly journals The role of socio‐economic status and energy‐density in Australian women of child‐bearing age

2020 ◽  
Vol 33 (5) ◽  
pp. 718-728
Author(s):  
R. Latter ◽  
L. J. Brown ◽  
K. M. Rae ◽  
M. E. Rollo ◽  
T. L. Schumacher
Keyword(s):  
Energy Density ◽  
Economic Status ◽  
Socio Economic Status ◽  
Child Bearing
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