COSMIC INFLATION IN BIANCHI TYPE IX SPACE WITH BULK VISCOSITY

2021 ◽  
Vol 10 (1) ◽  
pp. 527-534
Author(s):  
S. Sharma ◽  
L. Poonia
Keyword(s):  
Bulk Viscosity ◽  
Current Model ◽  
Cosmological Parameters ◽  
Higgs Field ◽  
Inflationary Universe ◽  
Expansion Scalar ◽  
Negative Constant ◽  
Proper Volume ◽  
Increasing Function ◽  
Special Case

In present paper we have constructed the Bianchitype-IX inflationary universe under framework of the effect of bulk viscosity and flat potential. To developed inflationary model we have consider the supplementary criteria that shear coefficient is directly proportional to expansion scalar which provides an appropriate relation with coefficients of metric $b=a^n$ where n is non-negative constant other than one.We conclude that rate of Higgs field decreases with time and proper volume V is increasing function of time which indicates that universe is expanded continuously. To find solutions of fields equations, we assume $ \xi \theta = \alpha$ (constant) as given by Brevik et al. where $\xi $is coefficient of bulk viscosity and $\theta$ expansion in model. The presence of bulk viscosity provides inflationary solution in current model. The model isotropize in special case. The cosmological parameters of model are also studied.

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.

scholarly journals Some Critical Remarks on the Inflationary Universe Concept

1988 ◽  
Vol 130 ◽  
pp. 63-65
Author(s):  
Gerhard Börner
Keyword(s):  
Large Scale ◽  
Higgs Field ◽  
Quantitative Model ◽  
Time Interval ◽  
Inflationary Universe ◽  
Fundamental Particle ◽  
The Standard Model ◽  
History Of ◽  
Simple Change ◽  
The Universe

The basic idea of inflation in cosmology is very simple: It is the assumption that the expansion factor R(t) of a Friedmann-Lemaltre cosmological model grows exponentially during a brief time interval in the very early universe. The phase of exponential growth is followed by a thermalizatlon stage and a subsequent “normal” evolution R(t)∼vt. This “Inflationary expansion“ can help to solve cosmological puzzles inherent in the standard model - such as the large-scale flatness, the horizon structure, the numerical value of the entropy in a comoving volume [for a review see Brandenberger 1985]. To turn this romantic idea of inflation into a quantitative model requires still a lot of work: The simple change in the thermal history of the universe must be derived from a fundamental particle theory. The models proposed so far do not inspire much confidence. In the following a few difficulties of the Higgs field idea, especially the Coleman-Weinberg formalism will be pointed out (section 1). In section 2 some problems connected with the investigation of initially strongly anisotropic or Inhomogeneous cosmological models will be mentioned.

scholarly journals Tachyon-polytropic inflation on the brane

Open Physics ◽  
2013 ◽  
Vol 11 (5) ◽  
Author(s):  
Mohammad Setare ◽  
Vahid Kamali
Keyword(s):  
Equation Of State ◽  
Cosmological Parameters ◽  
High Energy ◽  
Wilkinson Microwave Anisotropy Probe ◽  
Inflationary Universe ◽  
Universe Model ◽  
Exponential Potential ◽  
Energy Limit ◽  
High Energy Limit ◽  
Slow Roll

AbstractWe consider the tachyon-brane inflationary universe model in the context of a polytropic gas equation of state. In slow-roll approximation, we discuss general conditions of this model. For exponential potential, in high-energy limit the characteristics of the model are presented. By using the seven-year Wilkinson Microwave Anisotropy Probe (WMAP7) observational data, we constrain the cosmological parameters of the model.

Observational constraints of bulk viscous Friedmann–Robertson–Walker cosmology with hybrid expansion law

2020 ◽  
Vol 35 (27) ◽  
pp. 2050173
Author(s):  
Partha Sarathi Debnath
Keyword(s):  
Bulk Viscosity ◽  
Cosmological Parameters ◽  
Space Time ◽  
Observational Constraints ◽  
Closed Space ◽  
Data Set ◽  
Dissipative Effects ◽  
Special Cases ◽  
Bulk Viscous ◽  
Friedmann Robertson Walker

In this work, we study bulk viscous Friedmann–Robertson–Walker cosmologies with hybrid expansion law. The bulk viscous theory of dissipative effects described by Eckart theory, truncated Israel–Stewart theory and full Israel–Stewart theory are implemented here. The hybrid expansion law model of scale factor is a general analytic type of evolution from which one can recover power-law and exponential expansion as a special cases. Hybrid expansion law model are applied to describe the present accelerating phase and early phases of evolution. We have determined the cosmological parameters such as Hubble parameter, deceleration parameter, jerk parameter, energy density, bulk viscous pressure and coefficient of bulk viscosity of the universe to construct physically acceptable cosmological model. We have considered both flat and closed space–time of Friedmann–Robertson–Walker cosmology to implement hybrid expansion law with dissipative effect. The variations of the coefficient of bulk viscosity with cosmic evolution are studied here in Eckart, truncated and full Israel–Stewart theory for flat and closed space–time to obtain physically acceptable hybrid expansion models driven by viscosity. We have also estimated observational constraints of the parameters of hybrid expansion law model by considering recent observational data set. We further reveal possible connections of our models with [Formula: see text] tension problem.

Extremal properties of shot noise processes

1989 ◽  
Vol 21 (3) ◽  
pp. 513-525 ◽  
Author(s):  
Tailen Hsing ◽  
J. L. Teugels
Keyword(s):  
Shot Noise ◽  
Finite Interval ◽  
Domain Of Attraction ◽  
Time Process ◽  
Important Special Case ◽  
Shot Noise Process ◽  
Increasing Function ◽  
Special Case ◽  
Natural Way ◽  
Extremal Properties

Consider the shot noise process X(t):= Σih(t – τi), , where h is a bounded positive non-increasing function supported on a finite interval, and the are the points of a renewal process η on [0, ). In this paper, the extremal properties of {X(t)} are studied. It is shown that these properties can be investigated in a natural way through a discrete-time process which records the states of {X(t)} at the points of η. The important special case where η is Poisson is treated in detail, and a domain-of-attraction result for the compound Poisson distribution is obtained as a by-product.

Bulk-viscosity-driven asymmetric inflationary universe

1988 ◽  
Vol 37 (10) ◽  
pp. 2755-2760 ◽  
Author(s):  
J. A. S. Lima ◽  
R. Portugal ◽  
I. Waga
Keyword(s):  
Bulk Viscosity ◽  
Inflationary Universe

Interacting modified Chaplygin gas cosmology with varying viscosity

2014 ◽  
Vol 92 (11) ◽  
pp. 1470-1473
Author(s):  
K. Karimiyan ◽  
J. Naji
Keyword(s):  
Energy Density ◽  
Bulk Viscosity ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
Chaplygin Gas ◽  
Baryonic Matter ◽  
Modified Chaplygin Gas ◽  
Hubble Expansion ◽  
Interaction Interaction ◽  
Varying Viscosity

We study interacting modified Chaplygin gas, which has shear and bulk viscosities. We assume bulk viscosity is a function of density, and also consider sign-changeable interaction. Interaction is assumed between modified Chaplygin gas and baryonic matter. Then, the effects of viscosities on the cosmological parameters, such as energy, density, Hubble expansion parameter, scale factor, and deceleration parameter, are investigated. We can consider this model as a toy model of our universe.

scholarly journals Segregation lift: A general mechanism for the maintenance of polygenic variation under seasonally fluctuating selection

2017 ◽  
Author(s):  
Meike J. Wittmann ◽  
Alan O. Bergland ◽  
Marcus W. Feldman ◽  
Paul S. Schmidt ◽  
Dmitri A. Petrov
Keyword(s):  
Seasonal Changes ◽  
Natural Populations ◽  
Genetic Load ◽  
General Mechanism ◽  
Large Contribution ◽  
Fluctuating Selection ◽  
Previous Theory ◽  
Increasing Function ◽  
Special Case ◽  
Polygenic Variation

AbstractMost natural populations are affected by seasonal changes in temperature, rainfall, or resource availability. Seasonally fluctuating selection could potentially make a large contribution to maintaining genetic polymorphism in populations. However, previous theory suggests that the conditions for multi-locus polymorphism are restrictive. Here we explore a more general class of models with multi-locus seasonally fluctuating selection in diploids. In these models, loci first contribute additively to a seasonal score, with a dominance parameter determining the relative contributions of heterozygous and homozygous loci. The seasonal score is then mapped to fitness via a monotonically increasing function, thereby accounting for epistasis. Using mathematical analysis and individual-based simulations, we show that stable polymorphism at many loci is possible if currently favored alleles are sufficiently dominant with respect to the additive seasonal score (but not necessarily with respect to fitness itself). This general mechanism, which we call “segregation lift”, operates for various genotype-to-fitness maps and includes the previously known mechanism of multiplicative selection with marginal overdominance as a special case. We show that segregation lift may arise naturally in situations with antagonistic pleiotropy and seasonal changes in the relative importance of traits for fitness. Segregation lift is not affected by problems of genetic load and is robust to differences in parameters across loci and seasons. Under segregation lift, loci can exhibit conspicuous seasonal allele-frequency fluctuations, but often fluctuations may also be small and hard to detect. Via segregation lift, seasonally fluctuating selection might contribute substantially to maintaining genetic variation in natural populations.

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