ASSISTED INFLATION

2002 ◽  
Vol 17 (20) ◽  
pp. 2755-2755
Author(s):  
A. A. COLEY ◽  
R. J. VAN DEN HOOGEN
Keyword(s):  
Perfect Fluid ◽  
Scalar Fields ◽  
Cosmological Models ◽  
Late Time ◽  
Time Behaviour ◽  
Field Curvature ◽  
Scaling Solution ◽  
Dynamical Properties ◽  
Spatially Homogeneous ◽  
Parameter Values

The dynamical properties of spatially homogeneous and isotropic cosmological models containing a barotropic perfect fluid and multiple scalar fields with independent exponential potentials is investigated. It is shown that the assisted inflationary scaling solution is the global late-time attractor for the parameter values for which the model is inflationary, even when curvature and barotropic matter are included. For all other parameter values the multi-field curvature scaling solution is the global late-time attractor (in these solutions the curvature is not dynamically negligible asymptotically). Consequently, in general all of the scalar fields in multi-field models with exponential potentials are non-negligible in late-time behaviour, contrary to what is commonly believed.

scholarly journals A Riccati equation based approach to isotropic scalar field cosmologies

2014 ◽  
Vol 23 (07) ◽  
pp. 1450063 ◽  
Author(s):  
Tiberiu Harko ◽  
Francisco S. N. Lobo ◽  
M. K. Mak
Keyword(s):  
Scalar Field ◽  
Evolution Equation ◽  
Interaction Potential ◽  
Arbitrary Function ◽  
Field Potential ◽  
Type Equation ◽  
Scalar Fields ◽  
Cosmological Models ◽  
Late Time ◽  
Field Equations

Gravitationally coupled scalar fields ϕ, distinguished by the choice of an effective self-interaction potential V(ϕ), simulating a temporarily nonvanishing cosmological term, can generate both inflation and late time acceleration. In scalar field cosmological models the evolution of the Hubble function is determined, in terms of the interaction potential, by a Riccati type equation. In the present work, we investigate scalar field cosmological models that can be obtained as solutions of the Riccati evolution equation for the Hubble function. Four exact integrability cases of the field equations are presented, representing classes of general solutions of the Riccati evolution equation. The solutions correspond to cosmological models in which the Hubble function is proportional to the scalar field potential plus a linearly decreasing function of time, models with the time variation of the scalar field potential proportional to the potential minus its square, models in which the potential is the sum of an arbitrary function and the square of the function integral, and models in which the potential is the sum of an arbitrary function and the derivative of its square root, respectively. The cosmological properties of all models are investigated in detail, and it is shown that they can describe the inflationary or the late accelerating phase in the evolution of the universe.

scholarly journals Bianchi Type II, VIII, and IX Perfect Fluid Dark Energy Cosmological Models in Saez-Ballester and General Theory of Gravitation

2013 ◽  
Vol 2013 ◽  
pp. 1-11
Author(s):  
V. U. M. Rao ◽  
K. V. S. Sireesha ◽  
D. Neelima
Keyword(s):  
Dark Energy ◽  
Perfect Fluid ◽  
Bianchi Type ◽  
Cosmological Models ◽  
Type Ii ◽  
Geometrical Features ◽  
Viii And Ix ◽  
Theory Of Gravitation ◽  
Spatially Homogeneous ◽  
Einstein’S General Relativity

The paper deals with spatially homogeneous anisotropic Bianchi type II, VIII , and IX dark energy cosmological models filled with perfect fluid in the framework of Saez-Ballester (1986) theory, and Einstein's general relativity. Assuming that the two sources interact minimally and therefore their energy momentum tensors are conserved separately, we have considered different cases and presented anisotropic as well as isotropic cosmological models. Some important physical and geometrical features of the models, thus obtained, have been discussed.

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.

scholarly journals Late Time Attractors of Some Varying Chaplygin Gas Cosmological Models

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 769
Author(s):  
Martiros Khurshudyan ◽  
Ratbay Myrzakulov
Keyword(s):  
Dark Energy ◽  
Gravitational Interaction ◽  
Chaplygin Gas ◽  
Cosmological Models ◽  
Late Time ◽  
Time Behavior ◽  
Coincidence Problem ◽  
Energy Models ◽  
Non Linear ◽  
Bayesian Machine Learning

The goal of this paper is to study new cosmological models where the dark energy is a varying Chaplygin gas. This specific dark energy model with non-linear EoS had been often discussed in modern cosmology. Contrary to previous studies, we consider new forms of non-linear non-gravitational interaction between dark matter and assumed dark energy models. We applied the phase space analysis allowing understanding the late time behavior of the models. It allows demonstrating that considered non-gravitational interactions can solve the cosmological coincidence problem. On the other hand, we applied Bayesian Machine Learning technique to learn the constraints on the free parameters. In this way, we gained a better understanding of the models providing a hint which of them can be ruled out. Moreover, the learning based on the simulated expansion rate data shows that the models cannot solve the H0 tension problem.

The possibility of a stable flat dark energy-dominated Swiss-cheese brane-world universe

2020 ◽  
Vol 17 (05) ◽  
pp. 2050075
Author(s):  
Nasr Ahmed ◽  
Kazuharu Bamba ◽  
F. Salama
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Cosmological Models ◽  
Brane World ◽  
Fine Tuning ◽  
Energy Conditions ◽  
Late Time ◽  
Swiss Cheese ◽  
Black Strings ◽  
The Stability

In this paper, we study the possibility of obtaining a stable flat dark energy-dominated universe in a good agreement with observations in the framework of Swiss-cheese brane-world cosmology. Two different brane-world cosmologies with black strings have been introduced for any cosmological constant [Formula: see text] using two empirical forms of the scale factor. In both models, we have performed a fine-tuning between the brane tension and the cosmological constant so that the Equation of state (EoS) parameter [Formula: see text] for the current epoch, where the redshift [Formula: see text]. We then used these fine–tuned values to calculate and plot all parameters and energy conditions. The deceleration–acceleration cosmic transition is allowed in both models, and the jerk parameter [Formula: see text] at late-times. Both solutions predict a future dark energy-dominated universe in which [Formula: see text] with no crossing to the phantom divide line. While the pressure in the first solution is always negative, the second solution predicts a better behavior of cosmic pressure where the pressure is negative only in the late-time accelerating era but positive in the early-time decelerating era. Such a positive-to-negative transition in the evolution of pressure helps to explain the cosmic deceleration–acceleration transition. Since black strings have been proved to be unstable by some authors, this instability can actually reflect doubts on the stability of cosmological models with black strings (Swiss-cheese type brane-worlds cosmological models). For this reason, we have carefully investigated the stability through energy conditions and sound speed. Because of the presence of quadratic energy terms in Swiss-cheese type brane-world cosmology, we have tested the new nonlinear energy conditions in addition to the classical energy conditions. We have also found that a negative tension brane is not allowed in both models of the current work as the energy density will no longer be well defined.

Hypersurface-homogeneous cosmological models with dynamical equation of state parameter in Lyra geometry

2015 ◽  
Vol 93 (10) ◽  
pp. 1100-1105 ◽  
Author(s):  
Shri Ram ◽  
S. Chandel ◽  
M.K. Verma
Keyword(s):  
Dynamical Equation ◽  
State Parameter ◽  
Lyra Geometry ◽  
Cosmological Models ◽  
Anisotropic Fluid ◽  
Late Time ◽  
Field Equations ◽  
Homogeneous Cosmological Models ◽  
Negative Constant ◽  
Equation Of State Parameter

The hypersurface homogeneous cosmological models are investigated in the presence of an anisotropic fluid in the framework of Lyra geometry. Exact solutions of field equations are obtained by applying a special law of variation for mean Hubble parameter that gives a negative constant value of the deceleration parameter. These solutions correspond to anisotropic accelerated expanding cosmological models that isotropize for late time even in the presence of anisotropic fluid. The anisotropy of the fluid also isotropizes at late time. Some physical and kinematical properties of the model are also discussed.

scholarly journals The late-time behaviour of vortic Bianchi type VIII universes

2006 ◽  
Vol 23 (9) ◽  
pp. 3017-3035 ◽  
Author(s):  
Sigbjørn Hervik ◽  
Woei Chet Lim
Keyword(s):  
Bianchi Type ◽  
Late Time ◽  
Time Behaviour ◽  
Type Viii

The nonlinear patterns of the cosmic anisotropy: the spatially flat perfect fluid universes.

2021 ◽  
Author(s):  
Leandro Gustavo Gomes
Keyword(s):  
Perfect Fluid ◽  
Hubble Parameter ◽  
Late Time ◽  
Algebraic Equations ◽  
Anisotropic Model ◽  
Bianchi Models ◽  
Principal Directions

Abstract In this manuscript, we investigate the patterns of the cosmological anisotropy in the spatially flat Bianchi models filled with a perfect fluid. We analyse the factor 1 + ∆R, the ratio of the Hubble parameter in the anisotropic model over its isotropic counterpart. In general, ∆R starts to deviate significantly from zero at a specific redshift zA, which depends on the type of the fluid and the value of the anisotropy magnitude. We also show that the deceleration and the jerk along the principal directions of the expansion tensor are constrained by simple algebraic equations that do not depend on the type of matter present. These characteristic patterns form a valuable framework to probe the cosmological anisotropy in the late-time universe.

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