POWER-LOW EXPANSION IN k-ESSENCE COSMOLOGY

2004 ◽  
Vol 19 (10) ◽  
pp. 761-768 ◽  
Author(s):  
LUIS P. CHIMENTO ◽  
ALEXANDER FEINSTEIN
Keyword(s):  
Gravitational Field ◽  
Scalar Field ◽  
Field Model ◽  
Constant Function ◽  
Field Potentials ◽  
Field Equations ◽  
Large Window ◽  
The Family ◽  
Stable Solutions ◽  
Linear Scalar

We study spatially flat isotropic universes driven by k-essence. It is shown that Friedmann and k-field equations may be analytically integrated for arbitrary k-field potentials during evolution with a constant baryotropic index. It follows that there is an infinite number of dynamically different k-theories with equivalent kinematics of the gravitational field. We show that there is a large "window" of stable solutions, and that the dust-like behavior separates stable from unstable expansion. Restricting to the family of power law solutions, it is argued that the linear scalar field model, with constant function F, is isomorphic to a model with divergent speed of sound and this makes them less suitable for cosmological modeling than the nonlinear k-field solutions we find in this paper.

scholarly journals Einstein-aether theory in Weyl integrable geometry

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Andronikos Paliathanasis ◽  
Genly Leon ◽  
John D. Barrow
Keyword(s):  
Gravitational Field ◽  
Field Equation ◽  
Scalar Field ◽  
Field Model ◽  
Affine Connection ◽  
Dynamical Evolution ◽  
Field Equations ◽  
Gravitational Field Equation ◽  
Gravitational Field Equations ◽  
Geometric Origin

AbstractWe study the Einstein-aether theory in Weyl integrable geometry. The scalar field which defines the Weyl affine connection is introduced in the gravitational field equation. We end up with an Einstein-aether scalar field model where the interaction between the scalar field and the aether field has a geometric origin. The scalar field plays a significant role in the evolution of the gravitational field equations. We focus our study on the case of homogeneous and isotropic background spacetimes and study their dynamical evolution for various cosmological models.

scholarly journals Dynamics of scalar potentials in theory of gravity

2019 ◽  
Vol 97 (8) ◽  
pp. 880-894
Author(s):  
M. Zubair ◽  
Farzana Kousar ◽  
Saira Waheed
Keyword(s):  
Scalar Field ◽  
Field Potential ◽  
Graphical Analysis ◽  
Chaplygin Gas ◽  
Field Potentials ◽  
De Sitter ◽  
Field Equations ◽  
Barotropic Fluid ◽  
First Case ◽  
De Sitter Universe

In this paper, we explore the nature of scalar field potential in [Formula: see text] gravity using a well-motivated reconstruction scheme for flat Friedmann–Robertson–Walker (FRW) geometry. The beauty of this scheme lies in the assumption that the Hubble parameter can be expressed in terms of scalar field and vice versa. Firstly, we develop field equations in this gravity and present some general explicit forms of scalar field potential via this technique. In the first case, we take the de Sitter universe model and construct some field potentials by taking different cases for the coupling function. In the second case, we derive some field potentials using the power law model in the presence of different matter sources like barotropic fluid, cosmological constant, and Chaplygin gas for some coupling functions. From graphical analysis, it is concluded that using some specific values of the involved parameters, the reconstructed scalar field potentials are cosmologically viable in both cases.

scholarly journals Exact Solutions in Poincaré Gauge Gravity Theory

Universe ◽  
2019 ◽  
Vol 5 (5) ◽  
pp. 127 ◽  
Author(s):  
Yuri N. Obukhov
Keyword(s):  
Gravitational Field ◽  
Gravity Models ◽  
Field Potentials ◽  
De Sitter ◽  
Field Equations ◽  
Yang Mills ◽  
Gravitational Field Equations ◽  
Poincaré Symmetry ◽  
Gauge Gravity ◽  
Vacuum Solutions

In the framework of the gauge theory based on the Poincaré symmetry group, the gravitational field is described in terms of the coframe and the local Lorentz connection. Considered as gauge field potentials, they give rise to the corresponding field strength which are naturally identified with the torsion and the curvature on the Riemann–Cartan spacetime. We study the class of quadratic Poincaré gauge gravity models with the most general Yang–Mills type Lagrangian which contains all possible parity-even and parity-odd invariants built from the torsion and the curvature. Exact vacuum solutions of the gravitational field equations are constructed as a certain deformation of de Sitter geometry. They are black holes with nontrivial torsion.

scholarly journals Reconstructing f(R) gravity from a Chaplygin scalar field in de Sitter spacetimes

2018 ◽  
Vol 15 (02) ◽  
pp. 1850027 ◽  
Author(s):  
Heba Sami ◽  
Neo Namane ◽  
Joseph Ntahompagaze ◽  
Maye Elmardi ◽  
Amare Abebe
Keyword(s):  
General Relativity ◽  
Scalar Field ◽  
Field Model ◽  
Exact Formula ◽  
Chaplygin Gas ◽  
Reconstruction Technique ◽  
Field Potentials ◽  
De Sitter ◽  
Cosmological Expansion ◽  
Lagrangian Densities

We present a reconstruction technique for models of [Formula: see text] gravity from the Chaplygin scalar field in flat de Sitter spacetimes. Exploiting the equivalence between [Formula: see text] gravity and scalar–tensor (ST) theories, and treating the Chaplygin gas (CG) as a scalar field model in a universe without conventional matter forms, the Lagrangian densities for the [Formula: see text] action are derived. Exact [Formula: see text] models and corresponding scalar field potentials are obtained for asymptotically de Sitter spacetimes in early and late cosmological expansion histories. It is shown that the reconstructed [Formula: see text] models all have General Relativity (GR) as a limiting solution.

scholarly journals Nonminimal kinetic coupled gravity: Inflation on the warped DGP brane

2016 ◽  
Vol 31 (10) ◽  
pp. 1650047
Author(s):  
F. Darabi ◽  
A. Parsiya ◽  
K. Atazadeh
Keyword(s):  
Scalar Field ◽  
Coupling Constants ◽  
Kinetic Term ◽  
Field Potentials ◽  
Coupling Constant ◽  
Field Equations ◽  
Einstein Tensor ◽  
Brane Model ◽  
Walker Metric ◽  
Friedmann Robertson Walker

We consider the nonminimally kinetic coupled version of DGP brane model, where the kinetic term of the scalar field is coupled to the metric and Einstein tensor on the brane by a coupling constant [Formula: see text]. We obtain the corresponding field equations, using the Friedmann–Robertson–Walker metric and the perfect fluid, and study the inflationary scenario to confront the numerical analysis of six typical scalar field potentials with the current observational results. We find that among the suggested potentials and coupling constants, subject to the e-folding [Formula: see text], the potentials [Formula: see text], [Formula: see text] and [Formula: see text] provide the best fits with both Planck+WP+highL data and Planck+WP+highL+BICEP2 data.

scholarly journals QUINTESSENCE AND COSMIC ACCELERATION

2002 ◽  
Vol 11 (09) ◽  
pp. 1389-1397 ◽  
Author(s):  
M. K. MAK ◽  
T. HARKO
Keyword(s):  
Gravitational Field ◽  
Scalar Field ◽  
Field Potential ◽  
Cosmic Acceleration ◽  
Accelerated Expansion ◽  
Field Equations ◽  
Gravitational Field Equations ◽  
General Physical ◽  
Quintessence Field ◽  
The Universe

A cosmological model with perfect fluid and self-interacting quintessence field is considered in the framework of the spatially flat Friedmann–Robertson–Walker (FRW) geometry. By assuming that all physical quantities depend on the volume scale factor of the Universe, the general solution of the gravitational field equations can be expressed in an exact parametric form, with the volume taken as the parameter, and with the quintessence field as a free parameter. With an appropriate choice of the scalar field a class of exact parametric solutions is obtained, with an exponential type scalar field potential fixed via the gravitational field equations. The general physical behavior of the model is consistent with the recent cosmological scenario favored by supernova type Ia observations, indicating an accelerated expansion of the Universe.

scholarly journals Anisotropic power-law inflation in a two-scalar-field model with a mixed kinetic term

2017 ◽  
Vol 26 (07) ◽  
pp. 1750072 ◽  
Author(s):  
Tuan Q. Do ◽  
Sonnet Hung Q. Nguyen
Keyword(s):  
Scalar Field ◽  
Power Law ◽  
Field Model ◽  
Scalar Fields ◽  
Kinetic Term ◽  
Type I ◽  
Field Equations ◽  
Scalar Field Model ◽  
Phantom Scalar ◽  
The Stability

We examine whether an extended scenario of a two-scalar-field model, in which a mixed kinetic term of canonical and phantom scalar fields is involved, admits the Bianchi type I metric, which is homogeneous but anisotropic spacetime, as its power-law solutions. Then, we analyze the stability of the anisotropic power-law solutions to see whether these solutions respect the cosmic no-hair conjecture or not during the inflationary phase. In addition, we will also investigate a special scenario, where the pure kinetic terms of canonical and phantom fields disappear altogether in field equations, to test again the validity of cosmic no-hair conjecture. As a result, the cosmic no-hair conjecture always holds in both these scenarios due to the instability of the corresponding anisotropic inflationary solutions.

scholarly journals Stability of a Noncanonical Scalar Field Model during Cosmological Date

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Z. Ossoulian ◽  
T. Golanbari ◽  
H. Sheikhahmadi ◽  
Kh. Saaidi
Keyword(s):  
Fixed Point ◽  
Scalar Field ◽  
Energy Density ◽  
Field Model ◽  
Field Potential ◽  
Linear Perturbation ◽  
Field Equations ◽  
Gravitational Fields ◽  
The Universe ◽  
Nonlinear Field Equations

Using the noncanonical model of scalar field, the cosmological consequences of a pervasive, self-interacting, homogeneous, and rolling scalar field are studied. In this model, the scalar field potential is “nonlinear” and decreases in magnitude with increasing the value of the scalar field. A special solution of the nonlinear field equations ofϕthat has time dependency as fixed point is obtained. The fixed point relies on the noncanonical term of action andγ-parameter; this parameter appeared in energy density of scalar field redshift. By means of such fixed point the different eigenvalues of the equation of motion will be obtained. In different epochs in the evolution of the Universe for different values ofqandn, the potentials as a function of scalar field are attained. The behavior of baryonic perturbations in linear perturbation scenario as a considerable amount of energy density of scalar field at low redshifts prevents the growth of perturbations in the ordinary matter fluid. The energy density in the scalar field is not appreciably perturbed by nonrelativistic gravitational fields, in either the radiation or matter dominant or scalar field dominated epoch.

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