scholarly journals Cosmological solutions in Hořava-Lifshitz scalar field theory

2020 ◽  
Vol 75 (6) ◽  
pp. 523-532 ◽  
Author(s):  
Andronikos Paliathanasis ◽  
Genly Leon
Keyword(s):  
Scalar Field ◽  
Singularity Analysis ◽  
Exponential Potential ◽  
Field Equations ◽  
Explicit Integration ◽  
Gravitational Field Equations ◽  
Background Space ◽  
Painlevé Property ◽  
Cosmological Solutions ◽  
Scalar Field Cosmology

AbstractWe perform a detailed study of the integrability of the Hořava-Lifshitz scalar field cosmology in a Friedmann-Lemaître-Robertson-Walker background space-time. The approach we follow to determine the integrability is that of singularity analysis. More specifically, we test whether the gravitational field equations possess the Painlevé property. For the exponential potential of the scalar field, we are able to perform an analytic explicit integration of the field equations and write the solution in terms of a Laurent expansion and more specifically write the solution in terms of right Painlevé series.

scholarly journals Integrability and cosmological solutions in Einstein-æther-Weyl theory

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
Andronikos Paliathanasis ◽  
Genly Leon
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Conservation Law ◽  
Analytic Solutions ◽  
Special Interests ◽  
Field Equations ◽  
Background Space ◽  
Weyl Theory ◽  
Cosmological Solutions

AbstractWe consider a Lorentz violating scalar field cosmological model given by the modified Einstein-æther theory defined in Weyl integrable geometry. The existence of exact and analytic solutions is investigated for the case of a spatially flat Friedmann–Lemaître–Robertson–Walker background space. We show that the theory admits cosmological solutions of special interests. In addition, we prove that the cosmological field equations admit the Lewis invariant as a second conservation law, which indicates the integrability of the field equations.

scholarly journals Exact Kantowski–Sachs spacetimes in Einstein–Aether scalar field theory

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Genly Leon ◽  
Andronikos Paliathanasis ◽  
N. Dimakis
Keyword(s):  
Field Theory ◽  
Scalar Field ◽  
Functional Form ◽  
Analytic Solution ◽  
Analytic Solutions ◽  
Field Equations ◽  
Scalar Field Theory ◽  
Gravitational Field Equations ◽  
Background Space ◽  
Gravitational Model

AbstractExact and analytic solutions in Einstein–Aether scalar field theory with Kantowski–Sachs background space are determined. The theory of point symmetries is applied to determine the functional form of the unknown functions which defines the gravitational model. Conservation laws are applied to reduce the order of the field equations and write the analytic solution. Moreover, in order to understand the physical behaviour of the cosmological model a detailed analysis of the asymptotic behaviour for solutions of the gravitational field equations is performed.

scholarly journals New Anisotropic Exact Solution in Multifield Cosmology

Universe ◽  
2021 ◽  
Vol 7 (9) ◽  
pp. 323 ◽  
Author(s):  
Andronikos Paliathanasis
Keyword(s):  
Exact Solution ◽  
Scalar Field ◽  
Chiral Model ◽  
Stability Conditions ◽  
Field Equations ◽  
Background Space ◽  
Scalar Field Cosmology ◽  
The Stability

In the case of two-scalar field cosmology, and specifically for the Chiral model, we determine an exact solution for the field equations with an anisotropic background space. The exact solution can describe anisotropic inflation with a Kantowski–Sachs geometry and can be seen as the anisotropic analogue of the hyperbolic inflation. Finally, we investigate the stability conditions for the exact solution.

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 Exact scalar–tensor cosmological models

2017 ◽  
Vol 26 (07) ◽  
pp. 1750073 ◽  
Author(s):  
J. A. Belinchón ◽  
T. Harko ◽  
M. K. Mak
Keyword(s):  
Scalar Field ◽  
Cosmological Solution ◽  
Gravitational Theory ◽  
Field Equations ◽  
Group Approach ◽  
Gravitational Field Equations ◽  
Gravitational Theories ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

Scalar–tensor gravitational theories are important extensions of standard general relativity, which can explain both the initial inflationary evolution, as well as the late accelerating expansion of the universe. In the present paper, we investigate the cosmological solution of a scalar–tensor gravitational theory, in which the scalar field [Formula: see text] couples to the geometry via an arbitrary function [Formula: see text]. The kinetic energy of the scalar field as well as its self-interaction potential [Formula: see text] are also included in the gravitational action. By using a standard mathematical procedure, the Lie group approach, and Noether symmetry techniques, we obtain several exact solutions of the gravitational field equations describing the time evolutions of a flat Friedman–Robertson–Walker universe in the framework of the scalar–tensor gravity. The obtained solutions can describe both accelerating and decelerating phases during the cosmological expansion of the universe.

scholarly journals Determination of time evolution of the gravitational constant in the framework of Brans-Dicke Theory: An easy wa

2021 ◽  
Vol 11 (2) ◽  
pp. 163-168
Author(s):  
Sudipto Roy
Keyword(s):  
Scalar Field ◽  
Time Dependence ◽  
Gravitational Constant ◽  
Cosmological Parameters ◽  
Rate Of Change ◽  
The Novel ◽  
Field Equations ◽  
Relative Time ◽  
Gravitational Field Equations

The present article demonstrates a very simple mathematical way to determine the time-dependence of the dynamical gravitational constant () in the framework of the Brans-Dicke theory of gravity. Brans-Dicke field equations, for a matter-dominated, pressure-less and spatially flat universe with homogeneous and isotropic space-time, have been used for this formulation. The gravitational constant () is the reciprocal of the Brans-Dicke scalar field (). Using a simple ansatz, which represents the Brans-Dicke scalar field () as a function of time, the possible values of a constant parameter (constituting the ansatz) have been calculated with the help of the field equations, using the values of some cosmological parameters at the present time. The values of that parameter (belonging to the ansatz) lead to the conclusion that the scalar field () decreases and consequently the gravitational constant () increases with time. The value of the relative time-rate of change of the gravitational constant (i.e., ) has also been estimated and this quantity has been found to be independent of time. Time-dependence of and has been depicted graphically for all values of the parameter belonging to the ansatz. The novel features of this study are that the gravitational field equations did not have to be solved, unlike other studies, to arrive at the results and the mathematical scheme for calculations is extremely easy in comparison to other recent studies in this regard.

scholarly journals EXACT SOLUTIONS FOR COSMOLOGICAL MODELS WITH A SCALAR FIELD

2002 ◽  
Vol 17 (03) ◽  
pp. 375-381 ◽  
Author(s):  
H. MOTAVALI ◽  
M. GOLSHANI
Keyword(s):  
Scalar Field ◽  
Exact Solutions ◽  
Cosmological Models ◽  
Coupling Function ◽  
Noether Symmetry ◽  
Scalar Tensor Theory ◽  
Frw Cosmology ◽  
Field Equations ◽  
Tensor Theory ◽  
Cosmological Solutions

We consider the existence of a Noether symmetry in the scalar–tensor theory of gravity in flat Friedman–Robertson–Walker (FRW) cosmology. The forms of coupling function ω(ϕ) and generic potential V(ϕ) are obtained by requiring the existence of a Noether symmetry for such theory. We derive exact cosmological solutions of the field equations from a point-like Lagrangian.

A cyclic non-singular universe from Gauss–Bonnet and superstring corrections

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Rami Ahmad El-Nabulsi
Keyword(s):  
Scalar Field ◽  
Time Derivative ◽  
Low Energy ◽  
Exponential Potential ◽  
Field Equations ◽  
Superstring Theory ◽  
Higher Dimensional ◽  
Free Parameters ◽  
Higher Order Corrections ◽  
The Universe

Abstract In this study, we have constructed a viable cosmological model characterized by the presence of the Gauss–Bonnet four-dimensional invariant, higher-order corrections to the low energy effective action motivated from heterotic superstring theory and a general exponential potential comparable to those obtained in higher dimensional supergravities. The field equations were studied by assuming a particular relation between the Hubble parameter and the time derivative of the scalar field. It was observed that, for specific relations between the free parameters in the theory, the universe is cyclic, expands and contracts alternately without singularity with an equation of state oscillating around −1. The model is found to fit the recent astrophysical data.

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