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 EINSTEIN'S REAL "BIGGEST BLUNDER"

2012 ◽  
Vol 21 (11) ◽  
pp. 1242022 ◽  
Author(s):  
HOMER G. ELLIS
Keyword(s):  
Constant Term ◽  
Big Bang ◽  
Gravitational Mass ◽  
Field Equations ◽  
Gravitational Field Equations ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
Passive Gravitational Mass ◽  
The Universe ◽  
Active Gravitational Mass

Albert Einstein's real "biggest blunder" was not the 1917 introduction into his gravitational field equations of a cosmological constant term Λ, rather was his failure in 1916 to distinguish between the entirely different concepts of active gravitational mass and passive gravitational mass. Had he made the distinction, and followed David Hilbert's lead in deriving field equations from a variational principle, he might have discovered a true (not a cut and paste) Einstein–Rosen bridge and a cosmological model that would have allowed him to predict, long before such phenomena were imagined by others, inflation, a big bounce (not a big bang), an accelerating expansion of the universe, dark matter, and the existence of cosmic voids, walls, filaments and nodes.

scholarly journals THE EVOLUTION OF THE UNIVERSE WITH THE B–I TYPE PHANTOM SCALAR FIELD

2006 ◽  
Vol 15 (02) ◽  
pp. 199-214 ◽  
Author(s):  
WEI FANG ◽  
H. Q. LU ◽  
Z. G. HUANG ◽  
K. F. ZHANG
Keyword(s):  
Scalar Field ◽  
State Parameter ◽  
Phase Plane Analysis ◽  
Density Parameter ◽  
Late Time ◽  
Plane Analysis ◽  
Accelerating Expansion ◽  
Phantom Scalar ◽  
Expansion Of The Universe ◽  
The Universe

We consider the phantom cosmology with a Lagrangian [Formula: see text] originated from the nonlinear Born–Infeld type scalar field. This cosmological model can explain the accelerating expansion of the universe with the equation of state parameter w ≤ -1. We get a sufficient condition for an arbitrary potential that admits a late time attractor solution: the value of potential u(Xc) at the critical point (Xc, 0) should be maximum and greater than zero. We study a specific potential with the form of [Formula: see text] via phase plane analysis and compute the cosmological evolution by numerical analysis in detail. The results show that the phantom field survives till today (to account for the present observed accelerating expansion) without interfering with the nucleosynthesis of the standard model (the density parameter Ωϕ≃10-12 at the equipartition epoch), and also avoid the future collapse of the universe.

scholarly journals Inflation in anisotropic brane universe using tachyon field

2019 ◽  
Vol 28 (13) ◽  
pp. 1941010 ◽  
Author(s):  
Rikpratik Sengupta ◽  
Prasenjit Paul ◽  
Bikash Chandra Paul ◽  
Saibal Ray
Keyword(s):  
Gravitational Field ◽  
Cosmological Solution ◽  
Tachyon Field ◽  
Field Equations ◽  
Tachyonic Field ◽  
Bianchi I ◽  
Gravitational Field Equations ◽  
First Case ◽  
Cosmological Scenario ◽  
The Universe

Cosmological solution to the gravitational field equations in the generalized Randall–Sundrum model for an anisotropic brane with Bianchi-I geometry and perfect fluid as matter sources has been considered. The matter on the brane is described by a tachyonic field. The solution admits inflationary era and at a later epoch the anisotropy of the universe washes out. We obtain two classes of cosmological scenario: in the first case, universe evolves from singularity and in the second case, universe expands without singularity.

Kantowski–Sachs universe with dark energy fluid and massive scalar field

2020 ◽  
Vol 98 (11) ◽  
pp. 993-998
Author(s):  
K. Deniel Raju ◽  
M.P.V.V. Bhaskara Rao ◽  
Y. Aditya ◽  
T. Vinutha ◽  
D.R.K. Reddy
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Massive Scalar ◽  
Field Equations ◽  
Massive Scalar Field ◽  
Anisotropic Dark Energy ◽  
Expansion Of The Universe ◽  
The Universe

This study is mainly concerned with a spatially homogeneous and anisotropic Kantowski–Sachs cosmological model with anisotropic dark energy fluid and massive scalar field. We solve the field equations using (i) the shear scalar proportionality to the expansion scalar and (ii) a mathematical condition that is a consequence of the power law between the scalar field and the average scale factor of the universe, and the corresponding dark energy model is presented. The cosmological parameters of the model are computed and discussed, as well as the relevance of its dynamical aspects to the recent scenario of the accelerated expansion of the universe.

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 Noether symmetries of Einstein-aether scalar field cosmology

2020 ◽  
Vol 80 (11) ◽  
Author(s):  
Yusuf Kucukakca ◽  
Amin Rezaei Akbarieh
Keyword(s):  
Scalar Field ◽  
Noether Symmetry ◽  
Accelerated Expansion ◽  
Noether Symmetries ◽  
Field Equations ◽  
Symmetry Approach ◽  
Expansion Of The Universe ◽  
Frw Metric ◽  
Scalar Field Cosmology ◽  
The Universe

AbstractIn this paper, we explore an Einstein-aether cosmological model by adding the scalar field in which it has an interaction with the aether field. For the cosmological implications of the model, we consider that the universe can be described by the spatially flat FRW metric together with the matter dominated universe. Applying Noether symmetry approach to the point-like Lagrangian we determine the explicit forms of unknown functions i.e. the potential and coupling function. We solve the analytical cosmological solutions of the field equations admitting the Noether symmetry, basically divided into two parts. Our results show that the obtained solutions lead to an accelerated expansion of the universe. We also discuss the tensor perturbations within the framework of this model in order to get information about the mass of gravitational waves.

Alternative Gravitational Theories

2020 ◽  
pp. 146-176
Author(s):  
John W. Moffat
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Modified Gravity ◽  
Gravitational Theory ◽  
Alternative Theory ◽  
Gravitational Theories ◽  
Accelerating Expansion ◽  
Modified Gravity Theories ◽  
Expansion Of The Universe ◽  
Dynamics Of Galaxies

There have been many proposed modifications of gravitational theory, beginning with Einstein’s general relativity, modifying Newtonian gravity, and Weyl’s attempt at unifying gravity and electromagnetism. The standard model of cosmology, the Lambda CDM model, requires dark matter and dark energy to fit experimental data. There is a lack of direct evidence for dark matter and dark energy. An alternative theory called modified gravity (MOG) seeks to fit the observational data for the dynamics of galaxies and clusters of galaxies without dark matter. The MOG gravitational theory has a solution for a black hole that modifies the Schwarzschild and Kerr solutions, and can be tested using the data collected on supermassive black holes by the Event Horizon Telescope. There are many modified gravity theories proposed to explain the accelerating expansion of the universe, generally ascribed to dark energy. However, Einstein’s cosmological constant is the simplest explanation for the accelerating expansion.

Properties of the Dark Energy

2005 ◽  
Vol 201 ◽  
pp. 255-259
Author(s):  
Peter M. Garnavich ◽  
Yun. Wang
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Cosmological Constant ◽  
Domain Walls ◽  
Accelerating Expansion ◽  
Systematic Effects ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Unknown Component

A non-zero cosmological constant is only one of many possible explanations for the observed accelerating expansion of the Universe. Any smoothly distributed, “dark” energy with a significant negative pressure can drive the acceleration. One possible culprit is a dynamical scalar field, but there are many less popular models such as tangled cosmic strings or domain walls. Soon theorists are likely to think up a number of new energies that can accelerate the expansion, meaning that only better observations can solve this question. Dark energy can be parameterized by its equation of state, w = p/ρ, which in the most general form can vary over time. Unlike the CMB, supernova observations cover a range of redshift so they can, in principle, probe the variation in the equation of state of the unknown component. The current SN observations loosely constrain the equation of state to w < −0.6, ruling out non-intercommuting strings and textures (w = −1/3), but consistent with a cosmological constant (w = −1). The constraints achievable from future large SN surveys are limited by our ability to understand systematic effects in SN Ia luminosities. But a large sample of supernovae reaching out to z ˜ 2 should at least discriminate between a cosmological constant and a dynamical scalar field as the source of the observed acceleration.

scholarly journals ON TOPOLOGICAL DEFECTS AND COSMOLOGICAL CONSTANT

2014 ◽  
Vol 29 (01) ◽  
pp. 1450007 ◽  
Author(s):  
B. RAYCHAUDHURI ◽  
F. RAHAMAN ◽  
M. KALAM
Keyword(s):  
Cosmological Constant ◽  
Vacuum Energy ◽  
Ad Hoc ◽  
Topological Defects ◽  
Field Equations ◽  
Theoretical Support ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

Einstein introduced cosmological constant in his field equations in an ad hoc manner. Cosmological constant plays the role of vacuum energy of the universe which is responsible for the accelerating expansion of the universe. To give a theoretical support, it remains an elusive goal to modern physicists. We provide a prescription to obtain cosmological constant from the phase transitions of the early universe when topological defects, namely monopole might have existed.

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