scholarly journals Energy Conditions in a Generalized Second-Order Scalar-Tensor Gravity

2013 ◽  
Vol 2013 ◽  
pp. 1-15 ◽  
Author(s):  
M. Sharif ◽  
Saira Waheed
Keyword(s):  
Second Order ◽  
Energy Conditions ◽  
Field Equations ◽  
Frw Universe ◽  
Tensor Theory ◽  
Modified Gravity Theories ◽  
General Scalar ◽  
General Relativistic ◽  
Fluid Matter ◽  
Free Parameters

The study of energy conditions has many significant applications in general relativistic and cosmological contexts. This paper explores the energy conditions in the framework of the most general scalar-tensor theory with field equations involving second-order derivatives. For this purpose, we use flat FRW universe model with perfect fluid matter contents. By taking power law ansatz for scalar field, we discuss the strong, weak, null, and dominant energy conditions in terms of deceleration, jerk, and snap parameters. Some particular cases of this theory likek-essence model, modified gravity theories and so forth. are analyzed with the help of the derived energy conditions, and the possible constraints on the free parameters of the presented models are determined.

A NOETHER SYMMETRY STUDY IN SCALAR-TENSOR THEORY

1998 ◽  
Vol 13 (24) ◽  
pp. 4163-4171 ◽  
Author(s):  
B. MODAK ◽  
S. KAMILYA ◽  
S. BISWAS
Keyword(s):  
General Relativity ◽  
Functional Form ◽  
Noether Symmetry ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Tensor Theory ◽  
Exponential Expansion ◽  
General Scalar ◽  
Spatially Homogeneous ◽  
The Universe

In this work we study a general scalar-tensor theory in which the coupling and potential functions are determined from Noether symmetry arguments. We also obtain exact solutions of the field equations and found that the universe asymptotically follows an exponential expansion having no graceful exit. The study of the functional form of ω(φ) reveals that the theory asymptotically becomes an attractor of general relativity. We restrict ourselves to spatially homogeneous, isotropic flat universe.

Conformally symmetric Friedmann–Robertson–Walker metric in f(R,T) gravity

2020 ◽  
Vol 35 (10) ◽  
pp. 2050067
Author(s):  
Dog̃ukan Taṣer
Keyword(s):  
Perfect Fluid ◽  
Conformal Symmetry ◽  
Killing Vector ◽  
Energy Condition ◽  
Gravitational Theory ◽  
Cosmic Acceleration ◽  
Energy Conditions ◽  
Conformal Killing ◽  
Field Equations ◽  
Frw Universe

In this paper, conformal symmetric Freidmann–Robertson–Walker (FRW) universe with perfect fluid in the framework of [Formula: see text] gravitational theory is investigated. Firstly, field equations of FRW universe with perfect fluid are obtained for [Formula: see text] modified theory of gravity. The field equations of the model have been revised to understand physical nature between matter and geometry by means of conformal symmetry in [Formula: see text] gravitational theory. The exact solutions of conformal FRW universe with perfect fluid are attained for matter part of the [Formula: see text] model in the case of [Formula: see text]. The [Formula: see text] gravitational theory is one of the acceptable modifications of General Relativity (GR) in order to expound cosmic acceleration of the universe with no needing any exotic component. Nevertheless, the obtained model indicates exotic matter distribution for the current selection of arbitrary constants. Also, different value selections of arbitrary constants for the obtained model are able to predicate expanding or contracting universe with zero deceleration. Besides, it is shown that the FRW universe under the influence of the conformal Killing vector preserves to isotropic nature. Energy conditions are investigated. Also, it is shown that the constructed model satisfies strong energy condition (SEC) in all cases.

Bounce conditions in Kantowski–Sachs and Bianchi cosmologies in modified gravity theories

2015 ◽  
Vol 30 (14) ◽  
pp. 1550073 ◽  
Author(s):  
T. Singh ◽  
R. Chaubey ◽  
Ashutosh Singh
Keyword(s):  
Bianchi Type ◽  
Lyra Geometry ◽  
Energy Conditions ◽  
Modified Theories Of Gravity ◽  
Variable Cosmological Term ◽  
Bouncing Universe ◽  
Modified Gravity Theories ◽  
General Relativistic ◽  
Theories Of Gravity ◽  
The Universe

Many cosmological scenarios envisage either a bounce of the universe at early times, or a collapse locally to form a black hole which re-expands into a new expanding universe region. Energy conditions preclude this phenomena for ordinary matter in general relativistic universe, but scalar or other types of fields can violate some of these conditions, and so can, possibly, provide conditions for a bouncing universe. In this paper, we have investigated the necessary conditions for a bounce in Kantowski–Sachs (KS) and Bianchi type models in some modified theories of gravity like Hoyle–Narlikar creation field theory, Lyra geometry, general class of scalar–tensor theories, Einstein's theory with variable cosmological term.

scholarly journals The most general second-order field equations of bi-scalar-tensor theory in four dimensions

2015 ◽  
Vol 2015 (7) ◽  
Author(s):  
Seiju Ohashi ◽  
Norihiro Tanahashi ◽  
Tsutomu Kobayashi ◽  
Masahide Yamaguchi
Keyword(s):  
Second Order ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Four Dimensions ◽  
Tensor Theory

scholarly journals Does general relativity highlight necessary connections in nature?

Synthese ◽  
2021 ◽  
Author(s):  
Antonio Vassallo
Keyword(s):  
General Relativity ◽  
Laws Of Nature ◽  
Coupling Mechanism ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Bianchi Identities ◽  
Physical Role ◽  
General Relativistic ◽  
Differential Relations ◽  
Necessary Connections

AbstractThe dynamics of general relativity is encoded in a set of ten differential equations, the so-called Einstein field equations. It is usually believed that Einstein’s equations represent a physical law describing the coupling of spacetime with material fields. However, just six of these equations actually describe the coupling mechanism: the remaining four represent a set of differential relations known as Bianchi identities. The paper discusses the physical role that the Bianchi identities play in general relativity, and investigates whether these identities—qua part of a physical law—highlight some kind of a posteriori necessity in a Kripkean sense. The inquiry shows that general relativistic physics has an interesting bearing on the debate about the metaphysics of the laws of nature.

scholarly journals Post-Newtonian limit: second-order Jefimenko equations

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
David Pérez Carlos ◽  
Augusto Espinoza ◽  
Andrew Chubykalo
Keyword(s):  
Linear Equations ◽  
Space Time ◽  
Second Order ◽  
Field Equations ◽  
Gravitational Fields ◽  
Mass Distributions ◽  
Minkowski Space Time ◽  
Theory Of Gravitation ◽  
Gravity Probe ◽  
Gravitational Equations

Abstract The purpose of this paper is to get second-order gravitational equations, a correction made to Jefimenko’s linear gravitational equations. These linear equations were first proposed by Oliver Heaviside in [1], making an analogy between the laws of electromagnetism and gravitation. To achieve our goal, we will use perturbation methods on Einstein field equations. It should be emphasized that the resulting system of equations can also be derived from Logunov’s non-linear gravitational equations, but with different physical interpretation, for while in the former gravitation is considered as a deformation of space-time as we can see in [2–5], in the latter gravitation is considered as a physical tensor field in the Minkowski space-time (as in [6–8]). In Jefimenko’s theory of gravitation, exposed in [9, 10], there are two kinds of gravitational fields, the ordinary gravitational field, due to the presence of masses, at rest, or in motion and other field called Heaviside field due to and acts only on moving masses. The Heaviside field is known in general relativity as Lense-Thirring effect or gravitomagnetism (The Heaviside field is the gravitational analogous of the magnetic field in the electromagnetic theory, its existence was proved employing the Gravity Probe B launched by NASA (See, for example, [11, 12]). It is a type of gravitational induction), interpreted as a distortion of space-time due to the motion of mass distributions, (see, for example [13, 14]). Here, we will present our second-order Jefimenko equations for gravitation and its solutions.

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