scholarly journals Charged wormholes in f(R,T)-extended theory of gravity

2019 ◽  
Vol 28 (08) ◽  
pp. 1950098 ◽  
Author(s):  
P. H. R. S. Moraes ◽  
W. de Paula ◽  
R. A. C. Correa
Keyword(s):  
Degrees Of Freedom ◽  
Matter Content ◽  
Nonlinear Electrodynamics ◽  
Energy Conditions ◽  
Field Equations ◽  
Extended Theory ◽  
Extended Theories Of Gravity ◽  
Theories Of Gravity ◽  
Theory Of Gravity ◽  
Physical Quantities

Wormholes (WHs) are a solution for General Relativity field equations which characterize a passage or tunnel that connects two different regions of spacetime and is filled by some sort of exotic matter that does not satisfy the energy conditions. On the other hand, it is known that in extended theories of gravity, the extra degrees of freedom once provided may allow the energy conditions to be obeyed and, consequently, the matter content of the WH to be nonexotic. In this work, we obtain, as a novelty in the literature, solutions for charged WHs in the [Formula: see text]-extended theory of gravity. We show that the presence of charge in these objects may be a possibility to respect some stability conditions for their metric. Also, remarkably, the energy conditions are respected in the present approach. In addition, we argue that our framework can be very useful to study the possibility of evolving [Formula: see text] and [Formula: see text]-dimensional WH spacetime within the context of nonlinear electrodynamics, which open a new window to probe the physical quantities in a WH-type solution.

scholarly journals Evaporation/Antievaporation and energy conditions in alternative gravity

2018 ◽  
Vol 33 (04) ◽  
pp. 1850030 ◽  
Author(s):  
Andrea Addazi
Keyword(s):  
General Relativity ◽  
Degrees Of Freedom ◽  
Energy Conditions ◽  
Raychaudhuri Equation ◽  
Bonnet Gravity ◽  
Extended Theories Of Gravity ◽  
Theories Of Gravity ◽  
Extended Theories ◽  
Alternative Gravity

We discuss the evaporation and antievaporation instabilities of Nariai solution in extended theories of gravity. These phenomena were explicitly shown in several different extensions of General Relativity, suggesting that a universal cause is behind them. We show that evaporation and antievaporation are originated from deformations of energy conditions on the Nariai horizon. Energy conditions get new contributions from the extra propagating degrees of freedom, which can provide extra focalizing or antifocalizing terms in the Raychaudhuri equation. We show the two explicit cases of [Formula: see text]-gravity and Gauss–Bonnet gravity.

scholarly journals Gravitational waves in the extended theory of gravity

2021 ◽  
Author(s):  
Sourav Roy Chowdhury ◽  
Maxim Khlopov
Keyword(s):  
General Relativity ◽  
Gravitational Waves ◽  
Degrees Of Freedom ◽  
Standard Theory ◽  
New Approach ◽  
Extended Theories Of Gravity ◽  
Theories Of Gravity ◽  
Theory Of Gravity ◽  
New Formula ◽  
Extended Theories

Extended theories of gravity are considered as a new approach for solving the infrared and ultraviolet scale problems; the standard theory of gravity (general relativity) and observational evidence of gravitational waves and subsequent identification of the number of existing polarizations are an effective tool for testing general relativity and extended theories of gravity. The Newman–Penrose method is used to characterize the polarization modes for specific forms of [Formula: see text] in the present study. Both the forms of the [Formula: see text] theory belong to far more general variational class of gravitational waves, capable of presenting up to six separate polarizations states. We have introduced a new [Formula: see text] gravity model as an attempt to have a theory with more parametric regulations so that the model can be used to describe existing issues and discover different directions in gravity physics. The primary goal of this research is to look into the properties of gravitational waves with new cases. The model shows the existence of scalar degrees of freedom in [Formula: see text] gravity metric notation.

scholarly journals Investigating $f(R)$ gravity and cosmologies

2021 ◽  
Author(s):  
Vaibhav Kalvakota
Keyword(s):  
General Relativity ◽  
Lagrangian Density ◽  
Ricci Scalar ◽  
Metric Tensor ◽  
Extended Theory ◽  
Theories Of Gravity ◽  
Theory Of Gravity ◽  
Hilbert Action ◽  
Geometric Nature

The f (R) theory of gravity is an extended theory of gravity that is based on general relativity in the simplest case of $f(R) = R$. This theory extends such a function of the Ricci scalar into arbitrary functions that are not necessarily linear, i.e. could be of the form $f(R) = \alpha R^{2}$. The action for such a theory would be $S_{EH} = \frac{1}{2k} \int f(R) + L^{m}\; d^{4}x\sqrt{−g}$, where $S_{EH}$ is the Einstein-Hilbert action for our theory, $g$ is the determinant of the metric tensor $g_{\mu \nu}$ and $L^{m}$ is the Lagrangian density for matter. In this paper, we will look at some of the physical implications of such a theory, and the importance of such a theory in cosmology and in understanding the geometric nature of such f (R) theories of gravity.

Models of non-static and inhomogeneous gravitating source in Rastall gravity

2021 ◽  
Vol 18 (03) ◽  
pp. 2150042
Author(s):  
G. Abbas ◽  
M. Tahir ◽  
M. R. Shahzad
Keyword(s):  
Gravitational Collapse ◽  
Mass Function ◽  
Energy Conditions ◽  
Parametric Form ◽  
Field Equations ◽  
Expansion Formula ◽  
Spherical Source ◽  
Expansion Scalar ◽  
Theory Of Gravity ◽  
Trapped Surface

In this paper, we have explored the non-static anisotropic gravitational collapse and expansion solutions in Rastall theory of gravity. The field equations have been formulated for the non-static and inhomogeneous gravitating source. The Misner–Sharp mass function, auxiliary solution and trapped condition have been used to obtained a trapped surface. The auxiliary solutions have been used to obtain the expansion and collapse solutions; these solutions depend on [Formula: see text] and parameter [Formula: see text] (which appears due to parametric form of metric components); also the range of parameter [Formula: see text] has been examined. The expansion scalar [Formula: see text] depends on parameter [Formula: see text], in the case of expansion [Formula: see text] for [Formula: see text], while for collapse [Formula: see text] with [Formula: see text]. Also, the dynamics of the gravitating spherical source has been discussed graphically with the effects of Rastall parameter [Formula: see text]. For the physically reasonable fluid, the validity of energy conditions has been discussed for expansion and collapse solutions with the various values of [Formula: see text].

scholarly journals Scalar–tensor theories of gravity: validity of the cosmic no-hair conjecture

2011 ◽  
Vol 89 (9) ◽  
pp. 937-940
Author(s):  
Sudeshna Mukerji ◽  
Nairwita Mazumder ◽  
Ritabrata Biswas ◽  
Subenoy Chakraborty
Keyword(s):  
Coupling Parameter ◽  
Matter Field ◽  
Einstein Frame ◽  
Energy Conditions ◽  
Jordan Frame ◽  
Scalar Tensor Theory ◽  
Bianchi Models ◽  
Tensor Theory ◽  
Theories Of Gravity ◽  
Theory Of Gravity

This paper deals with the cosmic no-hair conjecture for anisotropic Bianchi models in the scalar–tensor theory of gravity. Herein, we have considered both the Jordan frame and the Einstein frame to describe the scalar–tensor theory of gravity and examine the conjecture. In the Jordan frame, one should restrict both the coupling function of the scalar field and the coupling parameter, in addition to the usual energy conditions for the matter field, to maintain the validity of the cosmic no-hair conjecture, while in the Einstein frame, the restrictions are purely on the energy conditions.

scholarly journals GRAVITATIONAL CHERENKOV RADIATION FROM EXTENDED THEORIES OF GRAVITY

2012 ◽  
Vol 27 (23) ◽  
pp. 1250136 ◽  
Author(s):  
M. DE LAURENTIS ◽  
S. CAPOZZIELLO ◽  
G. BASINI
Keyword(s):  
Cherenkov Radiation ◽  
Higher Order ◽  
Ricci Scalar ◽  
Field Equations ◽  
Massless Spin ◽  
Extended Theories Of Gravity ◽  
Theories Of Gravity ◽  
Scalar Invariants ◽  
Extended Theories

We linearize the field equations for higher order theories of gravity that contain scalar invariants other than the Ricci scalar. We find that besides a massless spin-2 field (the standard graviton), the theory contains also spin-0 and spin-2 massive modes with the latter being, in general, ghost modes. The rate at which such particles would emit gravitational Cherenkov radiation is calculated for some interesting physical cases.

scholarly journals To Conserve, or Not to Conserve: A Review of Nonconservative Theories of Gravity

Universe ◽  
2021 ◽  
Vol 7 (2) ◽  
pp. 38
Author(s):  
Hermano Velten ◽  
Thiago R. P. Caramês
Keyword(s):  
Conservation Law ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Additional Constraint ◽  
Field Equations ◽  
Relativistic Field ◽  
Extended Theories Of Gravity ◽  
General Relativistic ◽  
Theories Of Gravity ◽  
Extended Theories

Apart from the familiar structure firmly-rooted in the general relativistic field equations where the energy–momentum tensor has a null divergence i.e., it conserves, there exists a considerable number of extended theories of gravity allowing departures from the usual conservative framework. Many of these theories became popular in the last few years, aiming to describe the phenomenology behind dark matter and dark energy. However, within these scenarios, it is common to see attempts to preserve the conservative property of the energy–momentum tensor. Most of the time, it is done by means of some additional constraint that ensures the validity of the standard conservation law, as long as this option is available in the theory. However, if no such extra constraint is available, the theory will inevitably carry a non-trivial conservation law as part of its structure. In this work, we review some of such proposals discussing the theoretical construction leading to the non-conservation of the energy–momentum tensor.

scholarly journals f(R) View of Lyttleton-Bondi Cosmological Model in Peres Spacetime

2014 ◽  
Vol 8 ◽  
pp. 23-29
Author(s):  
S.N. Pandey ◽  
Sacheendra Shukla
Keyword(s):  
Cosmological Model ◽  
Gravitational Waves ◽  
Field Equations ◽  
Einstein Theory ◽  
Conformally Invariant ◽  
Theories Of Gravity ◽  
Theory Of Gravity

Over the last few years, among various alternatives to the Einstein theory of gravity, especially f(R) theories of gravity have received more importance due to number of interesting results in cosmology and astrophysics. Pandey [10] gave an f(R) theory of gravity to obtain conformally invariant gravitational waves in which field equations have the form given by (3). In this paper we have investigated Lyttleton Bondi Cosmological model in view of field equations of f(R) theory of gravity for Generalized Peres spacetime and finally a wave like solution is obtained.

scholarly journals A periodic varying deceleration parameter in f(R, T) gravity

2018 ◽  
Vol 33 (33) ◽  
pp. 1850193 ◽  
Author(s):  
P. K. Sahoo ◽  
S. K. Tripathy ◽  
Parbati Sahoo
Keyword(s):  
Deceleration Parameter ◽  
Momentum Conservation ◽  
Momentum Tensor ◽  
Oscillatory Behavior ◽  
Matter Content ◽  
Accelerated Expansion ◽  
Energy Conditions ◽  
Field Equations ◽  
Eos Parameter ◽  
Wide Range

The phenomenon of accelerated expansion of the present universe and a cosmic transit aspect is explored in the framework of a modified gravity theory known as f(R, T) gravity (where R is the Ricci scalar and T is the trace of the energy–momentum tensor of the matter content). The cosmic transit phenomenon signifies a signature flipping behavior of the deceleration parameter. We employ a periodic varying deceleration parameter and obtained the exact solution of field equations. The dynamical features of the model including the oscillatory behavior of the EOS parameter are studied. We have also explored the obvious violation of energy–momentum conservation in f(R, T) gravity. The periodic behavior of energy conditions for the model are also discussed with a wide range of the free parameters.

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