scholarly journals Cosmological models with squared trace in modified gravity

2020 ◽  
Vol 29 (15) ◽  
pp. 2050100
Author(s):  
B. Mishra ◽  
S. K. Tripathy ◽  
Saibal Ray
Keyword(s):  
Modified Gravity ◽  
Hubble Parameter ◽  
Energy Momentum Tensor ◽  
Cosmological Parameters ◽  
Momentum Tensor ◽  
Scale Factor ◽  
Specific Form ◽  
Cosmological Models ◽  
Modified Theory Of Gravity ◽  
Modified Theory

In this work, we present a few simple cosmological models under the modified theory of gravity in the particular form of [Formula: see text], where [Formula: see text] is the Ricci Scalar and [Formula: see text] is the trace of the energy–momentum tensor. Two special cosmological models are studied with (i) hyperbolic scale factor and (ii) specific form of the Hubble parameter. The models are observed to predict relevant cosmological parameters closer to the observational values. Both the models reduce to overlap with the [Formula: see text]CDM model at late times. We have discussed some interesting results related to wormhole solutions as evolved from our model. The possible occurrence of Big Trip in wormholes for the models are also discussed.

Gödel universe in f(R,T) gravity

2019 ◽  
Vol 28 (07) ◽  
pp. 1950089 ◽  
Author(s):  
Değer Sofuoğlu
Keyword(s):  
Arbitrary Function ◽  
Functional Form ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Ricci Scalar ◽  
Modified Theory Of Gravity ◽  
Theory Of Gravity ◽  
Tensor Formula ◽  
Modified Theory ◽  
Gödel Universe

In this study, we have considered Gödel universe in the context of [Formula: see text] modified theory of gravity, where the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar [Formula: see text] and the trace of the energy–momentum tensor [Formula: see text]. We have shown that the Gödel solution exists in this modified theory for more general functional form of [Formula: see text] function than it appears in the literature.

scholarly journals ON EXPONENTIAL MODIFIED GRAVITY

2013 ◽  
Vol 28 (24) ◽  
pp. 1350119 ◽  
Author(s):  
S. I. KRUGLOV
Keyword(s):  
Modified Gravity ◽  
Cosmological Parameters ◽  
De Sitter Space ◽  
De Sitter ◽  
Zero Curvature ◽  
Static Solutions ◽  
Modified Theory Of Gravity ◽  
Jordan And Einstein Frames ◽  
Modified Theory ◽  
Hilbert Action

A modified theory of gravity with the function F(R) = R exp (αR) instead of Ricci scalar R in the Einstein–Hilbert action is considered and analyzed. The action of the model is converted into Einstein–Hilbert action at small value of the parameter α. From local tests we obtain a bound on the parameter α ≤ 10-6 cm 2. The Jordan and Einstein frames are investigated and the potential of the scalar field in Einstein's frame is found. The mass of a scalar degree of freedom as a function of curvature is obtained. The static solutions of the model are found corresponding to the Schwarzschild–de Sitter space. We show that the de Sitter space is unstable but a solution with zero curvature is stable. The cosmological parameters of the model are calculated. It was demonstrated that the model passes the matter stability test.

Measure of complexity for dynamical self-gravitating structures

2020 ◽  
Vol 29 (09) ◽  
pp. 2050061
Author(s):  
Z. Yousaf ◽  
M. Z. Bhatti ◽  
T. Naseer
Keyword(s):  
Modified Gravity ◽  
Heat Dissipation ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Fluid Distribution ◽  
Source Terms ◽  
Matter Distribution ◽  
Structure Scalars ◽  
Definition Of ◽  
Modified Theory

We consider the definition of complexity for dynamical spherically self-gravitating matter distribution in the presence of heat dissipation introduced by Herrera [L. Herrera, A. Di Prisco and J. Ospino, Phys. Rev. D 98 (2018) 104059] and generalize it in [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] are the Ricci scalar and the trace of energy–momentum tensor, respectively. We measure the complexity of structure as well as pattern of evolution of the fluid distribution and examine these under the effects of dark source terms of modified gravity. Some dynamical and kinematical equations are observed in the dissipative and nondissipative cases in the background of modified theory. Finally, we discuss evolution of the structure scalars and stability of a condition where the complexity factor vanishes.

scholarly journals The cosmology in f(R,τ) gravity without dark energy

2016 ◽  
Vol 25 (03) ◽  
pp. 1650038 ◽  
Author(s):  
Gang Sun ◽  
Yong-Chang Huang
Keyword(s):  
Dark Energy ◽  
Ricci Curvature ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Scale Factor ◽  
Specific Form ◽  
Astronomical Observation ◽  
Distance Modulus ◽  
Observation Data ◽  
Adiabatic Condition

We examine the evolution of universe in [Formula: see text] gravity where [Formula: see text] is the Ricci curvature and [Formula: see text] is the trace of energy–momentum tensor. We focus on the specific form [Formula: see text] and explicitly find out the relation between [Formula: see text] and state of equation [Formula: see text] by adiabatic condition. All possible modes of evolution of the scale factor for the five kinds of state of equation, [Formula: see text] are exhibited. We simulate numerically the plots of redshift versus distance modulus for three interesting modes and then obtain the good fitting curve compared with the astronomical observation data.

Cosmological constant Λ in f(R,T) modified gravity

2016 ◽  
Vol 13 (05) ◽  
pp. 1650058 ◽  
Author(s):  
Gyan Prakash Singh ◽  
Binaya Kumar Bishi ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Cosmological Model ◽  
Cosmological Constant ◽  
Modified Gravity ◽  
Bianchi Type ◽  
Field Equations ◽  
Type Iii ◽  
Expansion Scalar ◽  
Modified Theory Of Gravity ◽  
Shear Scalar ◽  
Modified Theory

In this paper, we have studied the Bianchi type-III cosmological model in the presence of cosmological constant in the context of [Formula: see text] modified theory of gravity. Here, we have discussed two classes of [Formula: see text] gravity, i.e. [Formula: see text] and [Formula: see text]. In both classes, the modified field equations are solved by the relation expansion scalar [Formula: see text] that is proportional to shear scalar [Formula: see text] which gives [Formula: see text], where [Formula: see text] and [Formula: see text] are metric potentials. Also we have discussed some physical and kinematical properties of the models.

Charged gravastars in f(R,T,RμνTμν) gravity

2021 ◽  
pp. 2150084
Author(s):  
Z. Yousaf ◽  
M. Z. Bhatti
Keyword(s):  
Perfect Fluid ◽  
Energy Momentum Tensor ◽  
Equations Of State ◽  
Mathematical Formulation ◽  
Momentum Tensor ◽  
Spherically Symmetric ◽  
De Sitter ◽  
The Stability ◽  
Physical Features ◽  
Modified Theory

We explore the aspects of the electromagnetism on the stability of gravastar in a particular modified theory, i.e. [Formula: see text] where [Formula: see text], [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of energy–momentum tensor. We assume a spherically symmetric static metric coupled comprising of perfect fluid in the presence of electric charge. The purpose of this paper is to extend the results of [S. Ghosh, F. Rahaman, B. K. Guha and S. Ray, Phys. Lett. B 767 (2017) 380.] to highlight the effects of [Formula: see text] gravity in the formation of charged gravastars. We demonstrated the mathematical formulation, utilizing different equations of state, for the three respective regions (i.e. inner, shell, exterior) of the gravastar. We have matched smoothly the interior de Sitter and the exterior Reissner–Nordström metric at the hypersurface. At the end we extracted few conclusions by working on the physical features of the charged gravastar, mathematically and graphically.

The backreaction of massive scalar field on FLRW and de Sitter spaces

2020 ◽  
Vol 17 (03) ◽  
pp. 2050033
Author(s):  
M. R. Setare ◽  
M. Sahraee
Keyword(s):  
Scalar Field ◽  
Energy Momentum Tensor ◽  
Friedmann Equation ◽  
Vacuum Expectation ◽  
Momentum Tensor ◽  
Scale Factor ◽  
Massive Scalar ◽  
De Sitter ◽  
Massive Scalar Field ◽  
Quantum Energy

In this paper, we obtain the effect of backreaction on the scale factor of the Friedmann–Lemaître–Robertson–Walker (FLRW) and de Sitter spaces. We consider a non-minimally coupled massive scalar field to the curvature scalar. For our purpose, we use the results of vacuum expectation values of energy–momentum tensor, which have been obtained previously. By substituting the quantum energy density into the Friedmann equation, we obtain the linear order perturbation of the scale factor. So, the effect of backreaction leads to the new scale factor.

scholarly journals Rip cosmologies, wormhole solutions and big trip in the f(T,𝒯 ) theory of gravity

2020 ◽  
Vol 17 (08) ◽  
pp. 2050116 ◽  
Author(s):  
Maxime Z. Arouko ◽  
Ines G. Salako ◽  
A. D. Kanfon ◽  
M. J. S. Houndjo ◽  
Etienne Baffou
Keyword(s):  
Energy Momentum Tensor ◽  
Late Phase ◽  
Momentum Tensor ◽  
Cosmological Models ◽  
The Other ◽  
Throat Radius ◽  
Eos Parameter ◽  
Wormhole Throat ◽  
Initial Epoch ◽  
Theory Of Gravity

Rip cosmological models have been investigated in the framework of [Formula: see text] theory of gravity, where [Formula: see text] denotes the torsion and [Formula: see text] is the trace of the energy–momentum tensor. These phantom cosmological models revealed that at initial epoch a EoS parameter [Formula: see text] tends asymptotically at late phase to [Formula: see text] [Formula: see text]. On the other hand, Wormhole Solutions and Big Trip have been subject to an investigation. The wormhole throat radius [Formula: see text] and the conditions to be satisfied to produce the Big Trip phenomenon have been discussed.

Various dark energy models for variables G and Λ in f(R, T) modified theory

2019 ◽  
Vol 34 (13) ◽  
pp. 1950098 ◽  
Author(s):  
Can Aktaş
Keyword(s):  
Dark Energy ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Tachyon Field ◽  
Field Equations ◽  
Frw Universe ◽  
Linearly Varying Deceleration Parameter ◽  
Energy Models ◽  
Modified Theory ◽  
Friedmann Robertson Walker

In this paper, we have researched tachyon field, k-essence and quintessence dark energy (DE) models for Friedmann–Robertson–Walker (FRW) universe with varying G and [Formula: see text] in f(R, T) gravitation theory. The theory of f(R, T) is proposed by Harko et al. [Phys. Rev. D 84, 024020, 2011]. In this theory, R is the Ricci scalar and T is the trace of energy–momentum tensor. For the solutions of field equations, we have used linearly varying deceleration parameter (LVDP), the equation of state (EoS) and the ratio between [Formula: see text] and Hubble parameter. Also, we have discussed some physical behavior of the models with various graphics.

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