Cosmology in f(R, T) gravity with quadratic deceleration parameter

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Binaya K. Bishi ◽  
Aroonkumar Beesham ◽  
Kamal L. Mahanta
Keyword(s):  
Quadratic Form ◽  
Observational Data ◽  
Deceleration Parameter ◽  
Cosmic Time ◽  
Red Shift ◽  
Energy Conditions ◽  
Diagnostic Analysis ◽  
Field Equations ◽  
Om Diagnostic ◽  
Proposed Model

Abstract In this work, we have developed FLRW cosmological models in f(R, T) gravity. The solution of the modified field equations are obtained under the newly proposed Bakry and Shafeek, “The periodic universe with varying deceleration parameter of the second degree,” Astrophys. Space Sci., vol. 364, p. 135, 2019, quadratic form of the deceleration parameter. Further, we have discussed the state-finder parameter, om-diagnostic analysis and energy conditions of the proposed model. The variation of deceleration parameter with respect to cosmic time and red-shift is consistent with observational data.

scholarly journals Cylindrically Symmetric, Asymptotically Flat, Petrov Type D Spacetime with a Naked Curvature Singularity and Matter Collapse

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Faizuddin Ahmed
Keyword(s):  
Cosmic Time ◽  
Petrov Type ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Curvature Singularity ◽  
Field Equations ◽  
Asymptotically Flat ◽  
Type D ◽  
Cylindrically Symmetric ◽  
Petrov Type D

We present a cylindrically symmetric, Petrov type D, nonexpanding, shear-free, and vorticity-free solution of Einstein’s field equations. The spacetime is asymptotically flat radially and regular everywhere except on the symmetry axis where it possesses a naked curvature singularity. The energy-momentum tensor of the spacetime is that for an anisotropic fluid which satisfies the different energy conditions. This spacetime is used to generate a rotating spacetime which admits closed timelike curves and may represent a Cosmic Time Machine.

Analysis of compact stars in logarithmic-corrected R2 gravity

2019 ◽  
Vol 35 (02) ◽  
pp. 1950354 ◽  
Author(s):  
M. Farasat Shamir ◽  
Iffat Fayyaz
Keyword(s):  
Graphical Representation ◽  
Stellar Model ◽  
Compact Stars ◽  
Energy Conditions ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Logarithmic Corrections ◽  
Proposed Model ◽  
Physical Tests ◽  
Surface Redshift

We discuss the existence of compact stars in the context of [Formula: see text] gravity model, where additional logarithmic corrections are assumed. Here, [Formula: see text] is the Ricci scalar and [Formula: see text], [Formula: see text] are constant values. Further, the compact stars are considered to be anisotropic in nature, due to the spherical symmetry and high density. For this purpose, we derive the Einstein field equations by considering Krori–Barua spacetime. For our proposed model, the physical acceptability is verified by employing several physical tests like the energy conditions, Herrera cracking concept and stability condition. In addition to this, we also discuss some important properties such as mass–radius relation, surface redshift and the speed of sound are analyzed. Our results are compared with observational stellar mass data, namely, 4U 1820-30, Cen X-3, EXO 1785-248 and LMC X-4. The graphical representation of obtained solutions provide strong evidences for more realistic and viable stellar model.

On a Bianchi type-I space-time with bulk viscosity in f(R,T) gravity

2021 ◽  
Author(s):  
M. Koussour ◽  
M. Bennai
Keyword(s):  
Deceleration Parameter ◽  
Bianchi Type ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Type I ◽  
Field Equations ◽  
Bulk Fluid ◽  
Bianchi Type I ◽  
Deceleration Phase ◽  
Spatially Homogeneous

In this paper, we present a spatially homogeneous and anisotropic Bianchi type-I cosmological model with a viscous bulk fluid in [Formula: see text] gravity where [Formula: see text] and [Formula: see text] are the Ricci scalar and trace of the energy-momentum tensor, respectively. The field equations are solved explicitly using the hybrid law of the scale factor, which is related to the average Hubble parameter and gives a time-varying deceleration parameter (DP). We found the deceleration parameter describing two phases in the universe, the early deceleration phase [Formula: see text] and the current acceleration phase [Formula: see text]. We have calculated some physical and geometric properties and their graphs, whether in terms of time or redshift. Note that for our model, the bulk viscous pressure [Formula: see text] is negative and the energy density [Formula: see text] is positive. The energy conditions and the [Formula: see text] analysis for our spatially homogeneous and anisotropic Bianchi type-I model are also discussed.

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.

scholarly journals A reconstruction of modified holographic Ricci dark energy in f(R, T) gravity

2013 ◽  
Vol 91 (8) ◽  
pp. 632-638 ◽  
Author(s):  
Antonio Pasqua ◽  
Surajit Chattopadhyay ◽  
Iuliia Khomenko
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Cosmic Time ◽  
State Parameter ◽  
Diagnostic Analysis ◽  
Ricci Dark Energy ◽  
First Derivative ◽  
Proposed Model ◽  
Equation Of State Parameter ◽  
The Universe

In this paper, we consider a recently proposed model of dark energy (DE) know as modified holographic Ricci DE (which is function of the Hubble parameter and its first derivative with respect to cosmic time, t) in light of the f(R, T) model of modified gravity, considering the particular model f(R, T) = μR + νT, with μ and ν constants. The equation of state parameter ωΛ approaches but never reaches the value −1, implying a quintessence-like behavior of the model. The deceleration parameter q passes from decelerated to accelerated phase at a redshift of z ≈ 0.2, showing also a small dependence from the values of the parameters considered. Thanks to the statefinder diagnostic analysis, we observed that the ΛCDM phase for the considered model is attainable. We observed that the fractional energy densities for DE and dark matter, ΩΛ and Ωm, have an increasing and a decreasing pattern, respectively, with the evolution of the universe, indicating an evolution from matter to DE dominated universe. Finally, studying the squared speed of the sound [Formula: see text] for our model, we found that it is classically stable.

scholarly journals Dark Energy Constraints on Red-Shift-Based Gravity

2013 ◽  
Vol 2013 ◽  
pp. 1-8
Author(s):  
Setareh Dabbaghchian ◽  
Reza Saffari
Keyword(s):  
Dark Energy ◽  
Deceleration Parameter ◽  
Dark Energy Model ◽  
Taylor Expansion ◽  
Red Shift ◽  
Specific Function ◽  
Field Equations ◽  
Energy Models ◽  
Expansion Coefficients ◽  
Reconstructed Function

We have studied cosmological dynamics in gravity theory via cosmographic parameters. We have changed variables of field equations from time to red-shift and solved the achieved differential equation analytically for . Then we have used Taylor expansion to find general form of function around the present day value of scalar curvature. By introducing we would simplify our calculations; if we consider as a given function we would restrict our answers of . In this paper we offer a linear form of which leads us to a specific function, where is a constant which depends on the present day value of deceleration parameter. As an example, using Taylor expansion coefficients, we have compared our analytically calculated function with reconstructed function for Dark Energy models. To reconstruct action for Dark Energy models, we have used corresponding of each Dark Energy model for calculating Taylor expansion coefficients. As our function is linear, the Taylor expansion coefficients would be a function of present day value of deceleration parameter.

Magnetized string cosmological models of accelerated expansion of the Universe in f(R,T) theory of gravity

2018 ◽  
Vol 15 (05) ◽  
pp. 1850076 ◽  
Author(s):  
Anirudh Pradhan ◽  
Rekha Jaiswal
Keyword(s):  
Modified Gravity ◽  
Deceleration Parameter ◽  
Accelerated Expansion ◽  
Energy Conditions ◽  
Field Equations ◽  
Cosmological Perturbation ◽  
Spatial Direction ◽  
Theory Of Gravity ◽  
String Models ◽  
The Universe

A class of spatially homogeneous and anisotropic Bianchi-V massive string models have been studied in the modified [Formula: see text]-theory of gravity proposed by Harko et al. [Phys. Rev. D 84:024020, 2011] in the presence of magnetic field. For a specific choice of [Formula: see text], where [Formula: see text] and [Formula: see text]; [Formula: see text], [Formula: see text] being arbitrary parameters, solutions of modified gravity field equations have been generated. To find the deterministic solution of the field equations, we have considered the time varying deceleration parameter which is consistent with observational data of standard cosmology (SNIa, BAO and CMB). As a result to study the transit behavior of Universe, we consider a law of variation for the specifically chosen scale factor, which yields a time-dependent deceleration parameter comprising a class of models that depicts a transition of the Universe from the early decelerated phase to the recent accelerating phase. In this context, for the model of the Universe, the field equations are solved and corresponding cosmological aspects have been discussed. The Energy conditions in this modified gravity theory are also studied. Stability analysis of the solutions through cosmological perturbation is performed and it is concluded that the expanding solution is stable against the perturbation with respect to anisotropic spatial direction. Some physical and geometric properties of the models are also discussed.

Brans–Dicke scalar field cosmological model in Lyra’s geometry with time-dependent deceleration parameter

2018 ◽  
Vol 15 (11) ◽  
pp. 1850186
Author(s):  
Rashid Zia ◽  
Dinesh Chandra Maurya
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Deceleration Parameter ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Physical Parameters ◽  
Type I ◽  
Field Equations ◽  
Modified Gravity Theory ◽  
Lyra’S Geometry

From the recent observations, it is well known that the expansion rate of our universe varies with time (early decelerating and accelerating in the present epoch) which is an unsolved problem. This motivated to us to consider this paper and so we have developed a new cosmological model in Einstein’s modified gravity theory using two types of modifications: (i) Geometrical modification, in which we have used Lyra’s geometry in the curvature part of the Einstein field equations (EFE) and (ii) Modification in gravity (energy momentum tensor) on right hand side of EFE, as per the Brans–Dicke model. With these two modifications, we have obtained the exact solutions of Einstein Brans–Dicke field equations in Lyra’s geometry for a spatially homogeneous Bianchi type-I space-time with time variable deceleration parameter (DP). We have calculated various physical parameters for the model and found them consistent with recent observations. We have also examined the energy conditions for the model and found them satisfactory. We have found that the scalar field of Brans–Dicke theory behaves like a best fit dark energy candidate in the reference of Lyra’s geometry.

Cosmology in modified f(R,T)-gravity theory in a variant Λ(T) scenario-revisited

2017 ◽  
Vol 15 (01) ◽  
pp. 1850014 ◽  
Author(s):  
Umesh Kumar Sharma ◽  
Anirudh Pradhan
Keyword(s):  
Deceleration Parameter ◽  
Cosmic Time ◽  
Early Time ◽  
Momentum Tensor ◽  
Cosmological Models ◽  
Field Equations ◽  
Linearly Varying Deceleration Parameter ◽  
Stress Energy ◽  
Modified Formula ◽  
Stress Energy Momentum Tensor

Three new cosmological models of the present Universe are obtained with [Formula: see text] modified theory of gravity proposed by Harko et al. [Phys. Rev. D 84 (2011) 024020, arXiv:1104.2669 [gr-qc]] in a general class of Bianchi space-time. In this paper, we have generalized the modified [Formula: see text] field equations with [Formula: see text]-gravity, where [Formula: see text] and [Formula: see text] denote the curvature scalar and the trace of the stress–energy–momentum tensor, respectively. To find the deterministic solutions we have considered the linearly varying deceleration parameter [Formula: see text] proposed by Akarsu and Dereli [Cosmological models with linearly varying deceleration parameter, Int. J. Theor. Phys. 51 (2011) 612]. We have made the analyses of the variation of pressure, energy density and cosmological term with cosmic time. It is observed that our derived models are unstable in early time whereas they are stable at late and future time (i.e. at present epoch). The physical and geometric properties of all three models are studied in detail.

scholarly journals Magnetized strange quark model with Big Rip singularity in f(R, T) gravity

2017 ◽  
Vol 32 (21) ◽  
pp. 1750105 ◽  
Author(s):  
P. K. Sahoo ◽  
Parbati Sahoo ◽  
Binaya K. Bishi ◽  
S. Aygün
Keyword(s):  
Observational Data ◽  
Deceleration Parameter ◽  
Strange Quark ◽  
Big Bang ◽  
Distance Modulus ◽  
Type I ◽  
Field Equations ◽  
Big Rip ◽  
Standard Cosmology ◽  
Rotationally Symmetric

Locally rotationally symmetric (LRS) Bianchi type-I magnetized strange quark matter (SQM) cosmological model has been studied based on f(R, T) gravity. The exact solutions of the field equations are derived with linearly time varying deceleration parameter, which is consistent with observational data (from SNIa, BAO and CMB) of standard cosmology. It is observed that the model begins with big bang and ends with a Big Rip. The transition of the deceleration parameter from decelerating phase to accelerating phase with respect to redshift obtained in our model fits with the recent observational data obtained by Farook et al. [Astrophys. J. 835, 26 (2017)]. The well-known Hubble parameter H(z) and distance modulus [Formula: see text](z) are discussed with redshift.

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