scholarly journals Dynamics of an Anisotropic Universe inf(R,T)Theory

2016 ◽  
Vol 2016 ◽  
pp. 1-8 ◽  
Author(s):  
B. Mishra ◽  
Sankarsan Tarai ◽  
S. K. Tripathy
Keyword(s):  
Power Law ◽  
Modified Gravity ◽  
Bianchi Type ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Model Parameters ◽  
Anisotropic Universe ◽  
Expansion Of The Universe ◽  
Physical Features ◽  
The Universe

Dynamics of an anisotropic universe is studied inf(R,T)gravity using a rescaled functionalf(R,T), whereRis the Ricci Scalar andTis the trace of energy-momentum tensor. Three models have been constructed assuming a power law expansion of the universe. Physical features of the models are discussed. The model parameters are constrained from a dimensional analysis. It is found from the work that the anisotropic Bianchi typeVIh(BVIh) model in the modified gravity generally favours a quintessence phase when the parameterhis either-1or0. We may not get viable models in conformity with the present day observation forh=1.

scholarly journals Cosmological reconstruction of f(T, 𝒯) gravity

2014 ◽  
Vol 11 (08) ◽  
pp. 1450077 ◽  
Author(s):  
Davood Momeni ◽  
Ratbay Myrzakulov
Keyword(s):  
Scalar Field ◽  
Modified Gravity ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Chaplygin Gas ◽  
Massless Scalar ◽  
Massless Scalar Field ◽  
Two Fluids ◽  
Consistent Model ◽  
The Universe

Motivated by the newly proposal for gravity as the effect of the torsion scalar T and trace of the energy momentum tensor 𝒯, we investigate the cosmological reconstruction of different models of the Universe. Our aim here is to show that how this modified gravity model, f(T, 𝒯) is able to reproduce different epochs of the cosmological history. We explicitly show that f(T, 𝒯) can be reconstructed for ΛCDM as the most popular and consistent model. Also we study the mathematical reconstruction of f(T, 𝒯) for a flat cosmological background filled by two fluids mixture. Such model describes phantom–non-phantom era as well as the purely phantom cosmology. We extend our investigation to more cosmological models like perfect fluid, Chaplygin gas and massless scalar field. In each case we obtain some specific forms of f(T, 𝒯). These families of f(T, 𝒯) contain arbitrary function of torsion and trace of the energy momentum.

scholarly journals Bianchi Type I Cosmological Models with Expansion Driven by Particle Creation

2018 ◽  
Author(s):  
Kalyani Desikan
Keyword(s):  
Bianchi Type ◽  
Energy Momentum Tensor ◽  
Particle Creation ◽  
Momentum Tensor ◽  
Conservation Equation ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Energy Conservation Equation ◽  
The Universe

A study of Bianchi Type I cosmological model is undertaken in the framework of creation of particles. To accommodate the creation of new particles, the universe is regarded as an Open thermodynamical system. The energy conservation equation is modified with the incorporation of a creation pressure in the energy momentum tensor. Exact solutions of the field equations are obtained (i) for a particular choice of the particle creation function and (ii) by considering the deceleration parameter to be constant. In the first model the behavior of the solution at late times is investigated. The physical aspects of the model have also been discussed. In the case of the second model we have restricted our analysis to the power law behaviour for the average scale factor. This leads to a particular form for the particle creation function. The behavior of the solution is investigated and the physical aspects of the model have also been discussed for the matter dominated era.

scholarly journals A Cosmological Scenario from the Starobinsky Model within the f(R,T) Formalism

2019 ◽  
Vol 2019 ◽  
pp. 1-8 ◽  
Author(s):  
P. H. R. S. Moraes ◽  
P. K. Sahoo ◽  
G. Ribeiro ◽  
R. A. C. Correa
Keyword(s):  
Functional Form ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Starobinsky Model ◽  
Cosmological Scenario ◽  
Expansion Of The Universe ◽  
Theory Of Gravitation ◽  
Free Parameters ◽  
The Universe

In this paper we derive a novel cosmological model from the f(R,T) theory of gravitation, for which R is the Ricci scalar and T is the trace of the energy-momentum tensor. We consider the functional form f(R,T)=f(R)+f(T), with f(R) being the Starobinsky Model, named R+αR2, and f(T)=2γT, with α and γ being constants. We show that a hybrid expansion law form for the scale factor is a solution for the derived Friedmann-like equations. In this way, the model is able to predict both the decelerated and the accelerated regimes of expansion of the universe, with the transition redshift between these stages being in accordance with recent observations. We also apply the energy conditions to our material content solutions. Such an application makes us able to obtain the range of acceptability for the free parameters of the model, named α and γ.

scholarly journals Effects of Rastall parameter on perturbation of dark sectors of the Universe

2021 ◽  
pp. 2150082
Author(s):  
A. H. Ziaie ◽  
H. Shabani ◽  
S. Ghaffari
Keyword(s):  
Modified Gravity ◽  
Numerical Solutions ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Linear Regime ◽  
Minimal Coupling ◽  
Spherical Collapse ◽  
Modified Gravity Theory ◽  
Collapse Model ◽  
The Universe

In recent years, Rastall gravity is undergoing a considerable surge in popularity. This theory purports to be a modified gravity theory with a non-conserved energy–momentum tensor (EMT) and an unusual non-minimal coupling between matter and geometry. This work looks for the evolution of homogeneous spherical perturbations within the Universe in the context of Rastall gravity. Using the spherical Top-Hat collapse model, we seek for exact solutions in linear regime for density contrast of dark matter (DM) and dark energy (DE). We find that the Rastall parameter affects crucially the dynamics of density contrasts for DM and DE and the fate of spherical collapse is different in comparison to the case of general relativity (GR). Numerical solutions for perturbation equations in nonlinear regime reveal that DE perturbations could amplify the rate of growth of DM perturbations depending on the values of Rastall parameter.

scholarly journals ACCELERATED EXPANSION IN MODIFIED GRAVITY WITH A YUKAWA-LIKE TERM

2007 ◽  
Vol 16 (04) ◽  
pp. 687-697 ◽  
Author(s):  
K. ATAZADEH ◽  
H. R. SEPANGI
Keyword(s):  
Power Law ◽  
Modified Gravity ◽  
Newtonian Limit ◽  
Accelerated Expansion ◽  
Palatini Formalism ◽  
Expansion Of The Universe ◽  
Tensor Formulation ◽  
The Universe ◽  
Yukawa Term

We discuss the Palatini formulation of modified gravity including a Yukawa-like term. It is shown that in this formulation, the Yukawa term offers an explanation for the current exponential accelerated expansion of the universe and reduces to the standard Friedmann cosmology in the appropriate limit. We then discuss the scalar-tensor formulation of the model as a metric theory and show that the Yukawa term predicts a power-law acceleration at late-times. The Newtonian limit of the theory is also discussed in context of the Palatini formalism.

scholarly journals Gödel-type solution in f(R,T) modified gravity

2015 ◽  
Vol 30 (40) ◽  
pp. 1550214 ◽  
Author(s):  
A. F. Santos ◽  
C. J. Ferst
Keyword(s):  
Scalar Field ◽  
Perfect Fluid ◽  
Modified Gravity ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Matter Content ◽  
Type Solution ◽  
Special Cases ◽  
Tensor Formula ◽  
The Universe

In this paper, we will examine the problem of violation of causality in [Formula: see text] modified gravity, where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of the energy–momentum tensor [Formula: see text]. We investigate the causality problem in two special cases, in the first we consider the matter content of the universe as a perfect fluid and in the second case, the matter content is a perfect fluid plus a scalar field.

scholarly journals Cosmological consequences and statefinder diagnosis of a noninteracting generalized Chaplygin gas in f(R,T) gravity

2017 ◽  
Vol 26 (10) ◽  
pp. 1750120 ◽  
Author(s):  
Hamid Shabani
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Chaplygin Gas ◽  
Accelerated Expansion ◽  
Baryonic Matter ◽  
Statefinder Parameters ◽  
Generalized Chaplygin Gas ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

In this paper, we investigate cosmological consequences as well as statefinder diagnosis of a scenario for recently reported accelerated expansion of the universe in the framework of [Formula: see text] gravity theories. In these models, [Formula: see text] and [Formula: see text] denote the Ricci curvature scalar and the trace of the energy–momentum tensor (EMT), respectively. Our scenario assumes that the generalized Chaplygin gas (GCG) along with the baryonic matter are responsible for this observed phenomenon. We consider three classes of Chaplygin gas models which include three different forms of [Formula: see text] function; those models which employ the standard CG (SCG), models which use GCG in the high pressure regimes and finally, the third case is devoted to investigating high density regimes in the presence of GCG. We also test these models using recent Hubble parameter as well as type Ia supernova data. Finally, we compare the predicted present values of the statefinder parameters by these models to the astronomical data.

scholarly journals Mixed fluid cosmological model in f(R, T) gravity

2020 ◽  
Vol 98 (11) ◽  
pp. 1015-1022 ◽  
Author(s):  
Parbati Sahoo ◽  
Barkha Taori ◽  
K.L. Mahanta
Keyword(s):  
Cosmological Model ◽  
Bianchi Type ◽  
Type I ◽  
Time Varying ◽  
Eos Parameter ◽  
Barotropic Fluid ◽  
Rotationally Symmetric ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Mixed Fluid

We construct a locally rotationally symmetric (LRS) Bianchi type-I cosmological model in f(R, T) theory of gravity when the source of gravitation is a mixture of barotropic fluid and dark energy (DE) by employing a time-varying deceleration parameter. We observe through the behavior of the state finder parameters (r, s) that our model begins from the Einstein static era and goes to ΛCDM era. The equation of state (EOS) parameter (ωd) for DE varies from the phantom (ω < –1) phase to quintessence (ω > –1) phase, which is consistent with observational results. It is found that the discussed model can reproduce the current accelerating phase of the expansion of the universe.

scholarly journals De Sitter and power-law solutions in non-local Gauss–Bonnet gravity

2018 ◽  
Vol 15 (11) ◽  
pp. 1850188 ◽  
Author(s):  
E. Elizalde ◽  
S. D. Odintsov ◽  
E. O. Pozdeeva ◽  
S. Yu. Vernov
Keyword(s):  
Power Law ◽  
Sufficient Conditions ◽  
Model Parameters ◽  
Local Form ◽  
De Sitter ◽  
Dynamical Equations ◽  
Non Local ◽  
Necessary And Sufficient ◽  
The Universe ◽  
Universe Evolution

The cosmological dynamics of a non-locally corrected gravity theory, involving a power of the inverse d’Alembertian, is investigated. Casting the dynamical equations into local form, the fixed points of the models are derived, as well as corresponding de Sitter and power-law solutions. Necessary and sufficient conditions on the model parameters for the existence of de Sitter solutions are obtained. The possible existence of power-law solutions is investigated, and it is proven that models with de Sitter solutions have no power-law solutions. A model is found, which allows to describe the matter-dominated phase of the Universe evolution.

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