Cosmological model with variable deceleration parameter in f(R,T) modified gravity

2018 ◽  
Vol 15 (07) ◽  
pp. 1850115 ◽  
Author(s):  
Rishi Kumar Tiwari ◽  
Aroonkumar Beesham ◽  
Bhupendra Shukla
Keyword(s):  
Cosmological Model ◽  
Modified Gravity ◽  
Deceleration Parameter ◽  
Late Time ◽  
Type I ◽  
Field Equations ◽  
Geometrical Properties ◽  
Deceleration Phase ◽  
Modified Gravity Theory ◽  
The Universe

A study is made of the LRS Bianchi type-I cosmological model in [Formula: see text] modified gravity theory. Einstein’s field equations in [Formula: see text] gravity are solved by taking [Formula: see text] and the deceleration parameter [Formula: see text] to be a linear function of the Hubble parameter [Formula: see text]. The universe begins with an initial singular state and changes with time from an early deceleration phase to a late time acceleration phase. We have found that the jerk parameter [Formula: see text] in the model approaches that of the [Formula: see text] model at late times. We also discuss the physical and geometrical properties of the model.

scholarly journals Anisotropic Cosmological Model in a Modified Theory of Gravitation

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 226
Author(s):  
Rishi Kumar Tiwari ◽  
Aroonkumar Beesham ◽  
Soma Mishra ◽  
Vipin Dubey
Keyword(s):  
Cosmological Model ◽  
Modified Gravity ◽  
Bianchi Type ◽  
Late Time ◽  
Type I ◽  
Bianchi Models ◽  
Theory Of Gravitation ◽  
The Universe ◽  
Type Parameter ◽  
Modified Theory

Current observations indicate that, on a large enough scale, the universe is homogeneous and isotropic. However, this does not preclude the possibility of some anisotropy having occurred during the early stages of the evolution of the universe, which could then have been damped out later. This idea has aroused interest in the Bianchi models, which are homogeneous but anisotropic. Secondly, there is much interest in modified gravity these days due to the problems that the usual ΛCDM model faces in general relativity. Hence, in this paper, a study was conducted on the Bianchi type-I cosmological model in f(R,T)-modified gravity. Following some ideas from cosmography, a specific form of the deceleration parameter was assumed, leading to a model that exhibited a transition from early deceleration to late-time acceleration. The derived model approached isotropy at late times. The physical properties of the model were discussed, and expressions for the various parameters of the model were derived. It is also possible to make progress towards solving the cosmological constant problem, since in this model in f(R,T) gravity, a variable cosmological-type parameter arose, which was large early on but decreased to a constant value in later times.

scholarly journals Bianchi Type- I Bulk Viscosity with a DE Cosmological Model

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Daba Meshesha Gusu
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
Bulk Viscosity ◽  
Bianchi Type ◽  
Early Time ◽  
Observational Result ◽  
Type I ◽  
Field Equations ◽  
Geometrical Properties ◽  
The Universe

The finding article presents Bianchi type- I universe in the presence of bulk viscous and DE fluid nature of a cosmological model. The solutions of field equations were obtained by assuming hybrid expansion law. The physical significance of the obtained findings illustrates the dominance of bulk viscosity in early and dominance of dark energy fluid emergences in late. This leads to indicate the presence of bulk viscosity nature more effective in early time rather than late times, and also, it shows the dominance of dark energy in late times which grants the current observational result of the universe. Certain physical and geometrical properties of the model 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.

MODIFIED GRAVITY THEORY DUE TO POSITIVE AS WELL AS NEGATIVE CURVATURE INDUCED ACCELERATION

2012 ◽  
Vol 21 (02) ◽  
pp. 1250012
Author(s):  
PRIYADARSHI MAJUMDAR
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Negative Curvature ◽  
Gravity Theory ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Negative Power ◽  
Modified Gravity Theory ◽  
Phase Q ◽  
The Universe

We formulate a modified gravity theory that eliminates the need for dark energy and is stable for a Lagrangian containing R, R2 as well as 1/R terms (i.e. nonlinear contributions of the Ricci curvature with a non-analytic model of f(R) at R = 0) without considering any matter-dominated era. The terms with positive powers (1, 2) of the curvature support the inflationary epoch while the terms with negative power (-1) serves as effective dark energy, supporting current cosmic acceleration. We present a few analytical solutions of evolution equation for the deceleration parameter q as a function of Hubble parameter H and time t; specially in one solution, the universe evolves continuously from q = 1 (a radiation-dominated epoch) to q = -1/2 (dark-energy-dominated late-time accelerating phase) when the universe is sufficiently old. The solution is supported by numerical results. The transition from the decelerated (q > 0) to the accelerated phase (q < 0) of expansion takes place smoothly without having to resort to a study of asymptotic behavior.

scholarly journals Accelerating dark energy cosmological model in two fluids with hybrid scale factor

2017 ◽  
Vol 14 (09) ◽  
pp. 1750124 ◽  
Author(s):  
B. Mishra ◽  
P. K. Sahoo ◽  
Pratik P. Ray
Keyword(s):  
Dark Energy ◽  
Late Phase ◽  
Scale Factor ◽  
Accelerating Universe ◽  
Late Time ◽  
Field Equations ◽  
Geometrical Properties ◽  
Two Fluids ◽  
The Universe

In this paper, we have investigated the anisotropic behavior of the accelerating universe in Bianchi V spacetime in the framework of General Relativity (GR). The matter field we have considered is of two non-interacting fluids, i.e. the usual string fluid and dark energy (DE) fluid. In order to represent the pressure anisotropy, the skewness parameters are introduced along three different spatial directions. To achieve a physically realistic solutions to the field equations, we have considered a scale factor, known as hybrid scale factor, which is generated by a time-varying deceleration parameter. This simulates a cosmic transition from early deceleration to late time acceleration. It is observed that the string fluid dominates the universe at early deceleration phase but does not affect nature of cosmic dynamics substantially at late phase, whereas the DE fluid dominates the universe in present time, which is in accordance with the observations results. Hence, we analyzed here the role of two fluids in the transitional phases of universe with respect to time which depicts the reason behind the cosmic expansion and DE. The role of DE with variable equation of state parameter (EoS) and skewness parameters, is also discussed along with physical and geometrical properties.

scholarly journals Anisotropic cosmological models in f(R,T) gravity with variable deceleration parameter

2017 ◽  
Vol 14 (06) ◽  
pp. 1750097 ◽  
Author(s):  
Pradyumn Kumar Sahoo ◽  
Parbati Sahoo ◽  
Binaya Kumar Bishi
Keyword(s):  
Bulk Viscosity ◽  
Deceleration Parameter ◽  
Momentum Tensor ◽  
Matter Content ◽  
Accelerating Universe ◽  
Data Sets ◽  
Type I ◽  
Field Equations ◽  
Future Evolution ◽  
The Universe

The objective of this work enclosed with the study of spatially homogeneous anisotropic Bianchi type-I universe in [Formula: see text] gravity (where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of stress energy momentum tensor) in two different cases viz. [Formula: see text] and [Formula: see text] with bulk viscosity matter content. In this study, we consider a time varying deceleration parameter (DP), which generates an accelerating universe to obtain the exact solution of the field equations. The physical and kinematical properties of both the models are discussed in detail for the future evolution of the universe. We have explored the nature of WEC, DEC, SEC and energy density for both the cases. We have found that both the models, with bulk viscosity matter component, show an acceleration of the universe. We have also shown that the cosmic jerk parameter is compatible with the three kinematical data sets.

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.

Phase transition of LRS Bianchi type-I cosmological model in f(R,T) gravity

2020 ◽  
Vol 17 (12) ◽  
pp. 2050187
Author(s):  
R. K. Tiwari ◽  
D. Sofuoğlu ◽  
V. K. Dubey
Keyword(s):  
Cosmological Model ◽  
Bianchi Type ◽  
Early Time ◽  
Momentum Tensor ◽  
Late Time ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Accelerating Expansion ◽  
Acceleration Of The Universe

In this work, LRS Bianchi type-I cosmological model with perfect fluid source in [Formula: see text] gravity theory, where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of the stress energy-momentum tensor, has been studied in order to investigate early time deceleration and late time acceleration of the universe. By proposing a new special form of time-varying deceleration parameter in terms of Hubble parameter, the exact solution of the field equations has been obtained. The physical and geometric quantities of the model have been derived and their evolution has been discussed. Our model has an initial singularity and initially exhibits decelerating expansion and transits to accelerating expansion phase at last eras. The nature of the matter source of the model is consistent with the standard model in frame of the structure formation.

scholarly journals Lyra’s cosmology of homogeneous and isotropic universe in Brans–Dicke theory

2020 ◽  
pp. 2150029
Author(s):  
Rajendra Prasad ◽  
Lalit Kumar Gupta ◽  
Anil Kumar Yadav
Keyword(s):  
Cosmological Model ◽  
Deceleration Parameter ◽  
Wilkinson Microwave Anisotropy Probe ◽  
Density Parameter ◽  
Field Equations ◽  
Present Universe ◽  
Age Of The Universe ◽  
Geometrical Term ◽  
The Universe ◽  
Matter Energy

In this paper, we investigate a scalar field Brans–Dicke cosmological model in Lyra’s geometry which is based on the modifications in a geometrical term as well as energy term of Einstein’s field equations. We have examined the validity of the proposed cosmological model on the observational scale by performing statistical analysis from the latest [Formula: see text] and SN Ia observational data. We find that the estimated values of Hubble’s constant and matter energy density parameter is in agreement with their corresponding values, obtained from recent observations of Wilkinson Microwave Anisotropy Probe (WMAP) and Plank collaboration. We also derived the deceleration parameter, age of the universe and jerk parameter in terms of red-shift and computed its present values. The dynamics of the deceleration parameter in the derived model of the universe show a signature flipping from positive to a negative value and also indicate that the present universe is in the accelerating phase.

De Sitter and bounce solutions from anisotropy in extended gravity cosmology

2019 ◽  
Vol 34 (39) ◽  
pp. 1950321 ◽  
Author(s):  
B. Mishra ◽  
G. Ribeiro ◽  
P. H. R. S. Moraes
Keyword(s):  
Big Bang ◽  
Late Time ◽  
Type I ◽  
De Sitter ◽  
Field Equations ◽  
Extended Gravity ◽  
Numerical Fitting ◽  
De Sitter Universe ◽  
The Big Bang ◽  
The Universe

We investigate the consequences of incepting the Bianchi type I metric in the [Formula: see text] gravity theory field equations. We particularly derive solutions for a matter-dominated universe. From such a scenario, it is possible to predict a late-time de Sitter universe. Moreover, depending on the numerical fitting function for the scale factor, the universe is predicted to bounce and evade the Big Bang singularity.

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