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.

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.

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 Interaction of Bianchi type-I anisotropic cloud string cosmological model universe with electromagnetic field

2020 ◽  
Vol 17 (09) ◽  
pp. 2050133
Author(s):  
Kangujam Priyokumar Singh ◽  
Mahbubur Rahman Mollah ◽  
Rajshekhar Roy Baruah ◽  
Meher Daimary
Keyword(s):  
Electromagnetic Field ◽  
Cosmological Model ◽  
Bianchi Type ◽  
Physical Parameters ◽  
Type I ◽  
Field Equations ◽  
Rest Energy ◽  
Model Universe ◽  
Bianchi Type I ◽  
String Cosmological Model

Here, we have investigated the interaction of Bianchi type-I anisotropic cloud string cosmological model universe with electromagnetic field in the context of general relativity. In this paper, the energy-momentum tensor is assumed to be the sum of the rest energy density and string tension density with an electromagnetic field. To obtain exact solution of Einstein’s field equations, we take the average scale factor as an integrating function of time. Also, the dynamics and significance of various physical parameters of model are discussed.

Anisotropic Dark Energy Cosmological Model with Cosmic Strings

2020 ◽  
Author(s):  
T. Vinutha ◽  
V.U.M. Rao ◽  
Molla Mengesha
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Model ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Type I ◽  
Field Equations ◽  
Eos Parameter ◽  
Phantom Divide

The present study deals with a spatially homogeneous locally rotationally symmetric (LRS) Bianchi type-I dark energy cosmological model containing one dimensional cosmic string fluid source. The Einstein's field equations are solved by using a relation between the metric potentials and hybrid expansion law of average scale factor. We discuss accelerated expansion of our model through equation of state (ωde) and deceleration parameter (q). We observe that in the evolution of our model, the equation of state parameter starts from matter dominated phase ωde > -1/3 and ultimately attains a constant value in quintessence region (-1 < ωde < -1/3). The EoS parameter of the model never crosses the phantom divide line (ωde = 1). These facts are consistent with recent observations. We also discuss some other physical parameters.

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.

scholarly journals LRS Bianchi type-I Universe with anisotropic dark energy and special form of deceleration parameter in f (R, T) gravity

2018 ◽  
Vol 6 (1) ◽  
pp. 1
Author(s):  
Rajesh Wankhade ◽  
A.S. Bansod
Keyword(s):  
Deceleration Parameter ◽  
Special Form ◽  
Bianchi Type ◽  
Momentum Tensor ◽  
Physical Aspect ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Anisotropic Dark Energy ◽  
Bianchi Type I Universe

In this paper, LRS Bianchi type-I space-time is considered in the presence of perfect fluid source in the frame work of  gravity (Harko et al. in Phys.Rev. D 84:024020, 2011) where is an arbitrary function of Ricci scalar  and trace of the energy momentum tensor . The Einstein’s field equations have been solved by taking into account the special form of deceleration parameter (Singha A., Debnath U.: Int.J. Theor. Phys.48, 2009). We observe that in f (R, T) gravity, an extra acceleration is always present due to coupling between matter and geometry. The geometrical and physical aspect of the model is also studied.

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.

Energy conditions and modified gravity in anisotropic universe

2018 ◽  
Vol 96 (2) ◽  
pp. 225-232 ◽  
Author(s):  
H. Hossienkhani ◽  
V. Fayaz ◽  
A. Jafari
Keyword(s):  
Modified Gravity ◽  
General Scheme ◽  
Energy Condition ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Anisotropic Universe ◽  
Type I ◽  
De Sitter ◽  
Field Equations ◽  
New Formula

In this paper, energy conditions in a new [Formula: see text] modified gravity ([Formula: see text] and T represent the Gauss–Bonnet invariant and trace of the energy–momentum tensor, respectively) for anisotropic universe with perfect fluid are analyzed. In this model, we develop the general scheme for new [Formula: see text] modified gravity reconstruction from realistic anisotropic Bianchi type-I cosmology. Using de Sitter solution, the exact solutions of the field equations have been obtained. It is found that null and weak energy conditions are satisfied for the parameter range considered. As a result, the analyses show that the increase of anisotropy is attributed to the increase of weak energy condition.

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.

Models of charged self-gravitating source in f(R,T) theory

2018 ◽  
Vol 27 (16) ◽  
pp. 1950005 ◽  
Author(s):  
M. Sharif ◽  
Aisha Siddiqa
Keyword(s):  
Momentum Tensor ◽  
Energy Conditions ◽  
Radial Coordinate ◽  
Physical Parameters ◽  
Field Equations ◽  
Expansion Formula ◽  
Anisotropic Parameter ◽  
Spherical Source ◽  
Model Parameter ◽  
Theory Formula

We discuss the anisotropic nonstatic charged spherical source describing the phenomena of collapse and expansion in the context of [Formula: see text] theory ([Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of energy–momentum tensor). The Einstein–Maxwell field equations are formulated and an auxiliary solution is considered. We evaluate the corresponding expansion scalar [Formula: see text] and investigate the cases of collapse [Formula: see text] and expansion ([Formula: see text]). In both cases, we explore the influence of charge as well as model parameter on density, radial/tangential pressure, anisotropic parameter and mass through graphs. It is observed that the physical parameters vary with time for expansion while remain constant for collapse. However, the change with respect to the radial coordinate is the same for both cases. The model parameter has the same impact in both cases while charge affects only in the case of collapse. The energy conditions are satisfied for both solutions with particular values of the parameters.

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