scholarly journals Accelerating Universe with Viscous Cosmic String in Quadratic Form of Teleparallel Gravity

2019 ◽  
Vol 11 (3) ◽  
pp. 249-262
Author(s):  
S. R. Bhoyar ◽  
V. R. Chirde ◽  
S. H. Shekh
Keyword(s):  
Cosmic String ◽  
Teleparallel Gravity ◽  
Negative Slope ◽  
Accelerating Universe ◽  
Field Equations ◽  
Physical Behavior ◽  
Torsion Scalar ◽  
Bulk Viscous ◽  
The Universe ◽  
Physical Quantities

In this paper, we have investigated Kantowaski-Sachs cosmological model with bulk viscous and cosmic string in the framework of Teleparallel Gravity so called f(T) gravity, where T denotes the torsion scalar. The behavior of accelerating universe is discussed towards the particular choice of f(T) = Α(T) + β(T)m. The exact solutions of the field equations are obtained by applying variable deceleration parameter which is linear in time with a negative slope. The physical behavior of these models has been discussed using some physical quantities. Also, the function of the torsion scalar for the universe is evaluated.

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 Viscous cosmology in the Weyl-type f(Q, T) gravity

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
Gaurav N. Gadbail ◽  
Simran Arora ◽  
P. K. Sahoo
Keyword(s):  
Bulk Viscosity ◽  
Viscosity Coefficient ◽  
Momentum Tensor ◽  
Model Parameters ◽  
Field Equations ◽  
Eos Parameter ◽  
Bulk Viscous ◽  
The Impact ◽  
Bulk Viscosity Coefficient ◽  
The Universe

AbstractBulk viscosity is the only viscous influence that can change the background dynamics in a homogeneous and isotropic universe. In the present work, we analyze the bulk viscous cosmological model with the bulk viscosity coefficient of the form $$\zeta =\zeta _0+\zeta _1H+\zeta _2\left( \frac{\dot{H}}{H}+H\right) $$ ζ = ζ 0 + ζ 1 H + ζ 2 H ˙ H + H where, $$\zeta _0$$ ζ 0 , $$\zeta _1$$ ζ 1 and $$\zeta _2$$ ζ 2 are bulk viscous parameters, and H is the Hubble parameter. We investigate the impact of the bulk viscous parameter on dynamics of the universe in the recently proposed Weyl-type f(Q, T) gravity, where Q is the non-metricity, and T is the trace of the matter energy–momentum tensor. The exact solutions to the corresponding field equations are obtained with the viscous fluid and the linear model of the form $$f(Q, T)=\alpha Q+\frac{\beta }{6\kappa ^2}T$$ f ( Q , T ) = α Q + β 6 κ 2 T , where $$\alpha $$ α and $$\beta $$ β are model parameters. Further, we constrain the model parameters using the 57 points Hubble dataset the recently released 1048 points Pantheon sample and the combination Hz + BAO + Pantheon, which shows our model is good congeniality with observations. We study the possible scenarios and the evolution of the universe through the deceleration parameter, the equation of state (EoS) parameter, the statefinder diagnostics, and the Om diagnostics. It is observed that the universe exhibits a transition from a decelerated to an accelerated phase of the universe under certain constraints of model 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.

BULK VISCOUS BRANS–DICKE COSMOLOGICAL MODELS AND LATE-TIME ACCELERATION OF THE UNIVERSE

2003 ◽  
Vol 12 (05) ◽  
pp. 925-939 ◽  
Author(s):  
M. K. MAK ◽  
T. HARKO
Keyword(s):  
Energy Density ◽  
Momentum Tensor ◽  
Physical Parameters ◽  
Late Time ◽  
Field Equations ◽  
Bulk Viscous ◽  
Order Of Magnitude ◽  
Viscous Pressure ◽  
The Universe ◽  
Matter Energy

We consider the dynamics of a causal bulk viscous cosmological fluid filled flat homogeneous Universe in the framework of the Brans–Dicke theory. Three classes of exact solutions of the field equations are obtained and the behavior of the physical parameters is considered in detail. In this model the energy density associated to the Brans–Dicke scalar field is of the same order of magnitude as the matter energy density. The inclusion of the bulk viscous pressure term in the matter energy-momentum tensor leads to a non-decelerating evolution of the Universe.

scholarly journals SOME BIANCHI TYPE-V MODELS OF ACCELERATING UNIVERSE WITH DARK ENERGY

2011 ◽  
Vol 26 (09) ◽  
pp. 647-659 ◽  
Author(s):  
SURESH KUMAR ◽  
ANIL KUMAR YADAV
Keyword(s):  
Dark Energy ◽  
State Parameter ◽  
Accelerating Universe ◽  
Anisotropic Universe ◽  
Field Equations ◽  
Bianchi V ◽  
Variable Equation ◽  
Type V ◽  
The Universe

The paper deals with a spatially homogeneous and anisotropic universe filled with perfect fluid and dark energy components. The two sources are assumed to interact minimally together with a special law of variation for the average Hubble's parameter in order to solve the Einstein's field equations. The law yields two explicit forms of the scale factor governing the Bianchi-V spacetime and constant values of deceleration parameter. The role of dark energy with variable equation of state parameter has been studied in detail in the evolution of Bianchi-V universe. It has been found that dark energy dominates the universe at the present epoch, which is consistent with the observations. The universe achieves flatness after the dominance of dark energy. The physical behavior of the universe has been discussed in detail.

Scalar–tensor f(R) gravity model for late-time universe

2021 ◽  
Vol 36 (11) ◽  
pp. 2150075
Author(s):  
Tae Hoon Lee
Keyword(s):  
Gravity Model ◽  
Accelerating Universe ◽  
Late Time ◽  
Scalar Tensor Theory ◽  
Field Equations ◽  
Tensor Theory ◽  
Future Behavior ◽  
The Universe

We suggest an [Formula: see text] gravity model constructed in the framework of scalar–tensor theory. To field equations in the model, we obtain an accelerating universe solution for the late-time and discuss a future behavior of the universe.

scholarly journals Accelerating universe in modified teleparallel gravity theory

2019 ◽  
Vol 15 (S356) ◽  
pp. 397-399
Author(s):  
Shambel Sahlu ◽  
Joseph Ntahompagaze ◽  
Amare Abebe ◽  
David F. Mota
Keyword(s):  
State Parameter ◽  
Teleparallel Gravity ◽  
Gravity Theory ◽  
Gravity Models ◽  
Accelerating Universe ◽  
Late Time ◽  
Numerical Result ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

AbstractThis paper studies the cosmology of accelerating expansion of the universe in modified teleparallel gravity theory. We discuss the cosmology of f(T, B) gravity theory and its implication to the new general form of the equation of state parameter wTB for explaining the late-time accelerating expansion of the universe without the need for the cosmological constant scenario. We examine the numerical value of wTB in different paradigmatic f(T, B) gravity models. In those models, the numerical result of wTB is favored with observations in the presence of the torsion scalar T associated with a boundary term B and shows the accelerating expansion of the universe.

scholarly journals Accelerating universe with binary mixture of bulk viscous fluid and dark energy

2021 ◽  
pp. 2150148
Author(s):  
Nishant Singla ◽  
M. K. Gupta ◽  
Anil Kumar Yadav ◽  
G. K. Goswami
Keyword(s):  
Dark Energy ◽  
Binary Mixture ◽  
Viscous Fluid ◽  
Accelerating Universe ◽  
Model Parameters ◽  
Density Parameter ◽  
Bulk Viscous Fluid ◽  
Bulk Viscous ◽  
De Formula ◽  
The Universe

In this paper, we have proposed a model of accelerating universe with binary mixture of bulk viscous fluid and dark energy (DE) and probed the model parameters: present values of Hubble’s constant [Formula: see text], equation of state paper of DE [Formula: see text] and density parameter of DE [Formula: see text] with recent observational [Formula: see text] data (OHD) as well as joint Pantheon compilation of SN Ia data and OHD. Using cosmic chronometric technique, we obtain [Formula: see text] and [Formula: see text] by restricting our derived model with recent OHD and joint Pantheon compilation SN Ia data and OHD, respectively. The present age of the universe in derived model is estimated as [Formula: see text]. Also, we observe that derived model represents a model of transitioning universe with transition redshift [Formula: see text]. We have constrained the present value of jerk parameter as [Formula: see text] with joint OHD and Pantheon data. From this analysis, we observed that the model of the universe, presented in this paper, shows a marginal departure from [Formula: see text]CDM model.

scholarly journals Anisotropic Bianchi Type-III Bulk Viscous Fluid Universe in Lyra Geometry

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Priyanka Kumari ◽  
M. K. Singh ◽  
Shri Ram
Keyword(s):  
Cosmological Model ◽  
Viscous Fluid ◽  
Bianchi Type ◽  
Lyra Geometry ◽  
Scale Factor ◽  
Field Equations ◽  
Type Iii ◽  
Bulk Viscous Fluid ◽  
Bulk Viscous ◽  
The Universe

An anisotropic Bianchi type-III cosmological model is investigated in the presence of a bulk viscous fluid within the framework of Lyra geometry with time-dependent displacement vector. It is shown that the field equations are solvable for any arbitrary function of a scale factor. To get the deterministic model of the universe, we have assumed that (i) a simple power-law form of a scale factor and (ii) the bulk viscosity coefficient are proportional to the energy density of the matter. The exact solutions of the Einstein’s field equations are obtained which represent an expanding, shearing, and decelerating model of the universe. Some physical and kinematical behaviors of the cosmological model are briefly discussed.

scholarly journals Cosmological Particle Production and Causal Thermodynamics

1999 ◽  
Vol 52 (4) ◽  
pp. 659 ◽  
Author(s):  
M. K. Mak ◽  
T. Harko
Keyword(s):  
Particle Production ◽  
Particle Creation ◽  
Phenomenological Theory ◽  
Physical Parameters ◽  
Field Equations ◽  
Gravitational Field Equations ◽  
Inflationary Phase ◽  
Bulk Viscous ◽  
Minkowskian Geometry ◽  
The Universe

The full linear causal Israel–Stewart–Hiscock theory of bulk viscous processes in relativistic cosmological fluids is reformulated as an effective phenomenological theory for describing particle production processes in the early universe. Explicit expressions for the particle balance law and particle production rates are obtained that relate the particle creation rate to the bulk viscous (creation) pressure. The general formalism is applied to the case of a full causal cosmological fluid with bulk viscosity coecient proportional to the Hubble function. In this case the general solution of the gravitational field equations can be expressed in an exact parametric form. For an appropriate choice of the physical parameters, the dynamics of the universe can be modelled as starting from a vacuum quasi-Minkowskian geometry, followed by an inflationary period but ending in a non-inflationary phase. The influence of the matter creation processes on the evolution of the universe and the behaviour of the energy density, temperature and entropy are investigated.

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