scholarly journals Cosmological model with time varying deceleration parameter in F(R, G) gravity

2021 ◽  
Author(s):  
Santosh V. Lohakare ◽  
S K Tripathy ◽  
B Mishra
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Deceleration Parameter ◽  
Dynamical Behaviour ◽  
Ricci Scalar ◽  
Energy Conditions ◽  
Time Varying ◽  
Diagnostic Stability ◽  
Field Formalism ◽  
The Universe

Abstract In this paper, we study the dynamical behaviour of the universe in the F (R, G) theory of gravity, where R and G respectively denote the Ricci scalar and Gauss-Bonnet invariant. Our wide analysis encompasses the energy conditions, cosmographic parameters, Om(z) diagnostic, stability and the viability of reconstructing the referred model through a scalar field formalism. The model obtained here shows the quintessence like behaviour at late times.

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.

A time-varying deceleration parameter for unified description of cosmological evolution

2018 ◽  
Vol 15 (09) ◽  
pp. 1850145 ◽  
Author(s):  
Vijay Singh ◽  
Aroonkumar Beesham
Keyword(s):  
Scalar Field ◽  
Deceleration Parameter ◽  
Cosmological Evolution ◽  
Time Varying ◽  
Baryonic Matter ◽  
Statefinder Parameters ◽  
Stiff Matter ◽  
Variable Equation ◽  
The Universe ◽  
Unified Description

In this paper, we propose a new time-varying deceleration parameter for the description of a unified cosmological evolution (early inflation, deceleration and present acceleration) using Padé approximation. Within the background of Einstein’s general relativity and for a spatially flat homogeneous and isotropic model, the proposed deceleration parameter leads to a variable equation of state of effective matter that serves all matter within EoS [Formula: see text] (quintessence, relativistic and non-relativistic baryonic matter, stiff matter and cosmological constant), exactly in the same order as it required for various evolutionary phases of the universe. We consider a minimally coupled scalar field with self-interacting potential as the only matter source in the universe. The adopted scheme allows us to determine the potential for the scalar field that drives the cosmological evolution proposed by the deceleration parameter. We perform an explicit numerical computation where analytical solutions are not possible. We examine the validity of the model by depicting the statefinder parameters and comparing them with the recent observational outcomes of cosmography.

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 Almost-Pseudo-Ricci Symmetric FRW Universe with a Dynamic Cosmological Term and Equation of State

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 205
Author(s):  
Sanjay Mandal ◽  
Avik De ◽  
Tee-How Loo ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Equation Of State ◽  
Cosmological Parameters ◽  
Cosmological Term ◽  
Ricci Scalar ◽  
Energy Conditions ◽  
Late Time ◽  
Frw Universe ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

The objective of the present paper is to investigate an almost-pseudo-Ricci symmetric FRW spacetime with a constant Ricci scalar in a dynamic cosmological term Λ(t) and equation of state (EoS) ω(t) scenario. Several cosmological parameters are calculated in this setting and thoroughly studied, which shows that the model satisfies the late-time accelerating expansion of the universe. We also examine all of the energy conditions to check our model’s self-stability.

scholarly journals Complex Inflaton Field in Quantum Cosmology

1997 ◽  
Vol 06 (06) ◽  
pp. 649-671 ◽  
Author(s):  
A. Yu. Kamenshchik ◽  
I. M. Khalatnikov ◽  
A. V. Toporensky
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Equations Of Motion ◽  
Inflationary Cosmology ◽  
Complex Scalar ◽  
Inflaton Field ◽  
Absolute Value ◽  
Forbidden Regions ◽  
Complex Scalar Field ◽  
The Universe

We investigate the cosmological model with the complex scalar self-interacting inflaton field non-minimally coupled to gravity. The different geometries of the Euclidean classically forbidden regions are represented. The instanton solutions of the corresponding Euclidean equations of motion are found by numerical calculations supplemented by the qualitative analysis of Lorentzian and Euclidean trajectories. The applications of these solutions to the no-boundary and tunneling proposals for the wave function of the Universe are studied. Possible interpretation of obtained results and their connection with inflationary cosmology is discussed. The restrictions on the possible values of the new quasifundamental constant of the theory — non-zero classical charge — are obtained. The equations of motion for the generalized cosmological model with complex scalar field are written down and investigated. The conditions of the existence of instanton solutions corresponding to permanent values of an absolute value of scalar field are obtained.

Friedmann–Robertson–Walker (FRW) cosmological model in the present perspective

2019 ◽  
Vol 97 (6) ◽  
pp. 588-595 ◽  
Author(s):  
G.K. Goswami
Keyword(s):  
Cosmological Model ◽  
Perfect Fluid ◽  
Deceleration Parameter ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
State Parameter ◽  
Accelerating Universe ◽  
Frw Cosmological Model ◽  
The Universe ◽  
Friedmann Robertson Walker

In this paper, we have presented a cosmological model that represents spatially homogenous and isotropic accelerating universe from the perspective of the latest developments begun by Perlmutter and Riess in cosmology. For this, Friedmann–Robertson–Walker (FRW) space–time metric is considered and our universe is assumed to be filled with two types of fluids. One is ordinary baryonic perfect fluid and the other one is mysterious and bizarre dark energy perfect fluid with negative pressure. This creates a repulsive field that produces acceleration in the universe. We have used 581 Union 2.1 compilation data to statistically estimate present values of cosmological parameters Ωde, Ωm, Ωk and equation of state parameter ωde for our model. We have used 31 datasets of observed values of Hubble constant for various redshifts to estimate the present value of Hubble constant H0. On the basis of these we have calculated the present age of the universe, densities, and deceleration parameter. Evolution of deceleration parameter shows that our universe has gone through an accelerating phase two times. In the beginning, and at present. We have also calculated Particle horizon and the time at which acceleration began. Our results are close to latest surveys.

scholarly journals Generalized second law of thermodynamics on the apparent horizon in modified Gauss–Bonnet gravity

2016 ◽  
Vol 25 (04) ◽  
pp. 1650040 ◽  
Author(s):  
A. Abdolmaleki ◽  
T. Najafi
Keyword(s):  
Deceleration Parameter ◽  
Apparent Horizon ◽  
Accelerated Expansion ◽  
Energy Conditions ◽  
Second Law ◽  
De Sitter ◽  
Frw Universe ◽  
Curvature Invariant ◽  
Generalized Second Law ◽  
The Universe

Modified gravity (MG) and generalized second law (GSL) of thermodynamics are interesting topics in the modern cosmology. In this regard, we investigate the GSL of gravitational thermodynamics in the framework of modified Gauss–Bonnet (GB) gravity or [Formula: see text]-gravity. We consider a spatially FRW universe filled with the pressureless matter and radiation enclosed by the dynamical apparent horizon with the Hawking temperature. For two viable [Formula: see text] models, we first numerically solve the set of differential equations governing the dynamics of [Formula: see text]-gravity. Then, we obtain the evolutions of the Hubble parameter, the GB curvature invariant term, the density and equation of state (EoS) parameters as well as the deceleration parameter. In addition, we check the energy conditions for both models and finally examine the validity of the GSL. For the selected [Formula: see text] models, we conclude that both models have a stable de Sitter attractor. The EoS parameters behave quite similar to those of the [Formula: see text]CDM model in the radiation/matter dominated epochs, then they enter the phantom region before reaching the de Sitter attractor with [Formula: see text]. The deceleration parameter starts from the radiation/matter dominated eras, then transits from a cosmic deceleration to acceleration and finally approaches a de Sitter regime at late times, as expected. Furthermore, the GSL is respected for both models during the standard radiation/matter dominated epochs. Thereafter when the universe becomes accelerating, the GSL is violated in some ranges of scale factor. At late times, the evolution of the GSL predicts an adiabatic behavior for the accelerated expansion of the universe.

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.

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.

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