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.

scholarly journals Dynamic of the Accelerated Expansion of the Universe in the DGP Model

2011 ◽  
Vol 21 (3) ◽  
pp. 253 ◽  
Author(s):  
Vo Quoc Phong
Keyword(s):  
Experimental Data ◽  
Growth Rate ◽  
Cold Dark Matter ◽  
Growth Index ◽  
Cosmic Acceleration ◽  
Accelerated Expansion ◽  
Density Parameter ◽  
Type Ia ◽  
Age Of The Universe ◽  
The Universe

According to experimental data of SNe Ia (Supernovae type Ia), we will discuss in detial dynamics of the DGP model and introduce a simple parametrization of matter $\omega$, in order to analyze scenarios of the expanding universe and the evolution of the scale factor. We find that the dimensionless matter density parameter at the present epoch $\Omega^0_m=0.3$, the age of the universe $t_0= 12.48$ Gyr, $\frac{a}{a_0}=-2.4e^{\frac{-t}{25.56}}+2.45$. The next we study the linear growth of matter perturbations, and we assume a definition of the growth rate, $f \equiv \frac{dln\delta}{dlna}$. As many authors for many years, we have been using a good approximation to the growth rate $f \approx \Omega^{\gamma(z)}_m$, we also find that the best fit of the growth index, $\gamma(z)\approx 0.687 - \frac{40.67}{1 + e^{1.7. (4.48 + z)}}$, or $\gamma(z)= 0.667 + 0.033z$ when $z\ll1$. We also compare the age of the universe and the growth index with other models and experimental data. We can see that the DGP model describes the cosmic acceleration as well as other models that usually refers to dark energy and Cold Dark Matter (CDM).

scholarly journals The Large Number Hypothesis and Einstein's Theory of Gravitation

1985 ◽  
Vol 38 (4) ◽  
pp. 547 ◽  
Author(s):  
Yun-Kau Lau
Keyword(s):  
Cosmological Model ◽  
Cosmological Constant ◽  
Matter Density ◽  
Time Dependent ◽  
Field Equations ◽  
Large Number Hypothesis ◽  
Theory Of Gravitation ◽  
The Mean ◽  
Limiting Case ◽  
The Universe

In an attempt to reconcile the large number hypothesis (LNH) with Einstein's theory of gravitation, a tentative generalization of Einstein's field equations with time-dependent cosmological and gravitational constants is proposed. A cosmological model consistent with the LNH is deduced. The coupling formula of the cosmological constant with matter is found, and as a consequence, the time-dependent formulae of the cosmological constant and the mean matter density of the Universe at the present epoch are then found. Einstein's theory of gravitation, whether with a zero or nonzero cosmological constant, becomes a limiting case of the new generalized field equations after the early epoch.

scholarly journals Generalized Phenomenological Models of Dark Energy

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
Prasenjit Paul ◽  
Rikpratik Sengupta
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Energy Density ◽  
Cosmological Constant ◽  
Phenomenological Models ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Free Parameters ◽  
The Universe ◽  
Matter Energy

It was first observed at the end of the last century that the universe is presently accelerating. Ever since, there have been several attempts to explain this observation theoretically. There are two possible approaches. The more conventional one is to modify the matter part of the Einstein field equations, and the second one is to modify the geometry part. We shall consider two phenomenological models based on the former, more conventional approach within the context of general relativity. The phenomenological models in this paper consider a Λ term firstly a function of a¨/a and secondly a function of ρ, where a and ρ are the scale factor and matter energy density, respectively. Constraining the free parameters of the models with the latest observational data gives satisfactory values of parameters as considered by us initially. Without any field theoretic interpretation, we explain the recent observations with a dynamical cosmological constant.

scholarly journals A New Measurement of the Geometry of Space

1987 ◽  
Vol 124 ◽  
pp. 217-221
Author(s):  
Edwin D. Loh
Keyword(s):  
Big Bang ◽  
Recent Measurement ◽  
Density Parameter ◽  
Confidence Limits ◽  
Dimensionless Form ◽  
Primordial Nucleosynthesis ◽  
Geometrical Effects ◽  
Age Of The Universe ◽  
The Universe ◽  
Inflationary Models

This paper discusses the recent measurement of the number of galaxies vs. redshift and flux and presents new results pertaining to the two dimensionless geometrical quantities that describe the geometry of the conventional big-bang cosmology, the density parameter Ω and the dimensionless form λ = Λ/(3H02) of the cosmological constant. In contrast to the classical redshift-magnitude test as applied to the brightest galaxies in clusters, this new method is able to separate the effects of evolution from geometrical effects and is therefore able to measure the geometry of space. The 95% confidence limits are Ω - λ = 0.9−0 5+0 7 and −1.5 < Ω + λ < 7.1. The principal conclusions are these: (1) For both λ = 0 and inflationary models of the universe, this measurement and primordial nucleosynthesis imply a large density of nonbaryonic matter. (2) Hubble's constant H0 and the age of the universe τ are constrained by 0.60 < H0τ < 0.88 (95% confidence).

Age of the universe and the density parameter

1994 ◽  
Vol 33 (9) ◽  
pp. 1933-1934
Author(s):  
Marcelo Samuel Berman ◽  
Fernando de Mello Gomide
Keyword(s):  
Density Parameter ◽  
Age Of The Universe ◽  
The Universe

scholarly journals Theoretical estimates of integrated Sachs–Wolfe effect detection through the Australian Square Kilometre Array Pathfinder’s Evolutionary Map of the Universe (ASKAP- EMU) survey, with confusion, position uncertainty, shot noise, and signal-to-noise ratio analysis

2015 ◽  
Vol 93 (4) ◽  
pp. 384-394 ◽  
Author(s):  
Syed Faisal ur Rahman
Keyword(s):  
Root Mean Square ◽  
Shot Noise ◽  
Radio Continuum ◽  
Wilkinson Microwave Anisotropy Probe ◽  
Density Parameter ◽  
Mean Square ◽  
Signal To Noise ◽  
Position Uncertainty ◽  
Square Kilometre Array ◽  
The Universe

Detection of the late-time integrated Sachs–Wolfe (ISW) effect is an active area of study related to large-scale structures (LSSs). The ISW effect can be studied by observing the non-zero cross-correlation between cosmic microwave background (CMB) anisotropies with tracers of mass field, such as galaxy survey data. We study this effect by cross-correlating the CMB data and related cosmological parameters, as delineated by the Wilkinson Microwave Anisotropy Probe (WMAP), with the upcoming Evolutionary Map of the Universe (EMU) survey planned for the Australian Square Kilometre Array Pathfinder (ASKAP). ASKAP-EMU will conduct a deep radio continuum survey with a root-mean-square (rms) flux of 10 μJy per beam (1 Jy = 10–26 Wm–2Hz–1). The survey will cover the entire southern sky, extending to +30° declination. To infer the expected redshift distribution (dN/dz) and differential source count (S) that can be extracted from the galaxies surveyed via EMU, we use data from the S-cubed simulation of extragalactic radio continuum sources (S3-SEX) for the Square Kilometre Array Design Studies (SKADS). We also calculate various parameters including galaxy survey shot noise, root mean square confusion uncertainty, and position uncertainty for the survey, which can help in understanding the accuracy of the survey results and in performing the data analysis. We also discuss signal-to-noise ratios over a range of maximum redshifts and maximum multipole values with some discussion on constraints over dark energy density parameter (ΩΛ) and baryonic matter density parameter (Ωb).

ROLE OF EXTRA DIMENSION IN ACCELERATED EXPANSION

2008 ◽  
Vol 23 (06) ◽  
pp. 909-917 ◽  
Author(s):  
K. D. PUROHIT ◽  
YOGESH BHATT
Keyword(s):  
Cosmological Model ◽  
Extra Dimension ◽  
Accelerated Expansion ◽  
Field Equations ◽  
Four Dimensions ◽  
Scale Factors ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Kaluza Klein

A five-dimensional FRW-type Kaluza–Klein cosmological model is taken to study the role of extra dimension in the expansion of the universe. Relation between scale factors corresponding to conventional four dimensions and the extra dimension has been established. Field equations are solved in order to find out the effect of pressure corresponding to these scale factors. Conditions for accelerated expansion are derived.

scholarly journals Consistency Conditions of f(R,G)-Gravity Field Equations for Bianchi-Type III Metric

2021 ◽  
pp. 29-41
Author(s):  
Selçuk Güler ◽  
Ertan Güdekli
Keyword(s):  
Perfect Fluid ◽  
Bianchi Type ◽  
Energy Content ◽  
Anisotropic Universe ◽  
Field Equations ◽  
Consistency Conditions ◽  
Type Iii ◽  
Barotropic Equation ◽  
The Universe ◽  
Matter Energy

In this paper, we study the -gravitation theory under the assumption that the standard matter-energy content of the universe is a perfect fluid with linear barotropic equation of state within the framework of Bianchi-Type III model from the class of homogeneous and anisotropic universe models. However, whether such a restriction lead to any contradictions or inconsistencies in the field equations will create an issue that needs to be examined. Under the effective fluid approach, we will be concerned mainly the field equations in an orthonormal tetrad framework with an equimolar and examined the situation of establishing the functional form of  together with the scale factors, which are their solutions. Unlike similar studies, which are very few in the literature, instead of assuming preliminary solutions, we determined the consistency conditions of the field equations by assuming the matter energy content of the universe as an isotropic perfect fluid for Bianchi-Type III.

scholarly journals The flatness problem and the age of the Universe

2020 ◽  
Vol 495 (4) ◽  
pp. 3571-3575
Author(s):  
Phillip Helbig
Keyword(s):  
Early Universe ◽  
Time Scale ◽  
Cosmological Parameters ◽  
Hubble Constant ◽  
Fine Tuning ◽  
Density Parameter ◽  
Age Of The Universe ◽  
Short Time ◽  
The Universe ◽  
Flatness Problem

ABSTRACT Several authors have made claims, none of which has been rebutted, that the flatness problem, as formulated by Dicke and Peebles, is not really a problem but rather a misunderstanding. Nevertheless, the flatness problem is still widely perceived to be real. Most of the arguments against the idea of a flatness problem are based on the change with time of the density parameter Ω and normalized cosmological constant λ and, since the Hubble constant H is not considered, are independent of time-scale. An independent claim is that fine-tuning is required in order to produce a Universe which neither collapsed after a short time nor expanded so quickly that no structure formation could take place. I show that this claim does not imply that fine-tuning of the basic cosmological parameters is necessary, in part for similar reasons as in the more restricted flatness problem and in part due to an incorrect application of the idea of perturbing the early Universe in a gedankenexperiment; I discuss some typical pitfalls of the latter.

Sign in / Sign up

Export Citation Format

Share Document