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Friedmann–Lemaître–Robertson–Walker metric

About: Friedmann–Lemaître–Robertson–Walker metric is a research topic. Over the lifetime, 4113 publications have been published within this topic receiving 87752 citations. The topic is also known as: FLRW metric.


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Journal ArticleDOI
TL;DR: Under a suitable hypothesis on the behavior of the extrinsic curvature, it is found that an initially large �(t) rolls down rapidly to zero during the early stages of the universe.
Abstract: The cosmological constant problem is examined under the assumption that the extrinsic curvature of the space-time contributes to the vacuum. A compensation mechanism based on a variable cosmological term is proposed. Under a suitable hypothesis on the behavior of the extrinsic curvature, we find that an initially large �(t) rolls down rapidly to zero during the early stages of the universe. Using perturbation analysis, it is shown that such vacuum behaves essentially as a spin-2 field which is independent of the metric.

31 citations

Journal ArticleDOI
TL;DR: Some LRS Bianchi type V viscous-fluid cosmological models are investigated, in which the coefficient of shear viscosity is considered as proportional to the scale of expansion in the model as discussed by the authors.
Abstract: Some LRS Bianchi type V viscous-fluid cosmological models are investigated, in which the coefficient of shear viscosity is considered as proportional to the scale of expansion in the model. This leads toA=Bn, whereA andB are metric potentials,n being a constant. The coefficient of bulk viscosity is also assumed to be a power function of mass density. The cosmological constant is found to be a decreasing function of time, which is supported by results from recent type Ia supernovae observations. Some physical aspects of the models are also discussed.

31 citations

Journal ArticleDOI
TL;DR: In this paper, the authors follow the approach of induced-matter theory for a five-dimensional (5D) vacuum Brans-Dicke theory and employ a generalized FRW type solution.
Abstract: We follow the approach of induced-matter theory for a five-dimensional (5D) vacuum Brans–Dicke theory and introduce induced-matter and induced potential in four dimensional (4D) hypersurfaces, and then employ a generalized FRW type solution. We confine ourselves to the scalar field and scale factors be functions of the cosmic time. This makes the induced potential, by its definition, vanishes, but the model is capable to expose variety of states for the universe. In general situations, in which the scale factor of the fifth dimension and scalar field are not constants, the 5D equations, for any kind of geometry, admit a power–law relation between the scalar field and scale factor of the fifth dimension. Hence, the procedure exhibits that 5D vacuum FRW-like equations are equivalent, in general, to the corresponding 4D vacuum ones with the same spatial scale factor but a new scalar field and a new coupling constant, $${\tilde{\omega}}$$ . We show that the 5D vacuum FRW-like equations, or its equivalent 4D vacuum ones, admit accelerated solutions. For a constant scalar field, the equations reduce to the usual FRW equations with a typical radiation dominated universe. For this situation, we obtain dynamics of scale factors of the ordinary and extra dimensions for any kind of geometry without any priori assumption among them. For non-constant scalar fields and spatially flat geometries, solutions are found to be in the form of power–law and exponential ones. We also employ the weak energy condition for the induced-matter, that gives two constraints with negative or positive pressures. All types of solutions fulfill the weak energy condition in different ranges. The power–law solutions with either negative or positive pressures admit both decelerating and accelerating ones. Some solutions accept a shrinking extra dimension. By considering non-ghost scalar fields and appealing the recent observational measurements, the solutions are more restricted. We illustrate that the accelerating power–law solutions, which satisfy the weak energy condition and have non-ghost scalar fields, are compatible with the recent observations in ranges −4/3 < ω ≤ −1.3151 for the coupling constant and 1.5208 ≤ n < 1.9583 for dependence of the fifth dimension scale factor with the usual scale factor. These ranges also fulfill the condition $${\tilde{\omega} > -3/2}$$ which prevents ghost scalar fields in the equivalent 4D vacuum Brans–Dicke equations. The results are presented in a few tables and figures.

31 citations

Journal ArticleDOI
TL;DR: In this article, it was shown that the scalar-vacuum Brans-Dicke equations in 5D are equivalent to Brans Dicke theory in 4D with a self-interacting potential and an effective matter field.
Abstract: We show that the scalar-vacuum Brans–Dicke equations in 5D are equivalent to Brans–Dicke theory in 4D with a self-interacting potential and an effective matter field. The cosmological implication, in the context of FRW models, is that the observed accelerated expansion of the universe comes naturally from the condition that the scalar field is not a ghost, i.e. ω > −3/2. We find an effective matter-dominated 4D universe which shows accelerated expansion if −3/2 < ω < −1. We study the question of whether accelerated expansion can be made compatible with large values of ω, within the framework of a 5D scalar-vacuum Brans–Dicke theory with variable, instead of constant, parameter ω. In this framework, and based on a general class of solutions of the field equations, we demonstrate that accelerated expansion is incompatible with large values of ω.

31 citations

Journal ArticleDOI
TL;DR: In this paper, the authors explore warm inflation in the background of the theory of gravity using scalar fields for the FRW universe model and construct the field equations under slow-roll approximations.
Abstract: The aim of this paper is to explore warm inflation in the background of $f(\mathcal{G})$ theory of gravity using scalar fields for the FRW universe model. We construct the field equations under slow-roll approximations and evaluate the slow-roll parameters, scalar and tensor power spectra and their corresponding spectral indices using viable power-law model. These parameters are evaluated for a constant as well as variable dissipation factor during intermediate and logamediate inflationary epochs. We also find the number of e-folds and tensor-scalar ratio for each case. The graphical behavior of these parameters proves that the isotropic model in $f(\mathcal{G})$ gravity is compatible with observational Planck data.

31 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023150
2022352
2021196
2020204
2019214
2018191