scholarly journals The Perturbation of Material Density in f(R) Modified Gravity of Polynormal Exponential Form

10.29007/xqpk ◽  
2020 ◽  
Author(s):  
Van On Vo
Keyword(s):  
Cosmological Model ◽  
Modified Gravity ◽  
Linear Perturbation ◽  
Exponential Form ◽  
Material Density ◽  
Gravitational Model ◽  
Standard Cosmological Model ◽  
The Difference ◽  
Evolutionary Aspects ◽  
The Universe

In this paper, we investigate the linear perturbation of the material density of the universe in f(R) modified gravity of polynomial exponential form on the scale of distance below the cosmic horizon (sub-horizon). The results show that the model for the evolutionary aspects of the universe is slightly different from that in the standard cosmological model of ΛCDM. They can be used to show the difference between this modified gravitational model with the standard cosmological model of ΛCMD and other cosmological models. We also investigate the ration Ψ/ Φ and Geff / GN in the model and show that they are within allowable limits of experiments.

scholarly journals O UNIVERSO VIVO

2012 ◽  
Vol 19 (1.2) ◽  
Author(s):  
Francisco César de Sá Barreto ◽  
Luiz Paulo Ribeiro Vaz ◽  
Gabriel Armando Pellegatti Franco
Keyword(s):  
Cosmological Model ◽  
Chemical Elements ◽  
Big Bang ◽  
Living System ◽  
Irreversible Processes ◽  
Thermodynamics Of Irreversible Processes ◽  
Protons And Neutrons ◽  
Standard Cosmological Model ◽  
The Big Bang ◽  
The Universe

The standard cosmological model suggests that after the “Big Bang”, 14 billion of years ago, the universe entered a period of expansion and cooling. In the first one millionth of a second appear quarks, glúons, electrons and neutrinos, followed by the appearance of protons and neutrons. In this paper, we describe the “cosmic battle” between gravitation and energy, responsible for the lighter chemical elements and the formation of the stars. We describe the thermodynamics of irreversible processes of systems which are far away from equilibrium, a route that is followed by the universe, seen as a living system.

Gravity, stability and cosmological models

2017 ◽  
Vol 26 (12) ◽  
pp. 1743026
Author(s):  
Asher Yahalom
Keyword(s):  
Stability Analysis ◽  
Cosmological Model ◽  
Cosmological Constant ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Lorentzian Metric ◽  
Standard Cosmological Model ◽  
Flat Spacetimes ◽  
Stable Solutions ◽  
The Universe

Stability analysis plays a major rule in our understanding of nature. For example it was shown that among empty flat spacetimes only those with a Lorentzian metric are stable [A. Yahalom, Found Phys. 38 (2008) 489–497; Int. J. Mod. Phys. D 18(4) (2009) 2155–2158]. However, the universe is not empty and the energy momentum tensor is metric dependent an thus effects stability. In this essay we concentrate on simple perturbations of the standard cosmological model with and without cosmological constant which is based on a uniform mass distribution. The results suggest that while Euclidean, open or closed section models are valid solutions, the choice of stable solutions is limited. In particular, the popular Lambda-CDM model is unstable.

scholarly journals Cosmological evolution with interaction between dark energy and dark matter

2015 ◽  
Vol 24 (03) ◽  
pp. 1530007 ◽  
Author(s):  
Yuri L. Bolotin ◽  
Alexander Kostenko ◽  
Oleg A. Lemets ◽  
Danylo A. Yerokhin
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Model ◽  
Holographic Dark Energy ◽  
Main Task ◽  
Nonlinear Interactions ◽  
Dark Sector ◽  
Standard Cosmological Model ◽  
Linear And Nonlinear ◽  
The Universe

In this review we consider in detail different theoretical topics associated with interaction in the dark sector. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities. We consider a number of different models (including the holographic dark energy and dark energy in a fractal universe), with interacting dark energy and dark matter, have done a thorough analysis of these models. The main task of this review was not only to give an idea about the modern set of different models of dark energy, but to show how much can be diverse dynamics of the universe in these models. We find that the dynamics of a universe that contains interaction in the dark sector can differ significantly from the Standard Cosmological Model.

scholarly journals COSMOLOGY: A BIRD'S EYE VIEW

2006 ◽  
Vol 15 (12) ◽  
pp. 2187-2190 ◽  
Author(s):  
ALAN A. COLEY ◽  
SIGBJØRN HERVIK ◽  
WOEI CHET LIM
Keyword(s):  
Fluid Flow ◽  
Equation Of State ◽  
Cosmological Model ◽  
Finite Time ◽  
Dynamical Behavior ◽  
The Other ◽  
Flow Lines ◽  
Big Rip ◽  
The Difference ◽  
The Universe

We discuss the difference in views of the universe as seen by two different observers. While one of the observers follows a geodesic congruence defined by the geometry of the cosmological model, the other observer follows the fluid flow lines of a perfect fluid with a linear equation of state. We point out that the information these observers collect regarding the state of the universe can be radically different; while one observes a non-inflating, ever-expanding, ever-lasting universe, the other observer can experience a dynamical behavior reminiscent of that of quintessence or even that of a phantom cosmology leading to a "big rip" singularity within finite time (but without the need for exotic forms of matter).

scholarly journals Anisotropic Cosmological Model in a Modified Theory of Gravitation

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 226
Author(s):  
Rishi Kumar Tiwari ◽  
Aroonkumar Beesham ◽  
Soma Mishra ◽  
Vipin Dubey
Keyword(s):  
Cosmological Model ◽  
Modified Gravity ◽  
Bianchi Type ◽  
Late Time ◽  
Type I ◽  
Bianchi Models ◽  
Theory Of Gravitation ◽  
The Universe ◽  
Type Parameter ◽  
Modified Theory

Current observations indicate that, on a large enough scale, the universe is homogeneous and isotropic. However, this does not preclude the possibility of some anisotropy having occurred during the early stages of the evolution of the universe, which could then have been damped out later. This idea has aroused interest in the Bianchi models, which are homogeneous but anisotropic. Secondly, there is much interest in modified gravity these days due to the problems that the usual ΛCDM model faces in general relativity. Hence, in this paper, a study was conducted on the Bianchi type-I cosmological model in f(R,T)-modified gravity. Following some ideas from cosmography, a specific form of the deceleration parameter was assumed, leading to a model that exhibited a transition from early deceleration to late-time acceleration. The derived model approached isotropy at late times. The physical properties of the model were discussed, and expressions for the various parameters of the model were derived. It is also possible to make progress towards solving the cosmological constant problem, since in this model in f(R,T) gravity, a variable cosmological-type parameter arose, which was large early on but decreased to a constant value in later times.

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 EVOLUTION OF DISTRIBUTION FUNCTION FOR COSMOLOGICAL NEUTRINO

2013 ◽  
Vol 23 ◽  
pp. 379-385 ◽  
Author(s):  
HYUNG WON LEE ◽  
KYOUNG YEE KIM ◽  
REMO RUFFINI
Keyword(s):  
Distribution Function ◽  
Cosmological Model ◽  
Cosmological Models ◽  
Standard Cosmological Model ◽  
Degenerate Neutrino ◽  
The Universe ◽  
Quintessence Model

Recent experimental evidences show that the universe is accelerating. There are many modified cosmological models to explain this accelerating phase including ΛCDM, quintessence model, Brans-Dicke, f(R) gravity, and others. In this talk we want to check the possibility of explaining the current accelerating phase using standard cosmological model with degenerate neutrino. We will study the evolution of distribution function of degenerate neutrinos with standard Friedmann-Lemaître-Roberston-Walker(FLRW) background.

scholarly journals A hybrid model of viscous and Chaplygin gas to tackle the Universe acceleration

2021 ◽  
Vol 81 (4) ◽  
Author(s):  
A. Hernández-Almada ◽  
Miguel A. García-Aspeitia ◽  
M. A. Rodríguez-Meza ◽  
V. Motta
Keyword(s):  
Cosmological Model ◽  
Hybrid Model ◽  
Hubble Constant ◽  
Chaplygin Gas ◽  
Joint Analysis ◽  
Acoustic Oscillations ◽  
Generalized Chaplygin Gas ◽  
Om Diagnostic ◽  
Standard Cosmological Model ◽  
The Universe

AbstractMotivated by two seminal models proposed to explain the Universe acceleration, this paper is devoted to study a hybrid model which is constructed through a generalized Chaplygin gas with the addition of a bulk viscosity. We call the model a viscous generalized Chaplygin gas (VGCG) and its free parameters are constrained through several cosmological data like the Observational Hubble Parameter, Type Ia Supernovae, Baryon Acoustic Oscillations, Strong Lensing Systems, HII Galaxies and using Joint Bayesian analysis. In addition, we implement a Om-diagnostic to analyze the VGCC dynamics and its difference with the standard cosmological model. The hybrid model shows important differences when compared with the standard cosmological model. Finally, based on our Joint analysis we find that the VGCG could be an interesting candidate to alleviate the well-known Hubble constant tension.

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