scholarly journals Cosmological models with a hybrid scale factor

2021 ◽  
pp. 2140005
Author(s):  
S. K. Tripathy ◽  
B. Mishra ◽  
Maxim Khlopov ◽  
Saibal Ray
Keyword(s):  
General Relativity ◽  
Scale Factor ◽  
Cosmological Models ◽  
Late Time ◽  
Late Time Acceleration ◽  
Present Universe ◽  
Matter Fields

In this paper, we present some cosmological models with a hybrid scale factor (HSF) in the framework of general relativity (GR). The HSF fosters an early deceleration as well as a late-time acceleration and mimics the present Universe. The dynamical aspects of different cosmological models with HSF in the presence of different matter fields have been discussed.

A probe of cosmological models in modified teleparallel gravity

2021 ◽  
pp. 2150208
Author(s):  
Archana Dixit ◽  
Anirudh Pradhan ◽  
Dinesh Chandra Maurya
Keyword(s):  
Hubble Constant ◽  
Teleparallel Gravity ◽  
Cosmological Term ◽  
Cosmological Models ◽  
Model Parameters ◽  
Late Time ◽  
General Function ◽  
Eos Parameter ◽  
Variable Cosmological Term ◽  
Present Universe

In this paper, we have investigated the physical behavior of cosmological models in modified Teleparallel gravity with a general function [Formula: see text] where [Formula: see text] and [Formula: see text] are model parameters and [Formula: see text] is the torsion scalar. We have considered a homogeneous and isotropic Friedman universe filled with perfect fluid. We have derived the deceleration parameter [Formula: see text] in terms of equation of state (EoS) parameter [Formula: see text] and Hubble parameter [Formula: see text]. We have investigated the variation of [Formula: see text] over the observed values of Hubble constant in various observations within the range of redshift [Formula: see text]. Also, we have studied effective energy density [Formula: see text], effective pressure [Formula: see text] and effective EoS parameter [Formula: see text]. We have observed that the second term of [Formula: see text] function behaves just like variable cosmological term [Formula: see text] ([Formula: see text]) at late-time universe and causes the acceleration in expansion and works just like dark energy candidates. Also, we have evaluated the age of the present universe for various stages of matter [Formula: see text] and various [Formula: see text] functions.

scholarly journals DARK ENERGY IN PRACTICE

2010 ◽  
Vol 25 (29) ◽  
pp. 5253-5331 ◽  
Author(s):  
DOMENICO SAPONE
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Complete List ◽  
Late Time ◽  
Evolution Of The Universe ◽  
Late Time Acceleration ◽  
Energy Models ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Alternative Theories

In this paper we review a part of the approaches that have been considered to explain the extraordinary discovery of the late time acceleration of the Universe. We discuss the arguments that have led physicists and astronomers to accept dark energy as the current preferable candidate to explain the acceleration. We highlight the problems and the attempts to overcome the difficulties related to such a component. We also consider alternative theories capable of explaining the acceleration of the Universe, such as modification of gravity. We compare the two approaches and point out the observational consequences, reaching the sad but foresightful conclusion that we will not be able to distinguish between a Universe filled by dark energy or a Universe where gravity is different from General Relativity. We review the present observations and discuss the future experiments that will help us to learn more about our Universe. This is not intended to be a complete list of all the dark energy models but this paper should be seen as a review on the phenomena responsible for the acceleration. Moreover, in a landscape of hardly compelling theories, it is an important task to build simple measurable parameters useful for future experiments that will help us to understand more about the evolution of the Universe.

scholarly journals Viscous Fluid Bianchi Type V Cosmological Models with Late Time Acceleration

2016 ◽  
Vol 1 (3) ◽  
Author(s):  
J. P. Singh ◽  
◽  
Prashant S. Baghel ◽  
Abhay Singh ◽  
◽  
...  
Keyword(s):  
Viscous Fluid ◽  
Bianchi Type ◽  
Cosmological Models ◽  
Late Time ◽  
Late Time Acceleration ◽  
Type V ◽  
Bianchi Type V

scholarly journals POWER-LAWS f(R) THEORIES ARE COSMOLOGICALLY UNACCEPTABLE

2007 ◽  
Vol 16 (10) ◽  
pp. 1555-1561 ◽  
Author(s):  
LUCA AMENDOLA ◽  
DAVID POLARSKI ◽  
SHINJI TSUJIKAWA
Keyword(s):  
Dark Energy ◽  
Recent Work ◽  
Modified Gravity ◽  
Cosmic Time ◽  
Power Laws ◽  
Scale Factor ◽  
Late Time ◽  
Cosmic Expansion ◽  
Late Time Acceleration ◽  
Energy Models

In a recent paper,1 we have shown that f(R) = R + μRn modified gravity dark energy models are not cosmologically viable because during the matter era that precedes the accelerated stage the cosmic expansion is given by a ~ t1/2 rather than a ~ t2/3, where a is a scale factor and t is the cosmic time. A recent work by Capozziello et al.2 criticized our results presenting some apparent counter-examples to our claim in f(R) = μRn models. We show here that those particular Rn models can produce an expansion as a ~ t2/3 but this does not connect to a late-time acceleration. Hence, though acceptable f(R) dark energy models might exist, the Rn models presented in Capozziello et al. are not cosmologically viable, confirming our previous results in Ref. 1.

scholarly journals The asymptotic behavior of bouncing cosmological models in F(𝒢) gravity theory

2017 ◽  
Vol 14 (10) ◽  
pp. 1750148 ◽  
Author(s):  
Andrey N. Makarenko ◽  
Alexander N. Myagky
Keyword(s):  
Asymptotic Behavior ◽  
Early Universe ◽  
Asymptotic Expansions ◽  
Scale Factor ◽  
Cosmological Models ◽  
Gravity Theory ◽  
Late Time ◽  
Puiseux Series ◽  
Friedmann Equations

We reconstruct [Formula: see text] gravity theory with an exponential scale factor to realize the bouncing behavior in the early universe and examine the asymptotic behavior of late-time solutions in this model. We propose an approach for the construction of asymptotic expansions of solutions of the Friedmann equations on the basis of Puiseux series.

scholarly journals Considering Late-Time Acceleration in Some Cosmological Models

2013 ◽  
Vol 2013 ◽  
pp. 1-14 ◽  
Author(s):  
S. Davood Sadatian
Keyword(s):  
Scalar Field ◽  
Lorentz Invariance ◽  
Cosmological Models ◽  
Brane World ◽  
Late Time ◽  
World Model ◽  
Late Time Acceleration ◽  
Invariance Violation ◽  
Lorentz Invariance Violation

We study two cosmological models: a nonminimally coupled scalar field on brane world model and a minimally coupled scalar field on Lorentz invariance violation model. We compare some cosmological results in these scenarios. Also, we consider some types of Rip singularity solution in both models.

ASYMPTOTIC BEHAVIOR OF HOMOGENEOUS COSMOLOGICAL MODELS ON THE BRANE

2003 ◽  
Vol 18 (17) ◽  
pp. 1197-1203
Author(s):  
SUBENOY CHAKRABORTY
Keyword(s):  
Cosmological Term ◽  
Cosmological Models ◽  
Brane World ◽  
Late Time ◽  
Time Behavior ◽  
De Sitter ◽  
Bianchi Models ◽  
Bianchi Ix ◽  
Homogeneous Cosmological Models ◽  
Matter Fields

In this work, we have studied the late-time behavior of initially expanding homogeneous cosmological models with a positive cosmological term in Randall–Sundrum brane-world type scenarios. The matter fields are confined in the three-brane, onto which the five-dimensional Weyl tensor has a nonvanishing projection. It is found that all Bianchi models (except IX) exponentially evolve toward the de Sitter solution while the Bianchi IX model also isotropizes but with a restriction on the cosmological parameter.

COSMIC ACCELERATION AND MODIFIED GRAVITY

2007 ◽  
Vol 16 (12a) ◽  
pp. 2065-2074 ◽  
Author(s):  
MARK TRODDEN
Keyword(s):  
General Relativity ◽  
Dark Energy ◽  
Modified Gravity ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

I briefly discuss some attempts to construct a consistent modification to general relativity (GR) that might explain the observed late-time acceleration of the Universe and provide an alternative to dark energy. I describe the issues facing extensions to GR, illustrate these with a specific example, and discuss the resulting observational and theoretical obstacles.

Sign in / Sign up

Export Citation Format

Share Document