scholarly journals Chameleon field and the late time acceleration of the Universe

Pramana ◽  
2010 ◽  
Vol 74 (3) ◽  
pp. 481-489 ◽  
Author(s):  
Narayan Banerjee ◽  
Sudipta Das ◽  
Koyel Ganguly
Keyword(s):  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

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 Dirac Field as a Source of the Inflation in2+1Dimensional Teleparallel Gravity

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Ganim Gecim ◽  
Yusuf Sucu
Keyword(s):  
Early Time ◽  
Teleparallel Gravity ◽  
Noether Symmetry ◽  
Dirac Field ◽  
Late Time ◽  
Late Time Acceleration ◽  
Symmetry Approach ◽  
Gauge Term ◽  
Acceleration Of The Universe ◽  
The Universe

In this paper, we study early-time inflation and late-time acceleration of the universe by nonminimally coupling the Dirac field with torsion in the spatially flat Friedman-Robertson-Walker (FRW) cosmological model background. The results obtained by the Noether symmetry approach with and without a gauge term are compared. Additionally, we compare these results with that of the3+1dimensional teleparallel gravity under Noether symmetry approach. And we see that the study explains early-time inflation and late-time acceleration of the universe.

scholarly journals The Lambert W Function: A Newcomer in the Cosmology Class?

2019 ◽  
Vol 75 (1) ◽  
pp. 23-27
Author(s):  
Subhajit Saha ◽  
Kazuharu Bamba
Keyword(s):  
Equation Of State ◽  
Evolutionary History ◽  
Initial Singularity ◽  
Lambert W Function ◽  
Late Time ◽  
Unknown Parameters ◽  
Late Time Acceleration ◽  
History Of ◽  
Acceleration Of The Universe ◽  
The Universe

AbstractWe propose a novel equation of state (EoS) which explains the evolutionary history of a flat Friedmann–Lemaitre–Robertson–Walker universe. The uniqueness of this EoS lies in the fact that it incorporates the Lambert W function in a special fashion. It is explicitly demonstrated that with observationally relevant values of the unknown parameters ϑ1 and ϑ2, all the evolutionary phases of the universe can be reproduced. Moreover, it also shows that the initial singularity is unavoidable and asserts that the late-time acceleration of the universe would continue forever.

scholarly journals Invisible QCD as Dark Energy

Universe ◽  
2020 ◽  
Vol 6 (6) ◽  
pp. 75
Author(s):  
Andrea Addazi ◽  
Stephon Alexander ◽  
Antonino Marcianò
Keyword(s):  
Dark Energy ◽  
Stability Analysis ◽  
Equation Of State ◽  
Quantum Chromodynamics ◽  
Early Universe ◽  
Negative Pressure ◽  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

We account for the late time acceleration of the Universe by extending the Quantum Chromodynamics (QCD) color to a S U ( 3 ) invisible sector (IQCD). If the Invisible Chiral symmetry is broken in the early universe, a condensate of dark pions (dpions) and dark gluons (dgluons) forms. The condensate naturally forms due to strong dynamics similar to the Nambu–Jona-Lasinio mechanism. As the Universe evolves from early times to present times the interaction energy between the dgluon and dpion condensate dominates with a negative pressure equation of state and causes late time acceleration. We conclude with a stability analysis of the coupled perturbations of the dark pions and dark gluons.

Inflation and dark energy in f(R, X, ϕ) gravity

2018 ◽  
Vol 33 (36) ◽  
pp. 1850215 ◽  
Author(s):  
A. I. Keskin
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Observational Data ◽  
Observational Constraints ◽  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

In this study, we show the early inflation and the late-time acceleration of the universe in the model [Formula: see text], which shows a minimum connection between geometry and scalar field. Both a quintessential inflation and the super inflation mechanism are discussed in the model, and for both the cases the some conditions for n are obtained under the constraint of the observational data. However, the oscillations of the scalar field are analyzed in view of observational constraints. By means of the oscillations of the scalar field, besides the inflation of the universe a condition of n for the late-time quintessence type of dark energy is obtained.

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.

scholarly journals A LATE TIME ACCELERATION OF THE UNIVERSE WITH TWO SCALAR FIELDS: MANY POSSIBILITIES

2006 ◽  
Vol 21 (35) ◽  
pp. 2663-2670 ◽  
Author(s):  
NARAYAN BANERJEE ◽  
SUDIPTA DAS
Keyword(s):  
Scalar Field ◽  
Scalar Fields ◽  
Cosmic Acceleration ◽  
The Other ◽  
Field Conditions ◽  
Late Time ◽  
Late Time Acceleration ◽  
Acceleration Of The Universe ◽  
The Universe

In the present work, an attempt has been made to explain the recent cosmic acceleration of the universe with two mutually interacting scalar fields, one being the Brans–Dicke scalar field and the other a quintessence scalar field. Conditions have been derived for which the quintessence scalar field has an early oscillation and it grows during a later time to govern the dynamics of the universe.

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