scholarly journals Notes on the post-bounce background dynamics in bouncing cosmologies

2021 ◽  
Vol 2021 (10) ◽  
Author(s):  
Ok Song An ◽  
Jin U Kang ◽  
Thae Hyok Kim ◽  
Ui Ri Mun
Keyword(s):  
Scalar Field ◽  
Accelerated Expansion ◽  
Late Time ◽  
Exponential Potential ◽  
Cosmological Constraints ◽  
Cyclic Model ◽  
Negative Exponential ◽  
Bouncing Cosmologies

Abstract We investigate the post-bounce background dynamics in a certain class of single bounce scenarios studied in the literature, in which the cosmic bounce is driven by a scalar field with negative exponential potential such as the ekpyrotic potential. We show that those models can actually lead to cyclic evolutions with repeated bounces. These cyclic evolutions, however, do not account for the currently observed late-time accelerated expansion and hence are not cosmologically viable. In this respect we consider a new kind of cyclic model proposed recently and derive some cosmological constraints on this model.

scholarly journals A novel teleparallel dark energy model

2016 ◽  
Vol 25 (02) ◽  
pp. 1650025 ◽  
Author(s):  
Giovanni Otalora
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Teleparallel Gravity ◽  
Accelerated Expansion ◽  
Late Time ◽  
De Sitter ◽  
Sitter Group ◽  
Current State ◽  
Expansion Of The Universe ◽  
The Universe

Although equivalent to general relativity, teleparallel gravity (TG) is conceptually speaking a completely different theory. In this theory, the gravitational field is described by torsion, not by curvature. By working in this context, a new model is proposed in which the four-derivative of a canonical scalar field representing dark energy is nonminimally coupled to the “vector torsion”. This type of coupling is motivated by the fact that a scalar field couples to torsion through its four-derivative, which is consistent with local spacetime kinematics regulated by the de Sitter group [Formula: see text]. It is found that the current state of accelerated expansion of the universe corresponds to a late-time attractor that can be (i) a dark energy-dominated de Sitter solution ([Formula: see text]), (ii) a quintessence-type solution with [Formula: see text], or (iii) a phantom-type [Formula: see text] dark energy.

scholarly journals Constraining the ΛCDM and Galileon models with recent cosmological data

2017 ◽  
Vol 600 ◽  
pp. A40 ◽  
Author(s):  
J. Neveu ◽  
V. Ruhlmann-Kleider ◽  
P. Astier ◽  
M. Besançon ◽  
J. Guy ◽  
...  
Keyword(s):  
Cosmological Parameters ◽  
Acoustic Oscillation ◽  
Gravity Models ◽  
Accelerated Expansion ◽  
Data Sets ◽  
Late Time ◽  
Lunar Laser Ranging ◽  
Cosmological Constraints ◽  
Cosmological Data ◽  
Speed Of Propagation

Aims. The Galileon theory belongs to the class of modified gravity models that can explain the late-time accelerated expansion of the Universe. In previous works, cosmological constraints on the Galileon model were derived, both in the uncoupled case and with a disformal coupling of the Galileon field to matter. There, we showed that these models agree with the most recent cosmological data. In this work, we used updated cosmological data sets to derive new constraints on Galileon models, including the case of a constant conformal Galileon coupling to matter. We also explored the tracker solution of the uncoupled Galileon model. Methods. After updating our data sets, especially with the latest Planck data and baryonic acoustic oscillation (BAO) measurements, we fitted the cosmological parameters of the ΛCDM and Galileon models. The same analysis framework as in our previous papers was used to derive cosmological constraints, using precise measurements of cosmological distances and of the cosmic structure growth rate. Results. We show that all tested Galileon models are as compatible with cosmological data as the ΛCDM model. This means that present cosmological data are not accurate enough to distinguish clearly between the two theories. Among the different Galileon models, we find that a conformal coupling is not favoured, contrary to the disformal coupling which is preferred at the 2.3σ level over the uncoupled case. The tracker solution of the uncoupled Galileon model is also highly disfavoured owing to large tensions with supernovae and Planck+BAO data. However, outside of the tracker solution, the general uncoupled Galileon model, as well as the general disformally coupled Galileon model, remain the most promising Galileon scenarios to confront with future cosmological data. Finally, we also discuss constraints coming from the Lunar Laser Ranging experiment and gravitational wave speed of propagation.

BRANS-DICKE COSMOLOGY WITH FERMIONS AND CHAMELEON MECHANISM

2012 ◽  
Vol 07 ◽  
pp. 174-183
Author(s):  
DAO-JUN LIU ◽  
BIN YANG ◽  
XING-HUA JIN
Keyword(s):  
Scalar Field ◽  
Interaction Potential ◽  
The Self ◽  
Accelerated Expansion ◽  
Late Time ◽  
Fermion Field ◽  
Chameleon Mechanism ◽  
Expansion Of The Universe ◽  
Stable Solutions ◽  
The Universe

We study the cosmological dynamics of Brans-Dicke theory in which there are fermions with a coupling to BD scalar field as well as a self-interaction potential. The conditions that there exists a solution which is stable and represents a late-time accelerated expansion of the universe are found. It is shown that the late-time acceleration depends completely on the self-interaction of the fermion field if our investigation is restricted to the theory with positive BD parameter ω. Provided a negative ω is allowed, there will be another two class of stable solutions describing late-time accelerated expansion of the universe. Besides, we find that chameleon mechanism will be possessed in our theory when a suitable self-interaction of fermion field is considered.

scholarly journals Dynamics of two-scalar-field cosmological models beyond the exponential potential

2017 ◽  
Vol 26 (14) ◽  
pp. 1750164 ◽  
Author(s):  
Yu Li
Keyword(s):  
Scalar Field ◽  
Energy Density ◽  
Cosmological Models ◽  
The Other ◽  
Late Time ◽  
Exponential Potential ◽  
Multiple Attractors ◽  
Evolution Of The Universe ◽  
The Universe

In this paper, we discuss the dynamics of two- scalar-field cosmological models. Unlike in the situation of exponential potential, we find that there are late-time attractors in which one scalar field dominates the energy density of universe and the other one decay. We also discuss the possibility of multiple attractors model which is useful to realize the evolution of the universe from a scaling era to recent acceleration era. We also give the conditions of the existence of multiple attractors.

scholarly journals REQUIRED CONDITIONS FOR LATE TIME ACCELERATION AND EARLY TIME DECELERATION IN GENERALIZED SCALAR–TENSOR THEORIES

2003 ◽  
Vol 18 (04) ◽  
pp. 651-671 ◽  
Author(s):  
L. M. DIAZ-RIVERA ◽  
LUIS O. PIMENTEL
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Cosmological Parameters ◽  
Early Time ◽  
Weak Field ◽  
Scale Factor ◽  
Coupling Function ◽  
Accelerated Expansion ◽  
Late Time ◽  
Cosmological Constants

We consider a generalized scalar–tensor theory, where we let the coupling function ω(ϕ) and the effective cosmological constants Λ(ϕ) be undetermined. We obtain general expressions for ω(ϕ) and Λ(ϕ) in terms of the scalar field and the scale factor, and show that ω(ϕ) depends on the scalar field and the scale factor in a complicated way. In order to study the conditions for an accelerated expansion at the present time and a decelerated expansion in the past, we assume a power law evolution for the scalar field and the scale factor. We analyze the required conditions that allow our model to satisfy the weak field limits on ω(ϕ), and at the same time, to obtain the correct values of cosmological parameters, as the energy density Ωm0 and cosmological constant Λ(t0). We also study the conditions for a decelerated expansion at an early time dominated by radiation. We find values for ω(ϕ) and Λ(ϕ) consistent with the expectations of a where the cosmological constant decreases with the time and the coupling function increases until the values are accepted today.

On the late-time cosmology of a condensed scalar field

2016 ◽  
Vol 31 (12) ◽  
pp. 1650078
Author(s):  
Amir Ghalee
Keyword(s):  
Dark Matter ◽  
Scalar Field ◽  
Condensed Phase ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Kinetic Term ◽  
Late Time ◽  
Gradient Instability

We study the late-time cosmology of a scalar field with a kinetic term non-minimally coupled to gravity. It is demonstrated that the scalar field dominate the radiation matter and the cold dark matter (CDM). Moreover, we show that eventually the scalar field will be condensed and results in an accelerated expansion. The metric perturbations around the condensed phase of the scalar field are investigated and it has been shown that the ghost instability and gradient instability do not exist.

scholarly journals Dynamics of a scalar field, with a double exponential potential, interacting with dark matter

2015 ◽  
Vol 24 (08) ◽  
pp. 1550068 ◽  
Author(s):  
Vartika Gupta ◽  
Rakesh Kabir ◽  
Amitabha Mukherjee ◽  
Daksh Lohiya
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Effective Potential ◽  
Cosmological Evolution ◽  
Late Time ◽  
Exponential Potential ◽  
Double Exponential

We study the interaction between dark matter and dark energy, with dark energy described by a scalar field having a double exponential effective potential. We discover conditions under which such a scalar field driven solution is a late time attractor. We observe a realistic cosmological evolution which consists of sequential stages of dominance of radiation, matter and dark energy, respectively.

scholarly journals Intermediate Inflation or Late Time Acceleration?

2008 ◽  
Vol 2008 ◽  
pp. 1-16 ◽  
Author(s):  
Abhik Kumar Sanyal
Keyword(s):  
Scalar Field ◽  
Power Law ◽  
Cosmological Evolution ◽  
Expansion Rate ◽  
Accelerated Expansion ◽  
Kinetic Term ◽  
Late Time ◽  
Late Time Acceleration ◽  
Cosmic Evolution ◽  
Scaling Solution

The expansion rate of “intermediate inflation” lies between the exponential and power law expansion but corresponding accelerated expansion does not start at the onset of cosmological evolution. Present study of “intermediate inflation” reveals that it admits scaling solution and has got a natural exit form it at a later epoch of cosmic evolution, leading to late time acceleration. The corresponding scalar field responsible for such feature is also found to behave as a tracker field for gravity with canonical kinetic term.

scholarly journals QUINTESSENCE: A MINI-REVIEW

2008 ◽  
Vol 23 (17n20) ◽  
pp. 1252-1265 ◽  
Author(s):  
JÉRÔME MARTIN
Keyword(s):  
Scalar Field ◽  
High Energy Physics ◽  
Physical Nature ◽  
High Energy ◽  
Accelerated Expansion ◽  
Ordinary Matter ◽  
Chameleon Effect ◽  
Tests Of Gravity ◽  
Energy Physics

Models where the accelerated expansion of our Universe is caused by a quintessence scalar field are reviewed. In the framework of high energy physics, the physical nature of this field is discussed and its interaction with ordinary matter is studied and explicitly calculated. It is shown that this coupling is generically too strong to be compatible with local tests of gravity. A possible way out, the chameleon effect, is also briefly investigated.

scholarly journals Autonomous dynamical system description of de Sitter evolution in scalar assisted f(R) − ϕ gravity

2018 ◽  
Vol 15 (12) ◽  
pp. 1850212 ◽  
Author(s):  
K. Kleidis ◽  
V. K. Oikonomou
Keyword(s):  
Dynamical System ◽  
Numerical Analysis ◽  
Scalar Field ◽  
Analysis Approach ◽  
Single Variable ◽  
De Sitter ◽  
Exponential Potential ◽  
System Description ◽  
Variable Formula ◽  
Autonomous Dynamical System

In this paper we will study the cosmological dynamical system of an [Formula: see text] gravity in the presence of a canonical scalar field [Formula: see text] with an exponential potential by constructing the dynamical system in a way that it is rendered autonomous. This feature is controlled by a single variable [Formula: see text], which when it is constant, the dynamical system is autonomous. We focus on the [Formula: see text] case which, as we demonstrate by using a numerical analysis approach, leads to an unstable de Sitter attractor, which occurs after [Formula: see text] [Formula: see text]-foldings. This instability can be viewed as a graceful exit from inflation, which is inherent to the dynamics of de Sitter attractors.

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