scholarly journals Quintessence in low-energy effective theory

2018 ◽  
Vol 168 ◽  
pp. 08004
Author(s):  
Tae Hoon Lee
Keyword(s):  
Scalar Field ◽  
Effective Potential ◽  
Cosmological Solution ◽  
Low Energy ◽  
Effective Theory ◽  
Late Time ◽  
Inverse Power Law ◽  
Virtual Interactions ◽  
The Universe ◽  
Gravitational Equations

Considering a theory of Brans-Dicke gravity with general couplings of a heavy field, we derive the low-energy effective theory action in the universe of temperature much lower than the heavy field mass. Gravitational equations and the Brans-Dicke scalar field equation including an effective potential of the scalar field are obtained, which is induced through virtual interactions of the heavy field in the late-time universe. We find a deSitter cosmological solution stemming from the inverse power law effective potential of the scalar field and discuss the possibility that the late time acceleration of our universe can be described by means of the solution.

FIVE-DIMENSIONAL COSMOLOGICAL SCALING SOLUTION

2005 ◽  
Vol 20 (12) ◽  
pp. 923-928 ◽  
Author(s):  
BAORONG CHANG ◽  
HONGYA LIU ◽  
HUANYING LIU ◽  
LIXIN XU
Keyword(s):  
Dark Matter ◽  
Scalar Field ◽  
Phase Plane ◽  
Cosmological Solution ◽  
Phase Plane Analysis ◽  
Late Time ◽  
Plane Analysis ◽  
Scaling Solution ◽  
Frw Models ◽  
The Universe

A five-dimensional Ricci-flat cosmological solution is studied by assuming that the induced 4D matter contains two components: the usual fluid for dark matter as well as baryons and a scalar field with an exponential potential for dark energy. With use of the phase-plane analysis it is shown that there exist two late-time attractors one of which corresponds to a universe dominated by the scalar field alone and the other is a scaling solution in which the energy density of the scalar field remains proportional to that of the dark matter. It is furthermore shown that for this 5D scaling solution the universe expands with the same rate as in the 4D FRW models and not relies on which 4D hypersurface the universe is located in the 5D manifold.

Cosmic acceleration with tachyon field

2018 ◽  
Vol 33 (34) ◽  
pp. 1850199 ◽  
Author(s):  
A. I. Keskin
Keyword(s):  
Scalar Field ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Cosmic Acceleration ◽  
Late Time ◽  
De Sitter ◽  
Tachyon Field ◽  
Minimal Coupling ◽  
Acceleration Of The Universe ◽  
The Universe

In this study, we examine two models of the scalar field, that is, a normal scalar field and a tachyon scalar field in [Formula: see text] gravity to describe cosmic acceleration of the universe, where [Formula: see text], [Formula: see text] and [Formula: see text] are Ricci curvature scalar, trace of energy–momentum tensor and kinetic energy of scalar field [Formula: see text], respectively. Using the minimal-coupling Lagrangian [Formula: see text], for both the scalar models we obtain a viable cosmological system, where [Formula: see text] and [Formula: see text] are real constants. While a normal scalar field gives a system describing expansion from the deceleration to the late-time acceleration, tachyon field together with [Formula: see text] in the system produces a quintessential expansion which is very close to de Sitter point, where we find a new condition [Formula: see text] for inflation.

scholarly journals Chameleon field dynamics during inflation

2018 ◽  
Vol 27 (04) ◽  
pp. 1850041 ◽  
Author(s):  
Nasim Saba ◽  
Mehrdad Farhoudi
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
State Parameter ◽  
Big Bang ◽  
Late Time ◽  
Inflationary Model ◽  
Slow Roll ◽  
Equation Of State Parameter ◽  
The Common ◽  
The Universe

By studying the chameleon model during inflation, we investigate whether it can be a successful inflationary model, wherein we employ the common typical potential usually used in the literature. Thus, in the context of the slow-roll approximations, we obtain the e-folding number for the model to verify the ability of resolving the problems of standard big bang cosmology. Meanwhile, we apply the constraints on the form of the chosen potential and also on the equation of state parameter coupled to the scalar field. However, the results of the present analysis show that there is not much chance of having the chameleonic inflation. Hence, we suggest that if through some mechanism the chameleon model can be reduced to the standard inflationary model, then it may cover the whole era of the universe from the inflation up to the late time.

scholarly journals CAN BRANS–DICKE SCALAR FIELD ACCOUNT FOR DARK ENERGY AND DARK MATTER?

2006 ◽  
Vol 21 (15) ◽  
pp. 1241-1248 ◽  
Author(s):  
M. ARIK ◽  
M. C. ÇALIK
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Energy Density ◽  
Late Time ◽  
Energy Contribution ◽  
Time Solution ◽  
The Universe

By using a linearized non-vacuum late time solution in Brans–Dicke cosmology, we account for the 75% dark energy contribution but not for approximately 23% dark matter contribution to the present day energy density of the universe.

scholarly journals Unified universe history through phantom extended Chaplygin gas

2016 ◽  
Vol 94 (7) ◽  
pp. 659-670 ◽  
Author(s):  
B. Pourhassan
Keyword(s):  
Scalar Field ◽  
State Parameter ◽  
Chaplygin Gas ◽  
Late Time ◽  
Two Component ◽  
Equation Of State Parameter ◽  
Phantom Scalar ◽  
The Universe ◽  
Phantom Scalar Field ◽  
Universe Evolution

The universe evolution from inflation to late-time acceleration is investigated in a unified way, using a two-component fluid constituted from extended Chaplygin gas alongside a phantom scalar field. We extract solutions for the various cosmological eras, focusing on the behavior of the scale factor, the various density parameters and the equation-of-state parameter. Furthermore, we extract and discuss bouncing solutions. Finally, we examine the perturbations of the model, ensuring their stability and extracting the predictions for the tensor-to-scalar ratio.

scholarly journals Cosmological Dynamics of a Hybrid Chameleon Scenario

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Kourosh Nozari ◽  
Narges Rashidi
Keyword(s):  
Dynamical System ◽  
Phase Space ◽  
Scalar Field ◽  
Fixed Points ◽  
Effective Potential ◽  
Matter Density ◽  
Phantom Divide ◽  
Stable Attractor ◽  
System Technique ◽  
The Universe

We consider a hybrid scalar field which is nonminimally coupled to the matter and models a chameleon cosmology. By introducing an effective potential, we study the dependence of the effective potential's minimum and hybrid chameleon field's masses on the local matter density. In a dynamical system technique, we analyze the phase space of this two-field chameleon model, find its fixed points and study their stability. We show that the hybrid chameleon domination solution is a stable attractor and the universe in this setup experiences a phantom divide crossing.

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.

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 Exact scalar–tensor cosmological models

2017 ◽  
Vol 26 (07) ◽  
pp. 1750073 ◽  
Author(s):  
J. A. Belinchón ◽  
T. Harko ◽  
M. K. Mak
Keyword(s):  
Scalar Field ◽  
Cosmological Solution ◽  
Gravitational Theory ◽  
Field Equations ◽  
Group Approach ◽  
Gravitational Field Equations ◽  
Gravitational Theories ◽  
Accelerating Expansion ◽  
Expansion Of The Universe ◽  
The Universe

Scalar–tensor gravitational theories are important extensions of standard general relativity, which can explain both the initial inflationary evolution, as well as the late accelerating expansion of the universe. In the present paper, we investigate the cosmological solution of a scalar–tensor gravitational theory, in which the scalar field [Formula: see text] couples to the geometry via an arbitrary function [Formula: see text]. The kinetic energy of the scalar field as well as its self-interaction potential [Formula: see text] are also included in the gravitational action. By using a standard mathematical procedure, the Lie group approach, and Noether symmetry techniques, we obtain several exact solutions of the gravitational field equations describing the time evolutions of a flat Friedman–Robertson–Walker universe in the framework of the scalar–tensor gravity. The obtained solutions can describe both accelerating and decelerating phases during the cosmological expansion of the universe.

scholarly journals THE EVOLUTION OF THE UNIVERSE WITH THE B–I TYPE PHANTOM SCALAR FIELD

2006 ◽  
Vol 15 (02) ◽  
pp. 199-214 ◽  
Author(s):  
WEI FANG ◽  
H. Q. LU ◽  
Z. G. HUANG ◽  
K. F. ZHANG
Keyword(s):  
Scalar Field ◽  
State Parameter ◽  
Phase Plane Analysis ◽  
Density Parameter ◽  
Late Time ◽  
Plane Analysis ◽  
Accelerating Expansion ◽  
Phantom Scalar ◽  
Expansion Of The Universe ◽  
The Universe

We consider the phantom cosmology with a Lagrangian [Formula: see text] originated from the nonlinear Born–Infeld type scalar field. This cosmological model can explain the accelerating expansion of the universe with the equation of state parameter w ≤ -1. We get a sufficient condition for an arbitrary potential that admits a late time attractor solution: the value of potential u(Xc) at the critical point (Xc, 0) should be maximum and greater than zero. We study a specific potential with the form of [Formula: see text] via phase plane analysis and compute the cosmological evolution by numerical analysis in detail. The results show that the phantom field survives till today (to account for the present observed accelerating expansion) without interfering with the nucleosynthesis of the standard model (the density parameter Ωϕ≃10-12 at the equipartition epoch), and also avoid the future collapse of the universe.

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