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 Revisiting dynamics of interacting quintessence

2021 ◽  
Vol 81 (12) ◽  
Author(s):  
Patrocinio Pérez ◽  
Ulises Nucamendi ◽  
Roberto De Arcia
Keyword(s):  
Dynamical System ◽  
Dark Matter ◽  
Phase Space ◽  
Scalar Field ◽  
Cosmic Time ◽  
Matter Density ◽  
Kinetic Term ◽  
Dynamical System Theory ◽  
Exponential Potential ◽  
Alpha Beta

AbstractWe apply the tools of the dynamical system theory in order to revisit and uncover the structure of a nongravitational interaction between pressureless dark matter and dark energy described by a scalar field $$\phi $$ ϕ . For a coupling function $$Q = -(\alpha d\rho _m/dt + \beta d\rho _\phi /dt )$$ Q = - ( α d ρ m / d t + β d ρ ϕ / d t ) , where t is the cosmic time, we have found that it can be rewritten in the form $$Q = 3H (\alpha \rho _m + \beta (d\phi /dt)^2 )/(1-\alpha +\beta )$$ Q = 3 H ( α ρ m + β ( d ϕ / d t ) 2 ) / ( 1 - α + β ) , so that its dependence on the dark matter density and on the kinetic term of the scalar field is linear and proportional to the Hubble parameter. We analyze the scenarios $$\alpha =0$$ α = 0 , $$\alpha = \beta $$ α = β and $$\alpha = -\beta $$ α = - β , separately and in order to describe the cosmological evolution we have calculated various observables. A notable result of this work is that, unlike for the noninteracting scalar field with exponential potential where five critical points appear, in the case studied here, with the exception of the matter dominated solution, the remaining singular points are transformed into scaling solutions enriching the phase space. It is shown that for $$\alpha \ne 0$$ α ≠ 0 , a separatrix arises modifying prominently the structure of the phase space. This represents a novel feature no mentioned before in the literature.

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.

scholarly journals Observational Role of Dark Matter in f(R) Models for Structure Formation

2018 ◽  
Vol 46 ◽  
pp. 1860045
Author(s):  
Murli Manohar Verma ◽  
Bal Krishna Yadav
Keyword(s):  
Dynamical System ◽  
Dark Matter ◽  
Fixed Points ◽  
Gravity Models ◽  
Stability Conditions ◽  
Cosmological Observations ◽  
General Relativistic ◽  
The Stability ◽  
The Universe

The fixed points for the dynamical system in the phase space have been calculated with dark matter in the [Formula: see text] gravity models. The stability conditions of these fixed points are obtained in the ongoing accelerated phase of the universe, and the values of the Hubble parameter and Ricci scalar are obtained for various evolutionary stages of the universe. We present a range of some modifications of general relativistic action consistent with the [Formula: see text]CDM model. We elaborate upon the fact that the upcoming cosmological observations would further constrain the bounds on the possible forms of [Formula: see text] with greater precision that could in turn constrain the search for dark matter in colliders.

The “still point” cosmology

2005 ◽  
Vol 201 ◽  
pp. 514-515
Author(s):  
Ivan I. Shevchenko
Keyword(s):  
Scalar Field ◽  
Cosmological Constant ◽  
Hubble Parameter ◽  
Gravitational Constant ◽  
Critical Density ◽  
Matter Density ◽  
Future Evolution ◽  
The Future ◽  
The Universe

Recent results on supernovae as standard candles (Riess et al. 1998; Perlmutter et al. 1999) and on CMB anisotropy (Lineweaver 1998) indicate that ΩM ≍ 0.3-0.4, Ωv ≍ 0.6-0.7, ΩM + Ωv ≍ 1. By definition, ΩM = ρM/ρcr, ΩV = ρv/ρcr, where ρM is the matter density, ρv is the vacuum density; the critical density ρcr = 3H2/8πG; H is the Hubble parameter, G is the gravitational constant. In the standard Friedmann-Lemaître cosmologies, these results seriously constrain the non-dimensional cosmological constant (as defined below): Δ ≫ 1, meaning that the Universe expands forever. If a scalar field is present, the future evolution may be different.

scholarly journals Interacting Dark Matter andq-Deformed Dark Energy Nonminimally Coupled to Gravity

2016 ◽  
Vol 2016 ◽  
pp. 1-17
Author(s):  
Emre Dil
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Theoretical Description ◽  
Late Time ◽  
Dynamical Structure ◽  
Dark Sector ◽  
Accelerating Expansion ◽  
Stable Attractor ◽  
The Universe

In this paper, we propose a new approach to study the dark sector of the universe by considering the dark energy as an emergingq-deformed bosonic scalar field which is not only interacting with the dark matter, but also nonminimally coupled to gravity, in the framework of standard Einsteinian gravity. In order to analyze the dynamic of the system, we first give the quantum field theoretical description of theq-deformed scalar field dark energy and then construct the action and the dynamical structure of this interacting and nonminimally coupled dark sector. As a second issue, we perform the phase-space analysis of the model to check the reliability of our proposal by searching the stable attractor solutions implying the late-time accelerating expansion phase of the universe.

scholarly journals Dynamical System Perspective of Cosmological Models Minimally Coupled with Scalar Field

2020 ◽  
Vol 2020 ◽  
pp. 1-18
Author(s):  
S. Surendra Singh ◽  
Chingtham Sonia
Keyword(s):  
Dynamical System ◽  
Scalar Field ◽  
Fixed Points ◽  
Cosmic Acceleration ◽  
Stable Model ◽  
Exponential Potential ◽  
Total Energy Density ◽  
System Perspective ◽  
Special Cases ◽  
Potential Form

The stability criteria for the dynamical system of a homogeneous and isotropic cosmological model are investigated with the interaction of a scalar field in the presence of a perfect fluid. In this paper, we depict the dynamical system perspective to study qualitatively the scalar field cosmology under two special cases, with and without potential. In the absence of potential, we get a two-dimensional dynamical system, and we study the analytical as well as geometrical behavior. For the dynamical system with potential, we analyze different potential forms: simple exponential potential form (Vϕ=Voe−λϕ), double exponential potential form Vϕ=Voexp−Aexp2αϕ, and inverse power law potential form (Vϕ=Voϕ−α). We generate an autonomous system of ordinary differential equations (ASODE) for each case by introducing new dimensionless variables and obtain respective fixed points. We also analyze the type, nature, and stability of the fixed points and how their behavior reflects towards the cosmological scenarios. Throughout the whole work, the investigation of this model has shown us the deep connection between these theories and cosmic acceleration phenomena. The phase plots of the system at different conditions and different values of γ have been analyzed in detail, and their geometrical interpretations have been studied. The perturbation plots of the dynamical system have been analyzed with emphasis on our analytical findings. We have evaluated the total energy density (Ωϕ) at the fixed points and also found out the suitable range of γ and λ for a stable model.

Theoretical constraints on kinetic k-essence dark energy model in El-Nabulsi fractional action cosmology

2013 ◽  
Vol 91 (10) ◽  
pp. 844-849 ◽  
Author(s):  
Antonio Pasqua ◽  
Surajit Chattopadhyay
Keyword(s):  
Scalar Field ◽  
Dark Energy Model ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Kinetic Term ◽  
Phantom Divide ◽  
Fractional Action Cosmology ◽  
Present Universe ◽  
Phantom Divide Line ◽  
The Universe

In this work, we considered an effective scalar field theory described by a Lagrangian with a noncanonical kinetic term, which leads to accelerated expansion in the present Universe and is known as k-essence in the framework of the fractional action cosmology recently introduced by El-Nabulsi. We have chosen a particular ansatz for the scale factor and the scalar field, in which both are described as a power-law of the time, t. We have studied the behavior of some cosmological quantities in other models to obtain some useful information about the model considered. We observed that the equation of state parameter, w, has decreasing behavior and it never crosses the phantom divide line (i.e., w = –1). Studying the statefinder pair {r, s} and {w, w′}, we observed that the model considered is able to obtain the ΛCDM phase of the Universe.

Time-varying q-deformed dark energy interacts with dark matter

2017 ◽  
Vol 27 (01) ◽  
pp. 1750177
Author(s):  
Emre Dil ◽  
Erdinç Kolay
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Particle Creation ◽  
State Parameter ◽  
Late Time ◽  
Dynamical Structure ◽  
Stable Attractor ◽  
Energy Quantum ◽  
The Universe

We propose a new model for studying the dark constituents of the universe by regarding the dark energy as a [Formula: see text]-deformed scalar field interacting with the dark matter, in the framework of standard general relativity. Here we assume that the number of particles in each mode of the [Formula: see text]-deformed scalar field varies in time by the particle creation and annihilation. We first describe the [Formula: see text]-deformed scalar field dark energy quantum-field theoretically, then construct the action and the dynamical structure of these interacting dark sectors, in order to study the dynamics of the model. We perform the phase space analysis of the model to confirm and interpret our proposal by searching the stable attractor solutions implying the late-time accelerating phase of the universe. We then obtain the result that when interaction and equation-of-state parameter of the dark matter evolve from the present day values into a particular value, the dark energy turns out to be a [Formula: see text]-deformed scalar field.

scholarly journals DE VAUCOULEURS–IKEUCHI DIAGRAM AND COMMUTATION RELATIONS AMONG PHASE SPACE COORDINATES

2009 ◽  
Vol 24 (21) ◽  
pp. 1669-1676
Author(s):  
TAKESHI FUKUYAMA ◽  
TATSURU KIKUCHI
Keyword(s):  
Phase Space ◽  
Canonical Commutation Relation ◽  
Matter Density ◽  
The Self ◽  
Quantum Uncertainty ◽  
Commutation Relations ◽  
Cluster Of Galaxies ◽  
The Universe ◽  
Self Consistency ◽  
Scale Length

We consider the relations between de Vaucouleurs–Ikeuchi diagram and generalized commutation relations among the coordinates and momenta. All physical objects in the Universe ranging from elementary particles to super-cluster of galaxies are confined within the Triangle of the de Vaucouleurs–Ikeuchi diagram on the matter density versus scale length plane. These three boundaries are characterized by the quantum uncertainty principle, gravitational event horizon, and cosmological constant. These are specified by the nonzero commutation relations [xμ, pν], [xμ, xν] (strictly [xi, t]) and [pμ, pν], respectively. The canonical commutation relation [xi, pj] are slightly modified, which preserves the self consistency as a whole.

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