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 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 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.

Reconstruction of f(T) gravity in the context of standard Chaplygin gas as tachyon scalar field and study of the stability against gravitational perturbation

2019 ◽  
Vol 16 (07) ◽  
pp. 1950101
Author(s):  
Surajit Chattopadhyay ◽  
Soumyodipta Karmakar
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
State Parameter ◽  
Chaplygin Gas ◽  
Gravitational Perturbation ◽  
Gravitational Perturbations ◽  
Equation Of State Parameter ◽  
Speed Parameter ◽  
The Stability ◽  
The Universe

The present paper reports a study on the [Formula: see text] gravity reconstruction scheme in the context of considering standard Chaplygin gas as tachyon scalar field model of dark energy. The solution for reconstructed [Formula: see text] gravity has been obtained from reconstructed potential and scalar field of tachyon based on the standard Chaplygin gas. It has been observed that the equation of state parameter due to the reconstructed torsion contribution to the density and pressure behaves like quintom and is consistent with the observational value of the equation of state parameter for the current universe. The reconstructed [Formula: see text] has then been tested for gravitational perturbation by deriving the frictional term, the effective mass and the sound speed parameter for the gravitational potential and it has been found to be stable against gravitational perturbations through positive value of the squared speed of sound. Finally, statefinder diagnostics has been carried out and the reconstructed [Formula: see text] gravity is found to interpolate between dust and [Formula: see text]CDM phases of the universe.

scholarly journals PHANTOM COSMOLOGY WITH A NONLINEAR BORN–INFELD TYPE SCALAR FIELD

2005 ◽  
Vol 14 (02) ◽  
pp. 355-362 ◽  
Author(s):  
H. Q. LU
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Energy Condition ◽  
State Parameter ◽  
Strong Energy Condition ◽  
Strong Energy ◽  
Accelerating Expansion ◽  
Equation Of State Parameter ◽  
The Universe

Recent many physicists suggest that the dark energy in the universe might result from the Born–Infeld (B–I) type scalar field of string theory. The universe of B–I type scalar field with potential can undergo a phase of accelerating expansion. The corresponding equation of state parameter lies in the range of -1<ω<-⅓. The equation of state parameter of B–I type scalar field without potential lies in the range of 0≤ω≤1. We find that weak energy condition and strong energy condition are violated for phantom B–I type scalar field. The equation of state parameter lies in the range of ω<-1.

scholarly journals Ghost Dark Energy in the DGP Braneworld

2018 ◽  
Vol 2018 ◽  
pp. 1-10
Author(s):  
M. Abdollahi Zadeh ◽  
A. Sheykhi
Keyword(s):  
Dark Energy ◽  
Sound Speed ◽  
State Parameter ◽  
Late Time ◽  
Ghost Dark Energy ◽  
Equation Of State Parameter ◽  
Interaction Term ◽  
The Stability ◽  
The Universe ◽  
Dgp Braneworld

We investigate the ghost model of dark energy in the framework of DGP braneworld. We explore the cosmological consequences of this model by determining the equation of state parameter, ωD, the deceleration, and the density parameters. We also examine the stability of this model by studying the squared of the sound speed in the presence/absence of interaction term between dark energy and dark matter. We find out that in the absence of interaction between two dark sectors of the universe we have ωD→-1 in the late time, while in the presence of interaction ωD can cross the phantom line -1. In both cases the squared of sound speed vs2 does not show any signal of stability. We also determine the statefinder diagnosis of this model as well as the ωD-ωD′ plane and compare the results with the ΛCDM model. We find that ωD-ωD′ plane meets the freezing region in the absence of interaction between two dark sectors, while it meets both the thawing and the freezing regions in the interacting case.

COSMOLOGICAL EVOLUTION OF MODIFIED CHAPLYGIN GAS INTERACTING WITH BAROTROPIC BACKGROUND FLUID

2009 ◽  
Vol 24 (01) ◽  
pp. 63-72 ◽  
Author(s):  
YA-BO WU ◽  
JING HE ◽  
CONG WANG ◽  
DI WANG
Keyword(s):  
Autonomous System ◽  
Vacuum Energy ◽  
Dynamical Evolution ◽  
State Parameter ◽  
Chaplygin Gas ◽  
Strength Parameter ◽  
Modified Chaplygin Gas ◽  
Stable Attractor ◽  
Equation Of State Parameter ◽  
The Universe

Based on the observation that the equation of state parameter ω can cross the phantom dividing ω = -1 and has a 99% probability of being ω < -1, we introduce an interaction between the modified Chaplygin gas and the barotropic background fluid. By studying the dynamical evolution of the MCG model with interaction and the statefinder diagnostic in autonomous system, we find that the MCG vacuum-energy-dominated phase is the only stable attractor, the universe evolves from the matter-dominated phase to the MCG vacuum-energy-dominated phase, and the effect of the transfer strength parameter c is evident. In addition, we have plotted the evolution trajectories of the interacting CG, GCG and MCG models with barotropic background fluid in the statefinder parameter (s - r)-plane to illustrate the discriminations among these scenarios.

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 A study of phantom scalar field cosmology using Lie and Noether symmetries

2016 ◽  
Vol 25 (05) ◽  
pp. 1650051 ◽  
Author(s):  
Sourav Dutta ◽  
Subenoy Chakraborty
Keyword(s):  
Scalar Field ◽  
State Parameter ◽  
Einstein Gravity ◽  
Matter Field ◽  
Lie Symmetry ◽  
Kinetic Term ◽  
Noether Symmetries ◽  
Phantom Scalar ◽  
Scalar Field Cosmology ◽  
Phantom Scalar Field

The paper deals with phantom scalar field cosmology in Einstein gravity. At first, using Lie symmetry, the coupling function to the kinetic term and the potential function of the scalar field and the equation of state parameter of the matter field are determined and a simple solution is obtained. Subsequently, Noether symmetry is imposed on the Lagrangian of the system. The symmetry vector is obtained and the potential takes a very general form from which potential using Lie symmetry can be obtained as a particular case. Then, we choose a point transformation [Formula: see text] such that one of the transformed variables (say [Formula: see text]) is a cyclic for the Lagrangian. Using conserved charge (corresponding to the cyclic coordinate) and the constant of motion, solutions are obtained.

Thermodynamics in loop quantum cosmology with non-canonical scalar field model

2019 ◽  
Vol 16 (06) ◽  
pp. 1950081
Author(s):  
Ayesha Iqbal ◽  
Abdul Jawad
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Equilibrium Condition ◽  
Field Model ◽  
State Parameter ◽  
Second Law Of Thermodynamics ◽  
Second Law ◽  
Generalized Second Law ◽  
Equation Of State Parameter ◽  
The Universe

The cosmological scenario is built up within the framework of scalar field model possessing a noncanonical kinetic term in loop quantum gravity. The noncanonical scalar field is permitted to interact with dark matter field by assuming a specific form of coupling term. The equation of state parameter is set to be constant as well as variable (Chevallier–Polarski–Linder parametrization) and evaluated the behavior of universe through deceleration parameter and weak energy condition. These parameters favor the accelerated expansion of the universe for three values of equation of state parameter in both cases allowed by observational data. The squared speed of sound leads to the stability of the underlying models in both forms of equation of state parameter. Moreover, the validity of generalized second law of thermodynamics is analyzed by using first law of thermodynamics and assume the universe to be enclosed by apparent horizon. The Bekenstein, logarithmic and power-law entropy is being considered as entropy of horizon. The thermodynamic equilibrium condition is also discussed for all three cases of entropies. The generalized second law of thermodynamics and thermal equilibrium condition is satisfied for all the three types of entropies.

scholarly journals Bifurcations in Ratra–Peebles quintessence models and their extensions

2019 ◽  
Vol 79 (9) ◽  
Author(s):  
Franciszek Humieja ◽  
Marek Szydłowski
Keyword(s):  
System Approach ◽  
Bifurcation Theory ◽  
Late Time ◽  
De Sitter ◽  
Static Universe ◽  
Phantom Scalar ◽  
Generic Class ◽  
Acceleration Of The Universe ◽  
The Universe ◽  
Phantom Scalar Field

Abstract We have used the dynamical system approach in order to investigate the dynamics of cosmological models of the flat Universe with a non-minimally coupled canonical and phantom scalar field and the Ratra–Peebles potential. Applying methods of the bifurcation theory we have found three cases for which the Universe undergoes a generic evolution emerging from either the de Sitter or the static Universe state and finishing at the de Sitter state, without the presence of the initial singularity. This generic class of solutions explains both the inflation and the late-time acceleration of the Universe. In this class inflation is an endogenous effect of dynamics itself.

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