scholarly journals Dynamical system analysis of quintessence models with exponential potential — Revisited

2019 ◽  
Vol 34 (09) ◽  
pp. 1950069
Author(s):  
A. Savaş Arapoğlu ◽  
A. Emrah Yükselci
Keyword(s):  
Dynamical System ◽  
Phase Space ◽  
Equation Of State ◽  
System Analysis ◽  
Three Dimensional ◽  
State Parameter ◽  
Late Time ◽  
Exponential Potential ◽  
Effective Equation ◽  
Equation Of State Parameter

Dynamical system analysis of a universe model which contains matter, radiation and quintessence with exponential potential, [Formula: see text], is studied in the light of recent observations and the tensions between different datasets. The three-dimensional phase space is constructed by the energy density parameters and all the critical points of the model with their physical meanings are investigated. This approach provides an easy way of comparing the model directly with the observations. We consider a solution that is compatible with observations and is continuous in the phase space in both directions of time, past and future. Although in many studies of late-time acceleration, the radiation is neglected, here we consider all components together and this makes the calculated effective equation of state parameter more realistic. Additionally, a relation between potential parameter, [Formula: see text], and the value of quintessence equation of state parameter, [Formula: see text], today is found by using numerical analysis. We conclude that [Formula: see text] has to be small in order to explain the current accelerated phase of the universe and this result can be seen directly from the relation we obtain. Finally, we compare the usual dynamical system approach with the approach that we follow in this paper.

scholarly journals BRANE–BULK ENERGY EXCHANGE AND AGEGRAPHIC DARK ENERGY

2010 ◽  
Vol 19 (03) ◽  
pp. 305-316 ◽  
Author(s):  
AHMAD SHEYKHI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Normal State ◽  
Energy Exchange ◽  
State Parameter ◽  
Effective Equation ◽  
Agegraphic Dark Energy ◽  
Equation Of State Parameter ◽  
Bulk Energy

We consider the agegraphic models of dark energy in a braneworld scenario with brane–bulk energy exchange. We assume that the adiabatic equation for the dark matter is satisfied while it is violated for the agegraphic dark energy due to the energy exchange between the brane and the bulk. Our study shows that with the brane–bulk interaction, the equation of state parameter of agegraphic dark energy on the brane, wD, can have a transition from the normal state, where wD > -1, to the phantom regime, where wD < -1, while the effective equation of state for dark energy always satisfies [Formula: see text].

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 On a Slightly Different Power Law-Scaling for the Flat Universe

2020 ◽  
Vol 12 (4) ◽  
pp. 569-574
Author(s):  
C. Sivakumar ◽  
R. Francis
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Power Law ◽  
Hubble Parameter ◽  
State Parameter ◽  
Effective Equation ◽  
Flat Universe ◽  
Equation Of State Parameter ◽  
Age Of The Universe ◽  
The Universe

A slightly different power law-scaling fits to the picture of our 13.7 billion years old flat universe which is expanding presently at 67 km/s/Mpc with an acceleration. The model which is an attempt to retain power-law scaling in the light of the accepted facts about the universe we are living in, has a constant effective equation of state parameter as the cosmic fluid is a solution of matter, radiation and dark energy. It is successful in explaining the acceleration of universe which the normal power law fails if the present Hubble parameter is 67 km/s/Mpc and age of the universe is 13.7 billion years, and it is free from the defect of singularity.

Effect of brane tension on reheating parameters in small field inflation according to Planck-2018 data

2020 ◽  
Vol 35 (30) ◽  
pp. 2050191
Author(s):  
Z. Sakhi ◽  
K. El Bourakadi ◽  
A. Safsafi ◽  
M. Ferricha-Alami ◽  
H. Chakir ◽  
...  
Keyword(s):  
Equation Of State ◽  
State Parameter ◽  
Small Field ◽  
Brane Tension ◽  
Effective Equation ◽  
Equation Of State Parameter ◽  
Joint Constraints ◽  
Braneworld Inflation ◽  
Additional Constraints

We study a new reheating approach in the framework of standard and braneworld inflation. Using the technique developed in Ref. 1, we consider a small field arctangent potential and show that this approach can be similarly applied within Randall–Sundrum type 2 scenario and provide additional constraints to reheating temperature [Formula: see text] and duration of reheating [Formula: see text]. We found that in brane case the effective equation-of-state parameter [Formula: see text] must be close to 1, to satisfy Planck-2018 joint constraints on [Formula: see text].

scholarly journals Bulk viscosity in F(T, TG) gravity

2017 ◽  
Vol 95 (3) ◽  
pp. 262-266
Author(s):  
M. Sharif ◽  
Kanwal Nazir
Keyword(s):  
Equation Of State ◽  
Bulk Viscosity ◽  
State Parameter ◽  
Time Dependent ◽  
Effective Equation ◽  
Phantom Divide ◽  
Equation Of State Parameter ◽  
Phantom Divide Line ◽  
Dependent Viscosity ◽  
The Universe

The present paper is devoted to exploring the effect of bulk viscosity in the context of F(T, TG) gravity. We consider a time-dependent viscosity model with a particular expression of Hubble parameter. We evaluate viscous effective equation of state parameter for three well-known F(T, TG) models. The behavior of the accelerated expanding universe is explored graphically through the viscous equation of state parameter. This parameter indicates the phantom-dominated era as well as crosses the phantom divide line for all three models. We conclude that the universe shows a transition from quintessence to phantom region in the presence of bulk viscosity.

scholarly journals Study of Homogeneous and Isotropic Universe in f(R,Tφ) Gravity

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
M. Sharif ◽  
Aisha Siddiqa
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Hubble Parameter ◽  
State Parameter ◽  
Universe Model ◽  
Effective Equation ◽  
Isotropic Universe ◽  
First Order ◽  
Equation Of State Parameter

This paper is devoted to study the cosmological behavior of homogeneous and isotropic universe model in the context of f(R,Tφ) gravity, where φ is the scalar field. For this purpose, we follow the first-order formalism defined by H=W(φ). We evaluate Hubble parameter, effective equation of state parameter (ωeff), deceleration parameter, and potential of scalar field for three different values of W(φ). We obtain phantom era in some cases for the early times. It is found that exponential expression of W(φ) yields ωeff independent of time for flat universe and independent of model parameter otherwise. It is concluded that our model corresponds to ΛCDM for both initial and late times.

Cosmological evolution of non-interacting and interacting holographic dark energy model in Brans–Dicke theory

2018 ◽  
Vol 15 (07) ◽  
pp. 1850124 ◽  
Author(s):  
Milan Srivastava ◽  
C. P. Singh
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Coupling Parameter ◽  
State Parameter ◽  
Late Time ◽  
Coincidence Problem ◽  
Logarithmic Form ◽  
Equation Of State Parameter

The purpose of this paper is to study the dynamics of non-interacting and interacting holographic dark energy (HDE) models in the framework of Brans–Dicke (BD) cosmology. As system’s infrared cutoff, we consider the future event horizon. The scalar function of BD theory is assumed to be a logarithmic form of scale factor, which is claimed to avoid a constant result for deceleration parameter. We investigate the cosmological implications of this model in detail. We obtain the time-dependent equation of state parameter and deceleration parameter which describe the phase transition of the Universe. We observe that the model explains the early time inflation and late time acceleration including matter-dominated phase. It is also observed that the equation of state parameter may cross phantom divide line in late time evolution. The cosmic coincidence problem is also discussed for both the models. We observe that this logarithmic form of Brans–Dicke scalar field is more appropriate to achieve a less acute coincidence problem in non-interacting model whereas a soft coincidence can be achieved if coupling parameter in interacting model has small value.

scholarly journals Phase space analysis and singularity classification for linearly interacting dark energy models

2020 ◽  
Vol 80 (2) ◽  
Author(s):  
Muhsin Aljaf ◽  
Daniele Gregoris ◽  
Martiros Khurshudyan
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Late Time ◽  
De Sitter ◽  
Effective Equation ◽  
De Sitter Universe ◽  
Friedmann Cosmological Models ◽  
Interacting Dark Energy Models

Abstract In this paper, applying the Hartman–Grobman theorem we carry out a qualitative late-time analysis of some unified dark energy-matter Friedmann cosmological models, where the two interact through linear energy exchanges, and the dark energy fluid obeys to the dynamical equation of state of Redlich–Kwong, Modified Berthelot, and Dieterici respectively. The identification of appropriate late-time attractors allows to restrict the range of validity of the free parameters of the models under investigation. In particular, we prove that the late-time attractors which support a negative deceleration parameter correspond to a de Sitter universe. We show that the strength of deviation from an ideal fluid for the dark energy does not influence the stability of the late-time attractors, as well as the values of all the cosmological parameters at equilibrium, but for the Hubble function (which represents the age of the universe). Our analysis also shows that a singularity in the effective equation of state parameter for the dark energy fluid is not possible within this class of models.

scholarly journals The Hubble Tension, the M Crisis of Late Time H(z) Deformation Models and the Reconstruction of Quintessence Lagrangians

Universe ◽  
2021 ◽  
Vol 7 (8) ◽  
pp. 300
Author(s):  
Anastasios Theodoropoulos ◽  
Leandros Perivolaropoulos
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Equation ◽  
State Parameter ◽  
Kinetic Term ◽  
Late Time ◽  
Energy Parameters ◽  
Equation Of State Parameter ◽  
Deformation Models ◽  
Best Fit

We present a detailed and pedagogical analysis of recent cosmological data, including CMB, BAO, SnIa and the recent local measurement of H0. We thus obtain constraints on the parameters of these standard dark energy parameterizations, including ΛCDM, and H(z) deformation models such as wCDM (constant equation of state w of dark energy), and the CPL model (corresponding to the evolving dark energy equation-of-state parameter w(z)=w0+waz1+z). The fitted parameters include the dark matter density Ω0m, the SnIa absolute magnitude M, the Hubble constant H0 and the dark energy parameters (e.g., w for wCDM). All models considered lead to a best-fit value of M that is inconsistent with the locally determined value obtained by Cepheid calibrators (M tension). We then use the best-fit dark energy parameters to reconstruct the quintessence Lagrangian that would be able to reproduce these best-fit parameterizations. Due to the derived late phantom behavior of the best-fit dark energy equation-of-state parameter w(z), the reconstructed quintessence models have a negative kinetic term and are therefore plagued with instabilities.

Sign in / Sign up

Export Citation Format

Share Document