scholarly journals PARAMETRIZATION OF k-ESSENCE AND ITS KINETIC TERM

2006 ◽  
Vol 21 (21) ◽  
pp. 1683-1689 ◽  
Author(s):  
HUI LI ◽  
ZONG-KUAN GUO ◽  
YUAN-ZHONG ZHANG
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Kinetic Term ◽  
State Function ◽  
Effective Equation

We construct the non-canonical kinetic term of a k-essence field directly from the effective equation of state function wk(z), which describes the properties of the dark energy. Adopting the usual parametrizations of equation of state, we numerically reproduce the shape of the non-canonical kinetic term and discuss some features of the constructed form of k-essence.

scholarly journals POTENTIALS OF COUPLED QUINTESSENCE BASED ON A DILATON

2007 ◽  
Vol 22 (40) ◽  
pp. 3073-3082 ◽  
Author(s):  
Z. G. HUANG ◽  
Q. Q. SUN ◽  
W. FANG ◽  
H. Q. LU
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Dark Energy Model ◽  
Scalar Potential ◽  
Good Method ◽  
Gravitational Theory ◽  
Energy Model ◽  
State Function ◽  
Effective Equation ◽  
Quintessence Model

In this paper, we regard dilaton in Weyl-scaled induced gravitational theory as coupled quintessence, which is called DCQ model by us. Parametrization of the dark energy model is a good method by which we can construct the scalar potential directly from the effective equation of state function ωσ(z) describing the properties of the dark energy. Applying this method to the DCQ model, we consider four parametrizations of ω(z) and investigate the features of the constructed DCQ potentials, which possess two different evolutive behaviors called "O" mode and "E" mode. Lastly, we comprise the results of the constructed DCQ model with those of quintessence model numerically.

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 ON THE EFFECTIVE EQUATION OF STATE OF DARK ENERGY

2010 ◽  
Vol 19 (14) ◽  
pp. 2259-2264 ◽  
Author(s):  
MARTIN S. SLOTH
Keyword(s):  
Field Theory ◽  
Dark Energy ◽  
Equation Of State ◽  
Vacuum Energy ◽  
Planck Scale ◽  
Theory Model ◽  
Effective Field ◽  
Effective Equation ◽  
Ultraviolet Cutoff ◽  
Interesting Possibility

In an effective field theory model with an ultraviolet momentum cutoff, there is a relation between the effective equation-of-state of dark energy and the ultraviolet cutoff scale. It implies that a measure of the equation of state of dark energy different from minus one, ω ≠ -1, does not rule out vacuum energy as dark energy. It also indicates an interesting possibility that precise measurements of the infrared properties of dark energy can be used to probe the ultraviolet cutoff scale of effective quantum field theory coupled to gravity. In a toy model with a vacuum energy-dominated universe with a Planck scale cutoff, the dark energy effective equation of state is w eff ≈ -0.96.

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.

scholarly journals PARAMETRIZATION OF TACHYON FIELD

2007 ◽  
Vol 22 (16) ◽  
pp. 1175-1181 ◽  
Author(s):  
YING SHAO ◽  
YUAN-XING GUI ◽  
WEI WANG
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Tachyon Field ◽  
Effective Equation ◽  
Relativistic Matter

We assume that universe is dominated by non-relativistic matter and tachyon field and reconstruct the potential of tachyon field directly from the effective equation of state (EOS) of dark energy. We apply the method to four known parametrizations of equation of state and discuss the general features of the resulting potentials.

scholarly journals Aspects of late-time evolution in mimetic F(R) gravity

2016 ◽  
Vol 31 (33) ◽  
pp. 1650191 ◽  
Author(s):  
V. K. Oikonomou
Keyword(s):  
Dark Energy ◽  
Growth Factor ◽  
Equation Of State ◽  
Time Evolution ◽  
Early Time ◽  
Exponential Model ◽  
Late Time ◽  
Effective Equation ◽  
Dark Energy Density ◽  
Evolution Analysis

We demonstrate how to describe in an unified way early and late-time acceleration in the context of mimetic F(R) gravity. As we show, an exponential F(R) gravity model has appealing features, with regard to unification and we perform an analysis of the late-time evolution. The resulting picture is interesting since in the mimetic case, certain pathologies of some ordinary F(R) models are remedied in a consistent way, owing to the presence of the mimetic potential and the Lagrange multiplier. We quantify the late-time evolution analysis by studying the scaled dark energy density, the dark energy equation of state and the total effective equation of state, and as we show the late-time evolution is crucially affected by the functional form of the F(R) gravity. It is intriguing that the most appealing case corresponds to the exponential F(R) gravity which unifies late- and early-time acceleration. Finally, we study the behavior of the effective gravitational constant and the growth factor, and as we show, significant differences between the mimetic and ordinary F(R) exponential model are spotted in the growth factor.

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 HYBRID CHAPLYGIN GAS

2009 ◽  
Vol 24 (07) ◽  
pp. 541-555 ◽  
Author(s):  
HONGSHENG ZHANG ◽  
ZONG-HONG ZHU ◽  
LIHUA YANG
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Transient Behavior ◽  
Chaplygin Gas ◽  
De Sitter ◽  
Coincidence Problem ◽  
Effective Equation ◽  
Phantom Divide ◽  
Perturbation Growth

Hybrid Chaplygin gas model is put forward, in which the gases play the role of dark energy. For this model the coincidence problem is greatly alleviated. The effective equation of state of the dark energy may cross the phantom divide w = -1. Furthermore, the crossing behavior is decoupled from any gravity theories. In the present model, w < -1 is only a transient behavior. There is a de Sitter attractor in the future infinity. Hence, the big rip singularity, which often afflicts the models with matter whose effective equation of state less than -1, naturally disappears. There exist stable scaling solutions, both at the early universe and the late universe. We discuss the perturbation growth of this model. We find that the index is consistent with observations.

Cosmology of viscous holographic f(G) gravity and consequences in the framework of quintessence scalar field

2019 ◽  
Vol 16 (11) ◽  
pp. 1950176
Author(s):  
Swati Sinha ◽  
Surajit Chattopadhyay ◽  
Irina Radinschi
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Holographic Dark Energy ◽  
Inhomogeneous Equation ◽  
Late Time ◽  
Effective Equation ◽  
Future Singularity ◽  
Warm Inflation ◽  
The Universe

Work reported in this study demonstrates the reconstruction schemes for the [Formula: see text] gravity in the framework of bulk viscosity and holographic background evolution by considering the universe filled by the viscous fluid that is just special class of more general fluids as described in Nojiri and Odintsov [Inhomogeneous equation of state of the universe: Phantom era, future singularity, and crossing the phantom barrier, Phys. Rev. D 72 (2005) 023003]. The bulk viscous pressure has been considered as [Formula: see text], with [Formula: see text]. Considering the scale factor in power law form and taking holographic dark energy (HDE) with density [Formula: see text] and generalized extended holographic dark energy (EGHRDE) with density [Formula: see text], a specific case of Nojiri–Odintsov holographic DE ([Unifying phantom inflation with late-time acceleration: Scalar phantom–non-phantom transition model and generalized holographic dark energy, Gen. Relativ. Gravit. 38 (2006) 1285]) we have derived solutions for [Formula: see text] and the subsequent effective equation of state parameters have been found to behave like quintom irrespective of the choice of [Formula: see text]. Finally, considering [Formula: see text] as quintessence scalar field we have explored the possibility of quasi-exponential expansion and warm inflation.

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