scholarly journals DILATON COUPLED QUINTESSENCE MODEL IN THE ω - ω′ PLANE

2007 ◽  
Vol 16 (07) ◽  
pp. 1109-1117 ◽  
Author(s):  
Z. G. HUANG ◽  
H. Q. LU ◽  
W. FANG
Keyword(s):  
Dark Energy ◽  
Field Equation ◽  
Scalar Field ◽  
Equation Of State ◽  
State Parameter ◽  
Equation Of Motion ◽  
Gravitational Theory ◽  
Scalar Field Equation ◽  
Equation Of State Parameter ◽  
Quintessence Model

In this paper, we regard the dilaton in Weyl-scaled induced gravitational theory as a coupled quintessence. Based on this consideration, we investigate the dilaton coupled quintessence (DCQ) model in the ω - ω′ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to N (the logarithm of the scale factor a). We find the scalar field equation of motion in the ω - ω′ plane, and show mathematically the properties of attractor solutions which correspond to ωσ ~ -1, ωσ = 1. Finally, we find that our model is a tracking one which belongs to "freezing" type models classified in the ω - ω′ plane.

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.

Accreting Scalar-Field Models of Dark Energy Onto Morris-Thorne Wormhole

2016 ◽  
Vol 71 (10) ◽  
pp. 949-960
Author(s):  
Surajit Chattopadhyay ◽  
Antonio Pasqua ◽  
Irina Radinschi
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Power Law ◽  
State Parameter ◽  
Suitable Choice ◽  
Energy Models ◽  
Scalar Field Models ◽  
Equation Of State Parameter ◽  
Phantom Phase

AbstractThe present paper reports a study on accreting tachyon, Dirac-Born-Infeld essence and h-essence scalar field models of dark energy onto Morris-Thorne wormhole. Using three different parameterisation schemes and taking $H\, = \,{H_0}\, + \,{{{H_1}} \over t}$, we have derived the mass of the wormhole for all of the three parameterisation schemes that are able to get hold of both quintessence and phantom behaviour. With suitable choice of parameters, we observed that accreting scalar field dark energy models are increasing the mass of the wormhole in the phantom phase and the mass is decreasing in the quintessence phase. Finally, we have considered accretion with power law form of scale factor and without any parameterisation scheme for the equation of state parameter and observed the fact that phantom-type dark energy supports the existence of wormholes.

scholarly journals Tachyon field as a dark energy in Bianchi type-V spacetime

2015 ◽  
Vol 30 (01) ◽  
pp. 1550008 ◽  
Author(s):  
J. Sadeghi ◽  
H. Farahani
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Bianchi Type ◽  
Scalar Potential ◽  
State Parameter ◽  
Tachyon Field ◽  
Equation Of State Parameter ◽  
Type V ◽  
Bianchi Type V

In this paper, we consider Bianchi type-V spacetime and study a cosmological model of dark energy based on tachyon scalar field. We assumed three different kinds of matter without possibility of interaction with scalar dark energy. Assuming power law Hubble parameter in terms of scale factor we obtain evolution of scalar field, scalar potential and equation of state parameter.

scholarly journals A COMPARISON OF QUINTESSENCE AND NON-LINEAR BORN–INFELD SCALAR FIELD USING GOLD SUPERNOVA DATA

2006 ◽  
Vol 15 (11) ◽  
pp. 1947-1961 ◽  
Author(s):  
WEI FANG ◽  
H. Q. LU ◽  
B. LI ◽  
K. F. ZHANG
Keyword(s):  
Scalar Field ◽  
Equation Of State ◽  
Field Model ◽  
State Parameter ◽  
Scale Factor ◽  
Scalar Field Model ◽  
Equation Of State Parameter ◽  
Non Linear ◽  
Quintessence Model

We study the Non-Linear Born–Infeld (NLBI) scalar field model and quintessence model with two different potentials (V(ϕ) = -sϕ and [Formula: see text]). We investigate the differences between these two models. We explore the equation of state parameter w and the evolution of scale factor a(t) in both the NLBI scalar field and quintessence model. The present age of universe and the transition redshift are also obtained. We use the Gold dataset of 157 SN-Ia to constrain the parameters of the two models. All the results show that the NLBI model is slightly superior to the quintessence model.

A new potential for scalar field dark energy

2020 ◽  
Vol 17 (09) ◽  
pp. 2050139
Author(s):  
Abdulla Al Mamon
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Hubble Parameter ◽  
Time Derivative ◽  
Field Potential ◽  
State Parameter ◽  
Simple Relation ◽  
Scale Factor ◽  
Equation Of State Parameter

In this paper, we have investigated some cosmological consequences of a quintessence dark energy model. In particular, we have obtained the forms of the equation of state parameter, the deceleration parameter and the field potential by considering a simple relation between the scale factor and the time derivative of the scalar field, instead of assuming any functional form for the scalar field potential or the scale factor or the equation of state parameter. We have found that the model provides the desired early deceleration followed by present acceleration of the universe. The potential derived numerically in this work in the form [Formula: see text], where [Formula: see text], [Formula: see text] and [Formula: see text] are real constant parameters. It has also been found that our model mimics as the standard [Formula: see text]CDM model in future. Finally, we have also shown the evolution of the normalized Hubble parameter for our model and the [Formula: see text]CDM model and compared that with the latest Hubble parameter data.

scholarly journals Non-Extensive Thermodynamics Effects in the Cosmology of f(T) Gravity

Symmetry ◽  
2021 ◽  
Vol 13 (1) ◽  
pp. 75
Author(s):  
Asmaa G. Shalaby ◽  
Vasilis K. Oikonomou ◽  
Gamal G. L. Nashed
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Energy Equation ◽  
State Parameter ◽  
Gravitational Theory ◽  
Density Parameter ◽  
Dark Energy Density ◽  
Equation Of State Parameter ◽  
Relativistic Matter

Using f(T) gravitational theory, we construct modified cosmological models via the first law of thermodynamics by using the non-extensive thermodynamics framework, the effects of which are captured by the parameter δ. The resulting cosmological equations are modified compared to the standard Einstein-Hilbert ones, with the modifications coming from the f(T) gravitational theory and from the non-extensive parameter which quantifies the non-extensive thermodynamics effects quantified by the parameter δ, which when is set equal to unity, one recovers the field equations of f(T) gravity. We study in detail the cosmological evolution of the model in the presence of collisionless non-relativistic matter case, and we derive the exact forms of the dark energy density parameter and of the dark energy equation of state parameter, from which we impose constraints on the non-extensive thermodynamics parameter, δ, by using the Planck 2018 data on cosmological parameters. Accordingly, we repeat our calculations after including the relativistic matter along with the non-relativistic one, and we derive the new forms of the dark energy density parameter and of the dark energy equation of state parameter. Our study shows that the inclusion of non-extensive thermodynamic effects, quantified by the parameter δ, for a flat Friedmann-Robertson-Walker Universe, has measurable differences compared with the normal thermodynamics case. We confront our results with Type Ia supernovae observations for z≥0.4 and we obtain reasonably agreement with the observational data.

scholarly journals Twinlike models for parametrized dark energy

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
J. D. Dantas ◽  
J. J. Rodrigues
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Cosmic Time ◽  
State Parameter ◽  
Cosmological Models ◽  
Real Scalar ◽  
Flat Spacetime ◽  
Acceleration Parameter ◽  
Equation Of State Parameter

Abstract We study cosmological models involving a single real scalar field that has an equation of state parameter which evolves with cosmic time. We highlight some common parametrizations for the equation of state as a function of redshift in the context of twinlike theories. The procedure is used to introduce different models that have the same acceleration parameter, with the very same energy densities and pressure in flat spacetime.

scholarly journals QUINTESSENTIAL POWER-LAW COSMOLOGY: DARK ENERGY EQUATION OF STATE

2013 ◽  
Vol 28 (29) ◽  
pp. 1350122 ◽  
Author(s):  
BURIN GUMJUDPAI
Keyword(s):  
Dark Energy ◽  
Scalar Field ◽  
Equation Of State ◽  
Power Law ◽  
Field Potential ◽  
State Parameter ◽  
Power Exponent ◽  
Acoustic Oscillations ◽  
Equation Of State Parameter ◽  
Canonical Scalar Field

Power-law cosmology with scale factor as power of cosmic time, a ∝tα, is investigated. We review and discuss value of α obtained from various types of observation. Considering dark energy dominant era in late universe from z < 0.5, we use observational derived results from Cosmic Microwave Background (CMB) (WMAP7), Baryon Acoustic Oscillations (BAOs) and observational Hubble data to find power exponent α and other cosmological variables. α is found to be 0.99 ±0.02 ( WMAP7 + BAO +H0) and 0.99 ±0.04 (WMAP7). These values do not exclude possibility of acceleration at 1σ hence giving viability to power-law cosmology in general. When considering scenario of canonical scalar field dark energy with power-law cosmology, we derive scalar field potential, exact scalar field solution and equation of state parameter. We found that the scenario of power-law cosmology containing dynamical canonical scalar field predicts present equation of state parameter wϕ, 0 = -0.449±0.030 while the w CDM with WMAP7 data (model independent, w constant) allows a maximum (+1σ) value of wϕ, 0 at -0.70 which is off the prediction range. However, in case of varying wϕ, the wϕ, 0 value predicted from quintessential power-law cosmology is allowed within 1σ uncertainty.

FRW viscous fluid cosmological model with time-dependent inhomogeneous equation of state

2017 ◽  
Vol 15 (01) ◽  
pp. 1830001 ◽  
Author(s):  
G. S. Khadekar ◽  
Deepti Raut
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Quadratic Form ◽  
State Parameter ◽  
The Other ◽  
Time Dependent ◽  
Inhomogeneous Equation ◽  
Field Equations ◽  
Equation Of State Parameter ◽  
Viscous Models

In this paper, we present two viscous models of non-perfect fluid by avoiding the introduction of exotic dark energy. We consider the first model in terms of deceleration parameter [Formula: see text] has a viscosity of the form [Formula: see text] and the other model in quadratic form of [Formula: see text] of the type [Formula: see text]. In this framework we find the solutions of field equations by using inhomogeneous equation of state of form [Formula: see text] with equation of state parameter [Formula: see text] is constant and [Formula: see text].

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