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.

Viability of specific reconstructed f(T,𝒯 ) models

2019 ◽  
Vol 34 (30) ◽  
pp. 1950184
Author(s):  
M. Umair Shahzad ◽  
Nadeem Azhar ◽  
Abdul Jawad ◽  
Shamaila Rani
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Dark Energy Model ◽  
State Parameter ◽  
Pilgrim Dark Energy ◽  
Ghost Dark Energy ◽  
Energy Models ◽  
Equation Of State Parameter ◽  
Hubble Horizon ◽  
The Universe

The reconstruction scenario of well-established dark energy models such as pilgrim dark energy model and generalized ghost dark energy with Hubble horizon and [Formula: see text] models is being considered. We have established [Formula: see text] models and analyzed their viability through equation of state parameter and [Formula: see text] (where prime denotes derivative with respect to [Formula: see text]) plane. The equation of state parameter evolutes the universe in three different phases such as quintessence, vacuum and phantom. However, the [Formula: see text] plane also describes the thawing as well as freezing region of the universe. The recent observational data also favor our results.

scholarly journals Thermodynamical description of the ghost dark energy model

2015 ◽  
Vol 24 (07) ◽  
pp. 1550048 ◽  
Author(s):  
M. Honarvaryan ◽  
A. Sheykhi ◽  
H. Moradpour
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Dark Energy Model ◽  
State Parameter ◽  
Thermal Fluctuations ◽  
Mutual Interaction ◽  
Coincidence Problem ◽  
Ghost Dark Energy ◽  
Equation Of State Parameter ◽  
The Universe

In this paper, we point out thermodynamical description of ghost dark energy (GDE) and its generalization to the early universe. Thereinafter, we find expressions for the entropy changes of these dark energy (DE) candidates. In addition, considering thermal fluctuations, thermodynamics of the DE component interacting with a dark matter (DM) sector is addressed. We will also find the effects of considering the coincidence problem on the mutual interaction between the dark sectors, and thus the equation of state parameter of DE. Finally, we derive a relation between the mutual interaction of the dark components of the universe, accelerated with the either GDE or its generalization, and the thermodynamic fluctuations.

A study on the modified holographic Ricci dark energy in logarithmic f(T) gravity

2013 ◽  
Vol 91 (4) ◽  
pp. 351-354 ◽  
Author(s):  
Antonio Pasqua ◽  
Surajit Chattopadhyay
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Energy Density ◽  
Modified Gravity ◽  
State Parameter ◽  
Ricci Dark Energy ◽  
Equation Of State Parameter ◽  
Interaction Term ◽  
The Universe

In this paper, we have studied and investigated the behavior of a modified holographic Ricci dark energy (DE) model interacting with pressureless dark matter (DM) under the theory of modified gravity, dubbed logarithmic f(T) gravity. We have chosen the interaction term between DE and DM in the form Q = 3γHρm and investigated the behavior of the torsion, T, the Hubble parameter, H, the equation of state parameter, ωDE, the energy density of DE, ρDE, and the energy density contribution due to torsion, ρT, as functions of the redshift, z. We have found that T increases with the redshift, z, H increases with the evolution of the universe, ωDE has a quintessence-like behavior, and both energy densities increase going from higher to lower redshifts.

scholarly journals A COSMOLOGICAL MODEL WITH FERMIONIC FIELD AND GAUSS–BONNET TERM

2010 ◽  
Vol 25 (06) ◽  
pp. 1267-1278 ◽  
Author(s):  
R. RAKHI ◽  
G. V. VIJAYAGOVINDAN ◽  
K. INDULEKHA ◽  
NOBLE P. ABRAHAM
Keyword(s):  
Cosmological Model ◽  
State Parameter ◽  
The Self ◽  
Late Time ◽  
Fermionic Field ◽  
New Type ◽  
Interaction Term ◽  
The Stability ◽  
The Universe ◽  
Bonnet Term

In this work, a cosmological model inspired by string theory with Gauss–Bonnet term coupled to the fermionic field is taken into consideration. The self-interaction potential is considered as a combination of the scalar and pseudoscalar invariants. Here the cosmological contribution of the coupling of Gauss–Bonnet term with a non-Dirac fermionic field — characterized by an interaction term[Formula: see text] — is investigated. It is observed that the new type of coupling plays a significant role in the accelerating behavior of the universe. Specifically, in addition to the late time acceleration for the universe, [Formula: see text] produces an early decelerating behavior. The behavior of the equation-of-state parameter (w) is such that it guarantees the stability of the theory.

scholarly journals Nonlinearly interacting ghost dark energy in Brans–Dicke cosmology

2016 ◽  
Vol 94 (10) ◽  
pp. 1001-1007 ◽  
Author(s):  
E. Ebrahimi ◽  
H. Golchin
Keyword(s):  
Dark Energy ◽  
Nonlinear Interaction ◽  
Sound Speed ◽  
Statefinder Parameters ◽  
Acceleration Phase ◽  
Coincidence Problem ◽  
Ghost Dark Energy ◽  
Energy Models ◽  
Interaction Term ◽  
The Universe

In this paper we extend the form of interaction term into the nonlinear regime in the ghost dark energy model. A general form of the nonlinear interaction term is presented and cosmic dynamic equations are obtained. Next, the model is detailed for two special choices of the nonlinear interaction term. According to this the universe transits at suitable time (z ∼ 0.8) from deceleration to acceleration phase, which alleviate the coincidence problem. Squared sound speed analysis revealed that for one class of nonlinear interaction term [Formula: see text] can become positive. This point is an impact of the nonlinear interaction term and we never find such behavior in non-interacting and linearly interacting ghost dark energy models. Also, statefinder parameters are introduced for this model and we found that for one class the model meets the ΛCDM while in the second choice although the model approaches the ΛCDM, but never matches it.

Ghost dark energy in the deformed Hořava–Lifshitz cosmology

2019 ◽  
Vol 28 (06) ◽  
pp. 1950080
Author(s):  
A. Sheykhi ◽  
S. Ghaffari ◽  
H. Moradpour
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Density Parameter ◽  
Late Time ◽  
Ghost Dark Energy ◽  
Deceleration Phase ◽  
Classical Stability ◽  
Equation Of State Parameter ◽  
Generalized Ghost Dark Energy

We study the cosmological consequences of the ghost models of dark energy (DE) in the framework of Hořava–Lifshitz gravity. We calculate the equation-of-state parameter, the deceleration parameter, the classical stability and the dimensionless density parameter of the models in both noninteracting and interacting scenarios. We find that, for some values of the parameter, this model can admit a transition from the deceleration phase to the accelerated phase around [Formula: see text], while at the late time ([Formula: see text]) we have [Formula: see text] meaning that this model mimics a cosmological constant. We find that in the setup of Hořava–Lifshitz gravity, ghost dark energy (GDE) models are classically unstable. We observe that unlike the generalized ghost dark energy (GGDE), the ghost dark energy cannot provide proper behavior for all the cosmological parameters simultaneously, with the same values of the models’ couplings.

Cosmological evolution of Tsallis holographic dark energy model in LTB inhomogeneous gravity

2020 ◽  
Vol 29 (03) ◽  
pp. 2050023 ◽  
Author(s):  
Ayman A. Aly ◽  
Mohammed Abd Elrashied ◽  
Mustafa M. Selim
Keyword(s):  
Dark Energy ◽  
Sound Speed ◽  
Holographic Dark Energy ◽  
State Parameter ◽  
Energy Conditions ◽  
Holographic Dark Energy Model ◽  
Inhomogeneous Models ◽  
Hubble Horizon ◽  
The Stability ◽  
The Universe

The aim of this work is to analyze the modified form of holographic dark energy (DE) density suggested by Tsallis and Cirto within inhomogeneous models of the universe. This DE model is applied to IR cutoff equals the Hubble horizon. Some basic cosmological functions, such as the Hubble function, the deceleration function and the equation of state parameter, are reconstructed by choosing specific values of certain numerical parameters in this model. The stability of the model is studied by considering the square of sound speed and the strong, the weak and the dominant energy conditions (DEC). In addition, the variation of the diagnostic Omega, [Formula: see text] and [Formula: see text] parameters with the redshift and space are studied. The obtained results show a close behavior to that of the cosmological constant DE universe so it can be compared well with the recent observations.

scholarly journals Interacting generalized ghost dark energy in a non-flat universe

Open Physics ◽  
2013 ◽  
Vol 11 (7) ◽  
Author(s):  
Esmaeil Ebrahimi ◽  
Ahmad Sheykhi ◽  
Hamzeh Alavirad
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
State Parameter ◽  
Model Parameters ◽  
De Sitter ◽  
Frw Universe ◽  
Ghost Dark Energy ◽  
Equation Of State Parameter ◽  
The Universe ◽  
Generalized Ghost Dark Energy

AbstractWe investigate the generalized Quantum Chromodynamics (QCD) ghost model of dark energy in the framework of Einstein gravity. First, we study the non-interacting generalized ghost dark energy in a flat Friedmann-Robertson-Walker (FRW) background. We obtain the equation of state parameter, w D = p/ρ, the deceleration parameter, and the evolution equation of the generalized ghost dark energy. We find that, in this case, w D cannot cross the phantom line (w D > −1) and eventually the universe approaches a de-Sitter phase of expansion (w D → −1). Then, we extend the study to the interacting ghost dark energy in both a flat and non-flat FRW universe. We find that the equation of state parameter of the interacting generalized ghost dark energy can cross the phantom line (w D < −1) provided the parameters of the model are chosen suitably. Finally, we constrain the model parameters by using the Markov Chain Monte Carlo (MCMC) method and a combined dataset of SNIa, CMB, BAO and X-ray gas mass fraction.

scholarly journals Cosmological Evolution of Pilgrim Dark Energy inf(G)Gravity

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Abdul Jawad ◽  
Shamaila Rani
Keyword(s):  
Dark Energy ◽  
Energy Parameter ◽  
State Parameter ◽  
Freezing And Thawing ◽  
Pilgrim Dark Energy ◽  
Equation Of State Parameter ◽  
Hubble Horizon ◽  
The Stability ◽  
Phantom Phase ◽  
The Universe

We analyze the behavior of pilgrim dark energy with Hubble horizon inf(G)gravity. We reconstruct thef(G)models through correspondence phenomenon by assuming two values of pilgrim dark energy parameter(u=2, -2). We evaluate the equation of state parameter which shows evolution of the universe in the quintessence, vacuum, and phantom phase for both cases ofuand give favor the pilgrim dark energy phenomenon. Also, squared speed of sound exhibits the stability off(G)model for both cases ofu. ThewPDE-wPDE′also provides freezing and thawing regions in this scenario. In this framework, ther-splane also corresponds to different dark energy scenarios.

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.

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