scholarly journals CONSTRAINTS ON HOLOGRAPHIC DARK ENERGY MODELS USING THE DIFFERENTIAL AGES OF PASSIVELY EVOLVING GALAXIES

2007 ◽  
Vol 22 (01) ◽  
pp. 41-53 ◽  
Author(s):  
ZE-LONG YI ◽  
TONG-JIE ZHANG
Keyword(s):  
Dark Energy ◽  
Hubble Parameter ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Cosmic Time ◽  
Energy Models ◽  
Dark Energy Component ◽  
Best Fitting ◽  
Age Of The Universe ◽  
The Universe

Using the absolute ages of passively evolving galaxies observed at different redshifts, one can obtain the differential ages, the derivative of redshift z with respect to the cosmic time t (i.e. dz/dt). Thus, the Hubble parameter H(z) can be measured through the relation H(z) = -(dz/dt)/(1+z). By comparing the measured Hubble parameter at different redshifts with the theoretical one containing free cosmological parameters, one can constrain current cosmological models. In this paper, we use this method to present the constraint on a spatially flat Friedman–Robert–Walker universe with a matter component and a holographic dark energy component, in which the parameter c plays a significant role in this dark energy model. Firstly we consider three fixed values of c = 0.6, 1.0 and 1.4 in the fitting of data. If we set c free, the best fitting values are c = 0.26, Ωm0 = 0.16, h = 0.9998. It is shown that the holographic dark energy behaves like a quintom-type at the 1σ level. This result is consistent with some other independent cosmological constrains, which imply that c < 1.0 is favored. We also test the results derived from the differential ages using another independent method based on the lookback time to galaxy clusters and the age of the universe. It shows that our results are reliable.

scholarly journals Physical Acceptability of the Renyi, Tsallis and Sharma-Mittal Holographic Dark Energy Models in the f(T,B) Gravity under Hubble’s Cutoff

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 67
Author(s):  
Salim Harun Shekh ◽  
Pedro H. R. S. Moraes ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Field Equations ◽  
Eos Parameter ◽  
Two Fluids ◽  
Gravitational Field Equations ◽  
Energy Models ◽  
Different Types ◽  
The Universe

In the present article, we investigate the physical acceptability of the spatially homogeneous and isotropic Friedmann–Lemâitre–Robertson–Walker line element filled with two fluids, with the first being pressureless matter and the second being different types of holographic dark energy. This geometric and material content is considered within the gravitational field equations of the f(T,B) (where T is the torsion scalar and the B is the boundary term) gravity in Hubble’s cut-off. The cosmological parameters, such as the Equation of State (EoS) parameter, during the cosmic evolution, are calculated. The models are stable throughout the universe expansion. The region in which the model is presented is dependent on the real parameter δ of holographic dark energies. For all δ≥4.5, the models vary from ΛCDM era to the quintessence era.

Reconstructions of f(P) gravity from (m,n) type ordinary and entropy-corrected holographic and Pilgrim dark energy models

2021 ◽  
Author(s):  
Rahul Ghosh ◽  
Ujjal Debnath ◽  
Shuvendu Chakraborty
Keyword(s):  
Dark Energy ◽  
Power Law ◽  
Holographic Dark Energy ◽  
Gravity Models ◽  
Pilgrim Dark Energy ◽  
Energy Models ◽  
Ordinary Power ◽  
Age Of The Universe ◽  
The Universe ◽  
Modified Gravity Models

Modified gravity models are popular among cosmologists, as they can describe the cosmological evolution quite efficiently. Reconstruction of newly introduced [Formula: see text] gravity, with the help of ordinary, power-law entropy corrected and logarithmic entropy-corrected versions of Holographic dark energy (HDE) and Pilgrim dark energy (PDE) models have been studied in this work. For such reconstruction, we have considered the power-law scale factor [Formula: see text]. Further, the classical stabilities (the squared speed of sound method) of such reconstructions and their implications on the nature of the equation of state (EoS) parameters and deceleration parameter with respect to red-shift have also been examined. Finally, we have computed the age of the universe for reconstructed models.

scholarly journals CONSTRAINTS ON DARK ENERGY FROM THE OBSERVED EXPANSION OF OUR COSMIC HORIZON

2009 ◽  
Vol 18 (07) ◽  
pp. 1113-1127 ◽  
Author(s):  
FULVIO MELIA
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Cosmic Time ◽  
Accelerating Universe ◽  
De Sitter ◽  
Dark Energy Component ◽  
The Standard Model ◽  
Type Ia ◽  
Age Of The Universe ◽  
The Universe

Within the context of standard cosmology, an accelerating universe requires the presence of a third "dark" component of energy, beyond matter and radiation. The available data, however, are still deemed insufficient to distinguish between an evolving dark energy component and the simplest model of a time-independent cosmological constant. In this paper, we examine the cosmological expansion in terms of observer-dependent coordinates, in addition to the more conventional comoving coordinates. This procedure explicitly reveals the role played by the radius Rh of our cosmic horizon in the interrogation of the data. (In Rindler's notation, Rh coincides with the "event horizon" in the case of de Sitter, but changes in time for other cosmologies that also contain matter and/or radiation.) With this approach, we show that the interpretation of dark energy as a cosmological constant is clearly disfavored by the observations. Within the framework of standard Friedmann–Robertson–Walker cosmology, we derive an equation describing the evolution of Rh, and solve it using the WMAP and Type Ia supernova data. In particular, we consider the meaning of the observed equality (or near-equality) Rh(t0) ≅ ct0, where t0 is the age of the universe. This empirical result is far from trivial, for a cosmological constant would drive Rh(t) toward ct (t is the cosmic time) only once — and that would have to occur right now. Though we are not here espousing any particular alternative model of dark energy, for comparison we also consider scenarios in which dark energy is given by scaling solutions, which simultaneously eliminate several conundrums in the standard model, including the "coincidence" and "flatness" problems, and account very well for the fact that Rh(t0) ≈ ct0.

scholarly journals Cosmic Consequences of Kaniadakis and Generalized Tsallis Holographic Dark Energy Models in the Fractal Universe

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Abdul Jawad ◽  
Abdul Malik Sultan
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Apparent Horizon ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Energy Models ◽  
Expansion Of The Universe ◽  
The Stability ◽  
The Universe

We investigate the recently proposed holographic dark energy models with the apparent horizon as the IR cutoff by assuming Kaniadakis and generalized Tsallis entropies in the fractal universe. The implications of these models are discussed for both the interacting ( Γ = 3 H b 2 ρ m ) and noninteracting ( b 2 = 0 ) cases through different cosmological parameters. Accelerated expansion of the universe is justified for both models through deceleration parameter q . In this way, the equation of state parameter ω d describes the phantom and quintessence phases of the universe. However, the coincidence parameter r ~ = Ω m / Ω d shows the dark energy- and dark matter-dominated eras for different values of parameters. It is also mentioned here that the squared speed of sound gives the stability of the model except for the interacting case of the generalized Tsallis holographic dark energy model. It is mentioned here that the current dark energy models at the apparent horizon give consistent results with recent observations.

Analysis of entropy corrected holographic and new agegraphic dark energy models in generalized Rastall gravity

2020 ◽  
Vol 35 (28) ◽  
pp. 2050175
Author(s):  
Sayani Maity ◽  
Mahasweta Biswas ◽  
Ujjal Debnath
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Graphical Analysis ◽  
Future Singularity ◽  
Agegraphic Dark Energy ◽  
New Agegraphic Dark Energy ◽  
Energy Models ◽  
Dark Energy Component ◽  
The Stability

This work deals with two fluid system in the framework of generalized Rastall gravity theory. One component represents dark energy whereas the other is dark matter. For the dark energy component, entropy corrected holographic and entropy corrected new agegraphic dark energy models in power-law and logarithmic versions are taken into account. For this study, we assume two classes of scale factors in which one corresponds to the future singularity and another corresponds to the initial singularity. For each of the entropy corrected dark energy models, the cosmological parameters such as Hubble parameter, deceleration parameter and equation of state parameter are calculated and their implications are established. Furthermore, to describe the stability analysis of the models, the behaviors of the squared speed of sound are analyzed graphically for each of these models. From the graphical analysis of [Formula: see text] plane, the thawing or freezing regions of all the models are determined.

scholarly journals An accelerating cosmological model from a parametrization of Hubble parameter

2019 ◽  
Vol 35 (05) ◽  
pp. 2050011 ◽  
Author(s):  
S. K. J. Pacif ◽  
Md Salahuddin Khan ◽  
L. K. Paikroy ◽  
Shalini Singh
Keyword(s):  
Dark Energy ◽  
Cosmological Model ◽  
Hubble Parameter ◽  
Cosmological Parameters ◽  
Cosmic Time ◽  
Solution Procedure ◽  
Cosmic Acceleration ◽  
Model Parameters ◽  
Late Time ◽  
Field Equations

In view of late-time cosmic acceleration, a dark energy cosmological model is revisited wherein Einstein’s cosmological constant is considered as a candidate of dark energy. Exact solution of Einstein field equations (EFEs) is derived in a homogeneous isotropic background in classical general relativity. The solution procedure is adopted in a model-independent way (or the cosmological parametrization). A simple parametrization of the Hubble parameter (H) as a function of cosmic time t is considered which yields an exponential type of evolution of the scale factor (a) and also shows a negative value of deceleration parameter at the present time with a signature flip from early deceleration to late acceleration. Cosmological dynamics of the model obtained have been discussed illustratively for different phases of the evolution of the universe. The evolution of different cosmological parameters is shown graphically for flat and closed cases of Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime for the presented model (open case is incompatible to the present scenario). We have also constrained our model parameters with the updated (36 points) observational Hubble dataset.

scholarly journals Tsallis agegraphic dark energy model

2019 ◽  
Vol 34 (11) ◽  
pp. 1950086 ◽  
Author(s):  
M. Abdollahi Zadeh ◽  
A. Sheykhi ◽  
H. Moradpour
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Dark Energy Model ◽  
Late Time ◽  
Conformal Time ◽  
Classical Level ◽  
Agegraphic Dark Energy ◽  
Energy Models ◽  
Age Of The Universe ◽  
The Universe

Using the non-extensive Tsallis entropy and the holographic hypothesis, we propose a new dark energy (DE) model with timescale as infrared (IR) cutoff. Considering the age of the Universe as well as the conformal time as IR cutoffs, we investigate the cosmological consequences of the proposed DE models and study the evolution of the Universe filled by a pressureless matter and the obtained DE candidates. We find that although this model can describe the late time acceleration and the density, deceleration and the equation of state parameters show satisfactory behavior by themselves, these models are classically unstable unless the interaction between the two dark sectors of the Universe is taken into account. In addition, the results of the existence of a mutual interaction between the cosmos sectors are also addressed. We find out that the interacting models are stable at the classical level which is in contrast to the original interacting agegraphic dark energy models which are classically unstable [K. Y. Kim, H. W. Lee and Y. S. Myung, Phys. Lett. B 660, 118 (2008)].

scholarly journals Analysis off(R)Theory Corresponding to NADE and NHDE

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
M. Sharif ◽  
M. Zubair
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Future Evolution ◽  
Energy Models ◽  
Equation Of State Parameter ◽  
Effective Description

We develop the connection off(R)theory with new agegraphic and holographic dark energy models. The functionf(R)is reconstructed regarding thef(R)theory as an effective description for these dark energy models. We show the future evolution offand conclude that these functions represent distinct pictures of cosmological eras. The cosmological parameters such as equation of state parameter, deceleration parameter, statefinder diagnostic, andw−w′analysis are investigated which assure the evolutionary paradigm off.

ENTROPY CORRECTED HOLOGRAPHIC DARK ENERGY f(T) GRAVITY MODEL

2014 ◽  
Vol 29 (02) ◽  
pp. 1450015 ◽  
Author(s):  
M. SHARIF ◽  
SHAMAILA RANI
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Phase Plane ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Statefinder Parameters ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Evolution Trajectory

This paper is devoted to study the power-law entropy corrected holographic dark energy (ECHDE) model in the framework of f(T) gravity. We assume infrared (IR) cutoff in terms of Granda–Oliveros (GO) length and discuss the constructed f(T) model in interacting as well as in non-interacting scenarios. We explore some cosmological parameters like equation of state (EoS), deceleration, statefinder parameters as well as ωT–ωT′ analysis. The EoS and deceleration parameters indicate phantom behavior of the accelerated expansion of the universe. It is mentioned here that statefinder trajectories represent consistent results with ΛCDM limit, while evolution trajectory of ωT–ωT′ phase plane does not approach to ΛCDM limit for both interacting and non-interacting cases.

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.

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