Time evolution of dark energy and other cosmological parameters

2017 ◽  
Vol 30 (3) ◽  
pp. 255-263 ◽  
Author(s):  
Guibert U. Crevecoeur
Keyword(s):  
Dark Energy ◽  
Time Evolution ◽  
Cosmological Parameters

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.

scholarly journals Emergent Universe as an interaction in the dark sector

2017 ◽  
Vol 32 (28) ◽  
pp. 1750152
Author(s):  
Emiliano Marachlian ◽  
I. E. Sánchez G. ◽  
Osvaldo P. Santillán
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Linear Equation ◽  
Vacuum Energy ◽  
Cosmological Parameters ◽  
Emergent Universe ◽  
Dark Sector ◽  
Cosmological Scenario ◽  
Friedmann Robertson Walker

A cosmological scenario where dark matter interacts with a variable vacuum energy for a spatially flat Friedmann–Robertson–Walker (FRW) spacetime is proposed and analyzed to show that with a linear equation of state and a particular interaction in the dark sector it is possible to get a model of an Emergent Universe. In addition, the viability of two particular models is studied by taking into account the recent observations. The updated observational Hubble data and the JLA supernovae data are used in order to constraint the cosmological parameters of the models and estimate the amount of dark energy in the radiation era. It is shown that the two models fulfil the severe bounds of [Formula: see text] at the 2[Formula: see text] level of Planck.

scholarly journals Bianchi type-III Tsallis holographic dark energy model in Saez–Ballester theory of gravitation

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
M. Vijaya Santhi ◽  
Y. Sobhanbabu
Keyword(s):  
Dark Energy ◽  
Bianchi Type ◽  
Graphical Representation ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
State Parameter ◽  
Field Equations ◽  
Om Diagnostic ◽  
Hubble Radius ◽  
Theory Of Gravitation

AbstractIn this paper, we have investigated Tsallis holographic dark energy (infrared cutoff is the Hubble radius) in homogeneous and anisotropic Bianchi type-III Universe within the framework of Saez–Ballester scalar–tensor theory of gravitation. We have constructed non-interaction and interaction dark energy models by solving the Saez–Ballester field equations. To solve the field equations, we assume a relationship between the metric potentials of the model. We developed the various cosmological parameters (namely deceleration parameter q, equation of state parameter $$\omega _t$$ ω t , squared sound speed $$v_s^2$$ v s 2 , om-diagnostic parameter Om(z) and scalar field $$\phi $$ ϕ ) and well-known cosmological planes (namely $$\omega _t-\omega _t^{'}$$ ω t - ω t ′ plane, where $$'$$ ′ denotes derivative with respect to ln(a) and statefinders ($$r-s$$ r - s ) plane) and analyzed their behavior through graphical representation for our both the models. It is also, quite interesting to mention here that the obtained results are coincide with the modern observational data.

scholarly journals Observing Galaxy Clusters with eROSITA: Simulations

10.14311/1466 ◽  
2011 ◽  
Vol 51 (6) ◽  
Author(s):  
J. Hölzl ◽  
J. Wilms ◽  
I. Kreykenbohm ◽  
Ch. Schmid ◽  
Ch. Grossberger ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Dark Matter ◽  
Dark Energy ◽  
Galaxy Clusters ◽  
Cosmological Parameters ◽  
Mass Function ◽  
Angular Diameter ◽  
Monte Carlo Code ◽  
X Rays ◽  
Sky Survey

The eROSITA instrument on board the Russian Spectrum Roentgen Gamma spacecraft, which will be launched in 2013,will conduct an all sky survey in X-rays. A main objective of the survey is to observe galaxy clusters in order to constrain cosmological parameters and to obtain further knowledge about dark matter and dark energy. For the simulation of the eROSITA survey we present a Monte-Carlo code generating a mock catalogue of galaxy clusters distributed accordingto the mass function of [1]. The simulation generates the celestial coordinates as well as the cluster mass and redshift. From these parameters, the observed intensity and angular diameter are derived. These are used to scale Chandra cluster images as input for the survey-simulation.

scholarly journals Cosmological constraints from H ii starburst galaxy apparent magnitude and other cosmological measurements

2020 ◽  
Vol 497 (3) ◽  
pp. 3191-3203 ◽  
Author(s):  
Shulei Cao ◽  
Joseph Ryan ◽  
Bharat Ratra
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
Angular Size ◽  
Hubble Constant ◽  
Joint Analysis ◽  
Apparent Magnitude ◽  
Starburst Galaxy ◽  
Density Parameter ◽  
Acoustic Oscillations ◽  
Combined Data

ABSTRACT We use H ii starburst galaxy apparent magnitude measurements to constrain cosmological parameters in six cosmological models. A joint analysis of H ii galaxy, quasar angular size, baryon acoustic oscillations peak length scale, and Hubble parameter measurements result in relatively model-independent and restrictive estimates of the current values of the non-relativistic matter density parameter $\Omega _{\rm m_0}$ and the Hubble constant H0. These estimates favour a 2.0–3.4σ (depending on cosmological model) lower H0 than what is measured from the local expansion rate. The combined data are consistent with dark energy being a cosmological constant and with flat spatial hypersurfaces, but do not strongly rule out mild dark energy dynamics or slightly non-flat spatial geometries.

scholarly journals Exploring the dark universe: Constraints on dynamical dark energy models from CMB, BAO and growth rate measurements

2019 ◽  
Vol 28 (09) ◽  
pp. 1950118 ◽  
Author(s):  
Alexander Bonilla Rivera ◽  
Jorge Enrique García-Farieta
Keyword(s):  
Dark Energy ◽  
Observational Data ◽  
Cosmological Parameters ◽  
Growth Parameter ◽  
Information Criteria ◽  
Fine Tuning ◽  
Coincidence Problem ◽  
Shift Parameter ◽  
History Of ◽  
Dynamical Dark Energy

In order to explain the current acceleration of the universe, the fine-tuning problem of the cosmological constant [Formula: see text] and the cosmic coincidence problem, different alternative models have been proposed in the literature. We use the most recent observational data from CMB (Planck 2018 final data release) and LSS (SDSS, WiggleZ, VIPERS) to constrain dynamical dark energy (DE) models. The CMB shift parameter, which traditionally has been used to determine the main cosmological parameters of the standard model [Formula: see text], is employed in addition to data from redshift-space distortions through the growth parameter [Formula: see text] to constrain the mass variance [Formula: see text]. BAO data are also used to study the history of the cosmological expansion and the main properties of DE. From the evolution of [Formula: see text], we found a slowdown of acceleration behavior at low redshifts, and by using the Akaike and Bayesian Information Criteria (AIC, BIC), we discriminate different models to find those that are better suited to the observational data, finding that the interacting dark energy (IDE) model is the most favored by observational data, including information from SNIa and Hz. The analysis shows that the IDE model is followed closely by EDE and [Formula: see text] models, which in some cases fit better the observational data with individual probes.

Cosmological implications of dark energy models in modified gravity

2018 ◽  
Vol 15 (03) ◽  
pp. 1850034 ◽  
Author(s):  
Nadeem Azhar ◽  
Abdul Jawad ◽  
Sarfraz Ahmad ◽  
Iftikhar Ahmed
Keyword(s):  
Dark Energy ◽  
Modified Gravity ◽  
Cold Dark Matter ◽  
Cosmological Parameters ◽  
Accelerated Expansion ◽  
Pilgrim Dark Energy ◽  
Energy Models ◽  
Expansion Of The Universe ◽  
Qcd Ghost Dark Energy ◽  
Chern Simons

We discuss the interacting modified QCD ghost dark energy and generalized ghost pilgrim dark energy with cold dark matter in the framework of dynamical Chern–Simons modified gravity. We investigate the cosmological parameters such as Hubble parameter, deceleration parameter and equation of state. We also discuss the physical significance of various cosmological planes like [Formula: see text] and statefinders. It is found that the results of cosmological parameters as well as planes explain the accelerated expansion of the Universe and are compatible with observational data.

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.

Testing anisotropy and comparison of various supernova data constraints on dark energy model

2019 ◽  
Vol 34 (34) ◽  
pp. 1950276 ◽  
Author(s):  
H. Hossienkhani ◽  
H. Yousefi ◽  
N. Azimi
Keyword(s):  
Dark Energy ◽  
Dark Energy Model ◽  
Cosmological Parameters ◽  
Acoustic Oscillation ◽  
Maximum Likelihood Analysis ◽  
Accelerating Expansion ◽  
Combining Data ◽  
Likelihood Analysis ◽  
Data Constraints ◽  
The Universe

We study the possibly existing anisotropy in the accelerating expansion Universe with various supernovae data, the baryon acoustic oscillation and the observational Hubble data. We present combined results from these probes, deriving constraints on the equation of state (EoS), [Formula: see text], of dark energy (DE) and its energy density in the Universe. We fit the cosmological parameters simultaneously employing the maximum likelihood analysis. By combining data and considering anisotropy effects, we find that the EoS of DE are [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] within [Formula: see text] confidence level. Finally, introducing an anisotropy appears to improve the fit to observations with respect to that provided by an isotropic [Formula: see text]CDM model.

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.

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