scholarly journals MODELING TIME-VARYING DARK ENERGY WITH CONSTRAINTS FROM LATEST OBSERVATIONS

2012 ◽  
Vol 27 (10) ◽  
pp. 1250030 ◽  
Author(s):  
QING-JUN ZHANG ◽  
YUE-LIANG WU
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
Local Extremum ◽  
Joint Analysis ◽  
Type I ◽  
Time Varying ◽  
Two Parameters ◽  
Best Fit ◽  
Two Parameter ◽  
Extra Parameter

We introduce a set of two-parameter models for the dark energy equation of state (EOS) w(z) to investigate time-varying dark energy. The models are classified into two types according to their boundary behaviors at the redshift z = (0, ∞) and their local extremum properties. A joint analysis based on four observations ( SNe + BAO + CMB + H0) is carried out to constrain all the models. It is shown that all models get almost the same [Formula: see text] and the cosmological parameters (ΩM, h, Ωbh2) with the best-fit results (0.28, 0.70, 2.24), although the constraint results on two parameters (w0, w1) and the allowed regions for the EOS w(z) are sensitive to different models and a given extra model parameter. For three of Type I models which have similar functional behaviors with the so-called CPL model, the constrained two parameters w0 and w1 have negative correlation and are compatible with the ones in CPL model, and the allowed regions of w(z) get a narrow node at z~0.2. The best-fit results from the most stringent constraints in Model Ia give [Formula: see text] which may compare with the best-fit results [Formula: see text] in the CPL model. For four of Type II models which have logarithmic function forms and an extremum point, the allowed regions of w(z) are found to be sensitive to different models and a given extra parameter. It is interesting to obtain two models in which two parameters w0 and w1 are strongly correlative and appropriately reduced to one parameter by a linear relation w1∝(1+w0).

scholarly journals Consistency of nonlinear interacting ghost dark energy with recent observations

2017 ◽  
Vol 26 (11) ◽  
pp. 1750124 ◽  
Author(s):  
E. Ebrahimi ◽  
H. Golchin ◽  
A. Mehrabi ◽  
S. M. S. Movahed
Keyword(s):  
Dark Energy ◽  
Observational Data ◽  
Nonlinear Interaction ◽  
Acoustic Oscillation ◽  
Joint Analysis ◽  
Data Sets ◽  
Dark Energy Density ◽  
Ghost Dark Energy ◽  
Interaction Terms ◽  
Best Fit

In this paper, we investigate ghost dark energy model in the presence of nonlinear interaction between dark energy and dark matter. We also extend the analysis to the so-called generalized ghost dark energy (GGDE) which [Formula: see text]. The model contains three free parameters as [Formula: see text] and [Formula: see text] (the coupling coefficient of interactions). We propose three kinds of nonlinear interaction terms and discuss the behavior of equation of state, deceleration and dark energy density parameters of the model. We also find the squared sound speed and search for signs of stability of the model. To compare the interacting GGDE model with observational data sets, we use more recent observational outcomes, namely SNIa from JLA catalog, Hubble parameter, baryonic acoustic oscillation and the most relevant CMB parameters including, the position of acoustic peaks, shift parameters and redshift to recombination. For GGDE with the first nonlinear interaction, the joint analysis indicates that [Formula: see text], [Formula: see text] and [Formula: see text] at 1 optimal variance error. For the second interaction, the best fit values at [Formula: see text] confidence are [Formula: see text], [Formula: see text] and [Formula: see text]. According to combination of all observational data sets considered in this paper, the best fit values for third nonlinearly interacting model are [Formula: see text], [Formula: see text] and [Formula: see text] at [Formula: see text] confidence interval. Finally, we found that the presence of interaction is compatible in mentioned models via current observational datasets.

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.

Probing the anisotropy effects on the CPL parametrizations from light-curve SNIa, BAO and OHD datasets

2019 ◽  
Vol 16 (11) ◽  
pp. 1950177 ◽  
Author(s):  
H. Hossienkhani ◽  
N. Azimi ◽  
Z. Zarei
Keyword(s):  
Light Curve ◽  
Observational Data ◽  
Cosmological Parameters ◽  
Estimation Method ◽  
Likelihood Estimation ◽  
Anisotropic Universe ◽  
Type I ◽  
Acoustic Oscillations ◽  
Type Ia ◽  
Best Fit

Recent observers have shown that an anisotropy cosmic expansion may exist. In this work, we study the effects of low anisotropy with Bianchi type I model using the current observational data, which includes the supernova Legacy Survey (SNLS) sample of 238 SN events ([Formula: see text]) and 1048 Pantheon sample confirmed type Ia supernova (SNIa) covering the redshift range [Formula: see text]. Assuming an anisotropic universe, we use the two parametrizations of the dark energy equation-of-state, such as the [Formula: see text] (PA) and [Formula: see text] (PB), and then we fit the SNIa light-curve parameters and free cosmological parameters, simultaneously employing maximum likelihood estimation method. When combining the Baryon Acoustic Oscillations (BAO) and the observational Hubble data (OHD) measurements with the SNLS SN sample, we find [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] for the PA model and [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] for the PB model. When combining also Pantheon data, we obtain [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] for the PA model and [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] for the PB model. The analysis shows that by considering the anisotropy effects, it leads to more best-fit parameters in [Formula: see text]CDM model with the current observational data.

scholarly journals A Cosmological View on Milgrom’s Acceleration Constant

2018 ◽  
Author(s):  
Engel Roza
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Baryonic Matter ◽  
Stellar Rotation ◽  
Adequate Explanation ◽  
Cosmological Time ◽  
Age Of The Universe ◽  
Two Parameters ◽  
The Universe ◽  
Two Parameter

In this article a two-parameter model is developed for the universe. The two parameters are the age of the universe and Milgrom’s acceleration constant. It is shown that these are sufficient to calculate the amounts of matter and dark energy in the universe, as well as the contributions of dark matter and baryonic matter in the matter part. All this, not only for present time, but also as a function of cosmological time. The developed theory gives an adequate explanation for the phenomena of the accelerated scaling of the universe and the anomaly of the stellar rotation curves in galaxies. The numerical results are in agreement with those of the Lamda-CDM model.

Holographic Dark Energy Model With Time Varying Deceleration Parameter

2018 ◽  
Vol 6 (2) ◽  
pp. 25
Author(s):  
R P. Wankhade
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Deceleration Parameter ◽  
Holographic Dark Energy ◽  
Anisotropy Parameter ◽  
Type I ◽  
Time Varying ◽  
Field Equations ◽  
Large Expansion ◽  
The Universe

Two minimally interacting fluids; dark matter and holographic dark energy components has been studied in a spatially homogeneous and anisotropic Bianchi type-I space-time. The solutions of the Einstein’s field equations are obtained under the assumption of time varying deceleration parameter (Abdussattar and S. Prajapati, Astrophys. Space Sci. 331, 65, 2011) which represents transition of the universe from the early decelerating phase to the recent accelerating phase. It is shown that for large expansion the model reduces to model while for suitable choice of interaction between dark matter and holographic dark energy the anisotropy parameter of the universe approaches to zero for large cosmic time and the coincidence parameter increases with increase in time. Allowing for time dependent deceleration parameter the solutions of the field equations and some physical and geometric properties of the model along with physical acceptability of the solutions have also been discussed in details. 

Modèle de comportement dynamique cyclique de sols en grandes déformations

2000 ◽  
Vol 37 (3) ◽  
pp. 723-728 ◽  
Author(s):  
Paul Jouanna ◽  
Mokhtar Mabssout
Keyword(s):  
Dynamic Behaviour ◽  
Large Strains ◽  
Damping Factor ◽  
Empirical Law ◽  
Average Modulus ◽  
Two Parameters ◽  
Soil Behaviour ◽  
Two Parameter ◽  
Extra Parameter ◽  
Deformation Hysteresis

A two-parameter cyclic empirical law, as used traditionnally by the engineer, is not able to fit the dynamic behaviour of soils under large strains. When simulating the classical laboratory results, a Hardin-Drnevich law associated with Masing's rule, although able to fit satisfactorily the average strain modulus with only two parameters (Go, α), is not adapted for fitting the damping factor at moderate and high strains. To overcome this limitation, a modified empirical law with three parameters (Go, α, β) is proposed. According to the initial law, parameter Go characterizes low strains and parameter α allows simulating the average modulus. The extra parameter β is used for adjusting the damping factor, as obtained by Masing's rule, to the experimental results at high strain.Key words: soil behaviour, dynamic, cyclic, large deformation, hysteresis, damping.

scholarly journals Cosmological models of generalized ghost pilgrim dark energy (GGPDE) in the gravitation theory of Saez–Ballester

2021 ◽  
Author(s):  
Priyanka Garg ◽  
Archana Dixit ◽  
Anirudh Pradhan
Keyword(s):  
Dark Energy ◽  
Cosmological Parameters ◽  
Acoustic Oscillation ◽  
Type I ◽  
Microwave Background ◽  
Light Curve Analysis ◽  
Pilgrim Dark Energy ◽  
Type Ia ◽  
State Formula ◽  
Quintessence Field

In this paper, we study the mechanism of the cosmic model in the presence of generalized ghost pilgrim dark energy (GGPDE) and matter in locally rotationally symmetric (LRS) Bianchi type-I space-time by the utilization of new holographic DE in Saez–Ballester theory. Here, we discuss all the data for three scenarios, the first is supernovae type-Ia union data, the second is SN Ia data in combination with baryon acoustic oscillation and cosmic microwave background observations and the third is a combination with observational Hubble data and joint light-curve analysis observations. From this, we get a model of our universe, where transit state exists from deceleration to acceleration phase. Here, we have observed that the results yielded by cosmological parameters like [Formula: see text] (energy density), equation of state [Formula: see text], squared speed of sound [Formula: see text] and [Formula: see text]–[Formula: see text] are compatible with the recent observations. The [Formula: see text]–[Formula: see text] trajectories lie in both thawing and freezing regions and the correspondence of the quintessence field with GGPDE is also discussed. Some physical aspects of the GGPDE models are mainly highlighted.

Prediction of Haemoglobin Level by Some Probability Distribution

2020 ◽  
Vol 9 (1) ◽  
pp. 84-88
Author(s):  
Govinda Prasad Dhungana ◽  
Laxmi Prasad Sapkota
Keyword(s):  
Probability Distribution ◽  
Normal Distribution ◽  
Goodness Of Fit ◽  
Continuous Variable ◽  
Hemoglobin Level ◽  
Chi Square ◽  
Chi Square Test ◽  
Log Normal ◽  
Two Parameters ◽  
Best Fit

 Hemoglobin level is a continuous variable. So, it follows some theoretical probability distribution Normal, Log-normal, Gamma and Weibull distribution having two parameters. There is low variation in observed and expected frequency of Normal distribution in bar diagram. Similarly, calculated value of chi-square test (goodness of fit) is observed which is lower in Normal distribution. Furthermore, plot of PDFof Normal distribution covers larger area of histogram than all of other distribution. Hence Normal distribution is the best fit to predict the hemoglobin level in future.

scholarly journals Mixed fluid cosmological model in f(R, T) gravity

2020 ◽  
Vol 98 (11) ◽  
pp. 1015-1022 ◽  
Author(s):  
Parbati Sahoo ◽  
Barkha Taori ◽  
K.L. Mahanta
Keyword(s):  
Cosmological Model ◽  
Bianchi Type ◽  
Type I ◽  
Time Varying ◽  
Eos Parameter ◽  
Barotropic Fluid ◽  
Rotationally Symmetric ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Mixed Fluid

We construct a locally rotationally symmetric (LRS) Bianchi type-I cosmological model in f(R, T) theory of gravity when the source of gravitation is a mixture of barotropic fluid and dark energy (DE) by employing a time-varying deceleration parameter. We observe through the behavior of the state finder parameters (r, s) that our model begins from the Einstein static era and goes to ΛCDM era. The equation of state (EOS) parameter (ωd) for DE varies from the phantom (ω < –1) phase to quintessence (ω > –1) phase, which is consistent with observational results. It is found that the discussed model can reproduce the current accelerating phase of the expansion of the universe.

scholarly journals Testing the effect of H0 on fσ8 tension using a Gaussian Process method

2020 ◽  
Author(s):  
En-Kun Li ◽  
Minghui Du ◽  
Zhi-Huan Zhou ◽  
Hongchao Zhang ◽  
Lixin Xu
Keyword(s):  
Growth Rate ◽  
Dark Energy ◽  
Cosmological Constant ◽  
Gaussian Process ◽  
Dark Energy Model ◽  
Hubble Space Telescope ◽  
Λcdm Model ◽  
Space Distortion ◽  
Best Fit ◽  
Process Method

Abstract Using the fσ8(z) redshift space distortion (RSD) data, the $\sigma _8^0-\Omega _m^0$ tension is studied utilizing a parameterization of growth rate f(z) = Ωm(z)γ. Here, f(z) is derived from the expansion history H(z) which is reconstructed from the observational Hubble data applying the Gaussian Process method. It is found that different priors of H0 have great influences on the evolution curve of H(z) and the constraint of $\sigma _8^0-\Omega _m^0$. When using a larger H0 prior, the low redshifts H(z) deviate significantly from that of the ΛCDM model, which indicates that a dark energy model different from the cosmological constant can help to relax the H0 tension problem. The tension between our best-fit values of $\sigma _8^0-\Omega _m^0$ and that of the Planck 2018 ΛCDM (PLA) will disappear (less than 1σ) when taking a prior for H0 obtained from PLA. Moreover, the tension exceeds 2σ level when applying the prior H0 = 73.52 ± 1.62 km/s/Mpc resulted from the Hubble Space Telescope photometry. By comparing the $S_8 -\Omega _m^0$ planes of our method with the results from KV450+DES-Y1, we find that using our method and applying the RSD data may be helpful to break the parameter degeneracies.

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