scholarly journals Constraints on the interacting vacuum–geodesic CDM scenario

2019 ◽  
Vol 488 (3) ◽  
pp. 3423-3438 ◽  
Author(s):  
Matteo Martinelli ◽  
Natalie B Hogg ◽  
Simone Peirone ◽  
Marco Bruni ◽  
David Wands
Keyword(s):  
Cold Dark Matter ◽  
Vacuum Energy ◽  
High Redshift ◽  
Acoustic Oscillation ◽  
Linear Perturbation ◽  
Dark Sector ◽  
Microwave Background ◽  
Dynamical Interaction ◽  
Type Ia ◽  
Linear Perturbation Theory

Abstract We investigate an interacting dark sector scenario in which the vacuum energy is free to interact with cold dark matter (CDM), which itself is assumed to cluster under the sole action of gravity, i.e. it is in freefall (geodesic), as in ΛCDM. The interaction is characterized by a dimensionless coupling qV(z), in general a function of redshift. Aiming to reconstruct the evolution of the coupling, we use cosmic microwave background data from Planck 2015, along with baryon acoustic oscillation, redshift space distortion, and Type Ia supernova measurements to constrain various parametrizations of qV(z). We present the full linear perturbation theory of this interacting scenario and use Monte Carlo Markov Chains (MCMC) sampling to study five different cases: two cases in which we have ΛCDM evolution in the distant past, until a set redshift ztrans, below which the interaction switches on and qV is the single-sampled parameter, with ztrans fixed at ztrans = 3000 and 0.9, respectively; a case where we allow this transition redshift to vary along with qV; a case in which the vacuum energy is zero for z > ztrans and then begins to grow once the interaction switches on; and the final case in which we bin qV(z) in four redshift bins to investigate the possibility of a dynamical interaction, reconstructing the redshift evolution of the function using Gaussian processes. We find that, in all cases where the high-redshift evolution is not modified, the results are compatible with a vanishing coupling, thus finding no significant deviation from ΛCDM.

A PARAMETRIZED VARIABLE DARK ENERGY MODEL: STRUCTURE FORMATION AND OBSERVATIONAL CONSTRAINTS

2006 ◽  
Vol 15 (09) ◽  
pp. 1455-1472 ◽  
Author(s):  
S. ARBABI BIDGOLI ◽  
M. SADEGH MOVAHED ◽  
S. RAHVAR
Keyword(s):  
Dark Energy ◽  
Dark Energy Model ◽  
Large Scale ◽  
High Redshift ◽  
Growth Index ◽  
Energy Model ◽  
Linear Perturbation ◽  
Model Parameters ◽  
Type Ia ◽  
Parametrization Scheme

In this paper we investigate a simple parametrization scheme of the quintessence model given by Wetterich [Phys. Lett. B594, 17 (2004)]. The crucial parameter of this model is the bending parameter b, which is related to the amount of dark energy in the early universe. Using the linear perturbation and the spherical infall approximations, we investigate the evolution of matter density perturbations in the variable dark energy model, and obtain an analytical expression for the growth index f. We show that increasing b leads to less growth of the density contrast δ, and also decreases the growth index. Giving a fitting formula for the growth index at the present time, we verify that the approximation relation [Formula: see text] also holds in this model. To compare predictions of the model with observations, we use the Supernovae type Ia (SNIa) Gold Sample and the parameters of the large scale structure determined by the 2-degree Field Galaxy Redshift Survey (2dFGRS). The best fit values for the model parameters by marginalizing on the remained ones, are [Formula: see text], [Formula: see text] and [Formula: see text] at 1σ confidence level. As a final test we calculate the age of universe for different choices of the free parameters in this model and compare it with the age of old stars and some high redshift objects. Then we show that the predictions of this variable dark energy model are consistent with the age observation of old star and can solve the "age crisis" problem.

scholarly journals Contributions to the Local Gravitational Field from beyond the Local Supercluster

1987 ◽  
Vol 117 ◽  
pp. 435-443
Author(s):  
A. Yahil
Keyword(s):  
Gravitational Field ◽  
Background Radiation ◽  
Nonlinear Effects ◽  
Linear Perturbation ◽  
Density Parameter ◽  
Microwave Background ◽  
Dipole Component ◽  
Local Supercluster ◽  
Microwave Background Radiation ◽  
Linear Perturbation Theory

IRAS 60μ sources are used to map the local (≲200h−1 Mpc, Ho =100h km s−1 Mpc−1) gravitational field, and to determine its dipole component, on the assumption that the infrared radiation traces the matter. The dipole moment is found to point in the direction of the anisotropy of the microwave background radiation. Comparison of the two anisotropies, using linear perturbation theory, yields an estimate of the cosmological density parameter, Ω =0.85±0.16, with nonlinear effects increasing Ωo by ∼15%. The quadrupolar tidal field within the Local Supercluster, due presumably to the same density inhomogeneities, is detected in a kinematical study of the velocity field.

scholarly journals Astronomical bounds on the modified Chaplygin gas as a unified dark fluid model

2019 ◽  
Vol 623 ◽  
pp. A28
Author(s):  
Hang Li ◽  
Weiqiang Yang ◽  
Liping Gai
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Fluid Model ◽  
Chaplygin Gas ◽  
Linear Perturbation ◽  
Model Parameters ◽  
Modified Chaplygin Gas ◽  
Dark Fluid ◽  
Type Ia ◽  
Linear Perturbation Theory

The modified Chaplygin gas could be considered to abide by the unified dark fluid model because the model might describe the past decelerating matter dominated era and at present time it provides an accelerating expansion of the Universe. In this paper, we have employed the Planck 2015 cosmic microwave background anisotropy, type-Ia supernovae, observed Hubble parameter data sets to measure the full parameter space of the modified Chaplygin gas as a unified dark matter and dark energy model. The model parameters Bs, α, and B determine the evolutional history of this unified dark fluid model by influencing the energy density ρMCG = ρMCG0[Bs + (1 − Bs)a−3(1 + B)(1 + α)]1/(1 + α). We assumed the pure adiabatic perturbation of unified modified Chaplygin gas in the linear perturbation theory. In the light of Markov chain Monte Carlo method, we find that Bs = 0.727+0.040+0.075−0.039−0.079, α = −0.0156+0.0982+0.2346−0.1380−0.2180, B = 0.0009+0.0018+0.0030−0.0017−0.0030 at 2σ level. The model parameters α and B are very close to zero and the nature of unified dark energy and dark matter model is very similar to cosmological standard model ΛCDM.

scholarly journals The hierarchical build-up of bulges in CDM

2007 ◽  
Vol 3 (S245) ◽  
pp. 55-58
Author(s):  
Sadegh Khochfar
Keyword(s):  
Cold Dark Matter ◽  
High Redshift ◽  
Critical Mass ◽  
Elliptical Galaxies ◽  
Dynamical Interaction ◽  
Surface Mass ◽  
Order Of Magnitude ◽  
Minor Mergers ◽  
The Universe ◽  
Increasing Function

AbstractWe investigate the hierarchical build-up of stars in bulges within the standard Λ-cold dark matter scenario. By separating the population into stars born during starbursts that accompany the formation of spheroids in major mergers (starburst component), and stars that are previously formed in discs of progenitor galaxies (quiescent component) and added to the spheroid by dynamical interaction. Our results are summarised as follows: bulges that form early have larger starburst fraction and hence should be smaller than their counter parts that form later. The quiescent fraction in bulges is an increasing function of bulge mass, becoming constant at Mq/Mbul ~ 0.8, mainly due to the infall of satellite galaxies that contribute disc stars to the bulge. Minor mergers are an order of magnitude more frequent than major mergers and must play a significant role in the evolution of bulges. Above the critical mass Mc ~ 3 × 1010 M⊙ most of the stars in the universe are in spheroids, which at high redshift are exclusively elliptical galaxies and at low redshifts partly bulges. Due to the enhanced evolution of galaxies ending up in high density environments, the starburst fraction and the surface mass densities of bulges below Mc should be enhanced with respect to field galaxies. Dissipation during the formation of massive bulges in present day early-type spirals is less important than for the formation of present day elliptical galaxies of the same mass thereby explaining the possible difference in phase-space densities between spiral galaxies and elliptical galaxies.

scholarly journals Redshift parametrizations of dark energy and observational constraint on their parameters: Galileon gravity as background

2015 ◽  
Vol 30 (31) ◽  
pp. 1550151 ◽  
Author(s):  
Prabir Rudra ◽  
Chayan Ranjit ◽  
Sujata Kundu
Keyword(s):  
Dark Energy ◽  
Data Analysis ◽  
Theoretical Models ◽  
Acoustic Oscillation ◽  
Model Parameters ◽  
Distance Modulus ◽  
Microwave Background ◽  
Frw Universe ◽  
Type Ia ◽  
Best Fit

In this work, Friedmann–Robertson–Walker (FRW) universe filled with dark matter (DM) (perfect fluid with negligible pressure) along with dark energy (DE) in the background of Galileon gravity is considered. Four DE models with different equation of state (EoS) parametrizations have been employed namely, linear, Chevallier–Polarski–Lindler (CPL), Jassal–Bagla–Padmanabhan (JBP) and logarithmic parametrizations. From Stern, Stern+Baryonic Acoustic Oscillation (BAO) and Stern+BAO+Cosmic Microwave Background (CMB) joint data analysis, we have obtained the bounds of the arbitrary parameters [Formula: see text] and [Formula: see text] by minimizing the [Formula: see text] test. The best fit values and bounds of the parameters are obtained at 66%, 90% and 99% confidence levels which are shown by closed confidence contours in the figures. For the logarithmic model unbounded confidence contours are obtained and hence the model parameters could not be finitely constrained. The distance modulus [Formula: see text](z) against redshift [Formula: see text] has also been plotted for our predicted theoretical models for the best fit values of the parameters and compared with the observed Union2 data sample and SNe Type Ia 292 data and we have shown that our predicted theoretical models permits the observational datasets. From the data fitting it is seen that at lower redshifts [Formula: see text] the SNe Type Ia 292 data gives a better fit with our theoretical models compared to the Union2 data sample. So, from the data analysis, SNe Type Ia 292 data is the more favored data sample over its counterpart given the present choice of free parameters. From the study, it is also seen that the logarithmic parametrization model is less supported by the observational data. Finally, we have generated the plot for the deceleration parameter against the redshift parameter for all the theoretical models and compared the results with the work of Farooq et al., (2013).

scholarly journals Cosmological Constraints on the Coupling Model from Observational Hubble Parameter and Baryon Acoustic Oscillation Measurements

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 57
Author(s):  
Shulei Cao ◽  
Tong-Jie Zhang ◽  
Xinya Wang ◽  
Tingting Zhang
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Hubble Parameter ◽  
Cold Dark Matter ◽  
High Redshift ◽  
Coupling Model ◽  
Acoustic Oscillation ◽  
Baryon Acoustic Oscillation ◽  
Best Fitting ◽  
Age Of The Universe

In the paper, we consider two models in which dark energy is coupled with either dust matter or dark matter, and discuss the conditions that allow more time for structure formation to take place at high redshifts. These models are expected to have a larger age of the universe than that of ΛCDM [universe consists of cold dark matter (CDM) and dark energy (a cosmological constant, Λ)], so it can explain the formation of high redshift gravitationally bound systems which the ΛCDM model cannot interpret. We use the observational Hubble parameter data (OHD) and Hubble parameter obtained from cosmic chronometers method (H(z)) in combination with baryon acoustic oscillation (BAO) data to constrain these models. With the best-fitting parameters, we discuss how the age, the deceleration parameter, and the energy density parameters evolve in the new universes, and compare them with that of ΛCDM.

scholarly journals Cosmological bulk flow in the QCDM model: (in)consistency with ΛCDM

2021 ◽  
Vol 504 (1) ◽  
pp. 1304-1319
Author(s):  
A Salehi ◽  
M Yarahmadi ◽  
S Fathi ◽  
Kazuharu Bamba
Keyword(s):  
Cold Dark Matter ◽  
Bulk Flow ◽  
Microwave Background ◽  
Local Universe ◽  
Peculiar Velocities ◽  
Large Bulk ◽  
Likelihood Analysis ◽  
Type Ia ◽  
The Universe ◽  
Good Agreement

ABSTRACT We study the bulk flow of the local universe with Type Ia supernova data (a compilation of Union2 and Pantheon data) in the spatially flat homogeneous and isotropic space–time. In particular, we take the so-called QCDM models, which consist of cold dark matter (CDM) and a Q-component described by a scalar field with its self-interactions determined by an exponential potential. We use different cumulative redshift slices of the Union2 and Pantheon catalogues. A maximum-likelihood analysis of peculiar velocities confirms that, at low redshifts 0.015 < z < 0.1, the bulk flow is moving in the $l=272^{+17}_{-17}, b=33^{+12}_{-12}$, and $302^{+20}_{-20},3^{+10}_{-10}$ directions with $v _\mathrm{bulk} = 225^{+38}_{-35}$ and $246^{+64}_{-46}$ km s−1 for the Pantheon and Union2 data respectively, in good agreement with the direction of the cosmic microwave background dipole and with a number of previous studies at 1σ. However, for high redshifts 0.1 < z < 0.2, we get $v _\mathrm{bulk} = 708^{+110}_{-110}$ and $v_\mathrm{bulk}=1014^{+86}_{-114}\,\text{km\,s}^{-1}$ towards l = 318 ± 10°, b = −15 ± 9° and $l=254^{+16}_{-14},\ b=6^{+7}_{-10}$ for the Pantheon and Union2 data respectively. This indicates that for low redshifts our results are approximately consistent with the ΛCDM model; however, for high redshifts they disagree with ΛCDM and support the results of those studies that report a large bulk flow for the universe.

scholarly journals MODELING DARK ENERGY THROUGH AN ISING FLUID WITH NETWORK INTERACTIONS

2014 ◽  
Vol 23 (03) ◽  
pp. 1450023
Author(s):  
ORLANDO LUONGO ◽  
DAMIANO TOMMASINI
Keyword(s):  
Dark Energy ◽  
Vacuum Energy ◽  
Information Criterion ◽  
Acoustic Oscillation ◽  
Fine Tuning ◽  
Spin Interaction ◽  
Microwave Background ◽  
Spin Variable ◽  
Barotropic Fluid ◽  
Limiting Case

We show that the dark energy (DE) effects can be modeled by using an Ising perfect fluid with network interactions, whose low redshift equation of state (EoS), i.e. ω0, becomes ω0 = -1 as in the ΛCDM model. In our picture, DE is characterized by a barotropic fluid on a lattice in the equilibrium configuration. Thus, mimicking the spin interaction by replacing the spin variable with an occupational number, the pressure naturally becomes negative. We find that the corresponding EoS mimics the effects of a variable DE term, whose limiting case reduces to the cosmological constant Λ. This permits us to avoid the introduction of a vacuum energy as DE source by hand, alleviating the coincidence and fine tuning problems. We find fairly good cosmological constraints, by performing three tests with supernovae Ia (SNeIa), baryonic acoustic oscillation (BAO) and cosmic microwave background (CMB) measurements. Finally, we perform the Akaike information criterion (AIC) and Bayesian information criterion (BIC) selection criteria, showing that our model is statistically favored with respect to the Chevallier–Polarsky–Linder (CPL) parametrization.

COSMOLOGICAL DISTANCE MEASURE CONSTRAINTS ON THE DECELERATION PARAMETER

2009 ◽  
Vol 18 (09) ◽  
pp. 1381-1393 ◽  
Author(s):  
LIXIN XU ◽  
JIANBO LU ◽  
CHENGWU ZHANG
Keyword(s):  
Deceleration Parameter ◽  
Distance Measure ◽  
High Redshift ◽  
Acoustic Oscillations ◽  
Microwave Background ◽  
Cosmological Distance ◽  
Type Ia ◽  
Hubble Parameters ◽  
Ia Supernovae ◽  
Parameter Values

Constraints on a parametrized deceleration parameter, q(a) = q0+ q1(1 - a), are investigated using cosmological observations of type Ia supernovae (SN Ia), baryon acoustic oscillations (BAOs) and cosmic microwave background (CMB) and observational Hubble data (OHD) which correspond to the cosmological distance measure. When a high redshift dataset of CMB is added in the SN + BAO + OHD case, a stronger constraint is obtained than for the lower redshift case, SN + BAO + OHD. The evolutions of the deceleration and Hubble parameters with respect to redshift z are reconstructed from cosmic observations. With cosmic observations as constraints, it is found that a smaller current deceleration parameter and a larger transition redshift are obtained in the SN + BAO + OHD case than in the SN + BAO + OHD + CMB case. In the SN + BAO + OHD + CMB case, slightly larger Hubble parameter values will be obtained than in the SN + BAO + OHD case.

Cosmological implications of the dark matter equation of state

2017 ◽  
Vol 26 (03) ◽  
pp. 1750013 ◽  
Author(s):  
Weiqiang Yang ◽  
Hang Li ◽  
Yabo Wu ◽  
Jianbo Lu
Keyword(s):  
Dark Matter ◽  
Equation Of State ◽  
Cold Dark Matter ◽  
Evolution Equations ◽  
State Parameter ◽  
Acoustic Oscillation ◽  
Text Data ◽  
Equation Of State Parameter ◽  
Type Ia ◽  
Ia Supernovae

In this paper, we study a model which is composed of the cosmological constant and dark matter with nonzero equation of state parameter, which could be called as [Formula: see text]wDM. In the synchronous gauge, we obtain the perturbation equations of dark matter, and deduce the evolution equations of growth factor about the dark matter and baryons. Based on the Markov Chain Monte Carlo (MCMC) method, we constrain this model by the recently available cosmic observations which include cosmic microwave background (CMB) radiation, baryon acoustic oscillation (BAO), type Ia supernovae (SNIa) and [Formula: see text] data points from redshift-space distortion (RSD). The results present a tighter constraint on the model than the case without [Formula: see text] data. In 3[Formula: see text] regions, we find the dark matter equation of state parameter [Formula: see text]. The currently available cosmic observations do not favor the nonzero dark matter equation of state parameter, no deviation from the lambda cold dark matter ([Formula: see text]CDM) model is found in 1[Formula: see text] region.

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