Hubble Parameter Data Research Articles

Constraints on sigma _8 and degeneracies from linear Nash-Greene perturbations in subhorizon scale

Using a joint statistical analysis, we test a four-dimensional FLRW model embedded in a five-dimensional bulk based on the Nash-Greene embedding theorem. Performing a Markov Chain Monte Carlo (MCMC) modelling, we combine observational data sets as those of the recent growth data, the best-fit Planck2018/varLambda CDM parameters on the Cosmic Microwave Background (CMB), the Baryon Acoustic Oscillations (BAO) measurements, the Pantheon Supernovae type Ia and the Hubble parameter data. From linear Nash-Greene fluctuations of the metric, we show the related perturbed equations in longitudinal Newtonian gauge to obtain the evolution of growth matter. A mild alleviation may be obtained from the degeneracies on the model parameter analyzing the sigma tension between the growth amplitude factor and the matter content in the plane (sigma _8-varOmega _m) on the observations from CMB and Large Scale Structure (LSS) probes. The Akaike Information Criterion (AIC) is also applied and we find a relative statistical consistence of the present model with both varLambda CDM and wCDM models lower than 1% of percentage difference at early times on the evolution of the Hubble function H(z). We also apply the Om(z) diagnosis to distinguish the present model from varLambda CDM and wCDM models.

A new potential for scalar field dark energy

In this paper, we have investigated some cosmological consequences of a quintessence dark energy model. In particular, we have obtained the forms of the equation of state parameter, the deceleration parameter and the field potential by considering a simple relation between the scale factor and the time derivative of the scalar field, instead of assuming any functional form for the scalar field potential or the scale factor or the equation of state parameter. We have found that the model provides the desired early deceleration followed by present acceleration of the universe. The potential derived numerically in this work in the form [Formula: see text], where [Formula: see text], [Formula: see text] and [Formula: see text] are real constant parameters. It has also been found that our model mimics as the standard [Formula: see text]CDM model in future. Finally, we have also shown the evolution of the normalized Hubble parameter for our model and the [Formula: see text]CDM model and compared that with the latest Hubble parameter data.

Posing constraints on the free parameters of a new model of dark energy EoS: responses through cosmological behaviours

Since the late 1990's observations of type Ia Supernova, our universe is predicted to experience a late time cosmic acceleration. Theoretical support to this observation were intended to be built via proposition of a hypothetical fluid which staying inside the universe exerts negative pressure. Cosmologists have prescribed many candidates for this exotic fluid so far. In this alley, a popular method is to choose time dependent equation of state parameter $\omega = \frac{p}{\rho}$ and to parametrize it as a function of redshift. Again some common families of such parametrizations are constructed among which different members justify different properties of observed universe. Mainly, these were model dependent studies which comprise free parameters to be constrained by different observations. In this present article, a new expression for redshift parametrization is considered and we have constrain its free parameters for two Hubble parameter vs redshift data sets. These data sets are obtained depending on two basic methodologies known as different ages method and baryonic acoustic oscillation method. Different confidence contours for our model are located under the constraints of said data sets. Besides, different thermodynamic parameters related to the evolution of our universe are analysed. It is notified that our model indicates towards a delayed dark matter model which mimics EoS = $-1(\Lambda)$ phenomena at the present epoch. Deceleration parameters behaviour's are studied. It is noticed that a possibility of future deceleration may occur for this new model. Outcomes for both the data sets are compared with each other.

Quintessence and tachyon dark energy in interaction with dark matter: Observational constraints and model selection

We derive two field theory models of interacting dark energy, one in which dark energy is associated with the quintessence and another in which it is associated with the tachyon. In both, instead of choosing arbitrarily the potential of scalar fields, these are specified implicitly by imposing that the dark energy fields must behave as the new agegraphic dark energy. The resulting models are compared with the Pantheon supernovae sample, CMB distance information from Planck 2015 data, baryonic acoustic oscillations (BAO) and Hubble parameter data. For comparison, the noninteracting case and the [Formula: see text] model also are considered. By use of the AIC and BIC criteria, we have obtained strong evidence in favor of the two interacting models, and the coupling constants are nonvanishing at more than [Formula: see text] confidence level.

Observational constraints on the non-flat Lambda CDM model and a null test using the transition redshift

A natural extension of the standard cosmological model are models that include curvature as a free parameter. In this work we study in detail the observational constraints on the non-flat Lambda CDM model using the two main geometric tests: SNIa and Hubble parameter measurements. In general we show that the observational constraints on the parameters of the Lambda CDM model strongly depend on the curvature parameter. In particular, we study the constraints on the transition redshift (z_{t}) of a universe dominated by matter for a universe dominated by the cosmological constant. Using this observable we construct a new null test defining zeta = z_{t, flat}-z_{t, non flat}. This test depends only on the data of the Hubble parameter, the Hubble constant and the matter density parameter. However, it does not depend on derivative of an observable as generally many tests in the literature. To reconstruct this test, we use the Gaussian process method. When we use the best-fit parameters values of PLANCK/2018, we find no evidence of a disagreement between the data and the standard model (flat Lambda CDM), but if we use the value H_{0} from RIESS/2018 we found a disagreement with respect at the standard model. However, it is important to note that the Hubble parameter data has large errors for a solid statistical analysis.

Cosmological models, observational data and tension in Hubble constant

We analyze how predictions of cosmological models depend on a choice of described observational data, restrictions on flatness, and how this choice can alleviate the H tension. These effects are demonstrated in the wCDM model in comparison with the standard ΛCDM model. We describe the Pantheon sample observations of Type Ia supernovae, 31 Hubble parameter data points H(z) from cosmic chronometers, the extended sample with 57 H(z) data points and observational manifestations of cosmic microwave background radiation (CMB). For the wCDM and ΛCDM models in the flat case and with spatial curvature, we calculate χfunctions for all observed data in different combinations, estimate optimal values of model parameters and their expected intervals. For both considered models the results essentially depend on a choice of data sets. In particular, for the wCDM model with H(z) data, supernovae and CMB the 1σ estimations may vary from H = 67.52km /(s·Mpc) (for all N = 57 Hubble parameter data points) up to H = 70.87 /(s·Mpc) for the flat case (k = 0) and N = 31. These results might be a hint how to alleviate the problem of H tension: different estimates of the Hubble constant may be connected with filters and a choice of observational data.

A Modified Dynamical Model of Cosmology I Theory

Wheeler (1964) had formulated Mach’s principle as the boundary condition for general relativistic field equations. Here, we use this idea and develop a modified dynamical model of cosmology based on imposing Neumann boundary condition on cosmological perturbation equations. Then, it is shown that a new term appears in the equation of motion, which leads to a modified Poisson equation. In addition, a modified Hubble parameter is derived due to the presence of the new term. Moreover, it is proved that, without a cosmological constant, such a model has a late time-accelerated expansion with an equation of state converging to w < − 1 . Also, the luminosity distance in the present model is shown to differ from that of the Λ C D M model at high redshifts. Furthermore, it is found that the adiabatic sound speed squared is positive in radiation-dominated era and then converges to zero at later times. Theoretical implications of the Neumann boundary condition have been discussed, and it is shown that, by fixing the value of the conjugate momentum (under certain conditions), one could derive a similar version of modified dynamics. In a future work, we will confine the free parameters of the Neumann model based on hype Ia Supernovae, Hubble parameter data, and the age of the oldest stars.

Reconstruction of the cosmic equation of state for high redshift

We investigate the possibilities of reconstructing the cosmic equation of state (EoS) for high redshift. In order to obtain general results, we use two model-independent approaches. The first reconstructs the EoS using comoving distance and the second makes use of the Hubble parameter data. To implement the first method, we use a recent set of Gamma-Ray Bursts (GRBs) measures. To implement the second method, we generate simulated data using the Sandage–Loeb (SL) effect; for the fiducial model, we use the Lambda CDM model. In both cases, the statistical analysis is conducted through the Gaussian processes (non-parametric). In general, we demonstrate that this methodology for reconstructing the EoS using a non-parametric method plus a model-independent approach works appropriately due to the feasibility of calculation and the ease of introducing a priori information (H_ {0} and Omega _{m0}). In the near future, following this methodology with a higher number of high quality data will help obtain strong restrictions for the EoS.

Reconstructing equation of state of dark energy with principal component analysis

We represent a nonparametric method to reconstruct the equation of state for dark energy directly from observational Hubble parameter data. We use principal component analysis (PCA) to extract the signal from data with noise. Moreover, we modify Akaike information criterion (AIC) to guarantee the quality of reconstruction and avoid over-fitting simultaneously. The results show that our method is robust in reconstruction of dark energy equation of state. Although current observational Hubble parameter data alone can not give a strong constraint yet, our results indicate that future observations can significantly improve the quality of the reconstruction.

Constraining the evolution of the baryon fraction in the IGM with FRB and H(z) data

Extragalactic dispersion measures (DMs) obtained from observations of fast radio bursts (FRBs) are an excellent tool for probing intergalactic medium (IGM) and for conducting cosmography. However, the DM contribution from the IGM (DMIGM) depends on the fraction of baryon mass in the IGM, fIGM, which is not properly constrained. As fIGM(z) is geometrically related to the Hubble parameter H(z) and DMIGM(z), here we propose that combining two independent measurements of FRBs and H(z) in similar redshift ranges provides a novel and cosmology-free method to constrain the evolution of fIGM(z). Under the assumption that fIGM is evolving with redshift in a functional form, we forecast that the evolution of fIGM(z) can be well inferred in a combined analysis of ∼3000 DMIGM(z) derived from FRBs and ∼50 H(z) derived from the Hubble parameter data. Though the efficiency of our method is not as good as that of the other model-independent method involving the joint measurements of DM and luminosity distance of FRBs, our method offers a new model-independent way to constrain fIGM(z).

Cosmological test on viscous bulk models using Hubble parameter measurements and type Ia supernovae data

From a phenomenological point of view, we analyze the dynamics of the Universe at late times by introducing a polynomial and hyperbolic bulk viscosity into the Einstein field equations respectively. We constrain their free parameters using the observational Hubble parameter data and the Type Ia Supernovae dataset to reconstruct the deceleration q and the jerk j parameters within the redshift region 0<z<2.5. At current epochs, we obtain q_0 = -,0.680^{+0.085}_{-0.102} and j_0 = 2.782^{+1.198}_{-0.741} for the polynomial model and q_0 = -,0.539^{+0.040}_{-0.038} (-,0.594^{+0.056}_{-0.056}) and j_0 = 0.297^{+0.051}_{-0.050} (1.124^{+0.196}_{-0.178}) for the tanh (cosh) model. Furthermore, we explore the statefinder diagnostic that gives us evident differences with respect to the concordance model (LCDM). According to our results this kind of models is not supported by the data over LCDM.

Baryon acoustic oscillation, Hubble parameter, and angular size measurement constraints on the Hubble constant, dark energy dynamics, and spatial curvature

ABSTRACT In this paper, we use all available baryon acoustic oscillation, Hubble parameter, and quasar angular size data to constrain six dark energy cosmological models, both spatially flat and non-flat. Depending on the model and data combination considered, these data mildly favour closed spatial hypersurfaces (by as much as 1.7σ) and dark energy dynamics (up to a little over 2σ) over a cosmological constant Λ. The data also favour, at 1.8σ to 3.4σ, depending on the model and data combination, a lower Hubble constant than what is measured from the local expansion rate.

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

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.

A Pressure Parametric Dark Energy Model**Supported in part by the National Nature Science Foundation of China under Grant No. 11075077

In this paper, we propose a new pressure parametric model of the total cosmos energy components in a spatially flat Friedmann-Robertson-Walker (FRW) universe and then reconstruct the model into quintessence and phantom scenarios, respectively. By constraining with the datasets of the type Ia supernova (SNe Ia), the baryon acoustic oscillation (BAO) and the observational Hubble parameter data(OHD), we find that at the 1σ level and our universe slightly biases towards quintessence behavior. Then we use two diagnostics including Om(a) diagnostic and statefinder to discriminate our model from the cosmology constant cold dark matter (ΛCDM) model. From Om(a) diagnostic, we find that our model has a relatively large deviation from the ΛCDM model at high redshifts and gradually approaches the ΛCDM model at low redshifts and in the future evolution, but they can be easily differentiated from each other at the 1σ level all along. By the statefinder, we find that both of quintessence case and phantom case can be well distinguished from the ΛCDM model and will gradually deviate from each other. Finally, we discuss the fate of universe evolution (named the rip analysis) for the phantom case of our model and find that the universe will run into a little rip stage.

Prospect for Cosmological Parameter Estimation Using Future Hubble Parameter Measurements**Supported by the National Natural Science Foundation of China under Grant Nos. 11522540, 11690021, 11375153, 11675145, and the National Program for Support of Top-Notch Young Professionals, and the 2016 Program for Postdoctoral Fellowship of Zhejiang Province

We constrain cosmological parameters using only Hubble parameter data and quantify the impact of future Hubble parameter measurements on parameter estimation for the most typical dark energy models. We first constrain cosmological parameters using 52 current Hubble parameter data including the Hubble constant measurement from the Hubble Space Telescope. Then we simulate the baryon acoustic oscillation signals from WFIRST (Wide-Field Infrared Survey Telescope) covering the redshift range of z ∈ [0.5, 2] and the redshift drift data from E-ELT (European Extremely Large Telescope) in the redshift range of z ∈ [2,5]. It is shown that solely using the current Hubble parameter data could give fairly good constraints on cosmological parameters. Compared to the current Hubble parameter data, with the WFIRST observation the H(z) constraints on dark energy would be improved slightly, while with the E-ELT observation the H(z) constraints on dark energy is enormously improved.

Direct constraint on cosmic neutrino mass using observational Hubble parameter data

In order to explore the properties of cosmic neutrinos, i.e. sum of the neutrino mass (∑mυ) and the effective number of neutrino species (Neff), which affects the Hubble expansion rate H(z) and the power of observational Hubble parameter data (OHD) in constraining cosmological parameters under the ΛCDM model, we utilize OHD to constrain the properties of cosmic neutrinos and apply an accurate H(z) function with ∑mυ and Neff. First, we simulate new OHD beyond the existing 43 OHD. According to the predictions of measurements of H0 (the current H(z) value), baryon acoustic oscillations (BAO) peaks, Sandage-Loeb (SL) test and cosmic microwave background (CMB), we assume observational accuracy up to 2% and redshift 0 < z ≲ 5. With simulated H(z) data obtained from the fiducial model, we constrain the parameters including ∑mυ and Neff. When all parameters are set free, ∑mυ < 0.196 eV (95%) and Neff = 2.984 ± 0.826 (68%) are obtained, and when fixing Neff as the standard baseline 3.046, we attain ∑mυ < 0.240 eV (95%). These constrained results are much tighter than the ones obtained by the current OHD, which makes the prospect of OHD in constraining cosmological parameters more promising as its accuracy and quantity grow.

Constraint on the generalized Chaplygin gas as an unified dark fluid model after Planck 2015

Abstract The generalized Chaplygin gas could be considered as the unified dark fluid model because it might describe the past decelerating matter dominated era and at present time it provides an accelerating expansion of the Universe. In this paper, we employed the Planck 2015 cosmic microwave background anisotropy, type-Ia supernovae, observed Hubble parameter data sets to measure the full parameter space of the generalized Chaplygin gas as an unified dark matter and dark energy model. The model parameters B s and α determine the evolutional history of this unified dark fluid model by influencing the energy density ρ G C G = ρ G C G 0 [ B s + ( 1 − B s ) a − 3 ( 1 + α ) ] 1 ∕ ( 1 + α ) . We assume the pure adiabatic perturbation of unified generalized Chaplygin gas. In the light of Markov Chain Monte Carlo method, we found that B s = 0 . 75 9 − 0 . 032 − 0 . 046 + 0 . 020 + 0 . 051 and α = 0 . 080 1 − 0 . 0801 − 0 . 0801 + 0 . 0208 + 0 . 1087 at 2 σ level. The model parameter α is very close to zero, the nature of GCG model is very similar to cosmological standard model Λ CDM.

Updated constraints on f(T) models using direct and indirect measurements of the Hubble parameter

We extract observational constraints on f(T) gravity, using the recently proposed statistical method which is not affected by the value of H0 and thus it bypasses the problem of the disagreement in its exact numerical value between Planck and direct measurements. We use direct measurements of the Hubble parameter with the corresponding covariance matrix, and for completeness we perform a joint analysis using the latest data from Supernovae type Ia based on JLA sample, quasi-stellar objects, and Cosmic Microwave Background shift parameter from Planck. We analyze a large family of f(T) models, and we compare the fitting results with ΛCDM cosmology using the AIC statistical test. Utilizing only the Hubble parameter data we find that in the case of the power-law f(T) model a small but non-zero deviation from ΛCDM cosmology is slightly favored at 1-σ, nevertheless the corresponding AIC value shows a statistical equivalence with it. Finally, the join analysis reveals that all f(T) models are very efficient and in very good agreement with observations.

Constraints on dark energy dynamics and spatial curvature from Hubble parameter and baryon acoustic oscillation data

We use all available baryon acoustic oscillation distance measurements and Hubble parameter data to constrain the cosmological constant $\Lambda$, dynamical dark energy, and spatial curvature in simple cosmological models. We find that the consensus spatially flat $\Lambda$CDM model provides a reasonable fit to the data, but depending on the Hubble constant prior and cosmological model, it can be a little more than 1$\sigma$ away from the best-fit model, which can favor mild dark energy dynamics or non-flat spatial hypersurfaces.

Cosmological constraints on γ -gravity models

In this paper we place observational constraints on the well-known $\gamma$-gravity $f(R)$ model using the latest cosmological data, namely we use the latest growth rate, Cosmic Microwave Background, Baryon Acoustic Oscillations, Supernovae type Ia and Hubble parameter data. Performing a joint likelihood analysis we find that the $\gamma$-gravity model is in very good agreement with observations. Utilizing the AIC statistical test we statistically compare the current $f(R)$ model with $\Lambda$CDM cosmology and find that they are statistically equivalent. Therefore, $\gamma$-gravity can be seen as a useful scenario toward testing deviations from General Relativity. Finally, we note that we find somewhat higher values for the $f(R)$ best-fit values compared to those mentioned in the past in the literature and we argue that this could potential alleviate the halo-mass function problem.