Observational Hubble Parameter Data Research Articles

Cosmological constraints on dark energy in [formula omitted] gravity: A parametrized perspective

In this paper, we focus on the parametrization of the effective equation of state (EoS) parameter within the framework of f(Q) symmetric teleparallel gravity. Here, the gravitational action is represented by an arbitrary function of the non-metricity scalar Q. By utilizing a specific parametrization of the effective EoS parameter and a power-law model of f(Q) theory, namely f(Q)=βQm+1 (where β and m are arbitrary constants), we derive the cosmological solution of the Hubble parameter H(z). To constrain model parameters, we employ recent observational data, including the Observational Hubble parameter Data (OHD), Baryon Acoustic Oscillations data (BAO), and Type Ia supernovae data (SNe Ia). The current constrained value of the deceleration parameter is found to be q0=−0.50−0.01+0.01, indicating that the current Universe is accelerating. Furthermore, we examine the evolution of the density, EoS, and Om(z) diagnostic parameters to deduce the accelerating nature of the Universe. Finally, we perform a stability analysis with linear perturbations to confirm the model’s stability.

Observational constraints on the modification of standard ΛCDM cosmology with dark radiation

We revisit a cosmological model modified by an extra “radiation-like” energy component in the Universe, which can be interpreted as many physical phenomena. Here, we derive the constraint on the energy density from this modification with current cosmological observations, including Cosmic Microwave Background, Baryon Acoustic Oscillation, Observational Hubble Parameter data and Type Ia supernovae. Performing a Bayesian analysis gives at 95% confidence level. Our work shows the dark radiation energy is small. Alleviating H 0 tension by introducing this term can also be interpreted as the systematic error caused by the numerical method.

Exact Solutions and Cosmological Constraints in Fractional Cosmology

This paper investigates exact solutions of cosmological interest in fractional cosmology. Given μ, the order of Caputo’s fractional derivative, and w, the matter equation of state, we present specific exact power-law solutions. We discuss the exact general solution of the Riccati Equation, where the solution for the scale factor is a combination of power laws. Using cosmological data, we estimate the free parameters. An analysis of type Ia supernovae (SNe Ia) data and the observational Hubble parameter data (OHD), also known as cosmic chronometers, and a joint analysis with data from SNe Ia + OHD leads to best-fit values for the free parameters calculated at 1σ, 2σ and 3σ confidence levels (CLs). On the other hand, these best-fit values are used to calculate the age of the Universe, the current deceleration parameter (both at 3σ CL) and the current matter density parameter at 1σ CL. Finding a Universe roughly twice as old as the one of ΛCDM is a distinction of fractional cosmology. Focusing our analysis on these results, we can conclude that the region in which μ>2 is not ruled out by observations. This parameter region is relevant because fractional cosmology gives a power-law solution without matter, which is accelerated for μ>2. We present a fractional origin model that leads to an accelerated state without appealing to Λ or dark energy.

Testing backreaction effects with type Ia supernova data and observational Hubble parameter data

The backreaction term Q D and the averaged spatial Ricci scalar R D in the spatially averaged inhomogeneous Universe can be combined into effective perfect fluid energy density ϱ eff D and pressure p eff D that can be regarded as new effective sources for the backreaction effects. In order to model the realistic evolution of backreaction, we adopt the Chevallier-Polarski-Linder (CPL) parameterizations of the equation of state (EoS) of the effective perfect fluid. To deal with observations in the backreaction context, in this paper, we employ two metrics to describe the late time Universe, one of them is the standard Friedmann-Lemaître-Robertson-Walker(FLRW) metric, and the other is a template metric with an evolving curvature parameter introduced by Larena et. al. in their previous article. For comparison, we fit our CPL backreaction model as well as the well-known scaling backreaction model using type Ia supernova (SN Ia) data and observational Hubble parameter data (OHD) with these two metrics, and find out that parameter tensions between two different data sets are extremely larger in the template metric context for the scaling backreaction model, and moderately larger in the template metric context for the CPL backreaction model, therefore we conclude that the prescription of the geometrical instantaneous spatially-constant curvature κ D needs to be modified.

Study of a Viscous ΛWDM Model: Near-Equilibrium Condition, Entropy Production, and Cosmological Constraints

Extensions to a ΛDM model have been explored in order to face current tensions that occur within its framework, which encompasses broadening the nature of the dark matter (DM) component to include warmness and a non-perfect fluid description. In this paper, we investigated the late-time cosmological evolution of an exact solution recently found in the literature, which describes a viscous warm ΛDM model (ΛWDM) with a DM component that obeys a polytropic equation of state (EoS), which experiences dissipative effects with a bulk viscosity proportional to its energy density, with proportionality constant ξ0. This solution has the particularity of having a very similar behavior to the ΛCDM model for small values of ξ0, evolving also to a de Sitter type expansion in the very far future. We explore firstly the thermodynamic consistences of this solution in the framework of Eckart’s theory of non-perfect fluids, focusing on the fulfillment of the two following conditions: (i) the near-equilibrium condition and (ii) the positiveness of the entropy production. We explore the range of parameters of the model that allow to fulfill these two conditions at the same time, finding that a viscous WDM component is compatible with both ones, being in this sense, a viable model from the thermodynamic point of view. Furthermore, we constrained the free parameters of the model with the observational data coming from supernovae Ia (SNe Ia) and the observational Hubble parameter data (OHD), using these thermodynamics analyses to define the best priors for the cosmological parameters related to the warmness and the dissipation of the DM, showing that this viscous ΛWDM model can describe the combined SNe Ia+OHD data in the same way as the ΛCDM model. The cosmological constraint at 3σ CL gives us an upper limit on the bulk viscous constant of order ξ0∼106 Pa·s, which is in agreement with some previous investigations. Our results support that the inclusion of a dissipative WDM, as an extension of the standard cosmological model, leads to a both thermodynamically consistent and properly fitted cosmological evolution.

Model-independent Reconstruction of the Cosmological Scale Factor as a Function of Lookback Time

Abstract We present a model-independent method of reconstructing scale factor against lookback time from the Observational Hubble parameter Data (OHD). The reconstruction method is independent of dynamical models and is only based on the Friedmann–Robertson–Walker metric. We also calculate the propagation of error in the reconstruction process. The reconstruction data errors mainly come from trapezoidal rule approximation and the uncertainty from OHD. Furthermore, the model discrimination ability of original OHD and reconstructed a–t data is discussed under a dimensionless standard method. The a–t data can present the differences between cosmology models more clearly than H–z data by comparing their coefficients of variations. Finally, we add 50 simulated H(z) data to estimate the influence of future observation. More Hubble measurements in the future will help constrain cosmological parameters more accurately.

Testing Backreaction Effects with Type Ia Supernova Data and Observational Hubble Parameterdata

The backreaction term ${\cal Q}_\CD$ and the averaged spatial Ricci scalar $\average{\CR}$ in the spatially averaged inhomogeneous Universe can be used to combine into effective perfect fluid energy density $\varrho_{\rm eff}^{\CD}$ and pressure $p_{\rm eff}^{\CD}$ that can be regarded as new effective sources for the backreaction effects. In order to model the realistic evolution of backreaction, we adopt the Chevallier-Polarski-Linder(CPL) parameterizations of the equation of state(EoS) of the effective perfect fluid. To deal with observations in the backreaction context, in this paper, we employ two metrics to describe the the late time Universe, one of them is the standard Friedmann-Lema\^{\i}tre-Robertson-Walker(FLRW) metric, and the other is a template metric with an evolving curvature parameter introduced by Larena et. al. in \cite{larena2009testing}. We also fit the CPL backreaction model using type Ia supernova(SN Ia) data and observational Hubble parameter data(OHD) with these two metrics, and find out that parameter tensions between two different data sets are larger when the backreaction model is equipped with the template metric, therefore we conclude that the prescription of the geometrical instantaneous spatially-constant curvature $\kappa_{\CD}$ needs to be modified.

Using quasar X-ray and UV flux measurements to test the cosmic opacity with cosmography

The X-ray and UV flux measurements of 1598 quasars (QSOs) compiled by Risaliti and Lusso cover the redshift range of 0 . 036 ≤ z ≤ 5 . 1003 , and they are one of the few data sets that can probe the redshift range of z ∼ 2 . 4 − 5 . 1 . In this paper, we use these quasar measurements combining with the opacity-independent observational Hubble parameter data (OHD) to test the cosmic opacity. To be model-independent, we use the cosmography to describe the cosmic expansion history. In addition, four parameterizations of the optical depth, i.e. τ ( z ) = 2 ɛ z , τ ( z ) = ( 1 + z ) 2 ɛ − 1 , τ ( z ) = τ 1 z + τ 2 z 2 , τ ( z ) = τ 1 z + τ 2 z 2 + τ 3 z 3 , are used. Our results show that in a global fitting on the quasar data, the observations are consistent well with a transparent universe within a 1 σ confidence level (CL), whichever parametrization is used. And the cosmic opacity parameters have negligible influences on the cosmographic parameters and the quasar parameters characterizing the nonlinear relation between X-ray and UV flux measurements of quasars.

Measuring cosmological parameters with a luminosity–time correlation of gamma-ray bursts

ABSTRACT Gamma-ray bursts (GRBs), as a possible probe to extend the Hubble diagram to high redshifts, have attracted much attention recently. In this paper, we select two samples of GRBs that have a plateau phase in X-ray afterglow. One is short GRBs (SGRBs) with plateau phases dominated by magnetic dipole (MD) radiations. The other is long GRBs (LGRBs) with gravitational wave (GW) dominated plateau phases. These GRBs can be well standardized using the correlation between the plateau luminosity L0 and the end time of plateau tb. The so-called circularity problem is mitigated by using the observational Hubble parameter data and Gaussian process method. The calibrated L0 – tb correlations are also used to constrain Lambda cold dark matter (ΛCDM) and w(z) = w0 models. Combining the MD–LGRBs sample from Wang et al. (2021) and the MD–SGRBs sample, we find $\Omega _{\mathrm{ m}} = 0.33_{-0.09}^{+0.06}$ and ΩΛ = $1.06_{-0.34}^{+0.15}$ excluding systematic uncertainties in the non-flat ΛCDM model. Adding Type Ia supernovae from Pantheon sample, the best-fitting results are w0 = $-1.11_{-0.15}^{+0.11}$ and Ωm = $0.34_{-0.04}^{+0.05}$ in the w = w0 model. These results are in agreement with the ΛCDM model. Our result supports that selection of GRBs from the same physical mechanism is crucial for cosmological purposes.

Likelihood-free Cosmological Constraints with Artificial Neural Networks: An Application on Hubble Parameters and SNe Ia

Abstract The errors of cosmological data generated from complex processes, such as the observational Hubble parameter data (OHD) and the Type Ia supernova (SN Ia) data, cannot be accurately modeled by simple analytical probability distributions, e.g., a Gaussian distribution. To constrain cosmological parameters from these data, likelihood-free inference is usually used to bypass the direct calculation of the likelihood. In this paper, we propose a new procedure to perform likelihood-free cosmological inference using two artificial neural networks (ANNs), the masked autoregressive flow (MAF) and the denoising autoencoder (DAE). Our procedure is the first to use DAE to extract features from data, in order to simplify the structure of MAF needed to estimate the posterior. Tested on simulated Hubble parameter data with a simple Gaussian likelihood, the procedure shows the capability of extracting features from data and estimating posterior distributions without the need of tractable likelihood. We demonstrate that it can accurately approximate the real posterior, achieve performance comparable to the traditional Markov chain Monte Carlo method, and MAF obtains better training results for a small number of simulation when the DAE is added. We also discuss the application of the proposed procedure to OHD and Pantheon SN Ia data, and use them to constrain cosmological parameters from the non-flat ΛCDM model. For SNe Ia, we use fitted light-curve parameters to find constraints on H 0, Ω m , and ΩΛ similar to relevant work, using less empirical distributions. In addition, this work is also the first to use a Gaussian process in the procedure of OHD simulation.

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

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.

Polytropic gas cosmology in a 5-dimensional framework

In this research, we study the polytropic gas cosmology in a 5-dimensional form of the flat Friedmann–Robertson–Walker framework. In this context, we focus on the evolution of corresponding energy density and use the most recent data from the Type Ia Supernova, observational data of the cosmic Hubble parameter and the updated Planck-results to place constraints on the free parameters defined in the model. Making use of the calculations, we investigate also some physical features of the model in order to obtain some constraints on the auxiliary parameters given in the proposal.

Improving sampling and calibration of GRBs as distance indicators

Abstract We present a sample of 74 Gamma-Ray Bursts (GRBs) from the Fermi-GBM catalogue for which we compute the distance moduli and use them to constrain effective dark energy models. To overcome the circularity problem affecting GRBs as distance indicators, we calibrate the Amati relation of our sample with a cosmology-independent technique. Specifically, we use the latest observational Hubble parameter data, including associated systematics, to approximate the cosmic expansion through a Bezier parametric curve. We subsequently obtain the distance moduli of the GRBs and include the data in a suite of recent cosmological observations of the expansion history (Planck Compressed 2018, 2012 BOSS release of BAO data and Pantheon SNIa), to compute Bayesian posterior constraints for the standard cosmological model ΛCDM, as well as ωCDM, and the CPL parametrization. Throughout the analysis we strive to keep under control the error propagation and limit our GRBs sample to avoid observational bias. As a result, we find no evidence in favour of the alternatives to ΛCDM model. The latter agrees very well with our calibrated sample of GRBs and presently available luminosity distance probes.

Cosmic transit models in an extended gravity theory

We have investigated some cosmic transit models in the framework of an extended gravity theory where the usual Ricci scalar in the gravitational action is replaced by a sum of the Ricci scalar and a term proportional to the trace of the energy momentum tensor. A hybrid scale factor is assumed to simulate the cosmic transit behaviour. The hybrid scale factor has two parameters that describe the behaviour of the model at an initial epoch and at a late epoch. The parameters of the hybrid scale factor have been constrained from the cosmic transit behaviour. Four different cosmic transit models have been constructed and are confronted with the observational Hubble parameter data. A cosmographic test for the cosmic transit models is conducted to assess their dynamical evolution. The effect of the model parameters on the cosmic dynamics has been investigated.

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.

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.

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.

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.

Cosmological model-independent test of varLambda CDM with two-point diagnostic by the observational Hubble parameter data

Aiming at exploring the nature of dark energy (DE), we use forty-three observational Hubble parameter data (OHD) in the redshift range 0 < z leqslant 2.36 to make a cosmological model-independent test of the varLambda CDM model with two-point Omh^2(z_{2};z_{1}) diagnostic. In varLambda CDM model, with equation of state (EoS) w=-1, two-point diagnostic relation Omh^2 equiv varOmega _{mathrm{m}}h^2 is tenable, where varOmega _{mathrm{m}} is the present matter density parameter, and h is the Hubble parameter divided by 100 {mathrm {km, s^{-1} Mpc^{-1}}}. We utilize two methods: the weighted mean and median statistics to bin the OHD to increase the signal-to-noise ratio of the measurements. The binning methods turn out to be promising and considered to be robust. By applying the two-point diagnostic to the binned data, we find that although the best-fit values of Omh^2 fluctuate as the continuous redshift intervals change, on average, they are continuous with being constant within 1 sigma confidence interval. Therefore, we conclude that the varLambda CDM model cannot be ruled out.

Astronomical bounds on a cosmological model allowing a general interaction in the dark sector

Non-gravitational interaction between two barotropic dark fluids, namely the pressureless dust and the dark energy in a spatially flat Friedmann-Lema\^{i}tre-Robertson-Walker model has been discussed. It is shown that for the interactions which are linear in terms the energy densities of the dark components and their first order derivatives, the net energy density is governed by a second order differential equation with constant coefficients. Taking a generalized interaction, which includes a number of already known interactions as special cases, the dynamics of the universe is described for three types of the dark energy equation of state, namely that of interacting quintessence, interacting vacuum energy density and interacting phantom. The models have been constrained using the standard cosmological probes, Supernovae type Ia data from joint light curve analysis and the observational Hubble parameter data. Two geometric tests, the cosmographic studies and the $Om$ diagnostic have been invoked so as to ascertain the behaviour of the present model vis-a-vis the $\Lambda$-cold dark matter model. We further discussed the interacting scenarios taking into account the thermodynamic considerations.