Hubble Data Research Articles

Reconstruction of latetime cosmology using principal component analysis

We reconstruct late-time cosmology using the technique of Principal Component Analysis (PCA). In particular, we focus on the reconstruction of the dark energy equation of state from two different observational data-sets, Supernovae type Ia data, and Hubble parameter data. The analysis is carried out in two different approaches. The first one is a derived approach, where we reconstruct the observable quantity using PCA and subsequently construct the equation of state parameter. The other approach is the direct reconstruction of the equation of state from the data. A combination of PCA algorithm and calculation of correlation coefficients are used as prime tools of reconstruction. We carry out the analysis with simulated data as well as with real data. The derived approach is found to be statistically preferable over the direct approach. The reconstructed equation of state indicates a slowly varying equation of state of dark energy.

Cosmological search for sterile neutrinos after Planck 2018

Sterile neutrinos can affect the evolution of the universe, and thus using the cosmological observations can search for sterile neutrinos. In this work, we use the cosmic microwave background anisotropy data from the Planck 2018 release, combined with the latest baryon acoustic oscillation, type Ia supernova, and Hubble constant data, to constrain the cosmological models with considering sterile neutrinos. In order to test the influences of the properties of dark energy on the results of searching for sterile neutrinos, in addition to the Λ cold dark matter (ΛCDM) model, we also consider the wCDM model and the holographic dark energy (HDE) model. We find that the existence of sterile neutrinos is not preferred when the H0 local measurement is not included in the data combination. When the H0 measurement is included in the joint constraints, it is found that ΔNeff>0 is favored at about 2.7σ level for the ΛCDM model and at about 1–1.7σ level for the wCDM model. However, mν,sterileeff still cannot be well constrained and only upper limits can be given. In addition, we find that the HDE model is definitely ruled out by the current data. We also discuss the issue of the Hubble tension, and we conclude that involving sterile neutrinos in the cosmological models cannot truly resolve the Hubble tension.

Imprints of interacting dark energy on cosmological perturbations

We investigate the characteristic modifications in the evolving cosmological perturbations when dark energy interacts with dust-like matter, causing the latter’s background energy density fall off with time faster than usual. Focusing in particular to the late-time cosmic evolution, we show that such an interaction (of a specific form, arising naturally in a scalar-tensor formulation, or a wide range of modified gravity equivalents thereof), can have a rather significant effect on the perturbative spectrum, than on the background configuration which is not expected to get distorted much from [Formula: see text]CDM. Specifically, the matter density contrast, which is by and large scale-invariant in the deep sub-horizon limit, not only gets dragged as the interaction affects the background Hubble expansion rate, but also receives a contribution from the perturbation in the (scalar field induced) dark energy, which oscillates about a nonzero mean value. As such, the standard parametrization ansatz for the matter density growth factor becomes inadequate. So we modify it suitably, and also find a numerical fit of the growth index in terms of the background parameters, in order to alleviate the problems that arise otherwise. Such a fit enables direct estimations of the background parameters, as well as the growth parameter and the reduced Hubble parameter, which we duly carry out using a redshift space distortion (RSD) subsample and its combination with the observational Hubble data. On the whole, the parametric estimates show consistency with the general observational constraints on the background level cosmology, as well as the constraints on scalar-tensor gravity from astrophysical observations, apart from having significance in the domain of cosmological perturbations.

A Great Model Comparison Against the Cosmological Constant

Recently, a covariant formulation of non-equilibrium phenomena in the context of General Relativity was proposed in order to explain from first principles the observed accelerated expansion of the Universe, without the need for a cosmological constant, leading to the GREA theory. Here, we confront the GREA theory against the latest cosmological data, including type Ia supernovae, baryon acoustic oscillations, the cosmic microwave background (CMB) radiation, Hubble rate data from the cosmic chronometers and the recent $H_0$ measurements. We perform Markov Chain Monte Carlo analyses and a Bayesian model comparison, by estimating the evidence via thermodynamic integration, and find that when all the aforementioned data are included, but no prior on $H_0$, the difference in the log-evidence is $\sim -9$ in favor of GREA, thus resulting in overwhelming support for the latter over the cosmological constant and cold dark matter model ($\Lambda$CDM). When we also include priors on $H_0$, either from Cepheids or the Tip of the Red Giant Branch measurements, then due to the tensions with CMB data the GREA theory is found to be statistically equivalent with $\Lambda$CDM.

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.

Cosmographic Parameters in Model-independent Approaches

Abstract The cosmographic approach, a Taylor expansion of the Hubble function, has been used as a model-independent method to investigate the evolution of the universe in the presence of cosmological data. Apart from possible technical problems like the radius of convergence, there is an ongoing debate about the tensions that appear when one investigates some high-redshift cosmological data. In this work, we consider two common data sets, namely, Type Ia supernovae (Pantheon sample) and the Hubble data, to investigate advantages and disadvantages of the cosmographic approach. To do this, we obtain the evolution of cosmographic functions using the cosmographic method, as well as two other well-known model-independent approaches, namely, the Gaussian process and the genetic algorithm. We also assume a ΛCDM model as the concordance model to compare the results of mentioned approaches. Our results indicate that the results of cosmography compared with the other approaches are not exact enough. Considering the Hubble data, which are less certain, the results of q 0 and j 0 obtained in cosmography provide a tension at more than 3σ away from the best result of ΛCDM. Assuming both of the data samples in different approaches, we show that the cosmographic approach, because it provides some biased results, is not the best approach for reconstruction of cosmographic functions, especially at higher redshifts.

Head-to-Toe Measurement of El Gordo: Improved Analysis of the Galaxy Cluster ACT-CL J0102–4915 with New Wide-field Hubble Space Telescope Imaging Data

Abstract We present an improved weak-lensing (WL) study of the high-z (z = 0.87) merging galaxy cluster ACT-CL J0102–4915 (“El Gordo”) based on new wide-field Hubble Space Telescope imaging data. The new imaging data cover the ∼3.5 × ∼3.5 Mpc region centered on the cluster and enable us to detect WL signals beyond the virial radius, which was not possible in previous studies. We confirm the binary mass structure consisting of the northwestern (NW) and southeastern (SE) subclusters and the ∼2σ dissociation between the SE mass peak and the X-ray cool core. We obtain the mass estimates of the subclusters by simultaneously fitting two Navarro–Frenk–White (NFW) halos without employing mass–concentration relations. The masses are M 200 c NW = 9.9 − 2.2 + 2.1 × 1014 and M 200 c SE = 6.5 − 1.4 + 1.9 × 1014 M ⊙ for the NW and SE subclusters, respectively. The mass ratio is consistent with our previous WL study but significantly different from the previous strong-lensing results. This discrepancy is attributed to the use of extrapolation in strong-lensing studies because the SE component possesses a higher concentration. By superposing the two best-fit NFW halos, we determine the total mass of El Gordo to be M 200 c = 2.13 − 0.23 + 0.25 × 1015 M ⊙, which is ∼23% lower than our previous WL result [M 200c = (2.76 ± 0.51) × 1015 M ⊙]. Our updated mass is a more direct measurement, since we are not extrapolating to R 200c as in all previous studies. The new mass is compatible with the current ΛCDM cosmology.

Barrow Entropy Cosmology: an observational approach with a hint of stability analysis

In this work, we use an observational approach and dynamical system analysis to study the cosmological model recently proposed by Saridakis (2020), which is based on the modification of the entropy-area black hole relation proposed by Barrow (2020). The Friedmann equations governing the dynamics of the Universe under this entropy modification can be calculated through the gravity-thermodynamics conjecture. We investigate two models, one considering only a matter component and the other including matter and radiation, which have new terms compared to the standard model sourcing the late cosmic acceleration. A Bayesian analysis is performed in which using five cosmological observations (observational Hubble data, type Ia supernovae, HII galaxies, strong lensing systems, and baryon acoustic oscillations) to constrain the free parameters of both models. From a joint analysis, we obtain constraints that are consistent with the standard cosmological paradigm within 2σ confidence level. In addition, a complementary dynamical system analysis using local and global variables is developed which allows obtaining a qualitative description of the cosmology. As expected, we found that the dynamical equations have a de Sitter solution at late times.

State finder and Om diagnostics in modified and generalised Chaplygin gas from recent data

A modified and generalised Chaplygin gas (MCG, [Formula: see text] and GCG, [Formula: see text]) has been separately chosen here as a constituent of the universe. Concept of state finder and Om diagnostics are introduced to track the dark energy in the models. Here, observed Hubble data (OHD) and binned Pantheon data of supernovae are used to determine the best-fit equation-of-state (EoS) parameters of these models and these are compared with the [Formula: see text]CDM model. The best-fit value and expected values of cosmological jerk parameter [Formula: see text], snap parameter [Formula: see text] are determined, which are close to each other. A plot of [Formula: see text] with red-shift, with themselves, as well as with deceleration parameter [Formula: see text], shows the evolution of the universe and its possible future. Variations of [Formula: see text] and EoS parameter [Formula: see text] with red-shift show acceleration–deceleration phase transition in the recent past. Lastly, the state finder pair [Formula: see text] and Om diagnostic have been utilized to discriminate the models.

Constraining the evolution of cataclysmic variables via the masses and accretion rates of their underlying white dwarfs

ABSTRACT We report on the masses (MWD), effective temperatures ($\rm{T_\mathrm{eff}}$), and secular mean accretion rates ($\langle \dot{M} \rangle$) of 43 cataclysmic variable (CV) white dwarfs, 42 of which were obtained from the combined analysis of their Hubble Space Telescope ultraviolet data with the parallaxes provided by the Early Third Data Release of the Gaia space mission, and one from the white dwarf gravitational redshift. Our results double the number of CV white dwarfs with an accurate mass measurement, bringing the total census to 89 systems. From the study of the mass distribution, we derive $\langle M_\mathrm{WD} \rangle = 0.81^{+0.16}_{-0.20}\, \mathrm{M_\odot }$, in perfect agreement with previous results, and find no evidence of any evolution of the mass with orbital period. Moreover, we identify five systems with MWD < 0.5 M⊙, which are most likely representative of helium-core white dwarfs, showing that these CVs are present in the overall population. We reveal the presence of an anticorrelation between the average accretion rates and the white dwarf masses for the systems below the $2\!-\!3\,$ h period gap. Since $\langle \dot{M} \rangle$ reflects the rate of system angular momentum loss, this correlation suggests the presence of an additional mechanism of angular momentum loss that is more efficient at low white dwarf masses. This is the fundamental concept of the recently proposed empirical prescription of consequential angular momentum loss (eCAML) and our results provide observational support for it, although we also highlight how its current recipe needs to be refined to better reproduce the observed scatter in $\rm{T_\mathrm{eff}}$ and $\langle \dot{M} \rangle$, and the presence of helium-core white dwarfs.

Interacting Rényi holographic dark energy with parametrization on the interaction term

In this work, we study the Rényi holographic dark energy (RHDE) model in a flat FRW Universe where the infrared cut-off is taken care by the Hubble horizon and also by taking three different parametrizations of the interaction term between the dark matter and the dark energy. Analyzing graphically, the behavior of some cosmological parameters in particular deceleration parameter, equation of state (EoS) parameter, energy density parameter and squared speed of sound, in the process of the cosmic evolution, is found to be leading towards the late-time accelerated expansion of the RHDE model. Also, we find the departure for the derived models from the standard [Formula: see text]CDM model according to the evolution of jerk parameter. Moreover, we compare the model parameters by considering the observational Hubble data which consist of 51 points in the redshift range [Formula: see text].

Power-law cosmology in Weyl-type f(Q, T) gravity

Gravity is attributed to the spacetime curvature in classical general relativity (GR). But, other equivalent formulations or representations of GR, such as torsion or non-metricity, have altered the perception. We consider the Weyl-type f(Q, T) gravity, where Q represents the non-metricity and T is the trace of energy momentum tensor, in which the vector field $$\omega _{\mu }$$ determines the non-metricity $$Q_{\mu \nu \alpha }$$ of the spacetime. In this work, we employ the well-motivated $$f(Q, T)= \alpha Q+ \frac{\beta }{6k^{2}} T$$ , where $$\alpha $$ and $$\beta $$ are the model parameters. Furthermore, we assume that the universe is dominated by the pressure-free matter, i.e., the case of dust ( $$p=0$$ ). We obtain the solution of field equations similar to a power-law in Hubble parameter H(z). We investigate the cosmological implications of the model by constraining the model parameter $$\alpha $$ and $$\beta $$ using the recent 57 points Hubble data and 1048 points Pantheon supernovae data. To study various dark energy models, we use statefinder analysis to address the current cosmic acceleration. We also observe the Om diagnostic describing various phases of the universe. Finally, it is seen that the solution which mimics the power-law fits well with the Pantheon data than the Hubble data.

Exact solutions and constraints on the dark energy model in FRW Universe

The inflationary epoch and the late time acceleration of the expansion rate of universe can be explained by assuming a gravitationally coupled scalar field. In this article, we propose a new method of finding exact solutions in the background of flat Friedmann-Robertson-Walker (FRW) cosmological models by considering both scalar field and matter where the scalar field potential is a function of the scale factor. Our method provides analytical expressions for equation of state parameter of scalar field, deceleration parameter and Hubble parameter. This method can be applied to various other forms of scalar field potential, to the early radiation dominated epoch and very early scalar field dominated inflationary dynamics. Since the method produces exact analytical expression for $H(a)$ (i.e., H(z) as well), we then constrain the model with currents data sets, which includes-Baryon Acoustic Oscillations, Hubble parameter data and Type 1a Supernova data (Pantheon Dataset). As an extension of the method, we also consider the inverse problem of reconstructing scalar field potential energy by assuming any general analytical expression of scalar field equation of state parameter as a function of scale factor.

Friedmann cosmology with decaying vacuum density in Brans\u2013Dicke theory

In this paper, we study Friedmann cosmology with time-varying vacuum energy density in the context of Brans–Dicke theory. We consider an isotropic and homogeneous flat space, filled with a matter-dominated perfect fluid and a dynamical cosmological term varLambda (t) , obeying the equation of state of the vacuum. As the exact nature of a possible time-varying vacuum is yet to be found, we explore varLambda (t) given by the phenomenological law varLambda (t)=lambda +sigma H, where lambda and sigma are positive constants. We solve the model and then focus on two different cases varLambda _{H1} and varLambda _{H2} by assuming varLambda =lambda and varLambda =sigma H, respectively. Notice that varLambda _{H1} is the analog of the standard varLambda CDM, but within the Brans–Dicke cosmology. We find the analytical solution of the main cosmological functions such as the Hubble parameter, the scale factor, deceleration and equation of state parameters for these models. In order to test the viability of the cosmological scenarios, we perform two sets of joint observational analyses of the recent Type Ia supernova data (Pantheon), observational measurements of Hubble parameter data, Baryon acoustic oscillation/Cosmic microwave background data and Local Hubble constant for each model. For the sake of comparison, the same data analysis is performed for the varLambda CDM model. Each model shows a transition from decelerated phase to accelerated phase and can be viewed as an effective quintessence behavior. Using the model selection criteria AIC and BIC to distinguish from existing dark energy models, we find that the Brans–Dicke analog of the varLambda -cosmology (i.e. our model varLambda _{H1}) performs at a level comparable to the standard varLambda CDM, whereas varLambda _{H2} is less favoured.

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

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.

Cosmography using strong-lensing systems and cosmic chronometers

ABSTRACT Using a new sub-sample of observed strong gravitational lens systems, for the first time, we present the equation for the angular diameter distance in the y-redshift scenario for cosmography and use it to test the cosmographic parameters. In addition, we also use the observational Hubble data from cosmic chronometers and a joint analysis of both data are performed. Among the most important conclusions are that this new analysis for cosmography using strong-lensing systems (SLSs) is equally competitive to constrain the cosmographic parameters as others presented in literature. Additionally, we present the reconstruction of the effective equation of state inferred from our samples, showing that at z = 0 those reconstructions from SLSs and joint analysis are in concordance with the standard model of cosmology.

Constraints on holographic dark energy model with matter creation in Brans–Dicke theory and thermodynamic analysis

The adiabatic matter creation for a spatially flat, homogeneous and isotropic universe is discussed in holographic dark energy (HDE) in the context of Brans–Dicke theory. Since the HDE density is considered as a dynamical cosmological constant, it is natural to study it in a dynamical frame of Brans–Dicke theory. We show that HDE model with matter creation, whose infrared cutoff is set by the Hubble horizon, leads to solution that unify the early and late time acceleration. The latest observational data from supernovae (Pantheon sample), Hubble H ( z ) and latest local H 0 by SH0ES are used for constraining the model parameters. Using the Markov chain Monte Carlo method, we obtain the best fit values of the parameters for different models. It is found that the HDE model without matter creation does not achieve transition phase when the Hubble horizon is taken as an IR cut-off. However, it achieves the phase transition from decelerated phase to accelerated phase with same IR cut-off with the inclusion of gravitationally induced matter creation. The best fit values of HDE model with matter creation are fitted very well in Hubble error data. Using AIC and BIC, and geometrical diagnostic parameters, we compare the models with Λ CDM model and discuss the viability of the model. A detailed thermodynamic analysis is also carried out.

Towards a model-independent reconstruction approach for late-time Hubble data

Gaussian processes offers a convenient way to perform nonparametric reconstructions of observational data assuming only a kernel which describes the covariance between neighbouring points in a data set. We approach the ambiguity in the choice of kernel in Gaussian processes with two methods — (a) approximate Bayesian computation with sequential Monte Carlo sampling and (b) genetic algorithm — and use the overall resulting method to reconstruct the cosmic chronometers and supernovae type Ia data sets.The results have shown that the Matérn( ν = 5/2 ) kernel emerges on top of the two-hyperparameter family of kernels for both cosmological data sets. On the other hand, we use the genetic algorithm in order to select a most naturally-fit kernel among a competitive pool made up of a ten-hyperparameters class of kernels. Imposing a Bayesian information criterion-inspired measure of the fitness, the results have shown that a hybrid of the Radial Basis Function and the Matérn( ν = 5/2 ) kernel best represented both data sets. The kernel selection problem is not totally closed and may benefit from further analysis using other strategies to resolve an optimal kernel for a particular data set.

A new comparison between holographic dark energy and standard varLambda -cosmology in the context of cosmography method

The cosmography method is a model-independent technique used to reconstruct the Hubble expansion of the Universe at low redshifts. In this method, using the Hubble diagrams from Type Ia Supernovae (SNIa) in Pantheon catalog, quasars and Gamma-Ray Bursts (GRB), we put observational constraints on the cosmographic parameters in holographic dark energy (HDE) and concordance varLambda CDM models by minimizing the error function chi ^2 based on the statistical Markov Chain Monte Carlo (MCMC) algorithm. Then, we compare the results of the models with the results of the model-independent cosmography method. Except for the Pantheon sample, we observe that there is a big tension between standard cosmology and Hubble diagram observations, while the HDE model remains consistent in all cases. Then we use different combinations of Hubble diagram data to reconstruct the Hubble parameter of the model and compare it with the observed Hubble data. We observe that the Hubble parameter reconstructed from the model-independent cosmography method has the smallest deviation from the Hubble data and the varLambda CDM (HDE) model has the largest (middle) deviation, especially when we keep the observational data point 226^{+8.0}_{-0.8} at redshift z=2.36 in the analysis. On the contrary, in the redshift z <1, we see that the compatibility of varLambda CDM cosmology and observation is even better than the model independent cosmography method.

Improving data-driven model-independent reconstructions and updated constraints on dark energy models from Horndeski cosmology

In light of the statistical performance of cosmological observations, in this work we present an improvement on the Gaussian reconstruction of the Hubble parameter data H(z) from Cosmic Chronometers, Supernovae Type Ia and Clustering Galaxies in a model-independent way in order to use them to study new constraints in the Horndeski theory of gravity. First, we have found that the prior used to calibrate the Pantheon supernovae data significantly affects the reconstructions, leading to a 13σ tension on the H 0 value. Second, according to the χ2-statistics, the reconstruction carried out by the Pantheon data calibrated using the H 0 value measured by The Carnegie-Chicago Hubble Program is the reconstruction which fits best the observations of Cosmic Chronometers and Clustering of Galaxies datasets. Finally, we use our reconstructions of H(z) to impose model-independent constraints in dark energy scenarios as Quintessence and K-essence from general cosmological viable Horndeski models, landscape in where we found that a Horndeski model of the K-essence type can reproduce the reconstructions of the late expansion of the universe within 2σ.