Hubble Parameter Data Research Articles

Reconciling cosmological tensions with inelastic dark matter and dark radiation in a U(1) D framework

We propose a novel and comprehensive particle physics framework that addresses multiple cosmological tensions observed in recent measurements of the Hubble parameter, S 8, and Lyman-α forest data. Our model, termed `SIDR+z t ' (Self Interacting Dark Radiation with transition redshift), is based on an inelastic dark matter (IDM) scenario coupled with dark radiation, governed by a U(1) D gauge symmetry. This framework naturally incorporates cold dark matter (DM), strongly interacting dark radiation (SIDR), and the interactions between these components. The fluid-like behavior of the dark radiation component which originates from the self-quartic coupling of the U(1) D breaking scalar can suppress the free-streaming effects. Simultaneously, the interacting DM-DR system can attenuate the matter power spectrum at small scales. The inelastic nature of DM provides a distinct temperature dependence for the DM-DR interaction rate determined by the mass-splitting between the inelastic dark fermions which is crucial for resolving the Ly-α discrepancies. We present a cosmologically consistent analysis of the model by solving the relevant Boltzmann equations to obtain the energy density and number density evolution of different species of the model. The DR undergoes two “steps” of increased energy density when the heavier dark species freeze out and become non-relativistic, transferring their entropy to the dark radiation and enhancing ΔN eff. The analysis showcases the model's potential to uphold the Big Bang Nucleosynthesis (BBN) prediction of ΔN eff but dominantly producing additional contributions prior to recombination, while simultaneously achieving correct relic density of DM though an hybrid of freeze-in and non-thermal production.

A comprehensive data-driven odyssey to explore the equation of state of dark energy

For the first time, we reconstruct the dark energy equation of the state parameter w from the combination of background and perturbation observations, specifically combining the Hubble parameter data from cosmic chronometer observations and the logarithmic growth rate data from the growth rate observations. We do this analysis using posterior Gaussian process regression without considering any specific cosmological model or parametrization. However there are three main assumptions: (I) a flat Friedmann–Lemaître–Robertson–Walker (FLRW) metric is considered for the cosmological background, (II) there is no interaction between dark energy and matter sectors, and (III) for the growth of inhomogeneity, sub-Hubble approximation and linear perturbations are considered. This study is unique in the sense that the reconstruction of w is independent of any derived parameters such as the present values of the matter-energy density parameter and Hubble parameter. From the reconstruction, we look at how the dark energy equation of state evolves between redshifts 0 and 1.5, finding a slight hint of dynamical behavior in dark energy. However, the evidence is not significant. We also find a leaning towards non-phantom behavior over phantom behavior. We observe that the Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varLambda $$\\end{document}CDM model (w=-1)\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(w=-1)$$\\end{document} nearly touches the lower boundary of the 1σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma $$\\end{document} confidence region in the redshift range 0.6≲z≲0.85.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.6 \\lesssim z \\lesssim 0.85.$$\\end{document} However, it comfortably resides within the 2σ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\sigma $$\\end{document} confidence region in the whole redshift range under investigation, 0≤z≤1.5.\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0\\le z \\le 1.5.$$\\end{document} Consequently, the non-parametric, model-independent reconstruction of dark energy provides no compelling evidence to deviate from the Λ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\varLambda $$\\end{document}CDM model when considering cosmic chronometer and growth rate observations.

Model-independent test of the running Hubble constant from the Type Ia supernovae and the Hubble parameter data

ABSTRACT In this study, we model-independently investigate the behaviour of running Hubble constant, characterized by the fit function $H_{\rm 0}(z)=\tilde{H_{\rm {0}}}/(1+z)^{\alpha }$, where α represents the evolutionary parameter and ${\tilde{H_{\rm {0}}}}$ corresponds to the current value of Hubble constant. Our analysis utilizes the expansion rate E(z) data points measured from the Pantheon + Multi-Cycle Treasury compilation of Type Ia supernova data, the measurements of H0 obtained by Riess et al., and the Hubble parameter H(z) data obtained from the differential ages of passive galaxies [known as cosmic chronometer (CC) method] and from the baryon acoustic oscillation (BAO) in the radial direction of galaxy clustering. To resolve the redshift mismatch problem between the E(z) and H(z) data sets, we adopt the Hubble parameter data obtained via CC or BAO along with the measurements of H0 obtained by Riess et al. to reconstruct the H(z) function using the Gaussian process. Our constraint yields α values of 0.125 ± 0.063 or 0.095 ± 0.052 when combining six pairs of the E(z) data and the reconstructed H(z) points via CC or BAO. These findings reveal that the Hubble constant may evolve with redshift, exhibiting a slowly decreasing trend, with α coefficients consistent with zero only at 2.0σ or 1.8σ. Therefore, the running Hubble constant might offer a promising resolution to the Hubble tension, and its reliability should be further tested through high-precision measurement at higher redshifts, such as the upcoming gamma-ray bursts and quasars.

Analytical Gaussian process cosmography: unveiling insights into matter-energy density parameter at present

In this study, we introduce a novel analytical Gaussian Process (GP) cosmography methodology, leveraging the differentiable properties of GPs to derive key cosmological quantities analytically. Our approach combines cosmic chronometer (CC) Hubble parameter data with growth rate (f) observations to constrain the Ωm0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega _{\ extrm{m0}}$$\\end{document} parameter, offering insights into the underlying dynamics of the Universe. By formulating a consistency relation independent of specific cosmological models, we analyze under a flat FLRW metric and first-order Newtonian perturbation theory framework. Our analytical approach simplifies the process of Gaussian Process regression (GPR), providing a more efficient means of handling large datasets while offering deeper interpretability of results. We demonstrate the effectiveness of our methodology by deriving precise constraints on Ωm0h2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega _{\ extrm{m0}}h^2$$\\end{document}, revealing Ωm0h2=0.139±0.017\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega _\ extrm{m0}h^2=0.139\\pm 0.017$$\\end{document}. Moreover, leveraging H0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_0$$\\end{document} observations, we further constrain Ωm0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega _{\ extrm{m0}}$$\\end{document}, uncovering an inverse correlation between mean H0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$H_0$$\\end{document} and Ωm0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Omega _{\ extrm{m0}}$$\\end{document}. Our investigation offers a proof of concept for analytical GP cosmography, highlighting the advantages of analytical methods in cosmological parameter estimation.

Deep learning-assisted Hubble parameter analysis

We turn our attention on evaluating the most recent Hubble parameter data measured via the differential evolution of cosmic-chronometers from a deep learning perspective. To achieve this goal, we start our investigation by introducing the selected theoretical setup and compiling the most recent statistical data obtained in cosmology experiments. Then we implement a tuned version of the long-short term memory (LSTM) architecture and run it to predict possible values of the Cosmic Hubble parameter for different red-shift states. Since we observe a good correlation between the observed and predicted datasets of the Hubble parameter, we conclude that the machine learning approaches can play important roles in the future cosmology investigations.

Viscous effect in the late time evolution of phantom universe

We investigate the cosmological implications of a phantom dark energy model with bulk viscosity. We explore this model as a possible way to resolve the big rip singularity problem that plagues the phantom models. We use the latest type Ia supernova and Hubble parameter data to constrain the model parameters and find that the data favor a significant bulk viscosity over a non-constant potential term for the phantom field. We perform a dynamical analysis of the model and show that the only stable and physical attractor corresponds to a phantom-dominated era with a total equation of state that can be greater than -1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$-1$$\\end{document} due to the viscosity. We also study the general effect of viscosity on the phantom field and the late time evolution of the universe. We apply the statefinder diagnostic to the model and find that it approaches a nearby fixed point asymptotically, indicating that the universe can escape the big rip singularity with the presence of bulk viscosity. We conclude that bulk viscosity can play an important role in affecting the late-time behavior as well as alleviating the singularity problem of the phantom universe.

An [formula omitted] gravity based FLRW model and observational constraints

We attempt to construct a Friedmann–Lemaitre–Robertson–Walker (FLRW) cosmological model in f(R,T) gravity which exhibits a phase transition from deceleration to acceleration at present. We take f(R,T)=R+2λT, λ being an arbitrary constant. In our model, the λ parameter develops a negative pressure in the universe whose Equation of state is parameterized. The present values of model parameters such as density, Hubble, deceleration, Equation of state, and λ are estimated statistically by using the Chi-Square test. For this, we have used three different types of observational data sets: the 46 Hubble parameter data set, the SNeIa 715 data sets of distance modulus, and the 66 Pantheon data set (the latest compilation of SNeIa 40 bined plus 26 high red shift apparent magnitude mb data set in the red shift ranges from 0.014≤z≤2.26). We have calculated the transitional red shift and time. The estimated results for the present values of various model parameters are found as per expectations and surveys. Interestingly, we get the present value of the density ρ0, ≃1.5ρc. The critical density is estimated as ρc≃1.88h0210−29gm/cm3 in the literature. The higher value of the present density is attributed to the presence of some additional energies in the universe apart from baryon energy. We have examined the behavior of the pressure in our model. It is negative and produces acceleration in the universe. Its present value is obtained as p0≃−0.7ρ0.

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.

Evidence of a decreasing trend for the Hubble constant

The current discrepancy between the Hubble constant, H0, derived from the local distance ladder and from the cosmic microwave background is one of the most crucial issues in cosmology, as it may possibly indicate unknown systematics or new physics. Here, we present a novel non-parametric method to estimate the Hubble constant as a function of redshift. We establish independent estimates of the evolution of Hubble constant by diagonalizing the covariance matrix. From type Ia supernovae, baryon acoustic oscillation data and the observed Hubble parameter data, a decreasing trend in the Hubble constant with a significance of a 5.6σ confidence level is found. At low redshift, its value is dramatically consistent with that measured from the local distance ladder and it drops to the value measured from the cosmic microwave background at high redshift. Our results may relieve the Hubble tension, with a preference for recent solutions, especially with respect to novel physics.

H0=69.8±1.3 km s−1 Mpc−1 , Ωm0=0.288±0.017 , and other constraints from lower-redshift, non-CMB, expansion-rate data

We use updated Type Ia Pantheon+ supernova, baryon acoustic oscillation, and Hubble parameter (now also accounting for correlations) data, as well as new reverberation-measured C IV quasar data, and quasar angular size, H II starburst galaxy, reverberation-measured Mg II quasar, and Amati-correlated gamma-ray burst data to constrain cosmological parameters. We show that these data sets result in mutually consistent constraints and jointly use them to constrain cosmological parameters in six different spatially-flat and non-flat cosmological models. Our analysis provides summary model-independent determinations of two key cosmological parameters: the Hubble constant, $H_0=69.8\pm1.3$ $\rm{km \ s^{-1} \ Mpc^{-1}}$, and the current non-relativistic matter density parameter, $\Omega_{m0}=0.288\pm0.017$. Our summary error bars are 2.4 and 2.3 times those obtained using the flat $\Lambda$CDM model and Planck TT,TE,EE+lowE+lensing cosmic microwave background (CMB) anisotropy data. Our $H_0$ value is very consistent with that from the local expansion rate based on the Tip of the Red Giant Branch data, is 2$\sigma$ lower than that from the local expansion rate based on Type Ia supernova and Cepheid data, and is 2$\sigma$ higher than that in the flat $\Lambda$CDM model based on Planck TT,TE,EE+lowE+lensing CMB data. Our data compilation shows at most mild evidence for non-flat spatial hypersurfaces, but more significant evidence for dark energy dynamics, 2$\sigma$ or larger in the spatially-flat dynamical dark energy models we study.

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.

Modeling transit dark energy in f(R,Lm)-gravity

This research paper deals with a transit dark energy cosmological model in [Formula: see text]-gravity with observational constraints. For this, we consider a flat Friedman–Lamatre–Robertson–Walker (FLRW) space-time and have taken a cosmological constant-like parameter [Formula: see text] in our field equations. The model has two energy parameters [Formula: see text], which govern the mechanism of the universe, in particular its present accelerated phase. To make the model cope with the present observational scenario, we consider three types of observational data set: [Formula: see text] Hubble parameter data set, SNe Ia [Formula: see text] data sets of distance modulus and apparent magnitude, and [Formula: see text] datasets of SNe Ia bined compilation in the redshift [Formula: see text]. We have approximated the present values of the energy parameters by applying [Formula: see text] and [Formula: see text]-test in the observational and theoretical values of Hubble, distance modulus and apparent magnitude parameters. Also, we have measured the approximate present values of cosmographic coefficients [Formula: see text]. It is found that our approximated value-based model fits best with the observational module. We have found that as [Formula: see text] (or [Formula: see text]) then [Formula: see text]. The cosmic age of the present universe is also approximated and comes up to the expectation. Our model shows a transit phase of the present accelerating universe with a deceleration in the past and has a transition point.

Dark energy from the fifth dimension

After extending the Regge-Teitelboim formulation of gravity to include the case where the background embedding space is not flat, we examine the dynamics of the four-dimensional $k=0$ Robertson-Walker (RW) manifold embedded in various five-dimensional backgrounds. We find that when the background is five-dimensional de Sitter space, the RW manifold undergoes a transition from a de-accelerating phase to an accelerating phase. This occurs before the inclusion of matter, radiation or cosmological constant sources, and thus does not require a balance of different components. We obtain a reasonable two-parameter fit of this model to the Hubble parameter data.

Observational Hubble parameter data constraints on the interactive model of gravity with particle creation

In this study, we consider an open system from the thermodynamic perspective for an adiabatic FRW universe model in which particle creation occurs within the system. In this case, the modified continuity equation is obtained, and then, we make it correspond to the continuity equation of gravity. Therefore, we take gravity with a viscous fluid in the flat-FRW metric, where T is the torsion scalar. We assume the contents of the universe to be dark matter and dark energy and consider an interaction term between them. An interesting point of this study is that we make the modified continuity equation resulting from particle creation equivalent to the matter continuity equation resulting from gravity. The result of this evaluation establishes a relationship between the number of particles and scale factor. In what follows, we write the corresponding cosmological parameters in terms of the number of particles and also reconstruct the number of particles in terms of the redshift parameter. We then parameterize the Hubble parameter derived from power-law cosmology with 51 data points from the Hubble observational parameter data. Next, we plot the corresponding cosmological parameters for dark energy in terms of the redshift to investigate the accelerated expansion of the universe. In addition, by using the sound speed parameter, we discuss the stability and instability analyses of the present model in different eras of the universe. Finally, we plot the density parameter values for dark energy and dark matter in terms of the redshift parameter.

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.

Testing the Coincidence Problem with Strong Gravitational Lens, Type Ia Supernovae and Hubble Parameter Observational Data

In this paper, we use three different kinds of observational data, including 130 strong gravitational lensing (SGL) systems, type Ia supernovae (SNeIa: Pantheon and Union2.1) and 31 Hubble parameter data points (H(z)) from cosmic chronometers to constrain the phenomenological model (ρ x ∝ ρ m a ξ ). By combining these three kinds of data (Union2.1+SGL+H(z)), we get the parameter value at the confidence interval of 2σ, Ω X,0 = 0.69 ± 0.34, ω x = −1.24 ± 0.61, ξ = 3.8 ± 3.9 and H 0 = 70.22 ± 0.86 kms−1 Mpc−1. According to our results, we find that the ΛCDM model is still the model which is in best agreement with the observational data at present, and the coincidence problem is not alleviated. In addition, the Ω X and Ω m have the same order of magnitude in 0 < z < 1.26. Finally, we obtain the transition redshift z T = 0.645. If the transition occurs in z > 0.645, it is necessary to introduce the dark energy interacting with dark matter.

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.

Constraints on Cosmographic Functions of Cosmic Chronometers Data Using Gaussian Processes

We study observational constraints on the cosmographic functions up to the fourth derivative of the scale factor with respect to cosmic time, i.e., the so-called snap function, using the non-parametric method of Gaussian Processes. As observational data we use the Hubble parameter data. Also we use mock data sets to estimate the future forecast and study the performance of this type of data to constrain cosmographic functions. The combination between a non-parametric method and the Hubble parameter data is investigated as a strategy to reconstruct cosmographic functions. In addition, our results are quite general because they are not restricted to a specific type of functional dependency of the Hubble parameter. We investigate some advantages of using cosmographic functions instead of cosmographic series, since the former are general definitions free of approximations. In general, our results do not deviate significantly from $\Lambda CDM$. We determine a transition redshift $z_{tr}=0.637^{+0.165}_{-0.175}$ and $H_{0}=69.45 \pm 4.34$. Also assuming priors for the Hubble constant we obtain $z_{tr}=0.670^{+0.210}_{-0.120}$ with $H_{0}=67.44$ (Planck) and $z_{tr}=0.710^{+0.159}_{-0.111}$ with $H_{0}=74.03$(SH0ES). Our main results are summarized in table 2.

Using lower-redshift, non-CMB, data to constrain the Hubble constant and other cosmological parameters

Abstract We use updated Hubble parameter and baryon acoustic oscillation data, as well as other lower-redshift Type Ia supernova, Mg ii reverberation-measured quasar, quasar angular size, H ii starburst galaxy, and Amati-correlated gamma-ray burst data, to jointly constrain cosmological parameters in six cosmological models. The joint analysis provides model-independent determinations of the Hubble constant, H0 = 69.7 ± 1.2 $\rm {km \ s^{-1} \ Mpc^{-1}}$, and the current non-relativistic matter density parameter, Ωm0 = 0.295 ± 0.017. These error bars are factors of 2.2 and 2.3 larger than the corresponding error bars in the flat ΛCDM model from Planck TT,TE,EE+lowE+lensing cosmic microwave background anisotropy data. Based on the deviance information criterion (DIC), the flat ΛCDM model is most favored but mild dark energy dynamics and a little spatial curvature are not ruled out.