Cosmic Chronometers Research Articles

A new measurement of the expansion history of the Universe at z = 1.26 with cosmic chronometers in VANDELS

Aims. We aim to derive a new constraint on the expansion history of the Universe by applying the cosmic chronometers method in the VANDELS survey, studying the age evolution of high-redshift galaxies with a full-spectral-fitting approach. Methods. We selected a sample of 39 massive (log(M⋆/M⊙) > 10.8) and passive (log(sSFR/yr−1) < −11) galaxies from the fourth data release of the VANDELS survey at 1 < z < 1.5. To minimise the potential contamination by star-forming outliers, we selected our sample by combining different selection criteria, considering both photometric and spectroscopic information. The analysis of the observed spectral features provides direct evidence of an age evolution with redshift and of mass-downsizing, with more massive galaxies presenting stronger age-related features. To estimate the physical properties of the sample, we performed full spectral fitting with the code BAGPIPES, jointly analysing spectra and photometry of our sources without any cosmological assumption regarding the age of the population. Results. The derived physical properties of the selected galaxies are characteristic of a passive population, with short star formation timescales (⟨τ⟩ = 0.28 ± 0.02 Gyr), low dust extinction (⟨AV, dust⟩ = 0.43 ± 0.02 mag), and sub-solar metallicities (⟨Z/Z⊙⟩ = 0.44 ± 0.01) compatible with other measurements of similar galaxies in this redshift range. The stellar ages, even if no cosmological constraint is assumed in the fit, show a decreasing trend compatible with a standard cosmological model, proving the robustness of the method in measuring the ageing of the population. Moreover, they show a distinctive mass-downsizing pattern, with more massive galaxies (⟨log(M⋆/M⊙)⟩ = 11.4) being older than less massive ones (⟨log(M⋆/M⊙)⟩ = 11.15) by ∼0.8 Gyr. We thoroughly tested the dependence of our results on the assumed SFH, finding a maximum 2% fluctuation on median results using models with significantly different functional forms. The derived ages are combined to build a median age–redshift relation, which we used to perform our cosmological analysis. Conclusions. By fitting the median age–redshift relation with a flat ΛCDM model, assuming a Gaussian prior on ΩM, 0 = 0.3 ± 0.02 from late-Universe cosmological probes, we obtain a new estimate of the Hubble constant H0 = 67−15+14 km s−1 Mpc−1. In the end, we derive a new estimate of the Hubble parameter by applying the cosmic chronometers method to this sample, deriving a value of H(z = 1.26) = 135 ± 65 km s−1 Mpc−1 considering both statistical and systematic errors. While the error budget in this analysis is dominated by the scarcity of the sample, this work demonstrates the potential strength of the cosmic chronometers approach up to z > 1, especially in view of the next incoming large spectroscopic surveys such as Euclid.

Model-independent reconstruction of the interacting dark energy kernel: Binned and Gaussian process

Abstract The cosmological dark sector remains an enigma, offering numerous possibilities for exploration. One particularly intriguing option is the (non-minimal) interaction scenario between dark matter and dark energy. In this paper, to investigate this scenario, we have implemented Binned and Gaussian model-independent reconstructions for the interaction kernel alongside the equation of state; while using data from BAOs, Pantheon+ and Cosmic Chronometers. In addition to the reconstruction process, we conducted a model selection to analyze how our methodology performed against the standard ΛCDM model. The results revealed a slight indication, of at least 1σ confidence level, for some oscillatory dynamics in the interaction kernel and, as a by-product, also in the DE and DM. A consequence of this outcome is the possibility of a sign change in the direction of the energy transfer between DE and DM and a possible transition from a negative DE energy density in early-times to a positive one at late-times. While our reconstructions provided a better fit to the data compared to the standard model, the Bayesian Evidence showed an intrinsic penalization due to the extra degrees of freedom. Nevertheless these reconstructions could be used as a basis for other physical models with lower complexity but similar behavior.

Are we survivors of the sudden past singularity?

In this paper, we investigate the viability of cosmological models featuring a type II singularity that occurs during the past evolution of the Universe. We construct a scenario in which the singularity arises and then constrain the model parameters using observational data from type Ia supernovae, cosmic chronometers, and gamma ray bursts. We find that the resulting cosmological models based on scenarios with the past type II singularity cannot be excluded by kinematical tests using current observations.

Exponential [formula omitted] gravity with axion dark matter

The cosmological evolution within the framework of exponential F(R) gravity is analysed by assuming two forms for dark matter: (a) a standard dust-like fluid and (b) an axion scalar field. As shown in previous literature, an axion-like field oscillates during the cosmological evolution but can play the role of dark matter when approaching the minimum of its potential. Both scenarios are confronted with recent observational data including the Pantheon Type Ia supernovae, Hubble parameter estimations (Cosmic Chronometers), Baryon Acoustic Oscillations and Cosmic Microwave Background distances. The models show great possibilities in describing these observations when compared with the ΛCDM model, supporting the viability of exponential F(R) gravity. The differences between both descriptions of dark matter is analysed.

Measuring Hubble constant in an anisotropic extension of [formula omitted]CDM model

Cosmic Microwave Background (CMB) independent approaches are frequently used in the literature to provide estimates of Hubble constant (H0). In this work, we report CMB independent constraints on H0 in an anisotropic extension of ΛCDM model using the Big Bang Nucleosynthesis (BBN), Baryonic Acoustic Oscillations (BAOs), Cosmic Chronometer (CC), and Pantheon+ (PP) compilation of Type Ia supernovae and SH0ES Cepheid host distance anchors data. In the anisotropic model, we find H0=70.1−1.5+1.2(72.67±0.85)kms−1Mpc−1 both with 68% CL from BAO+BBN+CC+PP (BAO+BBN+CC+PPSH0ES) data. The analyses of the anisotropic model with the two combinations of datasets reveal that anisotropy is positively correlated with H0, and an anisotropy of the order 10−14 in the anisotropic model reduces the H0 tension by ∼2σ.

Cosmology with the late time isotropy of the Bianchi type I model in f(R,T) theory

In this study, we consider the Bianchi type I model in the framework of [Formula: see text] gravity theory. We solve the field equations with the help of an anisotropy parameter that can show the anisotropic behavior of the universe in the past and its approximation to isotropy today. For two different models, we examine the phase transition in the expansion of the universe by analyzing some cosmologic parameters. We conduct our investigation by applying the Markov Chain Monte-Carlo analysis and Bayesian technique to the Cosmic Chronometer, Phanteon and BAO datasets, taking into account the observational constraints on the parameters. We show that the two different models we obtained explain the transition from the slowing phase to the accelerating phase in the expansion of the universe, that the models behave in harmony with the [Formula: see text]CDM model today, and that the current values of the cosmological parameters predicted by the models are compatible with the values indicated by the observations and we conclude that the Model-I is more compatible than the Model-II in this conformity.

Cosmological tests of f(R,G,mathcal {T}) dark energy model in FRW universe

The paper is devoted to study the observational signatures of f(R,G,mathcal {T}) gravity in FRW universe. In this research article, we present a new cosmological model formulated within the f(R,G,mathcal {T}) framework. To constrain the model parameters, we employ the Markov Chain Monte Carlo (MCMC) technique, which enables us to explore the parameter space effectively, and used the 36 points of cosmic chronometers and 1701 points from Pantheon Plus data. We compare our proposed f(R,G,mathcal {T}) model with the widely accepted Lambda CDM model, considering different cosmological parameters, including deceleration, snap, and jerk. By evaluating these parameters, we gain valuable insights into the dynamics and evolution of the universe within the context of our new model. Moreover, various diagnostic tests have been conducted, such as Statefinder and Om diagnostic, to further investigate the behavior and consistency of our f(R,G,mathcal {T}) model. These tests offer deeper insights into the properties of our model and its compatibility with observational data. We subject our model to statistical analysis using Information Criteria, which serves as a rigorous quantitative assessment of the model’s goodness of fit to the data. This analysis aids in determining the level of agreement between our f(R,G,mathcal {T}) model and the observational data, thus establishing the viability and reliability of our proposed cosmological framework. Our findings highlight the potential of the f(R,G,mathcal {T}) framework in understanding the fundamental aspects of the universe’s evolution and dynamics. The comparative analysis with Lambda CDM, as well as the comprehensive diagnostic tests performed, demonstrate the efficacy and validity of our model in explaining the observed cosmological phenomena. These results contribute to the ongoing pursuit of accurate and comprehensive models that can provide a deeper understanding of the nature of our universe.

Modeling cosmic acceleration with a generalized varying deceleration parameter

Understanding the accelerating expansion of the Universe remains a fundamental challenge in modern cosmology. In this paper, we investigate a cosmological model parametrized by a generalized variable deceleration parameter to elucidate the dynamics driving cosmic acceleration. By employing constraints from the latest observational datasets, including Cosmic Chronometers (CC), Type Ia Supernovae (SNe), and Baryon Acoustic Oscillations (BAO), we assess the compatibility of the model with observational data. The chosen parametrization aligns with thermodynamic constraints on the deceleration parameter, further validating its reliability. Further, we estimate the present value of the Hubble parameter, transition redshift, deceleration parameter, and EoS parameter, which align with observational data. Lastly, our stability analysis confirms the model’s stability against small perturbations.

Constrained evolution of effective equation of state parameter in non-linear $$\qquad\qquad f\left( {R,L_{m} } \right)$$ dark energy model: insights from Bayesian analysis of cosmic chronometers and Pantheon samples

Constrained evolution of effective equation of state parameter in non-linear $$\qquad\qquad f\left( {R,L_{m} } \right)$$ dark energy model: insights from Bayesian analysis of cosmic chronometers and Pantheon samples

Impact of a newly parametrized deceleration parameter on the accelerating universe and the reconstruction of f(Q) non-metric gravity models

This article presents a novel parametrization of the deceleration parameter (DP) to investigate the cosmological scenario. The newly proposed parametric form of the DP is both physically plausible and model-independent. Constrained by a combined dataset of 31 cosmic chronometers (CC) data points, 26 non-correlated baryonic acoustic oscillations (BAO) points, and 1701 Pantheon+ data points from supernovae type Ia (SNeIa), we determine the model parameters using a Markov Chain Monte Carlo (MCMC) method. The analysis explores the kinematic behavior of the model, including the transition from deceleration to acceleration. The results indicate that the Universe is currently in an accelerated phase. Furthermore, we apply the obtained parameter values to constrain f(Q) gravity models and compare them with observations. This study provides valuable insights into the accelerating Universe and underscores the importance of employing a model-independent approach in cosmological investigations.

Pantheon+ tomography and Hubble tension

The recently released Type Ia supernovae (SNe Ia) sample, Pantheon+, is an updated version of Pantheon and has very important cosmological implications. To explore the origin of the enhanced constraining power and internal correlations of datasets in different redshifts, we perform a comprehensively tomographic analysis of the Pantheon+ sample without and with the Cepheid host distance calibration, respectively. Specifically, we take two binning methods to analyze the Pantheon+ sample, i.e., equal redshift interval and equal supernovae number for each bin. For the case of equal redshift interval, after dividing the sample to 10 bins, the first bin in the redshift range zin [0.00122, , 0.227235] dominates the constraining power of the whole sample. For the case of equal supernovae number, the first three low redshift bins prefer a large matter fraction Omega _m and only the sixth bin gives a relatively low cosmic expansion rate H_0. For both binning methods, we find no obvious evidence of evolution of H_0 and Omega _m at the 2,sigma confidence level. The inclusion of the SH0ES calibration can significantly compress the parameter space of background dynamics of the universe in each bin. When not considering the calibration, combining the Pantheon+ sample with cosmic microwave background, baryon acoustic oscillations, cosmic chronometers, galaxy clustering and weak lensing data, we give the strongest 1,sigma constraint H_0=67.88pm 0.42 km hbox {s}^{-1}hbox {Mpc}^{-1}. However, the addition of the calibration leads to a global shift of the parameter space from the combined constraint and H_0=68.66pm 0.42 km hbox {s}^{-1}hbox {Mpc}^{-1}, which is inconsistent with the Planck-2018 result at about 2,sigma confidence level.

Impact of dark energy on the equation of state in light of the latest cosmological data

Abstract We reconstruct the effective equation of state (EoS) within the framework of the general theory of relativity in a homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker universe, which is assumed to be composed of matter and dark energy (DE). Our analysis employs a dataset consisting of 31 cosmic chronometer data points, six data points of baryon acoustic oscillations, and 1048 type Ia supernovae from the Pantheon sample, and we determine the best-fitting values of the model parameters through Markov chain Monte Carlo simulation. We then use these parameter values to calculate various cosmological parameters, such as the DE EoS parameter, the energy density, the deceleration parameter, the state-finder parameters, and the Om(z) diagnostic. All the analyzed cosmological parameters show behavior consistent with the accelerated universe scenario.

Seven Hints That Early-Time New Physics Alone Is Not Sufficient to Solve the Hubble Tension

The Hubble tension has now grown to a level of significance which can no longer be ignored and calls for a solution which, despite a huge number of attempts, has so far eluded us. Significant efforts in the literature have focused on early-time modifications of ΛCDM, introducing new physics operating prior to recombination and reducing the sound horizon. In this opinion paper I argue that early-time new physics alone will always fall short of fully solving the Hubble tension. I base my arguments on seven independent hints, related to (1) the ages of the oldest astrophysical objects, (2) considerations on the sound horizon-Hubble constant degeneracy directions in cosmological data, (3) the important role of cosmic chronometers, (4) a number of “descending trends” observed in a wide variety of low-redshift datasets, (5) the early integrated Sachs-Wolfe effect as an early-time consistency test of ΛCDM, (6) early-Universe physics insensitive and uncalibrated cosmic standard constraints on the matter density, and finally (7) equality wavenumber-based constraints on the Hubble constant from galaxy power spectrum measurements. I argue that a promising way forward should ultimately involve a combination of early- and late-time (but non-local—in a cosmological sense, i.e., at high redshift) new physics, as well as local (i.e., at z∼0) new physics, and I conclude by providing reflections with regards to potentially interesting models which may also help with the S8 tension.

Geometric perspective for explaining Hubble tension: theoretical and observational aspects

The Universe expansion rate has two different but very precise values ( and km s−1Mpc−1) that are not compatible. This problem, known as a Hubble tension, adds to other cosmological questions such as the origin of dark energy and the flatness problem. In turn, alternative models have attempted to explain similar phenomena but without dark energy. The aim of this work was to explain the Hubble tension by using a geometrical interpretation of observational viewpoints in embedded manifolds. Our technique consists of a set of parametric projections of radially inhomogeneous metrics, linking indistinguishable behaviours of accelerated flat and non-accelerated closed universes. A dark-energy-like phenomenon emerges from the distortion of matter-independent hyperconical metrics. To contrast our model, numerical solutions of dark energy/matter densities and Hubble parameter were obtained and compared to the standard model fitted to the Pantheon Supernovae Ia sample and in contrast to the SH0ES LMC Cepheid findings. Finally, Hubble tension is modelled by the different extrinsic/intrinsic viewpoints of the manifold. Compared to the Planck Legacy’s 2018 release of km s−1Mpc−1, we found ΛCDM-dependent (intrinsic) ranges between 66.38 and 68.87 km s−1Mpc−1, which were theoretically derived by setting local compatibility of metrics. The ΛCDM-independent extrinsic viewpoint resulted in a Hubble parameter between 73 and 74 km s−1Mpc−1 (compared to km s−1Mpc−1 of SH0ES). Datasets of 1048 Pantheon Type Ia supernovae () and 34 cosmic chronometers combined with 7 radial baryon acoustic oscillation size-based samples () were used to constraint the model. According to this geometrical perspective, dark parameters (energy and matter) could partially or totally be considered ‘apparent physical quantities’, a consequence of the stereographic projection of the extrinsic curvature.

Model-independent cosmological insights from three newly reconstructed deceleration parameters with observational data

This article introduces three novel parametrizations of the deceleration parameter (DP) to explore the cosmological scenario. The newly introduced parametric forms of the DP are physically plausible and model-independent. We constrained the model parameters using a Markov Chain Monte Carlo (MCMC) method by utilizing a combined dataset of 31 cosmic chronometers (CC) data points, 26 non-correlated baryonic acoustic oscillations (BAO) points, and recently updated 1701 Pantheon+ data points from supernovae type Ia (SNeIa). To explore the kinematic behavior of the model, we analyze various aspects such as the transition from deceleration to acceleration, as well as the energy conditions. The current analysis of the three parametric models reveals that the Universe is currently in an accelerated phase, which is supported by the present values of the EoS parameter and the negative SEC behavior within specific redshift ranges for all three models. Additionally, all three parametric models meet the WEC, DEC, and NEC conditions across the entire range of redshift values. We use the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) model selection criteria to compare the performance of the models. Overall, this study offers valuable insights into the accelerating Universe and emphasizes the significance of adopting a model-independent approach in cosmological investigations.

Observational constraints on a logarithmic scalar field dark energy model and black hole mass evolution in the Universe

We propose a logarithmic parametrization form of energy density for the scalar field dark energy in the framework of the standard theory of gravity, which supports the necessary transition from the decelerated to the accelerated behavior of the Universe. The model under consideration is constrained by available observational data, including cosmic chronometers data-sets (CC), Baryonic Acoustic Oscillation (BAO) data-sets, and Supernovae (SN) data-sets, consisting of only two parameters alpha and beta . The combined CC+BAO+SN data-sets yields a transition redshift of z_{tr}=0.79^{+0.02}_{-0.02}, where the model exhibits signature-flipping and is consistent with recent observations. For the combined data-sets, the present value of the deceleration parameter is calculated to be q_{0}=-0.43^{+0.06}_{-0.06}. Furthermore, the analysis yields constraints on both the parameter density value for matter and the present value of the Hubble parameter, with values of Omega _{m0}=0.25849^{+0.00026}_{-0.00025} and H_{0}=67.79_{-0.59}^{+0.59} km/s/Mpc, respectively, consistent with the results obtained from Planck 2018. Finally, the study investigates how the mass of a black hole evolves over time in a Universe with both matter and dark energy. It reveals that the black hole mass increases initially but stops increasing as dark energy dominates.

Revisiting the Epoch of Cosmic Acceleration

We revisit the epoch of cosmic speed-up characterized by the redshift of transition from a decelerated to an accelerated phase. This redshift is termed the transition redshift (z t ). We use the spatially flat and non-flat variants of the most common ΛCDM and XCDM models to put constraints on the transition redshift along with the other model parameters. The data for this analysis come from the recent and updated Pantheon+ supernova (SN) data set and the Hubble parameter measurements obtained from Cosmic Chronometers. We consider both data sets with their respective covariance matrices incorporating all statistical and systematic uncertainties. We observe that using the combined data sets of H(z) and SNe, the best fit value of transition redshift lies in the range 0.61 < z t < 0.79 for all four dark energy models. Incidentally, we observe a positive curvature for the non-flat models, correlations between several model parameters and a strong degeneracy between the curvature and the equation of state parameter.

Hubble parameter reconstruction: A tool to explore the acceleration of the universe with observational constraints

This article introduces a novel parametric form of the Hubble parameter for exploring the accelerating cosmos in a model-independent manner. The model parameters are constrained using a Markov Chain Monte Carlo (MCMC) approach with a combined dataset spanning 31 cosmic chronometers (CC) data points, 26 non-correlated baryonic acoustic oscillations (BAO) points, and 1701 updated Pantheon+ supernovae type Ia (SNeIa) data points. We investigate the model’s kinematic behavior, including the transition from the deceleration phase to the acceleration phase, the jerk evolution, and the energy conditions. The results of the equation of state parameter suggest that our model behaves like the quintessence model and supports the current accelerating Universe. Additionally, we impose constraints on both the model parameters and the Hubble constant H0, and find that the values obtained for H0 align with other works obtained through reconstruction methods and observational data. Overall, this study provides valuable insights into the accelerating cosmos and highlights the importance of a model-independent approach in cosmological studies.

Hubble constant by natural selection: Evolution chips in the Hubble tension

The Approximate Bayesian Computation (ABC) algorithm considers natural selection in biology as a guiding principle for statistical model selection and parameter estimation. We take this ABC approach to cosmology and use it to infer which ΛCDM model anchored on a choice of a Hubble constant prior would be preferred by the data. We find in all of our runs that the Planck Hubble constant (H0=67.4±0.5 km s−1Mpc−1) always emerges naturally selected by the ABC over the SH0ES estimate (H0=73.30±1.04 km s−1Mpc−1). The result holds regardless of how we mix our data sets, including supernovae, cosmic chronometers, baryon acoustic oscillations, and growth data. Compared with the traditional MCMC, we find that the ABC always results with narrower cosmological constraints, but remain consistent inside the corresponding MCMC posteriors.

Measuring the Hubble constant with cosmic chronometers: a machine learning approach

Local measurements of the Hubble constant (H_0) based on Cepheids e Type Ia supernova differ by approx 5 sigma from the estimated value of H_0 from Planck CMB observations under Lambda CDM assumptions. In order to better understand this H_0 tension, the comparison of different methods of analysis will be fundamental to interpret the data sets provided by the next generation of surveys. In this paper, we deploy machine learning algorithms to measure the H_0 through a regression analysis on synthetic data of the expansion rate assuming different values of redshift and different levels of uncertainty. We compare the performance of different regression algorithms as Extra-Trees, Artificial Neural Network, Gradient Boosting, Support Vector Machines, and we find that the Support Vector Machine exhibits the best performance in terms of bias-variance tradeoff in most cases, showing itself a competitive cross-check to non-supervised regression methods such as Gaussian Processes.