Evolution Of Dark Energy Research Articles

Probing barrow entropy models with future event horizon as IR cutoff

We develop formulations for barrow holographic dark energy (BHDE) in both non-interacting and interacting scenarios within a cosmological framework, applying the conventional holographic principle. Model parameter constraints are determined through the Markov Chain Monte Carlo (MCMC) method, utilizing different datasets. The investigation excavates into the models' kinematic behavior, exploring the transition from deceleration to acceleration and tracking the evolution of the equation of state parameters. Further, these models can pretend the evolution of dark energy and matter in the Universe. Additionally, a thermodynamic analysis employing future event horizons is conducted, confirming the validation of the generalized second law of thermodynamics. The resultant of the BHDE models strongly suggests that the Universe is presently experiencing an accelerated phase attributed to dark energy.

Probing dark energy evolution post-DESI 2024

We study the evidence for dark energy (DE) evolution at low redshift, using baryonic acoustic oscillations (BAOs) from the DESI Early Data Release, Pantheon+ Type Ia supernovae (SNe-Ia), and redshift space distortions (RSDs) to constrain cosmological parameters. Furthermore, we make use of the angular acoustic scale to analyse the effect of introducing condensed CMB information on the cosmological parameters informing DE evolution. The analysis is divided into cases based on the variability of priors inferred from early-time physics. Using a quadratic parametrisation, X(z), for DE density, we find evidence for DE evolution in all cases, both with and without the angular acoustic scale. We reconstruct X(z) using best fit parameters and find that DE density starts to exhibit dynamical behaviour at z∼0.5, assuming negative values beyond z∼1.5. The data show no significant preference for X(z)CDM over a ΛCDM, with both models performing equally well according to our chosen metrics of reduced χ2 and the Durbin–Watson statistic.

A phenomenological approach to the dark energy models in the Finsler–Randers framework

This study extends two phenomenological models of dark energy within the framework of Finsler–Randers space–time, accommodating anisotropies. The models consider the cosmological constant Λ in two scenarios: one where Λ is proportional to the second time derivative of the scale factor ä, and another where it varies with the matter-energy density ρ. Earlier, such Λ-decaying cosmologies were proposed to address long-standing cosmological constant problems. However, following the discovery of late-time cosmic acceleration, the focus shifted to modeling dark energy. Since Λ is widely viewed as the most significant and suitable candidate for driving cosmic acceleration, it is worthwhile to revisit the phenomenological approach in this context. This work uses this approach to find solutions for the scale factor a(t) and other geometrical and physical parameters. Additionally, we analyze the evolution of density parameters Ωm, ΩΛ, and Ωκ, representing matter, dark energy, and curvature, from early to late times. The phenomenological approach is employed to solve the field equations, with model parameters constrained using recent observational data, yielding ranges consistent with observations. The solutions converge to the ΛCDM cosmology at early and late times. The added complexity introduced by Finsler–Randers geometry enhances accuracy compared to analogous solutions in Riemannian space–time.

Quintessential interpretation of the evolving dark energy in light of DESI observations

Quintessential interpretation of the evolving dark energy in light of DESI observations

Cosmological evolution of new Tsallis agegraphic dark energy with conformal time as IR-cutoff

This paper considers the only sectors to constitute the present universe as the dark matter and dark energy. The proposed new agegraphic dark energy model studies the gradual transition from matter to dark energy in sequential order, including the current dominance of the matter sector by dark energy. The model utilizes concepts of Tsallis entropy and the Karolyhazy relation with conformal time [Formula: see text] as the time scale. Various evolutionary aspects of the universe are characterized by Tsallis parameter [Formula: see text] and the model constant [Formula: see text]. Expressions for dynamic behavior of dark energy, as a differential equation, equation of state and deceleration parameters are obtained to describe the thermal history of universe evolution. Also, the stability of the model is analyzed through squared sound speed parameter. The analysis is made by considering an interaction as well as independence among the constituent sectors of the universe.

Exploring late-time cosmic acceleration: A study of a linear [formula omitted] cosmological model using observational data

Understanding the evolution of dark energy poses a significant challenge in modern cosmology, as it is responsible for the universe’s accelerated expansion. In this study, we focus on a specific f(T) cosmological model and analyze its behavior using observational data, including 31 data points from the CC dataset, 1048 points from the Pantheon SNe Ia samples, and 6 points from the BAO dataset. By considering a linear f(T) model with an additional constant term, we derive the expression for the Hubble parameter as a function of cosmic redshift for non-relativistic pressureless matter. We obtain the best-fit values for the Hubble constant, H0, and the model parameters α and β, indicating a stable model capable of explaining late-time cosmic acceleration without invoking a dark energy component. This is achieved through modifying field equations to account for the observed accelerated expansion of the universe.

Distinguishing ΛCDM from Evolving Dark Energy with Om Two-point Statistics: Implications from the Space-borne Gravitational-wave Detector

The Omh 2(z i , z j ) two-point diagnostics was proposed as a litmus test of the ΛCDM model, and measurements of the cosmic expansion rate H(z) have been extensively used to perform this test. The results obtained so far suggested a tension between observations and predictions of the ΛCDM model. However, the data set of H(z) direct measurements from cosmic chronometers and baryon acoustic oscillations was quite limited. This motivated us to study the performance of this test on a larger sample obtained in an alternative way. In this paper, we propose that gravitational-wave (GW) standard sirens could provide large samples of H(z) measurements in the redshift range of 0 < z < 5, based on the measurements of the dipole anisotropy of luminosity distance arising from the matter inhomogeneities of the large-scale structure and the local motion of the observer. We discuss the effectiveness of our method in the context of the space-borne DECi-herz Interferometer Gravitational-wave Observatory, based on a comprehensive H(z) simulated data set from binary neutron star merger systems. Our results indicate that in the GW domain, the Omh 2(z i , z j ) two-point diagnostics could effectively distinguish whether ΛCDM is the best description of our Universe. We also discuss the potential of our methodology in determining possible evidence for dark energy evolution, focusing on its performance on the constant and redshift-dependent dark energy equation of state.

Revisiting the dynamics of interacting vector-like dark energy

We revise the dynamics of interacting vector-like dark energy, a theoretical framework proposed to explain the accelerated expansion of the universe. By investigating the interaction between vector-like dark energy and dark matter, we analyze its effects on the cosmic expansion history and the thermodynamics of the accelerating universe. Our results demonstrate that the presence of interaction significantly influences the evolution of vector-like dark energy, leading to distinct features in its equation of state and energy density. We compare our findings with observational data and highlight the importance of considering interactions in future cosmological studies.

Early dark energy constraints with late-time expansion marginalization

Early dark energy (EDE) is an extension to the ΛCDM model that includes an additional energy density contribution near recombination. The model was proposed to reduce the tension between the measurements of the Hubble constant H 0 from the cosmic microwave background (CMB) and from the local cosmic distance ladder. Some analyses in the recent literature have shown intriguing hints for EDE. However, this model increases the tension in the derived clustering of galaxies (as measured by the so-called S 8 parameter) between CMB and large scale structure (LSS) measurements. This new tension limits the contribution of EDE during recombination, and thus its effect on the Hubble tension. In this work, we investigate whether the inclusion of a general, smooth late-time dark energy modification can increase back the EDE contribution when LSS data is included in the analysis. In order to generalize the late expansion with respect to the ΛCDM model, we substitute the cosmological constant by a late dark energy fluid model with a piecewise constant equation of state w(z) in redshift bins. We show that, when analysing this generalized model with combinations of CMB, LSS and type Ia supernovae data from several experiments no significant changes on S 8 and EDE parameter constraints is found. The contribution to the EDE fraction constraint with late-time expansion marginalization is f EDE = 0.067+0.019 -0.027 using 3 redshift bins, with similar results for 5 and 10 redshift bins. This work shows that in order to solve simultaneously the Hubble and S 8 tensions, one needs a mechanism for increasing the clustering of matter at late times different from a simple change in the background evolution of late dark energy.

An analytical late–Universe approach to the weaving of modern cosmology

ABSTRACT Combining cosmological probes has consolidated the standard cosmological model with per cent precision, but some tensions have recently emerged when certain parameters are estimated from the local or primordial Universe. The origin of this behaviour is still under debate; however, it is crucial to study as many probes as possible to cross-check the results with independent methods and provide additional pieces of information to the cosmological puzzle. In this work, by combining several late-Universe probes (0 &amp;lt; z &amp;lt; 10), namely, Type Ia supernovae, baryon acoustic oscillations, cosmic chronometers, and gamma-ray bursts, we aim to derive cosmological constraints independently of local or early-Universe anchors. To test the standard cosmological model and its various extensions, considering an evolving dark energy equation of state and the curvature as a free parameter, we analyse each probe individually and all their possible permutations. Assuming a flat Lambda cold dark matter (ΛCDM) model, the full combination of probes provides $H_0=67.2^{+3.4}_{-3.2}$ km s−1 Mpc−1 and Ωm = 0.325 ± 0.015 [68 per cent confidence level (C.L.)]. Considering a flat wCDM model, we measure $w_0=-0.91^{+0.07}_{-0.08}$ (68 per cent C.L.), while by relaxing the flatness assumption (ΛCDM model, 95 per cent C.L.) we obtain $\Omega _k=0.125^{+0.167}_{-0.165}$. Finally, we analytically characterize the degeneracy directions and the relative orientation of the probes’ contours. By calculating the figure-of-merit, we quantify the synergies among independent methods, estimate the constraining power of each probe, and identify which provides the best contribution to the inference process. Pending the new cosmological surveys, this study confirms the exigency for new emerging probes in the landscape of modern cosmology.

Astrometric Calibration and Performance of the Dark Energy Spectroscopic Instrument Focal Plane

The Dark Energy Spectroscopic Instrument, consisting of 5020 robotic fiber positioners and associated systems on the Mayall telescope at Kitt Peak, Arizona, is carrying out a survey to measure the spectra of 40 million galaxies and quasars and produce the largest 3D map of the universe to date. The primary science goal is to use baryon acoustic oscillations to measure the expansion history of the universe and the time evolution of dark energy. A key function of the online control system is to position each fiber on a particular target in the focal plane with an accuracy of 11 μm rms 2D. This paper describes the set of software programs used to perform this function along with the methods used to validate their performance.

Dark energy–matter equivalence by the evolution of cosmic equation of state

We consider a model-independent approach to constrain the equivalence redshift, zeq, at which dark energy and the total matter (cold dark matter and baryonic) equate their magnitudes. To this aim, in the context of a homogeneous and isotropic universe, we first consider a generic model where the dark energy contribution is provided by an unknown function of barotropic fluids. Afterwards, we compute the deceleration and jerk parameters, evaluating at our epoch, namely z=0, and at z=zeq. Thus, by Taylor expanding around current time the Hubble rate, luminosity and angular distances, we substitute the theoretical expressions obtained from the aforementioned generic dark energy model, defining a correspondence between quantities evaluated at z=0 and z=zeq. In so doing, we directly fit these quantities by means of current data sets, involving the most recent Pantheon type Ia supernovae, baryonic acoustic oscillation and Hubble rate points. We consider two hierarchies in our fitting procedures and compare our findings in the spatially-flat universe first and including spatial curvature, later. We assess constraints on the overall equation of state of the universe and its first derivative. We compare our results with those predicted by the standard ΛCDM paradigm. Specifically, our findings are in agreement at the 2σ confidence level, assuming a constant dark energy term. However, our analysis does not rule out the possibility of a slight evolution of dark energy, indicating a small deviation from the scenario of a pure cosmological constant. In particular, the possible departures appear consistent with a phenomenological ωCDM model, rather than more complicated dark energy parameterizations.

A new Om(z) diagnostic of dark energy in general relativity theory

In this paper, we propose a new parametrization of dark energy based on the Om(z) diagnostic tool behavior. For this purpose, we investigate a functional form of the Om(z) that predicts the popular dark energy dynamical models, namely phantom and quintessence. We also found the famous cosmological constant for specified values of the model’s parameters. We employed the Markov Chain Monte Carlo approach to constrain the cosmological model using Hubble, Pantheon samples, and BAO datasets. Finally, we used observational constraints to investigate the characteristics of dark energy evolution and compare our findings to cosmological predictions.

Cosmological implications of an interacting model of dark matter &amp; dark energy

In this paper, we have studied an interacting dark energy model. We have assumed the gravitational interaction between the matter fields i.e. between barotropic fluid and the dark energy. The dark energy evolution within the framework of spatially homogeneous and isotropic Friedmann-Robertson-Walker space-time. Therefore, we examine the cosmic evolution from the perspective of interacting scenario by selecting a suitable ansatz for the scale factor resulting from a parametrization of Hubble parameter. The evolution of the cosmological parameters are discussed in some details in the considered interacting scenario by calculating parameters and quantities such as deceleration parameter, energy density, pressure, equation of state (EoS) etc. Also, we have performed some cosmological tests and analysis in support of our obtained interacting model. Finally, we reconstruct the potential of the scalar field and refute the refined swampland conjecture using the equation of state of dark energy and the relationship between energy density and pressure with the scalar field and potential, and then thoroughly describe the findings.

Constraints on late time violations of the equivalence principle in the dark sector

If dark energy is dynamical due to the evolution of a scalar field, then in general it is expected that the scalar is coupled to matter. While couplings to the standard model particles are highly constrained by local experiments, bounds on couplings to dark matter (DM) are only obtained from cosmological observations and they are consequently weaker. It has recently been pointed out that the coupling itself can become non-zero only at the time of dark energy domination, due to the evolution of dark energy itself, leading to a violation of the equivalence principle (EP) in the dark sector at late times. In this paper we study a specific model and show that such late-time violations of the EP in the DM sector are not strongly constrained by the evolution of the cosmological background and by observables in the linear regime (e.g. from the cosmic microwave background radiation), although the model is not preferred over ΛCDM. A study of perturbations in non-linear regime is necessary to constrain late-time violations of the equivalence principle much more strongly.

Fast and accurate predictions of the non-linear matter power spectrum for general models of Dark Energy and Modified Gravity

ABSTRACT We embed linear and non-linear parametrizations of beyond standard cosmological physics in the halo model reaction framework, providing a model-independent prescription for the non-linear matter power spectrum. As an application, we focus on Horndeski theories, using the Effective Field Theory of Dark Energy (EFTofDE) to parametrize linear and quasi-non-linear perturbations. In the non-linear regime, we investigate both a non-linear parametrized post-Friedmann (nPPF) approach as well as a physically motivated and approximate phenomenological model based on the error function (Erf). We compare the parametrized approaches’ predictions of the non-linear matter power spectrum to the exact solutions, as well as state-of-the-art emulators, in an evolving dark energy scenario and two well-studied modified gravity models, finding sub-per cent agreement in the reaction using the Erf model at z ≤ 1 and k ≤ 5 h Mpc−1. This suggests only an additional three free constants, above the background and linear theory parameters, are sufficient to model non-linear, non-standard cosmology in the matter power spectrum at scales down to k ≤ 3h Mpc−1 within $2{{\ \rm per\ cent}}$ accuracy. We implement the parametrizations into ver.2.0 of the ReACT code: ACTio et ReACTio.

Cosmic evolution of holographic dark energy in f(Q,T) gravity

In this paper, we investigate the dynamic evolution of universe in the models of holographic dark energy with [Formula: see text] gravity framework where, [Formula: see text] is the non-metricity scalar and [Formula: see text] is the energy–momentum tensor trace. We have considered [Formula: see text] framework and investigated the evolution of cosmological quantities like energy density, equation of state (EoS) parameter and classical stability parameter with redshift. We parameterize the deceleration parameter and confront the Hubble parameter with the observational data. We investigate for the late-time accelerated expansion of universe and discuss the stability of the model by using adiabatic sound speed squared parameter. A comparison among these derived models suggest that the Renyi holographic dark energy model with GO cutoff satisfies the observational constraint of Planck+SNe+BAO on EoS parameter at present time as compared to other models. Diagnostic tools such as Statefinders and Om diagnostic have been used to classify the dark energy evolution regions.

Theoretical analysis on the Barrow holographic dark energy in the DGP braneworld

This paper further studies the cosmological evolution and geometry diagnosis of Barrow holographic dark energy (BHDE) in the DGP braneworld, specifically, by choosing the interaction between dark energy and dark matter item. [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] are discussed in the case of no interaction and four different interactions, the evolution laws of energy density parameters, deceleration parameters and EOS (equation of state) parameters of Barrow holographic dark energy. The results show that the Barrow holographic dark energy in the DGP braneworld conforms to the current cosmic evolution rule, already achieved the universe main ingredients from matter to the transition of energy, and explains the problem of cosmic acceleration. Further, in order to distinguish between the model and [Formula: see text]CDM model, this paper also geometrically diagnoses the model with the two ways of Statefinder hierarchy and Om[Formula: see text]. From their respective evolution image you can see, these two kinds of diagnosis methods can not only distinguish different from [Formula: see text]CDM model, but also can intuitively reflect the coupling parameters that can significantly affect the dark energy model.

Early or phantom dark energy, self-interacting, extra, or massive neutrinos, primordial magnetic fields, or a curved universe: An exploration of possible solutions to theH0andσ8problems

In this paper we explore the existing tensions in the local cosmological expansion rate, ${H}_{0}$, and amplitude of the clustering of the large-scale structure at $8{h}^{\ensuremath{-}1}\text{ }\text{ }\mathrm{Mpc}$, ${\ensuremath{\sigma}}_{8}$, as well as models that claim to alleviate these tensions. We consider seven models: evolving dark energy ($w\mathrm{CDM}$), extra radiation (${N}_{\mathrm{eff}}$), massive neutrinos, curvature, primordial magnetic fields (PMF), self-interacting neutrino models, and early dark energy (EDE). We test these models against three datasets that span the full range of measurable cosmological epochs, have significant precision, and are well-tested against systematic effects: the Planck 2018 cosmic microwave background data, the Sloan Digital Sky Survey baryon acoustic oscillation scale measurements, and the Pantheon catalog of type Ia supernovae. We use the recent SH0ES ${H}_{0}$ measurement and several measures of ${\ensuremath{\sigma}}_{8}$ (and its related parameter ${S}_{8}={\ensuremath{\sigma}}_{8}\sqrt{{\mathrm{\ensuremath{\Omega}}}_{\mathrm{m}}/0.3}$). We find that four models are above the ``strong'' threshold in Bayesian model selection, $w\mathrm{CDM}$, ${N}_{\mathrm{eff}}$, PMF, and EDE. However, only EDE also relieves the ${H}_{0}$ tension in the full datasets to below $2\ensuremath{\sigma}$. We discuss how the ${S}_{8}/{\ensuremath{\sigma}}_{8}$ tension is reduced in recent observations. However, even when adopting a strong tension dataset, no model alleviates the ${S}_{8}/{\ensuremath{\sigma}}_{8}$ tension, nor does better than $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ in the combined case of both ${H}_{0}$ and ${S}_{8}/{\ensuremath{\sigma}}_{8}$ tensions.

A scaling relation in [C ii]-detected galaxies and its likely application in cosmology

ABSTRACT We identify and investigate a possible correlation between the $\rm {[C\,II]} \,158{-}{\mu }m$ luminosity and linewidth in the $\rm {[C\,II]}$-detected galaxies. Observationally, the strength of the $\rm {[C\,II]}\, 158{-}{\mu }m$ emission line is usually stronger than that of the carbon monoxide (CO) emission line and this $\rm {[C\,II]}$ line has been used as another tracer of the galactic characteristics. Moreover, many $\rm {[C\,II]}$-detected galaxies are identified in z &amp;gt; 4. Motivated by previous studies of the CO luminosity–full width at half-maximum correlation relation (LFR) and the available new $\rm {[C\,II]}$ measurements, we compile samples of the $\rm {[C\,II]}$-detected galaxies in the literature and perform the linear regression analysis. The $\rm {[C\,II]}$ LFR is confirmed at a robust level. We also demonstrate the possible application of the $\rm {[C\,II]}$ LFR by utilizing it on the distance measurement of the high-z galaxy. As a result, we extend the cosmic spatial scale beyond the redshift z of 7. With the outcome of the distance measurement, we constrain the cosmology parameters in the Chevallier–Polarski–Linder model, which considers the evolution of dark energy. Consequently, the uncertainties of the w0 and wa are reduced significantly when the measured distance data of the $\rm {[C\,II]}$-detected galaxies are included in the cosmological parameter constraint, exemplifying the potential of using the $\rm {[C\,II]}$-detected galaxies as a tracer to constrain the cosmological parameters.