Dark Energy Models Research Articles

A description of classical and quantum cosmology for a single scalar field torsion gravity

In the background of homogeneous and isotropic flat FLRW spacetime, both classical and quantum cosmologies have been studied for teleparallel dark energy (DE) model. Using Noether symmetry analysis, not only the symmetry vector but also the coupling function in the Lagrangian and the potential of the scalar field have been determined. Also symmetry analysis identifies a cyclic variable in the Lagrangian along the symmetry vector and as a result the Lagrangian simplifies to a great extent so that classical solution is obtained. Subsequently, in quantum cosmology Wheeler–DeWitt (WD) equation has been constructed and the quantum version of the conserved momenta corresponding to Noether symmetry identifies the periodic part of the wave function of the universe and as a result the WD equation becomes solvable. Finally, quantum description shows finite nonzero probability at the classical big bang singularity.

Possible combinations of early and late time cosmologies through BAO scales

The theoretical scenarios of early universe and late time accelerated expansion constitute an open problem in cosmology. Relative Baryon Acoustic Oscillation (BAO) scales measured by 6dFGS, mathrm SDSS+2dFGRS, BOSS DR11 Lyalpha and BOSS DR11 QSO Lyalpha are used to investigate the parameter spaces of combinations of pre-recombination physics and late time cosmology. For pre-recombination physics we fix mathrm N_{eff}=3 and 4 and incorporate an Early Dark Energy (EDE) component. For late time cosmologies we consider curved Lambda CDM model, Dynamical Dark Energy (DDE) model with CPL parameterisation (omega _0,omega _1) of equation of state, Coupled Dark Energy (CDE) model with constant coupling and curved DGP brane-world scenario. Combination of a curved Lambda CDM (Omega _{textrm{k}}Lambda CDM) model with mathrm N_{eff}-EDE cosmology is found to be possible. For DDE, the relative BAO scales are achievable through omega _1 preferring the region omega _1< 0. For mathrm N_{eff}-EDE-CDE, the BAO scales are generated for both dark energy-dark matter and dark matter-dark energy conversion, however with exceptionally large value of dark energy density parameter and constant equation of state with omega _0 > -1. Curved DGP cosmology (Omega _textrm{k}DGP) is found to join with N_{textrm{eff}}-EDE cosmology through curvature parameter Omega _{mathrm{k(0)}}in [-0.002, -0.1] and cross-over parameter Omega _{mathrm{r_c}} in [0.08, 0.45]. Cosmic ages are calculated for the derived parameters of Omega _{textrm{k}}Lambda CDM, flat DDE and Omega _{textrm{k}}DGP models and compared with the ages of few globular clusters available in literature. Curved cosmologies are found to be promising.

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.

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.

Dark Energy Cosmological Models in Lyra Geometry for Bianchi-I Space Time

We construct cosmological models for dark energy based on Lyra’s geometry for the Bianchi-I space-time to understand the evolution of the universe. The specific choice of the deceleration parameter q=-frac{alpha _1}{t^2}+alpha _2-1 is used to determine the exact solutions of the field equations in Lyra geometry. The parameter alpha _1 has a dimension equal to the square of time. Further, we have discussed two cosmological models depending on the parameter alpha _2. Several physical parameters are obtained and the results in both the models are analyzed and presented graphically for the analysis of the results.

Growth of matter perturbations in some parametrization of dark energy models

In this work, we investigate the growth of matter perturbations in some known parameterizations of dark energy (DE) models i.e, CPL, JBP, BA, and a new parameterization of DE introduced in this study. We examine the growth of perturbations in the linear region by assuming the possibility of perturbations in DE. Then, we follow an overall likelihood analysis to put the same constraints on models using background and growth rate data, and we conclude that the reviewed DE parameterizations are compatible with the observational data at both background and perturbation levels. Furthermore, we find that DE parameterizations are comparable with each other, and with the Lambda CDM model. In particular, we obtain the following significant results: (i) the growth rate of matter perturbations in the homogeneous DE case is smaller than its value in the clustered case for CPL and BA models, while it is the opposite for JBP and the new model. (ii) The growth rate of matter perturbations related to the CPL and BA models have very similar behavior for both homogeneous and clustered DE cases at all redshift z. This is also true for JBP and the new model. (iii) We show that the growth rate of matter perturbations relevant to the models is lower than its value in the Lambda CDM model at low redshifts, and at high redshifts, the difference between them is insignificant. Finally, using AIC and BIC analysis, we conclude that the selection of a model that has better compatible with the observational data depends on the background and perturbation data.

Compact stars with dark energy in general relativity and modified gravity

We investigate realistic models of compact objects, focusing on neutron and strange stars, composed by dense matter and dark energy in the form of a simple fluid or scalar field interacting with matter. For the dark energy component, we use equations of state compatible with cosmological observations. This requirement strongly constrains possible deviations from the simple Λ-Cold Dark-Matter model with EoS pd=−ρd at least for small densities of the dark component. But we can propose that the density of dark energy interacting with matter can reach large values in relativistic stars and affects the star parameters such as the mass and radius. Simple models of dark energy are considered. Then we investigated possible effects from modified gravity choosing to study the R2 model combined with dark energy. Finally, the case of dark energy as scalar field non-minimally interacting with gravity is considered.

The Time Evolution of Mutual Information between Disjoint Regions in the Universe.

We study the time evolution of mutual information between mass distributions in spatially separated but casually connected regions in an expanding universe. The evolution of mutual information is primarily determined by the configuration entropy rate, which depends on the dynamics of the expansion and growth of density perturbations. The joint entropy between distributions from the two regions plays a negligible role in such evolution. Mutual information decreases with time in a matter-dominated universe, whereas it stays constant in a Λ-dominated universe. The ΛCDM model and some other models of dark energy predict a minimum in mutual information beyond which dark energy dominates the dynamics of the universe. Mutual information may have deeper connections to the dark energy and accelerated expansion of the universe.

H i intensity mapping with MeerKAT: forecast for delay power spectrum measurement using interferometer mode

ABSTRACT Neutral hydrogen (H i) intensity-mapping (IM) surveys are considered a promising tool for investigating the expansion history of the Universe. In this work, we explore the potential of MeerKAT H i IM observations in interferometer mode to estimate the power spectrum and constrain cosmological parameters within typical dark-energy models. We employ an approach called the ‘delay spectrum’, which allows us to separate the weak H i signal from foreground contamination in the frequency domain. Our findings indicate that the choice of survey fields significantly impacts the fractional errors on the power spectrum (ΔP/P) within a limited observational time of 10 h. As the integration time increases from 10–10 000 h, ΔP/P progressively decreases until cosmic variance begins to dominate. For a total observation time of 10 000 h, the lowest ΔP/P at low k can be achieved by tracking 100 points for the MeerKAT L band (900–1200 MHz) and 10 points for the MeerKAT UHF band (580–1000 MHz). Next, we assess the performance of H i IM in constraining typical dark-energy models. We find that the MeerKAT H i IM survey in interferometer mode demonstrates limited capability in constraining the dark-energy equation of state, even when combined with Planck data. Our analysis serves as a valuable guide for future MeerKAT observations in H i IM surveys.

New agegraphic dark energy model with bulk viscosity

New agegraphic dark energy (NADE) model with bulk viscosity is proposed by assuming that the universe is composed of the NADE and dark matter, and both the dark components have a bulk viscosity. At the matter-dominated epoch, the density parameter and the equation of state (EoS) of the viscous NADE are given by [Formula: see text] and [Formula: see text], respectively, where [Formula: see text] and [Formula: see text] are viscosity parameters. In the late time [Formula: see text], the NADE dominates [Formula: see text] and [Formula: see text]. Owing to the special analytic features at the matter-dominated epoch for the viscous NADE model, the initial condition [Formula: see text] at [Formula: see text] is used to solve the differential equation of [Formula: see text], and the other physical quantities can be obtained correspondingly. We also find that the viscosity of dark matter affects the current density and the start time of the cosmic acceleration. However, in the late time [Formula: see text] only depends on the viscosity of the dark energy. Furthermore, we investigate the viscous NADE model by means of statefinder diagnostic. The viscosity of dark matter significantly affects the evolution of the statefinder parameters. Therefore, the bulk viscosity plays a significant role in the cosmological evolution.

Constraining the spatial curvature with cosmic expansion history in a cosmological model with a non-standard sound horizon

Spatial curvature is one of the most fundamental parameters in our current concordance flat ΛCDM model of the Universe. The goal of this work is to investigate how the constraint on the spatial curvature is affected by an assumption on the sound horizon scale. The sound horizon is an essential quantity to use the standard ruler from the Cosmic Microwave Background (CMB) and Baryon Acoustic Oscillations (BAOs). As an example, we study the curvature constraint in an axion-like Early Dark Energy (EDE) model in light of recent cosmological datasets from Planck, the South Pole Telescope (SPT), and the Atacama Cosmology Telescope (ACT), as well as BAO data compiled in Sloan Digital Sky Survey Data Release 16. We find that, independent of the CMB datasets, the EDE model parameters are constrained only by the CMB power spectra as precisely and consistently as the flat case in previous work, even with the spatial curvature. We also demonstrate that combining CMB with BAO is extremely powerful to constrain the curvature parameter even with a reduction of the sound-horizon scale in an EDE model, resulting in Ω K = -0.0058± 0.0031 in the case of ACT+BAO after marginalizing over the parameters of the EDE model. This constraint is as competitive as the Planck+BAO result in a ΛCDM model, Ω K = -0.0001± 0.0018.

Gravitational lensing: dark energy models in non-flat FRW Universe

In a non-flat FRW model, we have considered our Universe to be filled with non-interacting dark energy and dark matter. For the dark energy models, we have assumed Tachyonic Field (TF), Generalized Cosmic Chaplygin Gas (GCCG), New Variable Modified Chaplygin Gas (NVMCG), Modified Chaplygin–Jacobi Gas (MCJG), and Modified Chaplygin–Abel Gas (MCAG). We then analyzed these dark energy models with varying cosmological parameters in their optical depth behaviour and presented our result graphically. Later on, a comparison of our findings of the corresponding models in flat and non-flat Universe with the Lambda CDM model has also been presented.

LRS Bianchi Type-II Cosmological Model with New Holographic Dark Energy in General Relativity with Quintessence

Abstract: In this paper, we investigate the LRS Bianchi Type-II universe filled with pressureless cold dark matter and non-interacting new holographic dark energy in the framework of general relativity. To obtain the deterministic solution of Einstein’s field equations, we assume the scalar of expansion to be proportional to the eigenvalue of the shear tensor. The expressions for some parameters of cosmological importance are obtained and physical and geometrical properties of the model are discussed. The correspondence between the new holographic dark energy and quintessence scalar field model is also established by comparing their equations of state and densities. Our results are consistent with the recent cosmological observations. Keywords: Bianchi type-II, Holographic principle, Dark energy, Quintessence.

Conformally and disformally coupled vector field models of dark energy

Conformally and disformally coupled vector field models of dark energy

Kaniadakis agegraphic dark energy

In this manuscript, we present a novel dark energy scenario based on Kaniadakis entropy, which is a generalization of Boltzmann–Gibbs entropy that arises from relativistic statistical theory and is characterized by a parameter K which quantifies the deviations from standard expressions, and we use the age of the Universe as infrared cutoff. The cosmological characteristics of the proposed dark energy model, as well as the evolution of the cosmos filled with pressure-free matter and the ensuing dark energy candidates, are investigated. The interaction as well as non-interaction among the two sectors will also be considered. The differential equation for the dark energy density parameter, including the expression of the equation of state and deceleration parameters, are derived. The analysis of deceleration parameter clearly shows the universe to transit from decelerated to accelerated phase around z≈0.6. The most recent 30 H(z) data samples and the 580 Union 2.1 SNIa data set were also used to limit the theoretical results. The squared sound speed is also plotted against redshift z to check the stability behavior of the model for both the cases.

LRS Bianchi Type-I String Cosmological Models in f Q Gravity

In the current study, we studied a f Q -gravitational, anisotropic, locally rotationally symmetric (LRS), Bianchi type-I spacetime universe. We have adopted the freely chosen function f Q = Q + α Q , where α is a model-free parameter. We assumed that the universe is filled with dusty string fluid and that the shear scalar ( σ ) and the expansion scalar ( θ ) are proportional to each other in order to solve field equations for the average Hubble parameter ( H ). The resultant Hubble function has been fitted with observational datasets H z and SNe Ia datasets of apparent magnitude m z in order to obtain the best fit values for the cosmological parameters. Utilizing these best fit values throughout the analysis, many cosmic phenomena are examined. We have investigated cosmographic coefficients such as H , q , j , a n d s to see if an accelerated transit phase dark energy model of the cosmos exists. Also, we have classified the dark energy models that are explored using Om diagnostic analysis; our universe model is a quintessential dark energy model. The age of the universe as it exists right now has been roughly calculated by the model.

Cosmo-dynamics of dark energy models resulting from a parametrization of H in f(Q, T) gravity

Cosmo-dynamics of dark energy models resulting from a parametrization of H in f(Q, T) gravity

Tachyonic dark energy in general relativity and teleparallel frameworks

This paper is intended to review the consequences of assuming tachyon scalar field as a candidate for dark energy from dynamical system technique and observational cosmology point of views. In the contexts of general relativity and teleparallel gravity, a variety of non-minimally coupled tachyon fields have been taken into consideration. These models provide us subclasses of scalar-tensor and scalar-torsion theories. This review covers the tachyonic chameleon, the non-minimally coupled tachyon field to the Gauss–Bonnet invariant and the tachyonic teleparallel dark energy models. Type Ia supernovae and baryonic acoustic oscillations datasets are the observational data that have been used to constrain the model parameters.

Observational Constraining Study of New Deceleration Parameters in FRW Universe

AbstractIn the current paper, a dark energy (DE) model reconstructed from the well‐motivated deceleration parameter (DP) is analyzed. A flat FRW Universe filled with radiation, dark matter (DM), and dark energy fluids is considered. The free parameters are constrained using measurements from Supernovae, Hubble, Gamma Ray Bursts, Quasars, and Baryon acoustic Oscillations. The model under study is found to be very supported by observation with respect to ΛCDM since . Besides, a cosmographic analysis is performed showing that the reconstructed model behaves similarly as ΛCDM does. Finally, a diagnostic analysis is performed reporting that the studied model behaves quintessence type at a late time.