SNe Ia Data Sets Research Articles

FLRW cosmology in metric-affine F(R,Q) gravity* *Supported by the Ministry of Science and Higher Education of the Republic of Kazakhstan (AP14870191)

We investigated some Friedmann-Lemaître-Robertson-Walker (FLRW) cosmological models in the context of metric-affine gravity, as proposed in [arXiv: 1205.5266v6]. Here, R and Q are the curvature and nonmetricity scalars using non-special connections, respectively. We obtained the modified field equations using a flat FLRW metric. We then found a connection between the Hubble constant , density parameter , and other model parameters in two different situations involving scalars u and w. Next, we used new observational datasets, such as the cosmic chronometer (CC) Hubble and Pantheon SNe Ia datasets, to determine the optimal model parameter values through a Markov chain Monte Carlo (MCMC) analysis. Using these best-fit values of the model parameters, we discussed the results and behavior of the derived models. Further, we discussed the Akaike information criterion (AIC) and Bayesian information criterion (BIC) for the derived models in the context of the Lambda cold dark matter (ΛCDM). We found that the geometrical sector dark equation of state parameter behaves just like a dark energy candidate. We also found that both models are transit phase models. Model-I approaches the ΛCDM model in the late-time universe, whereas Model-II approaches quintessence scenarios.

Dark energy nature of logarithmic f(R,Lm)-gravity models with observational constraints

This work explores the dark energy nature of logarithmic [Formula: see text]-gravity models with observational constraints, where [Formula: see text] represents the matter Lagrangian for perfect fluid and R is the Ricci-scalar curvature. With a matter Lagrangian [Formula: see text], a flat FLRW space–time metric and an arbitrary function [Formula: see text], where [Formula: see text] is a positive model parameter, we have derived the field equations of this model. By using the Hubble function, we have been able to solve the energy conservation equation and create a relationship between [Formula: see text], [Formula: see text] and [Formula: see text]. Using the most recent two observational datasets as 32 [Formula: see text] and 1048 Pantheon SNe Ia datasets, we conducted MCMC analysis. We have obtained best fit values of model parameters with [Formula: see text] errors and using these values, we have explored the cosmological properties of the model. We have performed om diagnostic analysis for the model and estimated the present age of the universe. Thus our derived model presents a transit phase decelerating to accelerating model without dark energy term [Formula: see text]. We found that the effective equation of state parameter is in the range [Formula: see text] over [Formula: see text] with present value [Formula: see text].

Cosmological constraints on time-varying cosmological terms: A study of FLRW universe models with [formula omitted]CDM cosmology

This paper explores models of the FLRW universe that incorporate a time-varying cosmological term Λ(t). Specifically, we assume a power-law form for the cosmological term as a function of the scale factor: Λ(t)=Λ0a(t)-α, where Λ0 represents the present value of the cosmological term. Then, we derive an exact solution to Einstein’s field equations within the framework of Λ(t)CDM cosmology and determine the best-fit values of the model parameters using the combined H(z) + SNe Ia dataset and MCMC analysis. Moreover, the deceleration parameter demonstrates the accelerating behavior of the universe, highlighting the transition redshift ztr, at which the expansion shifts from deceleration to acceleration, with confidence levels of 1-σ and 2-σ. In addition, we analyze the behavior of the Hubble parameter, jerk parameter, and Om(z) diagnostic. Our analysis leads us to the conclusion that the Λ(t)CDM model is consistent with present-day observations.

Modified f(Q,C) gravity dark energy models with observational constraints

We investigate an isotropic and homogeneous flat dark energy model in [Formula: see text] gravity theory that is linear in non-metricity Q and quadratic in boundary term C as [Formula: see text], where [Formula: see text] is a model parameter. We have solved the field equations in flat Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime geometry and considered a relation in the form of Hubble function in total energy density parameters [Formula: see text], [Formula: see text], and Hubble constant [Formula: see text]. We have compared our results with two observational datasets [Formula: see text] and Pantheon SNe Ia datasets by using MCMC analysis and have obtained the best fit present values of parameters. We have used these best fit values throughout in result analysis and discussion. We have found the equation of state (EoS) parameter as [Formula: see text] over [Formula: see text]. We have also investigated the Om diagnostic function and present age of the universe for these two datasets.

Two forms of dark energy in fractal cosmological model using specific Hubble parameter

The main objective of this article is to study the fractal FRW cosmological model consisting two forms of dark energy. We studied behavior of the universe in a fractal framework using dark energy accommodated in our universe. The solution of field equations are obtained by using Hubble parameter for transit scale factor H(z)=ϵa−δ+λ . We have obtained the best fitting values of the model parameters ϵ,δ and λ by constraining our model with latest Hubble and SNe-Ia data sets . Finally we perform state-finder diagnosis and observe that obtained model close to standard ΛCDM model.

Modified [formula omitted]-gravity string cosmological models with observational constraints

In the current study, we have investigated a modified f(Q)-gravity theory in an anisotropic, locally rotationally symmetric (LRS) Bianchi type-I spacetime universe model. The arbitrary function f(Q)=Q+Λ, where Λ is the “cosmological constant,” and Q is the non-metricity scalar, has been taken into consideration. To obtain the exact solution of the modified field equations, we considered a dusty string fluid matter source and the shear scalar (σ) is proportional to the expansion scalar (θ). 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. And utilizing these best fit values throughout the investigation, the many cosmic phenomena are examined. We have investigated the cosmographic coefficients like H,q,j,s to see if an accelerated dual mode expanding dark energy (DE) model of the universe exists. Our Om diagnostic study shows that our universe model is a quintessence example of a dark energy model. We have also calculated the universe’s present age.

Testing Cosmic Acceleration from the Late-Time Universe

We investigate the accelerated cosmic expansion in the late universe and derive constraints on the values of the cosmic key parameters according to different cosmologies such as ΛCDM, wCDM, and w0waCDM. We select 24 baryon acoustic oscillation (BAO) uncorrelated measurements from the latest galaxy surveys measurements in the range of redshift z∈[0.106,2.33] combined with the Pantheon SNeIa dataset, the latest 33 H(z) measurements using the cosmic chronometers (CCs) method, and the recent Hubble constant value measurement measured by Riess 2022 (R22) as an additional prior. In the ΛCDM framework, the model fit yields Ωm=0.268±0.037 and ΩΛ=0.726±0.023. Combining BAO with Pantheon plus the cosmic chronometers datasets we obtain H0=69.76±1.71 km s−1 Mpc−1 and the sound horizon result is rd=145.88±3.32 Mpc. For the flat wCDM model, we obtain w=−1.001±0.040. For the dynamical evolution of the dark energy equation of state, w0waCDM cosmology, we obtain wa=−0.848±0.180. We apply the Akaike information criterion approach to compare the three models, and see that all cannot be ruled out from the latest observational measurements.

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.

Transit string dark energy models in f(Q) gravity

In this paper, we have investigated an anisotropic cosmological model in [Formula: see text] gravity with string fluid in LRS Bianchi type-I universe. We have considered the arbitrary function [Formula: see text], where [Formula: see text] is model free parameter and [Formula: see text] is the cosmological constant. We have established a relationship between matter energy density parameter [Formula: see text] and dark energy density parameter [Formula: see text] through Hubble function using constant equation of state parameter [Formula: see text]. We have made observational constraint on the model using [Formula: see text]-test with observed Hubble datasets [Formula: see text] and SNe Ia datasets, and obtained the best fit values of cosmological parameters. We have used these best fit values in the result and discussion. We have discussed our result with cosmographic coefficients and found a transit phase dark energy model. Also, we analyzed the Om diagnostic function for anisotropic universe and found that our model is quintessence dark energy model.

Accelerating scenarios of viscous fluid universe in modified f(T) gravity

In this paper, we have investigated the physical behavior of cosmological models in modified teleparallel gravity with a linear function [Formula: see text] where [Formula: see text] and [Formula: see text] are model parameters and [Formula: see text] is the torsion scalar. We have considered a homogeneous and isotropic Friedman universe filled with bulk viscosity fluid. We have solved the field equations for the scale factor [Formula: see text] and found [Formula: see text] where [Formula: see text] and [Formula: see text] and [Formula: see text] is an integrating constant, [Formula: see text] is the equation of state (EoS) for normal matter and [Formula: see text] is generated from bulk viscosity fluid. We have calculated the several cosmological parameters for this scale factor and studied their physical and geometrical behavior along with the observational data sets [Formula: see text] and Union [Formula: see text] compilation of SNe Ia data sets. We have observed that the [Formula: see text] factor reveals the presence of cosmological constant and for [Formula: see text], the acceleration drives by the bulk viscosity of the fluid and it behaves just like dark energy model without cosmological constant. We have studied the effective EoS [Formula: see text] and found [Formula: see text]. We have evaluated the age of the present universe as [Formula: see text] Gyrs. Also, we have studied the nature of deceleration parameter with the signature-flipping point at [Formula: see text] and the present value of deceleration parameter [Formula: see text] is obtained as [Formula: see text], respectively, for both observational datasets.

A non-parametric test of variability of Type Ia supernovae luminosity and CDDR

The first observational evidence for cosmic acceleration appeared from Type Ia supernovae (SNe Type Ia) Hubble diagram from two different groups. However, the empirical treatment of SNe Type Ia and their ability to show cosmic acceleration have been the subject of some debate in the literature. In this work we probe the assumption of redshift-independent absolute magnitude (MB) of SNe along with its correlation with spatial curvature (Ωk0) and cosmic distance duality relation (CDDR) parameter (η(z)). This work is divided into two parts. Firstly, we check the validity of CDDR which relates the luminosity distance (dL) and angular diameter distance (dA) via redshift. We use the Pantheon SNe Ia dataset combined with the H(z) measurements derived from the cosmic chronometers. Further, four different redshift-dependent parametrizations of the distance duality parameter (η(z)) are used. The CDDR is fairly consistent for almost every parametrization within a 2σ confidence level in both flat and a non-flat universe. In the second part, we assume the validity of CDDR and emphasize on the variability of M_B and its correlation with Ωk0. We choose four different redshift-dependent parametrizations of MB. The results indicate no evolution of MB within 2σ confidence level. For all parametrizations, the best fit value of Ωk0 indicates a flat universe at 2σ confidence level. However a mild inclination towards a non flat universe is also observed. We have also examined the dependence of the results on the choice of different priors for H0.

Is there really a Hubble tension?

The heliocentric redshifts (z hel) reported for 150 type Ia supernovae in the Pantheon compilation are significantly discrepant from their corresponding values in the JLA compilation. Both catalogues include corrections to the redshifts and magnitudes of the supernovae to account for the motion of the heliocentric frame relative to the ‘CMB rest frame’, as well as corrections for the directionally coherent bulk motion of local galaxies with respect to this frame. The latter is done employing modelling of peculiar velocities which assume the ΛCDM cosmological model but nevertheless provide evidence for residual bulk flows which are discordant with this model (implying that the observed Universe is in fact anisotropic). Until recently such peculiar velocity corrections in the Pantheon catalogue were made at redshifts exceeding 0.2 although there is no data on which to base such corrections. We study the impact of these vexed issues on the 4.4σ discrepancy between the Hubble constant of H 0 = 67.4 ± 0.5 km s−1 Mpc−1 inferred from observations of CMB anisotropies by Planck assuming ΛCDM, and the measurement of H 0 = 73.5 ± 1.4 km s−1 Mpc−1 by the SH0ES project which extended the local distance ladder using type Ia supernovae. Using the same methodology as the latter study we find that for supernovae whose redshifts are discrepant between Pantheon and JLA with Δz hel > 0.0025, the Pantheon redshifts favour H 0 ≃ 72 km s−1 Mpc−1, while the JLA redshifts favour H 0 ≃ 68 km s−1 Mpc−1. Thus the discrepancies between SNe Ia datasets are sufficient to undermine the claimed ‘Hubble tension’. We further note the systematic variation of H 0 by ∼6–9 km s−1 Mpc−1 across the sky seen in multiple datasets, implying that it cannot be measured locally to better than ∼10% in a model-independent manner.

The models of transit cosmology along with observational constriction in f(Q,T) gravity

Xu et al. (Eur. Phys. J. C 79 (2019) 708) have anticipated the theory of Gravity. The modified study of [Formula: see text] is elucidated here as Cosmological model. In it the action holds a role as a capricious arbitrary function [Formula: see text]. At this juncture [Formula: see text] functions as non-metricity and for matter fluid, [Formula: see text] outlines as energy-momentum tensor. The function [Formula: see text] quadratic in [Formula: see text] and linear in [Formula: see text] as [Formula: see text] has been taken as our research in which [Formula: see text], [Formula: see text] and [Formula: see text] stand as model parameters, induced by [Formula: see text] gravity. A range of cosmological parameters have been attained by us such as in Universe viz. Hubble parameter [Formula: see text], Friedmann–Lemaitre–Robertson–Walker (FLRW), deceleration parameter [Formula: see text], etc. in terms of scale-factor and in terms of redshift [Formula: see text] by confining to the law of energy-conservation. The fittest values of the model parameters have been acquired by us as the observational constrictions on the model, by utilizing the accessible data sets like Hubble data sets [Formula: see text], union [Formula: see text] compilation of SNe Ia data sets and Joint Light Curve Analysis (JLA) data sets. We have applied [Formula: see text]-test formula. The values of various observational parameters have been premeditated by us viz. [Formula: see text], [Formula: see text], [Formula: see text] and state finder parameters [Formula: see text]. They are absolutely very close to the standard cosmological models. It has also been observed by us that the deceleration parameter [Formula: see text] exhibits signature-flipping (transition) point within the range [Formula: see text]. It is observed that it changes its phase from decelerated to accelerated expanding universe with equation of state (EoS) [Formula: see text] for [Formula: see text].

Dark energy nature of viscus universe in f(Q)-gravity with observational constraints

In this study, we have investigated the dark energy behavior of the viscus-fluid in [Formula: see text]-gravity in a flat, isotropic and homogeneous Friedmann–Lemaitre–Robertson–Walker (FLRW) space-time metric. We have considered the linear form of [Formula: see text] function as [Formula: see text] with [Formula: see text] and [Formula: see text] as model parameters. We have solved the field equations for the scale factor [Formula: see text] and found [Formula: see text], where [Formula: see text] and [Formula: see text] and [Formula: see text] is an integrating constant, [Formula: see text] is the EoS for normal matter and [Formula: see text] is generated from bulk-viscus fluid. We have calculated the several cosmological parameters for this scale factor and studied their physical and geometrical behavior along the observational data sets [Formula: see text] and Union [Formula: see text] compilation of SNe Ia data sets. We have observed that the [Formula: see text] factor reveals the presence of cosmological constant and for [Formula: see text], the acceleration drives by the bulk-viscosity of the fluid and it behaves just like dark energy model without cosmological constant. We have studied the effective EoS [Formula: see text] and found [Formula: see text]. We have evaluated the age of the present universe as [Formula: see text] Gyrs. and also, we have studied the nature of deceleration parameter with the signature-flipping point at [Formula: see text] and the present value of deceleration parameter [Formula: see text] is obtained as [Formula: see text].

Joint analysis of EDGES 21-cm line observations with standard candles and rulers in ΛCDM and non-adiabatic gCg models

A decomposed generalised Chaplygin gas (gCg) with energy flux from dark energy to dark matter, represented by a negative value for the gas parameter α , is shown to alleviate the tension between EDGES data and the cosmological standard model. Using EDGES data and employing a Bayesian statistical analysis, the agreement with the standard model is only marginal. However, if α is negative enough the gCg fits remarkably well the data, even in combination with SNe Ia datasets. On the other hand, when the CMB and BAO acoustic scales are included the preferred value for α is near zero, implying that a small deviation from Λ CDM is predicted.

Testing the Cosmic Distance Duality Relation with the Latest Strong Gravitational Lensing and Type Ia Supernovae

Abstract We perform a model-independent and comprehensive test on the cosmic distance duality relation (CDDR) by combining the latest observations of strong gravitational lensing (SGL) including a total of 161 well-measured systems from several surveys and observations of Type Ia supernovae (SNe Ia), i.e., the joint light-curve analysis of SNe Ia and the Pantheon SNe Ia. We parameterize the CDDR in the form of , and also consider general lens mass models including the dependence on the lens redshift and surface mass density. First, we update tests using the new SGL and the two SNe Ia data sets for the singular isothermal sphere model. The constraint results suggest a moderate tension with the CDDR using the Pantheon SN Ia with a slightly negative η 0. We find that η 0 deviates significantly from the CDDR at more than the 3σ level if the lens mass model depends on redshift. Supplementary tests show that the error from aperture correction and the parameterization method of the CDDR can hardly justify the deviation. Several of the models investigated show some evidence for deviations from the CDDR. However, there is a significant scatter in the inferred level of the CDDR violation, depending on the model describing the population of strong lenses. This variance is too large for us to conclude yet that the CDDR is violated and needs further investigation and future measurements to be verified.

Cosmological aspects of a hyperbolic solution in [formula omitted] gravity

This article deals with a cosmological scenario in f(R,T) gravity for a flat FLRW model of the universe. We consider the f(R,T) function as f(R)+f(T) which starts with a quadratic correction of the geometric term f(R) having structure f(R)=R+αR2, and a linear matter term f(T)=2λT. To achieve the solution of the gravitational field equations in the f(R,T) formalism, we take the form of a geometrical parameter, i.e. scale factor a(t)=sinh1n(βt) (Chawla et al., 2013), where β and n are model parameters. An eternal acceleration can be predicted by the model for 0<n<1, while the cosmic transition from the early decelerated phase to the present accelerated epoch can be anticipated for n≥1. The obtained model facilitates the formation of structure in the Universe according to the Jeans instability condition as our model transits from radiation dominated era to matter dominated era. We study the varying role of the equation of state parameter ω. We analyze our model by studying the behavior of the scalar field and discuss the energy conditions on our achieved solution. We examine the validity of our model via Jerk parameter, Om diagnostic, Velocity of sound and Statefinder diagnostic tools. We investigate the constraints on the model parameter n and H0 (Hubble constant) using some observational datasets: SNeIa dataset, H(z) (Hubble parameter) dataset, BAO (Baryon Acoustic Oscillation data) and their combinations as joint observational datasets H(z) + SNeIa and H(z) + SNeIa + BAO. It is testified that the present study is well consistent with these observations. We also perform some cosmological tests and a detailed discussion of the model.

Traversable geometric dark energy wormholes constrained by astrophysical observations

In this letter, we investigate the traversable wormholes in the holographic dark energy (HDE) model constrained by the modern astronomical observations. First of all, we constrain the HDE model by adopting different data-sets, explore the cosmological background evolution of the HDE model, and find that the HDE model will be fitting better than the Ricci dark energy (RDE) model for the same SNe Ia data-sets by using the the so-called Akaike Information Criterions (AIC) and Bayesian Information Criterions (BIC) . Furthermore, we discover that if taking the SNe Ia data-sets, the wormholes will appear (open) when the redshift $z<0.027$. Subsequently, several specific traversable wormhole solutions are obtained, including the constant redshift function, traceless stress energy tensor, a special choice for the shape function as well as the case of isotropic pressure. Except for the first case, it is very necessary to theoretically construct the traversable wormholes by matching the exterior geometries to the interior geometries. Naturally, one can easily find that the dimensions of the wormholes for the left cases are substantially finite.

A COMPREHENSIVE INVESTIGATION ON THE SLOWING DOWN OF COSMIC ACCELERATION

ABSTRACT Shafieloo et al. first proposed the possibility that the current cosmic acceleration (CA) is slowing down. However, this is rather counterintuitive because a slowing down CA cannot be accommodated in most mainstream cosmological models. In this work, by exploring the evolutionary trajectories of the dark energy equation of state w(z) and deceleration parameter q(z), we present a comprehensive investigation on the slowing down of CA from both the theoretical and the observational sides. For the theoretical side, we study the impact of different w(z) using six parametrization models, and then we discuss the effects of spatial curvature. For the observational side, we investigate the effects of different type Ia supernovae (SNe Ia), baryon acoustic oscillation (BAO), and cosmic microwave background (CMB) data. We find that (1) the evolution of CA is insensitive to the specific form of w ( z ) ; in contrast, a non-flat universe favors a slowing down CA more than a flat universe. (2) SNLS3 SNe Ia data sets favor a slowing down CA at a 1σ confidence level, while JLA SNe Ia samples prefer an eternal CA; in contrast, the effects of different BAO data are negligible. (3) Compared with CMB distance prior data, full CMB data favor a slowing down CA more. (4) Due to the low significance, the slowing down of CA is still a theoretical possibility that cannot be confirmed by the current observations.

Interacting scalar tensor cosmology in light of SNeIa, CMB, BAO and OHD observational data sets

In this work, an interacting chameleon-like scalar field scenario, by considering SNeIa, CMB, BAO, and OHD data sets, is investigated. In fact, the investigation is realized by introducing an ansatz for the effective dark energy equation of state, which mimics the behavior of chameleon-like models. Based on this assumption, some cosmological parameters, including the Hubble, deceleration, and coincidence parameters, in such a mechanism are analyzed. It is realized that, to estimate the free parameters of a theoretical model, by regarding the systematic errors it is better that the whole of the above observational data sets would be considered. In fact, if one considers SNeIa, CMB, and BAO, but disregards OHD, it maybe leads to different results. Also, to get a better overlap between the contours with the constraint $$\chi _\mathrm{{m}}^2\le 1$$ , the $$\chi _\mathrm{{T}}^2$$ function could be re-weighted. The relative probability functions are plotted for marginalized likelihood $$\mathscr {L} (\Omega _\mathrm{{m0}} ,\omega _1, \beta )$$ according to the two dimensional confidence levels 68.3, 90, and $$95.4\,\%$$ . Meanwhile, the value of the free parameters which maximize the marginalized likelihoods using the above confidence levels are obtained. In addition, based on these calculations the minimum value of $$\chi ^2$$ based on the free parameters of the ansatz for the effective dark energy equation of state is achieved.