CDM Model Research Articles

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.

Exploring the possibility of interacting quintessence model as an alternative to the $$\Lambda $$CDM model

Exploring the possibility of interacting quintessence model as an alternative to the $$\Lambda $$CDM model

Complex multidimensional fuzzy models of monitoring and rehabilitation processes for patients with uneven observation interval

Purpose. The work is devoted to the development of mathematical models and methods of fuzzy modeling of multidimensional time series (CDM) for the processes of monitoring and rehabilitation of patients with uneven intervals between observations. CDM takes into account the system properties and unity of the components of the studied processes by forming combined/complex multidimensional fuzzy models (CFTS). Methodology. The implementation of CFTS models takes into account the intrinsic features of these processes. The peculiarity of CFTS is that uneven intervals of observations, as well as other parameters, reflect the systemic unity of the controlled process, rather than the externally established form of observations, regulations. SFTS generalize models of multidimensional fuzzy time series of order n with m input parameters and one output parameter, i.e., different components may have different order of prehistory n, individual parameters may be measured by different types of data and forms of uncertainty. Findings. The article presents a comprehensive improved structure of CFTS models of order n with m input and one output parameter, which is adapted to the properties of monitoring and rehabilitation processes with uneven observation intervals. To form the SFTS, a step-by-step procedure is proposed that allows forming the composition of parameters. An example of modeling the process of rehabilitation of patients with diabetes based on the SFTS is presented, which demonstrates its differences and effectiveness. The comparative properties of SFTS and FTS models are presented. Originality. The development of CDM models and methods for monitoring and rehabilitation processes at uneven intervals is obtained, and complex SFTS models are formed. The difference between the SFTS is that the component of uneven intervals is represented as other multiparameters m, which can have different order of prehistory n, as well as different types of data and forms of uncertainty. A procedure for the step-by-step formation of the composition of the parameters of SFTS models is proposed. Practical value. SFTS models ensure the implementation of multiparameter monitoring and rehabilitation processes with uneven observation intervals, simplify the structure and reduce the number of relational relations, and eliminate the conflict of product rules in case of ensuring the required accuracy of results. The example of modeling the rehabilitation process for diabetics with such parameters as sugar level, interval between observations, and blood pressure has confirmed the reliability and practical significance of CFTS models.

Anisotropic dark energy models in f(R,Lm)-gravity

In this investigation, we have observed an anisotropic Bianchi type-I dark energy universe model in [Formula: see text] gravity with observational constraints, where [Formula: see text] is an arbitrary function of Ricci-scalar curvature [Formula: see text] and matter Lagrangian [Formula: see text]. For our investigation, we have considered a specific form of this function as [Formula: see text] with [Formula: see text] as model free parameters and [Formula: see text] is the “cosmological constant”. We have solved the field equations analytically and established a relationship between energy parameters [Formula: see text] and [Formula: see text] and obtained Hubble function [Formula: see text] in terms of redshift [Formula: see text]. We have compared this Hubble function with two observational datasets Union 2.1 plus bined and [Formula: see text] for obtaining the best fit values of model parameters and energy parameters, by applying [Formula: see text]-test. We have analyzed and discussed the results using these best fit values throughout the paper. We have found a accelerating transit phase phantom dark energy model which tends to [Formula: see text]CDM model at late-time universe.

A bias using the ages of the oldest astrophysical objects to address the Hubble tension

Recently different cosmological measurements have shown a tension in the value of the Hubble constant, H_0. Assuming the Lambda CDM model, the Planck satellite mission has inferred the Hubble constant from the cosmic microwave background (CMB) anisotropies to be H_0 = 67.4 pm 0.5 , text {km} , text {s}^{-1} , text {Mpc}^{-1}. On the other hand, low redshift measurements such as those using Cepheid variables and supernovae Type Ia (SNIa) have obtained a significantly larger value. For instance, Riess et al. reported H_0 = 73.04 pm 1.04 , text {km} , text {s}^{-1} , text {Mpc}^{-1}, which is 5sigma apart of the prediction from Planck observations. This tension is a major problem in cosmology nowadays, and it is not clear yet if it comes from systematic effects or new physics. The use of new methods to infer the Hubble constant is therefore essential to shed light on this matter. In this paper, we discuss using the ages of the oldest astrophysical objects (OAO) to probe the Hubble tension. We show that, although this data can provide additional information, the method can also artificially introduce a tension. Reanalyzing the ages of 114 OAO, we obtain that the constraint in the Hubble constant goes from slightly disfavoring local measurements to favoring them.

Constraints on the local cosmic void from the Pantheon supernovae data

In principle, the local cosmic void can be simply modeled by the spherically symmetric Lemaitre–Tolman–Bondi (LTB) metric. In practice, the real local cosmic void is probably not spherically symmetric. In this paper, to reconstruct a more realistic profile of the local cosmic void, we divide it into several segments. Each segment with certain solid angle is modeled by its own LTB metric. Meanwhile, we divide the 1048 type Ia supernovae (SNIa) of the Pantheon Survey into corresponding subsets according to their distribution in the galactic coordinate system. Obviously, each SNIa subset can only be used to reconstruct the profile of one segment. Finally, we can patch together an irregular profile for the local cosmic void with the whole Pantheon sample. Note that, the paucity of each data subset lead us to focus on the inner part of each void segment and assume that the half radii of the void segments are sufficient to constrain the whole segment. We find that, despite 2sigma signals of anisotropy limited to the depth of the void segments, the constraints on every void segment are consistent with Lambda CDM model at 95% CL. Moreover, our constraints are too weak to challenge the cosmic homogeneity and isotropy.

Very High Cycle Fatigue Life Prediction of SLM AlSi10Mg Based on CDM and SVR Models

A novel fatigue evolution model considering the effect of defect size and additive manufacturing building direction based on the theories of continuum damage mechanics and its numerical implementation in ABAQUS is proposed in this paper. First, the constitutive model, fatigue damage evolution model and their parameter calibration methods are presented. Second, using the ABAQUS platform, the proposed model is implemented with user-defined subroutines. After that, based on the proposed model and its numerical implementation, the fatigue life of additively manufactured AlSi10Mg is predicted and its applicability is verified through experimental results. Finally, a support vector regression model is established to predict the fatigue life, and its results are compared to those of the numerical finite element method. The results show that the support vector regression model makes better predictions than the finite element method.

Signature flip in deceleration parameter: a thermodynamic phase transition?

Using the Hayward–Kodama temperature for the apparent horizon, it is found that matter content in the Universe is not thermodynamically stable, and the entry to the late accelerated expansion is actually a second order phase transition. The cosmological model used for the purpose is one that imitates the varLambda CDM model, the favoured model for the present Universe.

A viable f(R) gravity model without oscillations in the effective dark energy

In this study, we propose a reparametrization of a specific viable [Formula: see text] gravity model to represent it as a perturbation of the [Formula: see text]CDM model. The [Formula: see text] gravity model under consideration includes two parameters, [Formula: see text] and [Formula: see text], which control how close the proposed model can be to [Formula: see text]CDM, allowing for arbitrary proximity. Furthermore, it is shown that the Hu–Sawicki (HS) model is a limiting case of this reparametrized model. Following the existing literature, we also derive an analytical approximation for the expansion rate [Formula: see text], which shows an excellent agreement between this analytical approximation and the numerical solution over a wide range of redshifts for realistic values of the deviation parameter [Formula: see text]. By appropriately selecting values for the model parameters, we plot the cosmological parameters [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text], as well as the statefinder quantities [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]. We find that their present values (at [Formula: see text]) are consistent with the observations from Planck 2018 and the values predicted by the [Formula: see text]CDM model. It is important to note that the examined cosmological and statefinder parameters do not exhibit significant oscillations of effective dark energy, which could lead to singular and unphysical solutions at high redshifts. This anomalous behavior has been avoided here by utilizing the approximate analytical solution for [Formula: see text]. Additionally, we conduct a detailed analysis of the evolution of matter density perturbations within the introduced [Formula: see text] gravity model. The results demonstrate that this viable [Formula: see text] gravity model is practically indistinguishable from the [Formula: see text]CDM model at the background level.

A new parametrization for bulk viscosity cosmology as extension of the $$\Lambda $$CDM model

A new parametrization for bulk viscosity cosmology as extension of the $$\Lambda $$CDM model

Unified inflation and dark energy with accelerated particle holographic model

In this paper and in the follows of the holographic approach to describe the primary acceleration and the late-time acceleration eras, we have considered and unified inflation and dark energy while accelerated particle holographic (APHM) density is used (Fazlollahi in Chin Phys C 47:035101, 2023). As discussed, establishing holographic model for constant roll inflation during the very early Universe leads one to explicit form of Hubble parameter which satisfies inflationary era. The validity of such holographic constant roll inflation with respect to the Planck data puts a certain bound on the infrared cut-off at the time of horizon crossing. Beside the mere inflation, the Hubble parameter gives explicit form for density of accelerated particle holographic model. It is shown such density due to inflationary bound condition on infrared cut-off could present late-time acceleration epoch. Consequently, inflation and late time expansion era unified in unique infrared cut-off model. Moreover, such corresponding fractional density gives more matter regimes during matter era. Nevertheless, studying matter structure formation during matter era reveals the model is not in conflict with {Lambda }CDM model.

Dynamic dark energy from the local limit of nonlocal gravity

Nonlocal gravity (NLG), a classical extension of Einstein’s theory of gravitation, has been studied mainly in linearized form. In particular, nonlinearities have thus far prevented the treatment of cosmological models in NLG. In this essay, we discuss the local limit of NLG and apply this limit to the expanding homogenous and isotropic universe. The theory only allows spatially flat cosmological models; furthermore, de Sitter spacetime is forbidden. The components of the model will have different dynamics with respect to cosmic time as compared to the standard [Formula: see text]CDM model; specifically, instead of the cosmological constant, the modified flat model of cosmology involves a dynamic dark energy component in order to account for the accelerated phase of the expansion of the universe.

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.

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.

Cosmological perturbations engendered by discrete relativistic species

Within the extension of the varLambda CDM model, allowing for the presence of neutrinos or warm dark matter, we develop the analytical cosmological perturbation theory. It covers all spatial scales where the weak gravitational field regime represents a valid approximation. Discrete particles – the sources of the inhomogeneous gravitational field – may be relativistic. Similarly to the previously investigated case of nonrelativistic matter, the Yukawa interaction range is naturally incorporated into the first-order scalar metric corrections.

JWST early Universe observations and ΛCDM cosmology

ABSTRACT Deep space observations of the JWST have revealed that the structure and masses of very early Universe galaxies at high redshifts ($z\sim15$), existing at $\sim$0.3 Gyr after the Big Bang, may be as evolved as the galaxies in existence for $\sim10$ Gyr. The JWST findings are thus in strong tension with the ${\rm{\Lambda}}$CDM cosmological model. While tired light (TL) models have been shown to comply with the JWST angular galaxy size data, they cannot satisfactorily explain isotropy of the cosmic microwave background (CMB) observations or fit the supernovae distance modulus versus redshift data well. We have developed hybrid models that include the tired light concept in the expanding universe. The hybrid ${\rm{\Lambda}}$CDM model fits the supernovae type 1a data well but not the JWST observations. We present a model with covarying coupling constants (CCC), starting from the modified FLRW metric and resulting Einstein and Friedmann equations, and a CCC + TL hybrid model. They fit the Pantheon + data admirably, and the CCC + TL model is compliant with the JWST observations. It stretches the age of the Universe to 26.7 Gyr with 5.8 Gyr at $z = 10$ and 3.5 Gyr at $z = 20$, giving enough time to form massive galaxies. It thus resolves the ‘impossible early galaxy’ problem without requiring the existence of primordial black hole seeds or modified power spectrum, rapid formation of massive population III stars, and super Eddington accretion rates. One could infer the CCC model as an extension of the ${\rm{\Lambda}}$CDM model with a dynamic cosmological constant.

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.

Dynamical system approach of interacting dark energy models with minimally coupled scalar field

We investigated the stability condition of [Formula: see text] gravity theory with interacting and noninteracting models by using dynamical system. We assume the [Formula: see text] function as [Formula: see text], where [Formula: see text] is the free parameter. We evaluated the critical points for this model and examined the stability behavior. We found two stable critical points for interacting model. The phase plots for this system are examined and the physical interpretation is discussed. We illustrate all the cosmological parameters such as [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] at each fixed point and compare the parameters with observational values. Further, we assume hybrid scale factor and the equation of redshift and time is [Formula: see text]. We transform all the parameters in terms of redshift by using this equation and examine the behavior of these parameters. Our model represents the accelerated expansion of the universe. The energy conditions are examined in terms of redshift and strong energy conditions are not satisfied for the model. We also find the statefinder parameters [Formula: see text] in terms of z and discuss the nature of r–s and r–q plane. For both pairs [Formula: see text] and [Formula: see text] our model represents the [Formula: see text]CDM model. Hence, we determine that our [Formula: see text] model is stable and it satisfies all the observational values.

Dark energy nature in logarithmic f(R,T) cosmology

This research paper is an investigation of dark energy nature of logarithmic [Formula: see text]-gravity cosmology in a flat FLRW space–time universe. We have derived modified Einstein’s field equations for the function [Formula: see text] where [Formula: see text] is the Ricci scalar curvature, [Formula: see text] is the trace of the stress energy momentum tensor, and [Formula: see text] is a model parameter. We have solved field equations in the form of two fluid scenarios as perfect fluid and dark fluid, where dark fluid term is derived in the form of perfect fluid source. We have made an observational constraint on the cosmological parameters [Formula: see text] and [Formula: see text] using [Formula: see text] test with observational datasets like Pantheon sample of SNe Ia and [Formula: see text]. With these constraints, we have discussed our model with deceleration parameter [Formula: see text], energy parameters [Formula: see text], EoS parameter [Formula: see text], etc. Also, we have done Om diagnostic analysis. The derived [Formula: see text] model shows a quintessence dark energy model [Formula: see text] and late-time universe approaches to [Formula: see text] CDM model.

Properties and observables of massive galaxies in self-interacting dark matter cosmologies

ABSTRACT We use hydrodynamic cosmological simulations to test the differences between cold and self-interacting dark matter models (CDM and SIDM) in the mass range of massive galaxies (1012 &amp;lt; M200/M⊙ h−1 &amp;lt; 1013.5). We consider two SIDM models: one with constant cross-section $\sigma /m_{\chi } = 1\, \mathrm{cm^2 \, g^{-1}}$ and one where the cross-section is velocity-dependent. Despite a weak trend in mass, we find that with the inclusion of baryons the differences between SIDM and CDM density profiles observed in the dark-matter-only case are almost erased. We also search for signatures of SIDM in the distribution of strong lensing Einstein radii and find that the distributions derived from CDM and SIDM hydro runs are both comparable to observational samples of strong lenses. We find that, looking at the total matter distribution, the interplay between self-interactions and baryons can greatly reduce the expected differences between CDM and SIDM models at this mass scale, making the discrimination between these DM models challenging. However, looking at the dark matter/baryonic fractions in the inner region of the haloes we show that the deviations of SIDM from CDM can still be found considering these components separately. These results highlight that one of the most promising paths to discriminate between CDM and SIDM is to focus on techniques able to distinguish between the dark matter and baryonic components in galaxies and clusters.