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- 2023| V.N. Karazin Kharkiv...Available observational data regarding current cosmological characteristics suggest that the universe is, to a large extent, both isotropic and homogeneous on a large scale. In this study, our objective is to analyze the Friedmann-Lemaitre-Robertson-Walker (FLRW) space-time using a perfect fluid distribution. We specifically investigate the framework of f (R, L m) gravity within certain constraints. To accomplish this, we concentrate on a specific nonlinear f (R, L m) model, represented by f (R, L m)= R/2+ L α m. The field equations are solved using the equation of state parameter of the form of the Chevallier-Polarski-Linder (CPL) parameterization. The deceleration parameter study finds an accelerating universe at late times. The transition redshift is found to be ztr= 0.89±0.25. Also, we discussed the physical and geometrical properties of the model.
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- The current study aims at investigating a modified theory of gravity called theory. Our focus is on a Gauss-Bonnet cosmological model that integrates a non-linear Gauss-Bonnet term and a linear trace term. We assume , where , and represent free parameters. To solve the field equations, we employ a specialized formulation of the deceleration parameter, represented as , where and are model parameters. Consequently, we determine the optimal values of the model parameters by aligning them with the latest observational datasets, including 57 data points from the Cosmic Chronometers datasets, Pantheon datasets, and BAO datasets. Furthermore, we analyze the physical behavior of the cosmographic parameters corresponding to the constrained values of the model parameters, as well as energy density and pressure. The evolution of the deceleration parameter predicts a transition from the decelerated to the accelerated phases of the universe. Importantly, our cosmological model effectively describes the observed cosmic acceleration in the late-time universe, eliminating the need to introduce an additional dark energy component in the field equations.
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- 2025| ElsevierThe ongoing Hubble tension, a significant discrepancy between early-and late-universe measurements of the Hubble constant 𝐻0, challenges the foundations of modern cosmology. A closely related issue, the 𝐻0−𝑟𝑑 tension, arises from the dependency of BAO-based inferences of 𝐻0on the assumed sound horizon at the drag epoch 𝑟𝑑. In this work, we investigate the cosmological implications of the 𝑓(𝑅,𝑇)=𝑅+2𝜆𝑇gravity model, which introduces a direct coupling between the Ricci scalar (𝑅) and the trace of the energy-momentum tensor (𝑇). By utilizing a Markov Chain Monte Carlo (MCMC) analysis with observational datasets, such as Baryon Acoustic Oscillations (BAO), Cosmic Chronometers (CC), and Standard Candles (SC), we constrain the model parameters and assess their compatibility with current cosmological observations. Our findings indicate a strong correlation between 𝐻0and 𝑟𝑑, confirming that different dataset combinations lead to systematically varying constraints on these parameters. The inclusion of the Riess 2019 prior (R19) results in higher values of 𝐻0, reinforcing the Hubble tension, while BAO-only data favors lower values, consistent with early-universe measurements. Additionally, we analyze the evolution of the main cosmologic parameters such as the deceleration parameter 𝑞(𝑧)and the equation of state parameter 𝜔(𝑧). Our results suggest that the 𝑓(𝑅,𝑇)model exhibits a quintessence-like behavior, with 𝜔(𝑧)>−1at present, indicating a dynamical dark energy component rather than a simple cosmological constant. Furthermore, we confirm that the present-day values of the matter and dark energy density parameters, Ω𝑚≈0.3and ΩΛ≈0.7, remain consistent with a spatially flat universe. These results highlight the role of modified gravity in addressing key tensions in cosmology and demonstrate that the 𝑓(𝑅,𝑇)framework provides a natural extension of ΛCDM.
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- Although the standard lambda cold dark matter cosmological model is quite successful in describing the universe, there are still several issues that are still not resolved. Some of these are the cosmological constant problem, certain anomalies in the cosmic microwave background radiation and whether general relativity is valid on large scales. Therefore, it is interesting to examine modified theories in an attempt to solve these problems, and to examine the entire range of possibilities that are allowed. In this work, we examine one of these modified theories, viz., f(R,T) gravity. We study the homogeneous and isotropic models in this theory, which have some pleasing features, such as no initial singularity, a dynamic cosmological term, and a transition from early deceleration to late-time acceleration as intimated by observations. The physical parameters of the model, as well as the energy conditions, are discussed and a viable cosmological model can be constructed.
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