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- In this paper, we investigate dust-fluid flat cosmological models in the recently proposed modified f(R,T,Lm)-gravity theory. We derive the field equations for the flat FLRW spacetime metric for the arbitrary function f(R,T,Lm)=R2+ÎąT+ÎēLmnâÎģ, where R is the Ricci curvature scalar, Lm is the matter Lagrangian, T is the trace of the energyâmomentum tensor Tij, and Îą, Îē, Îģ, and n are the model parameters. We solve these equations to obtain the Hubble function in terms of matter energy density parameters ÎĐÎą0, ÎĐÎē0, ÎĐÎģ0\, and Hubble constant H0. Then, we use the cosmic chronometer (CC) Hubble points dataset and the Pantheon dataset to do MCMC analysis of the Hubble function and find the best fit model parameters for the lowest Ï2 values. Subsequently, we investigate the effective equation of state parameter Ïeff and deceleration parameter q(z) for the present past epoch of the universe. We also perform analysis for energy conditions and state finder parameters to discuss the different stages of the dark energy models.
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- In this work, we have developed an FLRW type model of a universe which displays transition from deceleration in the past to the acceleration at the present. For this, we have considered field equations of f(R,T) gravity and have taken f (R, T ) = R + 2ÎŧT , Îŧ being an arbitrary constant. We have estimated the Îŧ parameter in such a way that the transition red shift is found similar in the deceleration parameter, pressure and the equation of state parameter Ï. The present value of Hubble parameter is estimated on the basis of the three types of observational data set: latest compilation of 46 Hubble data set, SNe Ia 580 data sets of distance modulus and 66 Pantheon data set of apparent magnitude which comprised of 40 SN Ia bined and 26 high redshift dataâs in the range 0.014 âĪ z âĪ 2.26. These data are compared with theoretical results through the Ï2 statistical test. Interestingly, the model satisfies all the three weak, strong and dominant energy conditions. The model fits well with observational findings. We have discussed some of the physical aspects of the model, in particular the age of the universe.
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- We attempt to construct a FriedmannâLemaitreâRobertsonâWalker (FLRW) cosmological model in f (R, T ) gravity which exhibits a phase transition from deceleration to acceleration at present. We take f (R, T ) = R + 2ÎŧT , Îŧ being an arbitrary constant. In our model, the Îŧ parameter develops a negative pressure in the universe whose Equation of state is parameterized. The present values of model parameters such as density, Hubble, deceleration, Equation of state, and Îŧ are estimated statistically by using the Chi-Square test. For this, we have used three different types of observational data sets: the 46 Hubble parameter data set, the SNeIa 715 data sets of distance modulus, and the 66 Pantheon data set (the latest compilation of SNeIa 40 bined plus 26 high red shift apparent magnitude mb data set in the red shift ranges from 0.014 âĪ z âĪ 2.26). We have calculated the transitional red shift and time. The estimated results for the present values of various model parameters are found as per expectations and surveys. Interestingly, we get the present value of the density Ï0, â 1.5Ïc . The critical density is estimated as Ïc â 1.88 h 2 0 10â29 gm/cm3 in the literature. The higher value of the present density is attributed to the presence of some additional energies in the universe apart from baryon energy. We have examined the behavior of the pressure in our model. It is negative and produces acceleration in the universe. Its present value is obtained as p0 â â0.7Ï0.
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- In the present work, we investigate the power-law entropy corrected holographic dark energy (PLECHDE) model with Hubble horizon cutoff. We use 46 observational Hubble data points in the redshift range 0 âĪ ð§ âĪ 2.36 to determine the present Hubble constant ðŧ0 and the model parameter ð. It represents a phase transition of the universe from deceleration to acceleration and has the transition point at ð§ðĄ = 0.71165. We investigate the observational constraints on the model and calculate some relevant cosmological parameters. We examine the modelâs validity by drawing state-finder parameters that yield the result compatible with the modern observational data. The modelâs physical and geometrical characteristics are also explored, and they are shown to match well with current observations of observational Hubble data (OHD) and the latest joint light curves(JLA) datasets.
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- In this paper, we have analyzed the significance of bulk viscosity in an axially symmetric Bianchi type-I model to study the accelerated expansion of the universe. We have considered four bulk viscosity parameterizations for the matter-dominated cosmological model. The function of the two significant Hubble ðŧ(ð§) and deceleration parameters are discussed in detail. The energy parameters of the universe are computed using the most recent observational Hubble data (57 data points) in the redshift range 0.07 âĪ ð§ âĪ 2.36. In this model, we obtained all feasible solutions with the viscous component and analyzed the universeâs expansion history. Finally, we analyzed the statefinder diagnostic and found some interesting results. The outcomes of our developed model now properly align with observational results.
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- In this paper, an attempt is made to construct a FriedmannâLemaitreâRobertsonâWalker model in gravity with a perfect fluid that yields acceleration at late times. We take as . As in the CDM model, we take the matter to consist of two components, viz., and such that . The parameter is the matter density (baryons dark matter), and is the density associated with the Ricci scalar and the trace of the energyâmomentum tensor, which we shall call dominant matter. We find that at present is dominant over , and that the two are in the ratio 3:1â3:2 according to the three data sets: (i) 77 Hubble OHD data set, (ii) 580 SNIa supernova distance modulus data set and (iii) 66 pantheon SNIa data which include high red shift data in the range . We have also calculated the pressures and densities associated with the two matter densities, viz., , , and , respectively. It is also found that at present, is greater than . The negative dominant matter pressure creates acceleration in the universe. Our deceleration and snap parameters show a change from negative to positive, whereas the jerk parameter is always positive. This means that the universe is at present accelerating and in the past it was decelerating. State finder diagnostics indicate that our model is at present a dark energy quintessence model. The various other physical and geometric properties of the model are also discussed.
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- This paper examines the stability of the transition from the early decelerating stage of the Universe to the recent accelerating stage for the perfect fluid cosmological locally rotationally symmetric (LRS) Bianchi-I model in ð(ð ,ð) theory. To determine the solution of field equations, the idea of a time varying deceleration parameter (DP) which yields a scale factor, for which the Universe attains a phase transition scenario and is consistent with recent cosmological observations, is used. The time-dependent h DP yields a scale factor a = exp â 1 Îē 2Îēt +k i , where Îē and k are respectively arbitrary and integration constants. By using the recent constraints (H0 = 73.8, and q0 = â0.54) from Type Ia Supernova (SN Ia) data in combination with Baryonic Acoustic Oscillations (BAO) and Cosmic Microwave Background (CMB) observations (Giostri et al.), we obtain the values of Îē = 0.0062 and k = 0.000016 for which we have derived a cosmological model from the early decelerated phase to the present accelerating phase. By applying other recent constraints (H0 = 73.8, q0 = â0.73) from SNe Ia Union data (Cunha), we obtain the values of Îē = 0.0036 and k = 0.000084 for which we have derived a cosmological model in the accelerating phase only. We have compared both models with experimental data. The stability of the background solution has been examined also for the metric perturbations alongside the properties of future singularities in a Universe ruled by dark energy with phantom type fluid. We demonstrate the presence of a stable fixed point with a condition of state Ï < â1 and numerically affirm this is really a late-time attractor in the ghost overwhelmed Universe. Some physical and geometric properties of the model are found and examined.
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