arXiv subjects

Gopikant Goswami

Publications and source records attributed to Gopikant Goswami.

4 recordsLinked to original sources

arXiv2023

An f(R,T) Gravity Based FLRW Model and Observational Constraints

We attempt to construct a Friedmann-Lemaitre-Robertson-Walker(FLRW) cosmological model in $f(R, T)$ gravity which exhibits a phase transition from deceleration to acceleration at present. We take $f(R,T) = R + 2 λT$, $λ$ being an arbitrary constant. In our model, the $λ$ 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 $λ$ 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 $m_b$ data set in the red shift ranges from $0.014 \leq z \leq 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 $ρ_0$, $\simeq 1.5 ρ_c $. The critical density is estimated as $ρ_c\simeq 1.88 ~ h_0^2~10^{-29}~gm/cm^3 $ 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 $p_0 \simeq - 0.7 ρ_0$.

gr-qc↗

arXiv2023

The Reconstruction of Constant Jerk Parameter with $f(R,T)$ Gravity in Bianchi-I spacetime

We have developed a Bianchi I cosmological model of the universe in $f(R,T)$ gravity theory which fit good with the present day scenario of accelerating universe. The model displays transition from deceleration in the past to the acceleration at the present. As in the $Λ$CDM model, we have defined the three energy parameters $Ω_m$, $Ω_μ$ and $Ω_σ$ such that $Ω_m$ + $Ω_μ$ + $Ω_σ$ = 1. The parameter $Ω_m$ is the matter energy density (baryons + dark matter), $Ω_μ$ is the energy density associated with the Ricci scalar $R$ and the trace $T$ of the energy momentum tensor and $Ω_σ$ is the energy density associated with the anisotropy of the universe. We shall call $Ω_μ$ dominant over the other two due to its higher value. We find that the $Ω_μ$ and the other two in the ratio 3:1. 46 Hubble OHD data set is used to estimate present values of Hubble $H_0$, deceleration $q_0$ and jerk $j$ parameters. 1$σ$, 2$σ$ and 3$σ$ contour region plots for the estimated values of parameters are presented. 580 SNIa supernova distance modulus data set and 66 pantheon SNIa data which include high red shift data in the range $0\leq z\leq 2.36$ have been used to draw error bar plots and likelihood probability curves for distance modulus and apparent magnitude of SNIa supernova's. We have calculated the pressures and densities associated with the two matter densities, viz., $p_μ$, $ρ_μ$, $p_m$ and $ρ_m$, respectively. The present age of the universe as per our model is also evaluated and it is found at par with the present observed values.

gr-qc↗

arXiv2023

Reconstruction of an Observationally Constrained $f(R, T)$ gravity model

In this paper, an attempt is made to construct a Friedmann-Lemaitre-Robertson-Walker model in $f(R,T)$ gravity with a perfect fluid that yields acceleration at late times. We take $f(R,T)$ as $R$ + $8πμT$. As in the $Λ$CDM model, we take the matter to consist of two components, viz., $Ω_m$ and $Ω_μ$ such that $Ω_m$ + $Ω_μ$=1. The parameter $Ω_m$ is the matter density (baryons + dark matter), and $Ω_μ$ is the density associated with the Ricci scalar $R$ and the trace $T$ of the energy momentum tensor, which we shall call dominant matter. We find that at present $Ω_μ$ is dominant over $Ω_m$, and that the two are in the ratio 3:1 to 3:2 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 $0\leq z\leq 2.36$. We have also calculated the pressures and densities associated with the two matter densities, viz., $p_μ$, $ρ_μ$, $p_m$ and $ρ_m$, respectively. It is also found that at present, $ρ_μ$ is greater than $ρ_m$. The negative dominant matter pressure $p_μ$ 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.

gr-qc↗

arXiv2023

The Reconstruction of Constant Jerk Parameter with $f(R,T)$ Gravity

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 $f(R,T) = R + 2 λT$, $λ$ being an arbitrary constant. We have estimated the $λ$ parameter in such a way that the transition red shift is found similar in the deceleration parameter, pressure and the equation of state parameter $ω$. 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 binned and 26 high redshift data's in the range $0.014 \leq z \leq 2.26 $. These data are compared with theoretical results through the $ χ^2 $ 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.

gr-qc↗