arXiv subjects
Publications and source records attributed to G. C. Samanta.
In this paper an explicit cosmological model which allows cosmological singularities are discussed. The generalized power-law and asymptotic expansions of the baro-tropic fluid index $ω$ and equivalently the deceleration parameter $q$, in terms of cosmic time $'t'$ are considered. Finally, the strength of the found singularities is discussed.
The authors considered the bulk viscous fluid in $f(R, T)$ gravity within the framework of Kaluza-Klein space time. The bulk viscous coefficient $(ξ)$ expressed as $ξ=ξ_0+ξ_1\frac{\dot{a}}{a}+ξ_2\frac{\ddot{a}}{\dot{a}}$, where $ξ_0$, $ξ_1$ and $ξ_2$ are positive constants. We take $p=(γ-1)ρ$, where $0\leγ\le2$ as an equation of state for perfect fluid. The exact solutions to the corresponding field equations are given by assuming a particular model of the form of $f(R, T)=R+2f(T)$, where $f(T)=λT$, $λ$ is constant. We studied the cosmological model in two stages, in first stage: we studied the model with no viscosity, and in second stage: we studied the model involve with viscosity. The cosmological model involve with viscosity is studied by five possible scenarios for bulk viscous fluid coefficient $(ξ)$. The total bulk viscous coefficient seems to be negative, when the bulk viscous coefficient is proportional to $ξ_2\frac{\ddot{a}}{\dot{a}}$, hence the second law of thermodynamics is not valid, however, it is valid with the generalized second law of thermodynamics. The total bulk viscous coefficient seems to be positive, when, the bulk viscous coefficient is proportional to $ξ=ξ_1\frac{\dot{a}}{a}$, $ξ=ξ_1\frac{\dot{a}}{a}+ξ_2\frac{\ddot{a}}{\dot{a}}$ and $ξ=ξ_0+ξ_1\frac{\dot{a}}{a}+ξ_2\frac{\ddot{a}}{\dot{a}}$, so the second law of thermodynamics and the generalized second law of thermodynamics is satisfied throughout the evolution. We calculate statefinder parameters of the model and observed that, it is different from the $\wedge$CDM model. Finally, some physical and geometrical properties of the models are discussed.
In this article, we considered the bulk viscous fluid in the formalism of modified gravity in which the general form of a gravitational action is $f(R, T)$ function, where $R$ is the curvature scalar and $T$ is the trace of the energy momentum tensor within the frame of flat FRW space time. The cosmological model dominated by bulk viscous matter with total bulk viscous coefficient expressed as a linear combination of the velocity and acceleration of the expansion of the universe in such a way that $ξ=ξ_0+ξ_1\frac{\dot{a}}{a}+ξ_2\frac{\ddot{a}}{\dot{a}}$, where $ξ_0$, $ξ_1$ and $ξ_2$ are constants. We take $p=(γ-1)ρ$, where $0\leγ\le2$ as an equation of state for perfect fluid. The exact solutions to the corresponding field equations are obtained by assuming a particular model of the form of $f(R, T)=R+2f(T)$, where $f(T)=λT$, $λ$ is constant. We studied the four possible scenarios for different values of $γ$, such as $γ=0$, $γ=\frac{2}{3}$, $γ=1$ and $γ=\frac{4}{3}$ with the possible positive and negative ranges of $λ$ to observe the accelerated expansion history of the universe. Finally, a big-rip singularity is observed.