Narrow Results

A one-component dark energy fluid model of the late universe is considered $(w<-1)$ when the fluid, initially assumed laminar, makes a transition into a turbulent state of motion. Spatial isotropy is assumed so that only the bulk viscosities are included ($\zeta$ in the laminar epoch and ${\zeta }_{\mathrm{\text{turb}}}$ in the turbulent epoch). Both viscosities are assumed to be constants. We derive a formula, new as far as we know, for the time dependence of the temperature $T(t)$ in the laminar case when viscosity is included. Assuming that the laminar/turbulent transition takes place at some time $t_s$ before the big rip is reached, we then analyze the positive temperature jump experienced by the fluid at $t=t_{\ast }$ if ${\zeta }_{\mathrm{\text{turb}}}>\zeta$. This is just as one would expect physically. The corresponding entropy production is also considered. A special point emphasized in the paper is the analogy that exists between the cosmic fluid and a so-called Maxwell fluid in viscoelasticity.

Locally rotationally symmetric (LRS) Bianchi type-I magnetized strange quark matter (SQM) cosmological model has been studied based on f(R, T) gravity. The exact solutions of the field equations are derived with linearly time varying deceleration parameter, which is consistent with observational data (from SNIa, BAO and CMB) of standard cosmology. It is observed that the model begins with big bang and ends with a Big Rip. The transition of the deceleration parameter from decelerating phase to accelerating phase with respect to redshift obtained in our model fits with the recent observational data obtained by Farook et al. [Astrophys. J.835, 26 (2017)]. The well-known Hubble parameter H(z) and distance modulus $\mu$(z) are discussed with redshift.

We have presented the Big Rip singularity in $f(R,T)$ gravity with tilt congruences and creation field. We have solved the field equations by considering a conformally flat universe and the condition $B=A^n$, where $n$ is a constant. The solutions of the field equations have also been investigated by using the method of [J. V. Narlikar and T. Padmanabhan, Phys. Rev. D 32, 1928 (1985)] in which the creation field $C$ is a function of time $t$. Some geometric aspects of the model are also discussed by using MATLAB.

We study spherically symmetric spacetime with anisotropic fluid in the scalar–tensor theory of gravity based on Lyra geometry. We suggest two different solutions of field equations for the theory by using Casimir effect. Obtained static and nonstatic solutions are similar to nonexpanding Lorentzian wormhole and expanding FRW-type wormhole, respectively. Furthermore, we study singularities of obtained solutions. We emphasize whether the expanding and nonexpanding wormholes conform with Big Rip or Big Crunch scenarios. Also, physical and geometrical properties of the solutions have been discussed.

The $f(R)$ theories of gravity are the most popular, simple and well-succeeded extension of Einstein’s General Relativity. They can account for some observational issues of standard cosmology with no need for evoking the dark sector of the universe. In the present paper, we will investigate LRS Bianchi type-I spacetime in $f(R)$ gravity theory within the phantom energy-dominated era. We show that in this formalism the phantom energy-dominated universe is a transient stage and in the further stage of the universe dynamics, it is dominated, once again, by dark energy. Such an important feature is obtained from the model, rather than imposed to it, and may have a relation to loop quantum cosmology.

In this paper, we have explored cold dark matter and holographic dark energy cosmological model with big rip singularity. To obtain the solution of the field equation, we supposed that scalar expansion $𝜃$ is proportional to shear scalar ${\sigma }^2$, which leads to $P_1={(P_2)}^n$, where $P_1$, $P_2$ are metric potentials and $n$ is constant. Big bang and big rip singularity are investigated. The state-finder parameter is analyzed. The physical and geometrical parameters of the universe are explained.