Narrow Results

We consider Little Rip (LR) and Pseudo Rip (PR) cosmological models with two interacting ideal fluids, corresponding to dark energy and dark matter. The interaction between the dark energy and the dark matter fluid components is described in terms of the parameters in the equations of state for the LR and PR universes. In contrast to a model containing only a pure dark energy, the presence of the interaction term between the fluid components in the gravitational equations leads to a modification of the equation of state parameters. The properties of the early universe in this formalism are pointed out.

In this paper, we investigate the evolution of the equation of state of the interacting viscous dark energy in $f(R)$ gravity. We first consider the case when the dark energy does not interact with the dark matter and after, the case where there is a coupling between these dark components. The viscosity and the interaction between the two fluids are parameterized by constants $\xi$ and $\delta$ respectively for which a detailed investigation on the cosmological implications has been done. In the later part of the paper, we explore some bulk viscosity models with Little and Pseudo Rip infinite time singularities within $f(R)$ modified gravity. We obtain analytic expressions for characteristic properties of these cosmological models.

This paper is devoted to explore bouncing cosmology in $f(T,{𝒯})$ modified gravity. In the background of $f(T,{𝒯})$ modified theory with $T$ being Torsion scalar and ${𝒯}$ being the trace of energy–momentum tensor, the Hubble parameter is considered for the isotropic, flat, and homogenous universe. The standard bouncing scale factor has employed the exponential term to unify bounce with late-time acceleration. Phase portrait analysis reveals us that Minkowskian origin transfers to de Sitter origin in $(H,Ḣ)$-plane and as past infinite time $t\to -\infty$$\Rightarrow$$a(t)\to 0$ and $(H,Ḣ)\to$ constant which corresponds to some physical cosmological scenarios. Since field equations of $f(T,{𝒯})$ gravity are of second order, a one-dimensional autonomous system has been extracted. Finally, outcomes have been plotted graphically, and any type of singular behavior has not been experienced. The study of the equation of state parameter against cosmic time reveals that phantom phase is quite significant for both models. The inertial force in terms of Hubble parameter and cosmic time gives rise to pseudo Rip. The study of cosmographic parameters tells us that the present model corresponds to $\mathrm{\Lambda }$CDM at a large value of cosmic time.

By making use of two viable Lagrangian $f(T,{𝒯})$ models, we investigate the behavior of the state parameter of the interacting viscous dark energy. We, from constant deceleration parameter, explore the cosmological implications of the viscosity and interaction between the dark energy and dark matter in terms of redshift. We then construct the viscosity and the interaction parameters that are respectively parameterized by $d_o^{\eta }({\rho }_{\mathrm{\text{DE}}})$ and $\xi$ and obtain interesting results. Later, we investigate the behavior of some bulk viscosity models describing little rip and pseudo rip future singularities within $f(T,{𝒯})$ modified gravity. We obtain interesting gravitational equations of motion for viscous dark energy coupled with dark matter. The solution of these equations gives us an analytic expression for characteristic properties of these cosmological models.

In this paper, we study Little Rip (LR) and Pseudo Rip (PR) cosmological models containing two coupled fluids: dark energy and dark matter. We assume a spatially flat Friedmann–Robertson–Walker (FRW) universe. The interaction between the dark energy and the dark matter fluid components is described in terms of the parameters in the generalized Equation of State (EoS) in presence of the bulk viscosity. We consider entropic cosmology and use a description based on a new generalized entropy function, which was proposed by Nojiri–Odintsov–Faraoni [From nonextensive statistics and black hole entropy to the holographic dark universe, Phys. Rev. D105(4) (2022) 044042]. Conditions for the appearance of the (LR) and the (PR) in terms of the parameters of the (EoS) are obtained. Introducing an energy density ${\rho }_g$ corresponding to a specified entropy function $S_g$, together with an interaction term $Q$ in the gravitational equations of motion, we derive modified forms of the EoS parameters. We discuss the corrections of the thermodynamic parameters associated with the generalized entropy function. Properties of the late universe as well as in the early universe in this formalism are pointed out.