Analysis of different scenarios with new Tsallis holographic dark energies and bulk viscous fluid in the framework of Chern–Simons modified gravity

In this work, we have studied various cosmological parameters in the presence of viscous new Tsallis holographic dark energies for interacting scenarios in the framework of Chern–Simons modified gravity. The bulk viscosity has been considered with the bulk viscous pressure chosen in the form [Formula: see text]. Hubble parameter [Formula: see text] has been obtained from the above choice of scale factor and in this viscous scenario, the effective pressure has been obtained in Chern–Simons framework whose field equation, cosmological consequences have been investigated. It has been observed that for the interaction scenario in the presence of bulk viscosity the EoS parameter is staying above [Formula: see text], which indicates quintessence behavior. Hence, for the universe filled with a bulk viscous fluid can have the possibility of avoidance of big-rip, although the earlier transition from quintessence to phantom is not avoidable.

Accelerating universe with binary mixture of bulk viscous fluid and dark energy

In this paper, we have proposed a model of accelerating universe with binary mixture of bulk viscous fluid and dark energy (DE) and probed the model parameters: present values of Hubble’s constant [Formula: see text], equation of state paper of DE [Formula: see text] and density parameter of DE [Formula: see text] with recent observational [Formula: see text] data (OHD) as well as joint Pantheon compilation of SN Ia data and OHD. Using cosmic chronometric technique, we obtain [Formula: see text] and [Formula: see text] by restricting our derived model with recent OHD and joint Pantheon compilation SN Ia data and OHD, respectively. The present age of the universe in derived model is estimated as [Formula: see text]. Also, we observe that derived model represents a model of transitioning universe with transition redshift [Formula: see text]. We have constrained the present value of jerk parameter as [Formula: see text] with joint OHD and Pantheon data. From this analysis, we observed that the model of the universe, presented in this paper, shows a marginal departure from [Formula: see text]CDM model.

Degenerate Bogdanov–Takens bifurcations in a bulk viscous cosmology

Using the dynamical system theory we show that the Friedmann–Robertson–Walker (FRW) cosmological model with bulk viscous fluid in the presence of cosmological constant is equivalent to a degenerate two dimensional Bogdanov–Takens normal form. The equation of state parameter, $$\omega $$ ω , the bulk viscosity coefficient, $$\xi $$ ξ , and the cosmological constant, $$\Lambda $$ Λ , define the necessary parameters for unfolding the degenerate Bogdanov-Takens system. The fixed points of the system are discussed together with the variation of their stability properties upon changing the relevant parameters $$\omega , \Lambda $$ ω , Λ and $$\xi $$ ξ . The variation of the stability properties are visualized by the appropriate bifurcation diagrams. Phase portrait for finite domain and global phase portrait are displayed and the issue of the structural stability is discussed. Typical issues such as late acceleration or inflation that can be induced by viscosity and could have relevance to observational cosmology are also discussed.

Universe with quadratic equation of state: A dynamical systems perspective

This paper deals with the dynamical systems analysis of Friedmann–Robertson–Walker (FRW) model of the Universe in the framework of general relativity with quadratic equation of state and bulk viscosity. The evolution equations are transformed into an autonomous system of differential equations using suitable variables transformation. Stability analysis of cosmological models with quadratic equation of state parameter are discussed in detail in two different scenarios viz, first Universe filled with barotropic fluid and second filled with bulk viscous fluid. The nature of critical points is analyzed for both cases accordance with respective eigenvalues. We have also analyzed the stable attractor for both cases and examined their properties from the point of cosmological view.

Bianchi Type V Universe and Bulk Viscous Models with Time Dependent Gravitational Constant and Cosmological Constant in General Relativity

This paper deals with Bulk Viscous Models and Bianchi type- universe in the standard general relativity theory by assuming where constants, is the density. Einstein field equations ( ) have been solved in the presence of a variable gravitational constant as well as a variable cosmological constant together with a bulk viscous fluid. In order to find a deterministic solution of EFEs, a simple form of Hubble parameter being constant when where has been considered here that shows the signature flip from early deceleration to present acceleration. Moreover, the bulk viscous coefficient is allowed to vary with the density as . The physical and geometrical behavior are described in detail for the obtained model. The model obtained here is in good agreement with the present cosmological observations.

Dynamics of Bianchi V Ih universe with bulk viscous fluid in modified gravity

In this paper, the dynamical behavior of the anisotropic universe has been investigated in [Formula: see text] theory of gravity. The functional [Formula: see text] has been rescaled in the form [Formula: see text], where [Formula: see text] is the Ricci scalar and [Formula: see text] is the trace of energy momentum tensor. Three cosmological models are constructed using the power law expansion in Bianchi type [Formula: see text] ([Formula: see text]) universe for three different values of [Formula: see text], where the matter field is considered to be of bulk viscous fluid. It is observed that the anisotropic [Formula: see text] model in the modified theory of gravity is in agreement with a quintessence phase for the value of [Formula: see text] and [Formula: see text]. We could not obtain a viable cosmological model in accordance with the present day observations for [Formula: see text]. The bulk viscous coefficient in both the cases are found to be positive and remain constant at late time. The physical behaviors of the models along with the energy conditions are also studied.