Truncated Israel Stewart Theory Research Articles

On the feasibility of truncated Israel–Stewart model in the context of late acceleration

A dissipative model of the Universe based on the causal relativistic truncated Israel–Stewart theory is analysed in the context of recent accelerated expansion of the Universe. The bulk viscosity and relaxation time are taken as ξ = αρ s and respectively. For s = 1/2, we found an analytical solution for the Hubble parameter of the model. We have estimated the model parameters by treating γ = 1 and γ as a free parameter using the latest cosmological data. The model predicts a prior decelerated phase and an end de Sitter phase as in the standard ΛCDM model. The dynamical system analysis shows that the prior decelerated epoch is an unstable equilibrium, while the far future de Sitter epoch is stable. The age of the Universe obtained around 13.66 Gyr, which is close to the recent observations. The second law of thermodynamics is found to be satisfied throughout the evolution in this model. The feasibility of the model has been checked by contrasting with models based on the full Israel–Stewart and the Eckart viscous theories. The truncated viscous model appears more compatible with astronomical observations than the Eckart and full causal viscous models.

Bouncing scenario with causal cosmology

We present the cosmological model of a bouncing universe with causal fluid in the universe. The dissipative effects of the causal cosmic fluid is probed with both truncated Israel–Stewart theory and full Israel–Stewart theory. The following classes of non-vanishing scale factors of bouncing cosmology are considered with a viscous fluid: (i) the power-law bouncing model, (ii) the exponential bouncing model and (iii) the matter bouncing model in the Einstein gravity. The cosmological parameters of the Hubble parameter, deceleration parameter, jerk parameter, energy density and bulk viscous pressure of the universe are determined in the theories to obtain realistic cosmologies. The observational constraints of the parameters of bouncing cosmological models are estimated making use of the observed cosmological data. The physical and geometrical aspects of the cosmological models based on the imposed constraints are also discussed.

Observational constraints of bulk viscous Friedmann–Robertson–Walker cosmology with hybrid expansion law

In this work, we study bulk viscous Friedmann–Robertson–Walker cosmologies with hybrid expansion law. The bulk viscous theory of dissipative effects described by Eckart theory, truncated Israel–Stewart theory and full Israel–Stewart theory are implemented here. The hybrid expansion law model of scale factor is a general analytic type of evolution from which one can recover power-law and exponential expansion as a special cases. Hybrid expansion law model are applied to describe the present accelerating phase and early phases of evolution. We have determined the cosmological parameters such as Hubble parameter, deceleration parameter, jerk parameter, energy density, bulk viscous pressure and coefficient of bulk viscosity of the universe to construct physically acceptable cosmological model. We have considered both flat and closed space–time of Friedmann–Robertson–Walker cosmology to implement hybrid expansion law with dissipative effect. The variations of the coefficient of bulk viscosity with cosmic evolution are studied here in Eckart, truncated and full Israel–Stewart theory for flat and closed space–time to obtain physically acceptable hybrid expansion models driven by viscosity. We have also estimated observational constraints of the parameters of hybrid expansion law model by considering recent observational data set. We further reveal possible connections of our models with [Formula: see text] tension problem.

Observational constraints of emergent universe in f(R,T) gravity with bulk viscosity

Emergent universe (EU) cosmological models with viscosity in a modified gravity which contains a general function [Formula: see text], where [Formula: see text] and [Formula: see text] denote the curvature scalar and the trace of the energy–momentum tensor, respectively, are studied in a flat Friedmann–Robertson–Walker metric. Cosmological solutions are obtained in [Formula: see text] theory of gravity, which represented as [Formula: see text] with bulk viscosity that described by Eckart theory, truncated Israel Stewart theory and full Israel Stewart Theory. The physical and geometrical features of the EU models in [Formula: see text] gravity, where [Formula: see text] and [Formula: see text] are coupling parameters, with bulk viscosity are studied in details. Constraints of the EU models parameters in [Formula: see text] gravity with bulk viscosity are estimated from observational data set. The stability analysis of the equilibrium points admitting cosmological solutions of the dynamical system associated with the evolution in the modified gravity is studied in Eckart theory, truncated Israel Stewart theory and full Israel Stewart theory.

Observational constraints of emergent universe in brane-world with Gauss–Bonnet term and dissipative effect

Cosmological solutions in the Randall–Sundrum (RS) type II brane-world model including Gauss–Bonnet (GB) term, in the presence of a bulk viscous cosmological fluid are discussed. Transport equations described by Eckart and Israel Stewart are implemented here. Cosmological models admitting emergent universe (EU) of the early universe is explored here in the presence of imperfect fluid described by Eckart theory and Truncated Israel Stewart (TIS) theory and Full Israel Stewart (FIS) theory. We also study the permitted values of the EU model parameters by considering cosmological observational dataset. The stability analysis of the equilibrium points of the dynamical system associated with the evolution in the RS brane including GB term are studied in Eckart theory, TIS theory and FIS theory.

Observational constraints on emergent universe model with non-linear viscous fluid

A flat emergent universe (EU) with a non-linear equation of state ( $$p=A \rho +f(\rho )$$ ) is studied considering bulk viscosity. In the paper we obtain cosmological models with viscous fluid described by truncated Israel–Stewart theory. Using autonomous system of field equations the stability of the solutions are analyzed. The observational constraints on the model parameters are determined for different matter energy compositions of the universe with non-linear viscosity in the EU scenario.

Bulk viscous cosmological model in f(R,T) theory of gravity

In this paper, we have presented bulk viscous cosmological model of the universe in the modified gravity theory in which the Lagragian of the gravitational action contains a general function [Formula: see text], where [Formula: see text] and [Formula: see text] denote the curvature scalar and the trace of the energy–momentum tensor, respectively, in the framework of a flat Friedmann–Robertson–Walker model with isotropic fluid. We obtain cosmological solution in [Formula: see text] theory of gravity, specially of particular choice [Formula: see text], where [Formula: see text] is a constant, in the presence of bulk viscosity that are permitted in Eckart theory, Truncated Israel Stewart (TIS) theory and Full Israel Stewart (FIS) theory. The physical and geometrical properties of the models in Eckart, TIS theory and FIS theory are studied in detail. The analysis of the variation of bulk viscous pressure, energy density, scale factor, Hubble parameter and deceleration parameter with cosmic evolution is done in the respective theories. The models are analyzed by comparison with recent observational data. The cosmological models are compatible with observations.

Israel-Stewart Approach to Viscous Dissipative Extended Holographic Ricci Dark Energy Dominated Universe

This paper reports a study on the truncated Israel-Stewart formalism for bulk viscosity using the extended holographic Ricci dark energy (EHRDE). Under the consideration that the universe is dominated by EHRDE, the evolution equation for the bulk viscous pressureΠin the framework of the truncated Israel-Stewart theory has been taken asτΠ˙+Π=-3ξH, whereτis the relaxation time andξis the bulk viscosity coefficient. Considering effective pressure as a sum of thermodynamic pressure of EHRDE and bulk viscous pressure, it has been observed that under the influence of bulk viscosity the EoS parameterwDEis behaving like phantom, that is,wDE≤-1. It has been observed that the magnitude of the effective pressurepeff=p+Πis decaying with time. We also investigated the case for a specific choice of scale factor; namely,a(t)=(t-t0)β/(1-α). For this choice we have observed that a transition from quintessence to phantom is possible for the equation of state parameter. However, theΛCDM phase is not attainable by the state-finder trajectories for this choice. Finally it has been observed that in both of the cases the generalized second law of thermodynamics is valid for the viscous EHRDE dominated universe enveloped by the apparent horizon.

On the viability of the truncated Israel–Stewart theory in cosmology

We apply the causal Israel–Stewart theory of irreversible thermodynamics to model the matter content of the Universe as a dissipative fluid with bulk and shear viscosity. Along with the full transport equations we consider their widely used truncated version. By implementing a dynamical systems approach to Bianchi type IV and V cosmological models with and without cosmological constant, we determine the future asymptotic states of such Universes and show that the truncated Israel–Stewart theory leads to solutions essentially different from the full theory. The solutions of the truncated theory may also manifest unphysical properties. Finally, we find that in the full theory shear viscosity can give a substantial rise to dissipative fluxes, driving the fluid extremely far from equilibrium, where the linear Israel–Stewart theory ceases to be valid.

Qualitative analysis of dissipative cosmologies

The evolution of a homogeneous and isotropic dissipative fluid is analyzed using dynamical systems techniques. The dissipation is driven by bulk viscous pressure and the truncated Israel-Stewart theory is used. Although almost all solutions inflate, we show that only a few of them can be considered as physical solutions since the dominant energy condition is not satisfied.

VISCOUS COSMOLOGICAL MODELS IN (1 + 1) DIMENSIONS

Cosmological solutions in (1 + 1) dimensions in the theory of gravity given by Mann have been obtained in the presence of dissipative phenomena. We have studied both the truncated Israel–Stewart theory and the full causal theory in these lower dimensions. In the full causal theory, we discuss two cases, one with the temperature obeying a power law behavior and the other without this assumption. Some of the solutions found in the truncated Israel–Stewart theory and in the full causal theory are comparable to those obtained by Chimento and Cossarini in (1 + 1) dimensions in Eckart theory.

Qualitative analysis of viscous fluid cosmological models satisfying the Israel-Stewart theory of irreversible thermodynamics

Isotropic and spatially homogeneous viscous fluid cosmological models are investigated using the truncated Israel-Stewart theory of irreversible thermodynamics to model the bulk viscous pressure. The governing system of differential equations is written in terms of dimensionless variables and a set of dimensionless equations of state is then utilized to complete the system. The resulting dynamical system is analysed using geometric techniques from dynamical systems theory to find the qualitative behaviour of the Friedmann-Robertson-Walker models with bulk viscosity. In these models there exists a free parameter such that the qualitative behaviour of the models can be quite different (for certain ranges of values of this parameter) from that found in models satisfying the Eckart theory studied previously. In addition, the conditions under which the models inflate are investigated.