scholarly journals Transport coefficients of bulk viscous pressure in the 14-moment approximation

2014 ◽  
Vol 90 (2) ◽  
Author(s):  
G. S. Denicol ◽  
S. Jeon ◽  
C. Gale
Keyword(s):  
Transport Coefficients ◽  
Moment Approximation ◽  
Bulk Viscous ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure

scholarly journals Cosmic Evolution of Viscous QCD Epoch in Causal Eckart Frame

Universe ◽  
2021 ◽  
Vol 7 (5) ◽  
pp. 112
Author(s):  
Eman Abdel Hakk ◽  
Abdel Nasser Tawfik ◽  
Afaf Nada ◽  
Hayam Yassin
Keyword(s):  
Energy Density ◽  
Energy Flow ◽  
Equations Of State ◽  
Temporal Evolution ◽  
Particle Diffusion ◽  
Cosmic Evolution ◽  
Bulk Viscous ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure ◽  
Particle Current

It is conjectured that in cosmological applications the particle current is not modified but finite heat or energy flow. Therefore, comoving Eckart frame is a suitable choice, as it merely ceases the charge and particle diffusion and conserves charges and particles. The cosmic evolution of viscous hadron and parton epochs in casual and non-casual Eckart frame is analyzed. By proposing equations of state deduced from recent lattice QCD simulations including pressure p, energy density ρ, and temperature T, the Friedmann equations are solved. We introduce expressions for the temporal evolution of the Hubble parameter H˙, the cosmic energy density ρ˙, and the share η˙ and the bulk viscous coefficient ζ˙. We also suggest how the bulk viscous pressure Π could be related to H. We conclude that the relativistic theory of fluids, the Eckart frame, and the finite viscous coefficients play essential roles in the cosmic evolution, especially in the hadron and parton epochs.

scholarly journals FULL CAUSAL BULK VISCOUS COSMOLOGIES WITH TIME-VARYING CONSTANTS

2003 ◽  
Vol 12 (05) ◽  
pp. 861-883 ◽  
Author(s):  
JOSÉ ANTONIO BELINCHÓN ◽  
INDRAJIT CHAKRABARTY
Keyword(s):  
Equations Of State ◽  
Functional Dependence ◽  
Physical Parameters ◽  
Time Varying ◽  
Field Equations ◽  
Bulk Viscous ◽  
Varying Constants ◽  
Time Varying Constants ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure

We study the evolution of a flat Friedmann–Robertson–Walker Universe, filled with a bulk viscous cosmological fluid, in the presence of time varying "constants." The dimensional analysis of the model suggests a proportionality between the bulk viscous pressure of the dissipative fluid and the energy density. Using this assumption and with the choice of the standard equations of state for the bulk viscosity coefficient, temperature and relaxation time, the general solution of the field equations can be obtained, with all physical parameters having a power-law time dependence. The symmetry analysis of this model, performed using Lie group techniques, confirms the uniqueness of the solution for this functional form of the bulk viscous pressure. In order to find another possible solution we relax the hypotheses and assume a concrete functional dependence for the "constants."

scholarly journals Dynamics of modified Chaplygin gas inflation on the Brane with bulk viscous pressure

2017 ◽  
Vol 26 (04) ◽  
pp. 1750031 ◽  
Author(s):  
Abdul Jawad ◽  
Amara Ilyas ◽  
Shamaila Rani
Keyword(s):  
Spectral Index ◽  
Power Spectra ◽  
Chaplygin Gas ◽  
Entropy Density ◽  
Index Formula ◽  
Modified Chaplygin Gas ◽  
Tensor Power ◽  
Bulk Viscous ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure

We investigate the role of bulk viscous pressure on the warm inflationary modified Chaplygin gas (MCG) in braneworld framework in the presence of standard scalar field. We assume the intermediate inflationary scenario in strong dissipative regime and constructed the inflaton, potential, entropy density, slow-roll parameters, scalar and tensor power spectra, scalar spectral index and tensor-to-scalar ratio. We develop various trajectories such as [Formula: see text], [Formula: see text] and [Formula: see text] (where [Formula: see text] is the spectral index, [Formula: see text] is the running of spectral index, [Formula: see text] is the number of e-folds and [Formula: see text] is tensor-to-scalar ratio) for variable as well as constant dissipation and bulk viscous coefficients at high dissipative regime. It is interesting to remark here that our results of these parameters are compatible with recent observational data such as WMAP [Formula: see text], BICEP[Formula: see text] and Planck data.

Dynamics of bulk viscous pressure effected inflation in braneworld scenario

2016 ◽  
Vol 81 ◽  
pp. 61-71 ◽  
Author(s):  
Abdul Jawad ◽  
Amara Ilyas ◽  
Shamaila Rani
Keyword(s):  
Bulk Viscous ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure

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

2019 ◽  
Vol 16 (01) ◽  
pp. 1950005 ◽  
Author(s):  
Partha Sarathi Debnath
Keyword(s):  
Cosmological Model ◽  
Cosmological Solution ◽  
Momentum Tensor ◽  
General Function ◽  
Geometrical Properties ◽  
Modified Gravity Theory ◽  
Bulk Viscous ◽  
Theory Of Gravity ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure

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.

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

2016 ◽  
Vol 2016 ◽  
pp. 1-14 ◽  
Author(s):  
Surajit Chattopadhyay
Keyword(s):  
Dark Energy ◽  
Bulk Viscosity ◽  
Apparent Horizon ◽  
State Parameter ◽  
Effective Pressure ◽  
Ricci Dark Energy ◽  
Eos Parameter ◽  
Bulk Viscous ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure

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.

HAMILTONIAN FLUIDS IN A FRW COSMOLOGY

2000 ◽  
Vol 09 (05) ◽  
pp. 581-590
Author(s):  
R. TRIAY ◽  
H. H. FLICHE ◽  
M. NOVELLO ◽  
L. R. DE FREITAS
Keyword(s):  
Dynamical System ◽  
Hamiltonian Formulation ◽  
Frw Cosmology ◽  
Quantum Processes ◽  
Bulk Viscous ◽  
Cosmological Solutions ◽  
Expansion Of The Universe ◽  
Viscous Pressure ◽  
Bulk Viscous Pressure ◽  
The Universe

With the ulterior motivation in mind to investigate the contribution of quantum processes on the dynamics of the expansion of the universe, we investigate dissipative cosmological solutions which preserve the isotropy and the homogeneity. For performing such an investigation, we derive a method which enables us to describe a 2D dynamical system by a Hamiltonian formulation. As formal example, an admissible form for the bulk (viscous) pressure is derived.

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

2021 ◽  
pp. 2150151
Author(s):  
Chayan Ranjit ◽  
Sayeedul Islam ◽  
Surajit Chattopadhyay ◽  
Ertan Gudekli
Keyword(s):  
Viscous Fluid ◽  
Bulk Viscosity ◽  
Modified Gravity ◽  
Cosmological Parameters ◽  
Eos Parameter ◽  
Bulk Viscous Fluid ◽  
Bulk Viscous ◽  
Viscous Pressure ◽  
Chern Simons ◽  
Bulk Viscous Pressure

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.

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