Equations of state and transport equations in viscous cosmological models

1993 ◽  
Vol 48 (4) ◽  
pp. 1597-1601 ◽  
Author(s):  
Mohamed Zakari ◽  
David Jou
Keyword(s):  
Equations Of State ◽  
Transport Equations ◽  
Cosmological Models

RECONSTRUCTION OF 5D COSMOLOGICAL MODELS FROM THE EQUATION OF STATE OF DARK ENERGY

2006 ◽  
Vol 15 (02) ◽  
pp. 215-224 ◽  
Author(s):  
LI XIN XU ◽  
HONG YA LIU ◽  
CHENG WU ZHANG
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Arbitrary Function ◽  
Equations Of State ◽  
Cosmological Models ◽  
Cosmological Solutions ◽  
The Universe

We consider a class of five-dimensional cosmological solutions which contain two arbitrary function μ(t) and ν(t). We find that the arbitrary function μ(t) contained in the solutions can be rewritten in terms of the redshift z as a new arbitrary function f(z). We further show that this new arbitrary function f(z) can be solved for four known parameterized equations of state of dark energy. Then 5D models can be reconstructed and the evolution of the density and deceleration parameters of the universe can be determined.

scholarly journals COSMOLOGICAL MODELS WITH A VARYING Λ-TERM IN LYRA'S GEOMETRY

2012 ◽  
Vol 27 (29) ◽  
pp. 1250164 ◽  
Author(s):  
V. K. SHCHIGOLEV
Keyword(s):  
Vector Field ◽  
Exact Solutions ◽  
Equations Of State ◽  
Displacement Vector ◽  
Cosmological Models ◽  
Displacement Vector Field ◽  
Varying Λ ◽  
Lyra’S Geometry ◽  
Model Equations ◽  
The Universe

Cosmological models in Lyra's geometry are constructed and investigated with the assumption of a minimal interaction of matter with the displacement vector field and the dynamical Λ-term. Exact solutions of the model equations are obtained for the different equations of state of the matter, that fills the universe, and for the certain assumptions on the decaying law for Λ.

scholarly journals Equations of state for ions in non-LTE plasmas

1992 ◽  
Vol 10 (3) ◽  
pp. 495-504 ◽  
Author(s):  
S. Eliezer ◽  
E. Mínguez
Keyword(s):  
Equations Of State ◽  
Planck Equation ◽  
Transport Equations ◽  
Rate Equations ◽  
Hydrodynamic Equations ◽  
Ion Density ◽  
Stochastic Force ◽  
General Transport ◽  
Explicit Rate ◽  
Fokker Planck

For nonlocal thermodynamic equilibrium (LTE), the equations of state are not well defined and therefore the hydrodynamic equations are not applicable. In this case, the general transport equations (e.g., Boltzmann or Fokker–Planck) should be used. However, the coupling between atomic physics (rate equations) and the transport equations is extremely complicated. This article shows how the information given by the rate equations is translated into an effective potential. This “potential” theory is explicitly shown for two cases: lithium-like iron plasmas and aluminum plasmas. Moreover, it is suggested that the “collision terms,” and all other interactions that are not taken into account by the explicit rate equations, are described by a stochastic force given by a Langevin equation or equivalently by a Fokker-Planck equation in the ion density space.

scholarly journals LITTLE RIP AND PSEUDO RIP PHENOMENA FROM COUPLED DARK ENERGY

2013 ◽  
Vol 28 (37) ◽  
pp. 1350172 ◽  
Author(s):  
I. BREVIK ◽  
A. V. TIMOSHKIN ◽  
Y. RABOCHAYA
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Early Universe ◽  
Equations Of State ◽  
Cosmological Models ◽  
Ideal Fluids ◽  
Interaction Term ◽  
Gravitational Equations

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.

scholarly journals Scalar and vector perturbations in a universe with nonlinear perfect fluid

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
Ezgi Canay ◽  
Ruslan Brilenkov ◽  
Maxim Eingorn ◽  
A. Savaş Arapoğlu ◽  
Alexander Zhuk
Keyword(s):  
Energy Density ◽  
Perfect Fluid ◽  
Nonlinear Equations ◽  
Equations Of State ◽  
Cosmological Models ◽  
Perfect Fluids ◽  
Screening Approach ◽  
Linear And Nonlinear ◽  
Discrete Inhomogeneities

AbstractWe study a three-component universe filled with dust-like matter in the form of discrete inhomogeneities (e.g., galaxies) and perfect fluids characterized by linear and nonlinear equations of state. Within the cosmic screening approach, we develop the theory of scalar and vector perturbations. None of the energy density contrasts associated with the distinct components is treated as small. Consequently, the derived equations are valid at both sub- and super-horizon scales and enable simulations for a variety of cosmological models.

scholarly journals New dynamical features of pure k-essential cosmologies

2021 ◽  
Author(s):  
Ugo Moschella ◽  
Mario Novello
Keyword(s):  
Energy Density ◽  
Equations Of State ◽  
Cosmological Models ◽  
Cosmic Evolution ◽  
Interesting Possibility ◽  
Dynamical Features ◽  
Dynamical Properties ◽  
Phase Surface ◽  
Multivalued Functions ◽  
Effective Speed

We come back on the dynamical properties of [Formula: see text]-essential cosmological models and show how the interesting phenomenological features of those models are related to the existence of boundaries in the phase surface. We focus our attention to the branching curves where the energy density has an extremum and the effective speed of sound diverges. We discuss the behaviour of solutions of a general class of cosmological models exhibiting such curves and give two possible interpretations; the most interesting possibility regards the arrow of time that is reversed in trespassing the branching curve. This study teaches to us something new about general FLRW cosmologies where the fluids driving the cosmic evolution have equations of state that are multivalued functions of the energy density and other thermodynamical quantities.

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