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.

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 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.

ASSISTED INFLATION

2002 ◽  
Vol 17 (20) ◽  
pp. 2755-2755
Author(s):  
A. A. COLEY ◽  
R. J. VAN DEN HOOGEN
Keyword(s):  
Perfect Fluid ◽  
Scalar Fields ◽  
Cosmological Models ◽  
Late Time ◽  
Time Behaviour ◽  
Field Curvature ◽  
Scaling Solution ◽  
Dynamical Properties ◽  
Spatially Homogeneous ◽  
Parameter Values

The dynamical properties of spatially homogeneous and isotropic cosmological models containing a barotropic perfect fluid and multiple scalar fields with independent exponential potentials is investigated. It is shown that the assisted inflationary scaling solution is the global late-time attractor for the parameter values for which the model is inflationary, even when curvature and barotropic matter are included. For all other parameter values the multi-field curvature scaling solution is the global late-time attractor (in these solutions the curvature is not dynamically negligible asymptotically). Consequently, in general all of the scalar fields in multi-field models with exponential potentials are non-negligible in late-time behaviour, contrary to what is commonly believed.

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 ON THEORY OF REGULAR ACCELERATING UNIVERSE IN RIEMANN–CARTAN SPACETIME

2013 ◽  
Vol 28 (21) ◽  
pp. 1350090 ◽  
Author(s):  
A. V. MINKEVICH
Keyword(s):  
Energy Density ◽  
Hubble Parameter ◽  
Scalar Fields ◽  
Cosmological Models ◽  
Accelerating Universe ◽  
Cosmological Expansion ◽  
Isotropic Cosmology ◽  
In The Beginning ◽  
Curvature Tensors

Isotropic cosmology built in the Riemann–Cartan spacetime is investigated. Properties of homogeneous isotropic cosmological models filled with usual gravitating matter and scalar fields are studied in the beginning of cosmological expansion near the limiting energy density. It is shown that cosmological models are regular not only with respect to the Hubble parameter and the energy density but also with respect to the torsion and curvature tensors.

scholarly journals Relic gravitational waves in cosmological models based on the modified gravity theories

2021 ◽  
Vol 2081 (1) ◽  
pp. 012002
Author(s):  
I V Fomin ◽  
S V Chervon
Keyword(s):  
Energy Density ◽  
Gravitational Waves ◽  
Modified Gravity ◽  
Direct Detection ◽  
Cosmological Models ◽  
Observational Constraints ◽  
Cosmological Perturbations ◽  
Modified Gravity Theories ◽  
Relic Gravitational Waves ◽  
Gravity Theories

Abstract We consider cosmological models based on the generalized scalar-tensor gravity, which correspond to the observational constraints on the parameters of cosmological perturbations for any model’s parameters. The estimates of the energy density of relic gravitational waves for such a cosmological models were made. The possibility of direct detection of such a gravitational waves using modern and prospective methods was discussed as well.

scholarly journals Nakedly singular counterpart of Schwarzschild’s incompressible star. A barotropic continuity condition in the center

2019 ◽  
Vol 51 (11) ◽  
Author(s):  
Łukasz Bratek ◽  
Joanna Jałocha ◽  
Andrzej Woszczyna
Keyword(s):  
Energy Density ◽  
Incompressible Fluid ◽  
Equations Of State ◽  
Continuity Condition ◽  
Interior Solution ◽  
Regularity Conditions ◽  
Initial Condition ◽  
Static Sphere ◽  
Proper Energy

Abstract A static sphere of incompressible fluid with uniform proper energy density is considered as an example of exact star-like solution with weakened central regularity conditions characteristic of a nakedly singular spherical vaccuum solution. The solution is a singular counterpart of the Schwarzschild’s interior solution. The initial condition in the center for general barotropic equations of state is established.

scholarly journals Cohesive Energy Densities Versus Internal Pressures of Near and Supercritical Fluids

Molecules ◽  
2019 ◽  
Vol 24 (5) ◽  
pp. 961 ◽  
Author(s):  
Michal Roth
Keyword(s):  
Energy Density ◽  
Internal Pressure ◽  
Molar Volume ◽  
Intermolecular Interactions ◽  
Supercritical Fluids ◽  
Cohesive Energy ◽  
Equations Of State ◽  
Reduced Pressure ◽  
Cohesive Energy Density ◽  
Internal Pressures

Over half a century ago, Wiehe and Bagley suggested that a product of the internal pressure and molar volume of a liquid measures the energy of nonspecific intermolecular interactions whereas the cohesive energy reflects the total energy of intermolecular interactions in the liquid. This conjecture, however, has never been considered in connection with near and supercritical fluids. In this contribution, the cohesive energy density, internal pressure and their ratios are calculated from high precision equations of state for eight important fluids including water. To secure conformity to the principle of corresponding states when comparing different fluids, the calculations are carried out along the line defined by equality between the reduced temperature and the reduced pressure of the fluid (Tr = Pr). The results provide additional illustration of the tunability of the solvent properties of water that stands apart from those of other near and supercritical fluids in common use. In addition, an overview is also presented of the derivatives of cohesive energy density, solubility parameter and internal pressure with respect to temperature, pressure and molar volume.

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