Influence of thermal radiation on singular behavior of the Universe

2021 ◽  
pp. 128-133
Author(s):  
A.N. Makarenko ◽  
◽  
A.V. Timoshkin ◽  
Keyword(s):  
Equation Of State ◽  
Thermal Radiation ◽  
Thermal Effects ◽  
Qualitative Change ◽  
Viscous Fluids ◽  
Singular Behavior ◽  
Viscosity Property ◽  
Big Rip ◽  
Logarithmic Equation ◽  
The Universe

Cosmological models with inhomogeneous viscous fluids with a logarithmic equation of state in the Friedmann-Lemaitre-Robertson-Walker universe are considered. The influence of thermal effects caused by Hawking radiation on the visible horizon of the Universe on the change in the type of singularity of the dark Universe is investigated. It is shown that under the influence of thermal radiation, taking into account the viscosity property of a dark fluid, a qualitative change in the type of the Big Rip singularity is possible, which can lead to the absence of a singularity in the Universe at all.

scholarly journals ATTRACTOR SOLUTION IN COUPLED YANG–MILLS FIELD DARK ENERGY MODELS

2009 ◽  
Vol 18 (09) ◽  
pp. 1331-1342 ◽  
Author(s):  
WEN ZHAO
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
De Sitter ◽  
Yang Mills ◽  
Constraint Equations ◽  
Energy Models ◽  
Big Rip ◽  
Attractor Solution ◽  
The Universe ◽  
Mills Field

We investigate the attractor solution in the coupled Yang–Mills field dark energy models with the general interaction term, and obtain the constraint equations for the interaction if the attractor solution exists. The research also shows that, if the attractor solution exists, the equation of state of dark energy must evolve from wy > 0 to wy ≤ -1, which is slightly suggested by the observation. At the same time, the total equation of state in the attractor solution is w tot = -1, the universe is a de Sitter expansion, and the cosmic big rip is naturally avoided. These features are all independent of the interacting forms.

scholarly journals THE UNIFIED EQUATION OF STATE FOR DARK MATTER AND DARK ENERGY

2005 ◽  
Vol 20 (19) ◽  
pp. 1443-1449 ◽  
Author(s):  
WEI WANG ◽  
YUANXING GUI ◽  
SUHONG ZHANG ◽  
GUANGHAI GUO ◽  
YING SHAO
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Special Function ◽  
Simple Analysis ◽  
Evolution Of The Universe ◽  
Big Rip ◽  
The Universe

We assume that dark matter and dark energy satisfy the unified equation of state: p = B(z)ρ, with p = pdE, ρ = ρdm+ρdE, where the pressure of dark matter pdm = 0 has been taken into account. A special function [Formula: see text] is presented, which can well describe the evolution of the universe. In this model, the universe will end up with a Big Rip. By further simple analysis, we know other choices of the function B can also describe the universe but lead to a different doomsday.

scholarly journals COSMOLOGY: A BIRD'S EYE VIEW

2006 ◽  
Vol 15 (12) ◽  
pp. 2187-2190 ◽  
Author(s):  
ALAN A. COLEY ◽  
SIGBJØRN HERVIK ◽  
WOEI CHET LIM
Keyword(s):  
Fluid Flow ◽  
Equation Of State ◽  
Cosmological Model ◽  
Finite Time ◽  
Dynamical Behavior ◽  
The Other ◽  
Flow Lines ◽  
Big Rip ◽  
The Difference ◽  
The Universe

We discuss the difference in views of the universe as seen by two different observers. While one of the observers follows a geodesic congruence defined by the geometry of the cosmological model, the other observer follows the fluid flow lines of a perfect fluid with a linear equation of state. We point out that the information these observers collect regarding the state of the universe can be radically different; while one observes a non-inflating, ever-expanding, ever-lasting universe, the other observer can experience a dynamical behavior reminiscent of that of quintessence or even that of a phantom cosmology leading to a "big rip" singularity within finite time (but without the need for exotic forms of matter).

scholarly journals DARK ENERGY WITH DARK SPINORS

2010 ◽  
Vol 25 (02) ◽  
pp. 101-110 ◽  
Author(s):  
CHRISTIAN G. BÖHMER ◽  
JAMES BURNETT
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Time Frame ◽  
Accelerating Universe ◽  
Phantom Divide ◽  
The Past ◽  
Big Rip ◽  
Reasonable Time Frame ◽  
Spinor Model ◽  
The Universe

Ever since the first observations that we are living in an accelerating universe, it has been asked what dark energy is. There are various explanations, all of which have various drawbacks or inconsistencies. Here we show that using a dark spinor field it is possible to have an equation of state that crosses the phantom divide, becoming a dark phantom spinor which evolves into dark energy. This type of equation of state has been mildly favored by experimental data, however, in the past there were hardly any theories that satisfied this crossing without creating ghosts or causing a singularity which results in the universe essentially ripping. The dark spinor model converges to dark energy in a reasonable time frame avoiding the big rip and without attaining negative kinetic energy as it crosses the phantom divide.

scholarly journals Viscous accelerating universe with nonlinear and logarithmic equation of state fluid

2019 ◽  
Vol 16 (10) ◽  
pp. 1950150
Author(s):  
I. Brevik ◽  
A. N. Makarenko ◽  
A. V. Timoshkin
Keyword(s):  
Equation Of State ◽  
Accelerated Expansion ◽  
Accelerating Universe ◽  
Late Time ◽  
Viscosity Effects ◽  
Logarithmic Equation ◽  
The Universe ◽  
Gravitational Equations ◽  
Universe Evolution ◽  
Friedmann Robertson Walker

We describe the accelerated expansion of the late-time universe using a generalized equation of state (EoS) when account is taken of bulk viscosity. We assume a homogeneous and isotropic Friedmann–Robertson–Walker spacetime. Solutions of the gravitational equations for dark energy are obtained in implicit form. Characteristic properties of the universe evolution in the presence of the viscosity effects are discussed. Finally, the dynamics of the accelerated expansion of the viscous universe are discussed on the basis of a modified logarithmic-corrected EoS.

THE EVOLUTION OF GENERALIZED CHAPLYGIN GAS

2006 ◽  
Vol 21 (15) ◽  
pp. 1233-1239 ◽  
Author(s):  
YABO WU ◽  
XUEMEI DENG ◽  
JIANBO LU ◽  
SONG LI ◽  
XIUYI YANG
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Deceleration Parameter ◽  
Critical Density ◽  
Chaplygin Gas ◽  
Generalized Chaplygin Gas ◽  
Big Rip ◽  
The Future ◽  
The Universe

We consider the generalized Chaplygin gas (GCG) proposal for the unification of dark matter and dark energy with p = pdeand ρ = ρdm+ρde. The unified equation of state for GCG has been obtained: [Formula: see text]. On the basis of the function χ(z), some cosmological quantities such as the fractional contributions of different components of the universe Ωi(i respectively denotes baryons, dark matter and dark energy) to the critical density, the equation of state for dark energy ωde, the deceleration parameter q are all obtained, which are consistent with observations. In addition, the transition from deceleration to acceleration is described in our model. We find that the behavior of GCG will be like ΛCDM in the future. So, it has been ruled out in our model that our universe will end up with Big Rip in the future.

FRW viscous cosmology with inhomogeneous equation of state and future singularity

2015 ◽  
Vol 30 (29) ◽  
pp. 1550144 ◽  
Author(s):  
G. S. Khadekar ◽  
Deepti Raut ◽  
V. G. Miskin
Keyword(s):  
Equation Of State ◽  
Bulk Viscosity ◽  
Dynamical Equation ◽  
Cosmological Evolution ◽  
Time Dependent ◽  
Inhomogeneous Equation ◽  
Future Singularity ◽  
Big Rip ◽  
Dependent Parameter ◽  
The Universe

A universe media is considered as a bulk viscosity described by inhomogeneous equation of state (EOS) of the form [Formula: see text], where [Formula: see text] is a time-dependent parameter. A generalized dynamical equation for the scale factor of the universe is proposed to describe the cosmological evolution, in which we assume the bulk viscosity and time-dependent parameter [Formula: see text] are linear combination of two terms of the form: [Formula: see text] and [Formula: see text], i.e.[Formula: see text]one is constant and other is proportional to Hubble parameter [Formula: see text]. In this framework, we demonstrate that this model can be used to explain the dark energy dominated universe, and the inhomogeneous term of specific form introduced in EOS, may lead to three kinds of fates of cosmological evolution: no future singularity, big rip or Type[Formula: see text]III singularity as presented by [S. Nojiri and S. D. Odintsov, Phys. Rev. D 72, 023003 (2005)].

scholarly journals Dynamical system analysis of FLRW models with Modified Chaplygin gas

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ali Osman Yılmaz ◽  
Ertan Güdekli
Keyword(s):  
Dynamical System ◽  
Equation Of State ◽  
Energy Density ◽  
System Analysis ◽  
Chaplygin Gas ◽  
Modified Chaplygin Gas ◽  
State Spaces ◽  
The Universe ◽  
Matter Energy ◽  
Far Future

AbstractWe investigate Friedmann–Lamaitre–Robertson–Walker (FLRW) models with modified Chaplygin gas and cosmological constant, using dynamical system methods. We assume $$p=(\gamma -1)\mu -\dfrac{A}{\mu ^\alpha }$$ p = ( γ - 1 ) μ - A μ α as equation of state where $$\mu$$ μ is the matter-energy density, p is the pressure, $$\alpha$$ α is a parameter which can take on values $$0<\alpha \le 1$$ 0 < α ≤ 1 as well as A and $$\gamma$$ γ are positive constants. We draw the state spaces and analyze the nature of the singularity at the beginning, as well as the fate of the universe in the far future. In particular, we address the question whether there is a solution which is stable for all the cases.

Analysis of Single- and Two-Phase Flows in Turbopump Inducers

1967 ◽  
Vol 89 (4) ◽  
pp. 577-586 ◽  
Author(s):  
P. Cooper
Keyword(s):  
Equation Of State ◽  
Flow Field ◽  
Thermal Effects ◽  
Single Phase ◽  
Fluid Pressure ◽  
Three Dimensional ◽  
Pressure Rise ◽  
Recent Theory ◽  
Two Phase ◽  
Overall Efficiency

A model is developed for analytically determining pump inducer performance in both the single-phase and cavitating flow regimes. An equation of state for vaporizing flow is used in an approximate, three-dimensional analysis of the flow field. The method accounts for losses and yields internal distributions of fluid pressure, velocity, and density together with the resulting overall efficiency and pressure rise. The results of calculated performance of two sample inducers are presented. Comparison with recent theory for fluid thermal effects on suction head requirements is made with the aid of a resulting dimensionless vaporization parameter.

Sign in / Sign up

Export Citation Format

Share Document