scholarly journals The development of spherically symmetrical perturbation in cosmological models with dark energy. An approximation of the ideal liquid

2007 ◽  
Vol 11 (4) ◽  
pp. 473-480 ◽  
Author(s):  
Yu. Kulinich ◽  
B. Novosyadlyj ◽  
V. Pelykh
Keyword(s):  
Dark Energy ◽  
Ideal Liquid ◽  
Cosmological Models ◽  
Symmetrical Perturbation ◽  
The Ideal

scholarly journals Late Time Attractors of Some Varying Chaplygin Gas Cosmological Models

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 769
Author(s):  
Martiros Khurshudyan ◽  
Ratbay Myrzakulov
Keyword(s):  
Dark Energy ◽  
Gravitational Interaction ◽  
Chaplygin Gas ◽  
Cosmological Models ◽  
Late Time ◽  
Time Behavior ◽  
Coincidence Problem ◽  
Energy Models ◽  
Non Linear ◽  
Bayesian Machine Learning

The goal of this paper is to study new cosmological models where the dark energy is a varying Chaplygin gas. This specific dark energy model with non-linear EoS had been often discussed in modern cosmology. Contrary to previous studies, we consider new forms of non-linear non-gravitational interaction between dark matter and assumed dark energy models. We applied the phase space analysis allowing understanding the late time behavior of the models. It allows demonstrating that considered non-gravitational interactions can solve the cosmological coincidence problem. On the other hand, we applied Bayesian Machine Learning technique to learn the constraints on the free parameters. In this way, we gained a better understanding of the models providing a hint which of them can be ruled out. Moreover, the learning based on the simulated expansion rate data shows that the models cannot solve the H0 tension problem.

The possibility of a stable flat dark energy-dominated Swiss-cheese brane-world universe

2020 ◽  
Vol 17 (05) ◽  
pp. 2050075
Author(s):  
Nasr Ahmed ◽  
Kazuharu Bamba ◽  
F. Salama
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Cosmological Models ◽  
Brane World ◽  
Fine Tuning ◽  
Energy Conditions ◽  
Late Time ◽  
Swiss Cheese ◽  
Black Strings ◽  
The Stability

In this paper, we study the possibility of obtaining a stable flat dark energy-dominated universe in a good agreement with observations in the framework of Swiss-cheese brane-world cosmology. Two different brane-world cosmologies with black strings have been introduced for any cosmological constant [Formula: see text] using two empirical forms of the scale factor. In both models, we have performed a fine-tuning between the brane tension and the cosmological constant so that the Equation of state (EoS) parameter [Formula: see text] for the current epoch, where the redshift [Formula: see text]. We then used these fine–tuned values to calculate and plot all parameters and energy conditions. The deceleration–acceleration cosmic transition is allowed in both models, and the jerk parameter [Formula: see text] at late-times. Both solutions predict a future dark energy-dominated universe in which [Formula: see text] with no crossing to the phantom divide line. While the pressure in the first solution is always negative, the second solution predicts a better behavior of cosmic pressure where the pressure is negative only in the late-time accelerating era but positive in the early-time decelerating era. Such a positive-to-negative transition in the evolution of pressure helps to explain the cosmic deceleration–acceleration transition. Since black strings have been proved to be unstable by some authors, this instability can actually reflect doubts on the stability of cosmological models with black strings (Swiss-cheese type brane-worlds cosmological models). For this reason, we have carefully investigated the stability through energy conditions and sound speed. Because of the presence of quadratic energy terms in Swiss-cheese type brane-world cosmology, we have tested the new nonlinear energy conditions in addition to the classical energy conditions. We have also found that a negative tension brane is not allowed in both models of the current work as the energy density will no longer be well defined.

Bianchi type-VI0 cosmological models with anisotropic dark energy

2010 ◽  
Vol 332 (2) ◽  
pp. 497-502 ◽  
Author(s):  
K. S. Adhav ◽  
A. S. Bansod ◽  
S. L. Munde ◽  
R. G. Nakwal
Keyword(s):  
Dark Energy ◽  
Bianchi Type ◽  
Cosmological Models ◽  
Anisotropic Dark Energy ◽  
Bianchi Type Vi0

scholarly journals DO RECENT SUPERNOVAE Ia OBSERVATIONS TEND TO RULE OUT ALL THE COSMOLOGIES?

2007 ◽  
Vol 16 (10) ◽  
pp. 1641-1651 ◽  
Author(s):  
RAM GOPAL VISHWAKARMA
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Gravitational Lensing ◽  
Weakly Interacting Massive Particles ◽  
Cosmological Models ◽  
Accelerated Expansion ◽  
Standard Candle ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Rule Out

Dark energy and the accelerated expansion of the universe have been the direct predictions of the distant supernovae Ia observations which are also supported, indirectly, by the observations of the CMB anisotropies, gravitational lensing and the studies of galaxy clusters. Today these results are accommodated in what has become the concordance cosmology: a universe with flat spatial sections t = constant with about 70% of its energy in the form of Einstein's cosmological constant Λ and about 25% in the form of dark matter (made of perhaps weakly-interacting massive particles). Though the composition is weird, the theory has shown remarkable successes at many fronts. However, we find that as more and more supernovae Ia are observed, more accurately and towards higher redshift, the probability that the data are well-explained by the cosmological models decreases alarmingly, finally ruling out the concordance model at more than 95% confidence level. This raises doubts against the "standard candle"-hypothesis of the supernovae Ia and their use in constraining the cosmological models. We need a better understanding of the entire SN Ia phenomenon in order to extract cosmological consequences from them.

scholarly journals LITTLE RIP COSMOLOGICAL MODELS WITH TIME-DEPENDENT EQUATION OF STATE

2012 ◽  
Vol 27 (36) ◽  
pp. 1250210 ◽  
Author(s):  
I. BREVIK ◽  
V. V. OBUKHOV ◽  
K. E. OSETRIN ◽  
A. V. TIMOSHKIN
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Models ◽  
Time Dependent ◽  
De Sitter Spacetime ◽  
De Sitter ◽  
Energy Models ◽  
Sitter Spacetime ◽  
The Universe ◽  
Far Future

Specific dark energy models, leading to the Little Rip (LR) cosmology in the far future, are investigated. Conditions for the occurrence of LR in terms of the parameters present in the proposed equation of state for the dark energy cosmic fluid are studied. Estimates about the time needed before the occurrence of the small singularity in the standard LR model in which the universe approaches the de Sitter spacetime asymptotically, are given.

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 Gurzadyan–Xue dark energy

2006 ◽  
Vol 23 (15) ◽  
pp. 5049-5061 ◽  
Author(s):  
G V Vereshchagin ◽  
G Yegorian
Keyword(s):  
Dark Energy ◽  
Cosmological Models
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