scholarly journals Phantom dark energy with varying-mass dark matter particles: Acceleration and cosmic coincidence problem

2010 ◽  
Vol 693 (1) ◽  
pp. 1-10 ◽  
Author(s):  
Genly Leon ◽  
Emmanuel N. Saridakis
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Coincidence Problem ◽  
Phantom Dark Energy ◽  
Varying Mass ◽  
Cosmic Coincidence Problem

SCALING DARK ENERGY IN A FIVE-DIMENSIONAL BOUNCING COSMOLOGICAL MODEL

2005 ◽  
Vol 14 (11) ◽  
pp. 1947-1957 ◽  
Author(s):  
LIXIN XU ◽  
HONGYA LIU
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Model ◽  
Cold Dark Matter ◽  
Coincidence Problem ◽  
Energy Models ◽  
Phantom Dark Energy ◽  
Hyperbolic Form ◽  
Induced Matter ◽  
The Universe

We consider a five-dimensional Ricci flat bouncing cosmological model in which the four-dimensional induced matter contains two components at late times — the cold dark matter (CDM) + baryons and dark energy. We find that the arbitrary function f(z) contained in the solution plays a similar role as the potential V(ϕ) in quintessence and phantom dark energy models. To resolve the coincidence problem, it is generally believed that there is a scaling stage in the evolution of the universe. We analyze the condition for this stage and show that a hyperbolic form of the function f(z) can work well in this property. We find that during the scaling stage (before z ≈ 2), the dark energy behaves like (but not identical to) a cold dark matter with an adiabatic sound speed [Formula: see text] and px ≈ 0. After z ≈ 2, the pressure of the dark energy becomes negative. The transition from deceleration to acceleration happens at zT ≈ 0.8 which, as well as other predictions of the 5D model, agrees with current observations.

scholarly journals INTERACTION BETWEEN DARK ENERGY AND DARK MATTER: OBSERVATIONAL CONSTRAINTS FROM OHD, BAO, CMB AND SNe Ia

2013 ◽  
Vol 22 (14) ◽  
pp. 1350082 ◽  
Author(s):  
SHUO CAO ◽  
NAN LIANG
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Observational Constraints ◽  
Coincidence Problem ◽  
Cosmological Constraints ◽  
Coincidence Index ◽  
Acceleration Of The Universe ◽  
Interaction Term ◽  
Negative Coupling ◽  
The Universe

In order to test if there is energy transfer between dark energy (DE) and dark matter (DM), we investigate cosmological constraints on two forms of nontrivial interaction between the DM sector and the sector responsible for the acceleration of the universe, in light of the newly revised observations including OHD, CMB, BAO and SNe Ia. More precisely, we find the same tendencies for both phenomenological forms of the interaction term Q = 3γHρ, i.e. the parameter γ to be a small number, |γ| ≈ 10-2. However, concerning the sign of the interaction parameter, we observe that γ > 0 when the interaction between dark sectors is proportional to the energy density of dust matter, whereas the negative coupling (γ < 0) is preferred by observations when the interaction term is proportional to DE density. We further discuss two possible explanations to this incompatibility and apply a quantitative criteria to judge the severity of the coincidence problem. Results suggest that the γm IDE model with a positive coupling may alleviate the coincidence problem, since its coincidence index C is smaller than that for the γd IDE model, the interacting quintessence and phantom models by four orders of magnitude.

scholarly journals Cosmological constant, matter, cosmic inflation and coincidence

2020 ◽  
Vol 35 (15) ◽  
pp. 2050123
Author(s):  
She-Sheng Xue
Keyword(s):  
Dark Matter ◽  
Acoustic Wave ◽  
Cosmological Constant ◽  
Einstein Equation ◽  
Large Scale ◽  
Particle Production ◽  
Cosmological Term ◽  
Coincidence Problem ◽  
Cosmic Inflation ◽  
Cosmic Coincidence Problem

We present a possible understanding to the issues of cosmological constant, inflation, dark matter and coincidence problems based only on the Einstein equation and Hawking particle production. The inflation appears and results agree to observations. The CMB large-scale anomaly can be explained and the dark-matter acoustic wave is speculated. The entropy and reheating are discussed. The cosmological term [Formula: see text] tracks down the matter [Formula: see text] until the radiation-matter equilibrium, then slowly varies, thus the cosmic coincidence problem can be avoided. The relation between [Formula: see text] and [Formula: see text] is shown and can be examined at large redshifts.

scholarly journals Thermodynamical description of the ghost dark energy model

2015 ◽  
Vol 24 (07) ◽  
pp. 1550048 ◽  
Author(s):  
M. Honarvaryan ◽  
A. Sheykhi ◽  
H. Moradpour
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Dark Energy Model ◽  
State Parameter ◽  
Thermal Fluctuations ◽  
Mutual Interaction ◽  
Coincidence Problem ◽  
Ghost Dark Energy ◽  
Equation Of State Parameter ◽  
The Universe

In this paper, we point out thermodynamical description of ghost dark energy (GDE) and its generalization to the early universe. Thereinafter, we find expressions for the entropy changes of these dark energy (DE) candidates. In addition, considering thermal fluctuations, thermodynamics of the DE component interacting with a dark matter (DM) sector is addressed. We will also find the effects of considering the coincidence problem on the mutual interaction between the dark sectors, and thus the equation of state parameter of DE. Finally, we derive a relation between the mutual interaction of the dark components of the universe, accelerated with the either GDE or its generalization, and the thermodynamic fluctuations.

Constraints on interacting dark energy from time delay lenses

2016 ◽  
Vol 25 (01) ◽  
pp. 1650003 ◽  
Author(s):  
Yu Pan ◽  
Shuo Cao ◽  
Li Li
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Time Delay ◽  
Energy Density ◽  
Coincidence Problem ◽  
Multiple Images ◽  
Interaction Models ◽  
Strong Lensing ◽  
Interaction Term ◽  
Additional Constraints

We use the time delay measurements between multiple images of lensed sources in 18 strongly gravitationally lensed (SGL) systems to put additional constraints on three phenomenological interaction models for dark energy (DE) and dark matter (DM). The compatibility among the fits on the three models seems to imply that the coupling between DE and DM is a small value close to zero, which is compatible with the previous results for constraining interacting DE parameters. We find that, among the three interacting DE models, the [Formula: see text]IDE model with the interaction term [Formula: see text] proportional to the energy density of DM provides relatively better fits to recent observations. However, the coincidence problem is still very severe in the framework of three interacting DE models, since the fitting results do not show any preference for a nonzero coupling between DE and DM. More importantly, we have studied the significance of the current strong lensing data in deriving the interacting information between dark sectors, which highlights the importance of strong lensing time delay measurements to provide additional observational fits on alternative cosmological models.

scholarly journals Testing the Cosmic Coincidence Problem and the Nature of Dark Energy

2001 ◽  
Vol 87 (14) ◽  
Author(s):  
Neal Dalal ◽  
Kevork Abazajian ◽  
Elizabeth Jenkins ◽  
Aneesh V. Manohar
Keyword(s):  
Dark Energy ◽  
Coincidence Problem ◽  
Cosmic Coincidence Problem

scholarly journals There is no coincidence after all!

2020 ◽  
Vol 29 (14) ◽  
pp. 2043013
Author(s):  
Saurya Das
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Early Universe ◽  
Negative Pressure ◽  
Einstein Condensate ◽  
Coincidence Problem ◽  
Bose Einstein Condensate ◽  
Bose Einstein ◽  
Equal Density

We show that if Dark Matter is made up of light bosons, they form a Bose–Einstein condensate in the early Universe. This in turn naturally induces a Dark Energy of approximately equal density and exerting negative pressure. This explains the so-called coincidence problem.

scholarly journals Quantum Mechanical Explanation for Dark energy, Cosmic Coincidence, Flatness, Age and Size of Universe

2019 ◽  
Author(s):  
Biswaranjan Dikshit
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Vacuum Energy ◽  
Quantum Mechanical ◽  
Coincidence Problem ◽  
Dark Energy Density ◽  
Astronomical Observations ◽  
The Universe ◽  
Matter Energy ◽  
Cosmic Coincidence Problem

Although general relativity has been successful in explaining many astronomical phenomena, few problems about the contents and evolution of the universe have remained mysterious since last century. Most important of them is the cosmological constant problem in which conventional calculation of vacuum (or dark) energy density using quantum mechanics leads to a value ~10114 J/m3 which is ~10123 times more than the vacuum energy (5.3&times;10-10 J/m3) estimated from astronomical observations of expanding universe. Similarly, cosmic coincidence problem questions why the matter energy density (ordinary plus dark matter) is of the same order as the vacuum energy density at present time. Finally, the mechanism responsible for spatial flatness and expansion of the universe are not clearly understood. In this paper, by taking the vacuum as a finite and closed quantum oscillator, we solve all of the above-mentioned problems. At first, by using purely quantum mechanical approach, we predict that the dark energy density is c4/(GR2) = 5.27&times;10-10 J/m3 (where R is radius of 3-sphere of universe) and matter energy density is c4/(2GR2) = 2.6&times;10-10 J/m3 which match well with astronomical observations. We also prove that the dark energy has always been ~66.7% and matter energy has been ~33.3% of total energy and hence, the so called cosmic coincidence problem doesn&rsquo;t exist. Next, we show how flatness of space could be maintained since the early stage of universe. Finally, using our model, we derive the expression for age and radius of universe which match well with the astronomical data.

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