scholarly journals There can be no dark energy or space expansion because radiation pressure forces can cause the universe to expand

2021 ◽  
Vol 2014 (1) ◽  
pp. 012010
Author(s):  
G Zhang ◽  
X Wang
Keyword(s):  
Dark Energy ◽  
Radiation Pressure ◽  
Space Expansion ◽  
The Universe

scholarly journals The Constant of the Universe Expansion Acceleration ΓH, the Einstein Variation of c and Parameters VH, Ω, Ʌ and ɣ

2020 ◽  
Vol 12 (3) ◽  
pp. 28
Author(s):  
J. G. Lartigue
Keyword(s):  
Dark Energy ◽  
Gravitational Field ◽  
Additional Condition ◽  
Expansion Velocity ◽  
Gravitational Acceleration ◽  
Universe Expansion ◽  
Physical Universe ◽  
C Value ◽  
Space Expansion ◽  
The Universe

The Hubble-Lemaitre equation v=H∙r  (cm∙s-1) represented a linear function of the radial Space expansion velocity, if H would be a constant. Sometimes it has been assumed as H = 1/t, which sends back to the classical v = r/t. However, the later discovered acceleration required the additional condition for H to be, also, a function of time; or, opposed, the existence of a not yet defined dark energy. In a previous paper [1] it had been proposed a provisional expression for a constant Universe expansion acceleration as function of distance: Γ= H2( cm∙s-2). Now, the substitution of r as a function of time, takes to five new equations of H, the Hubble velocity vH , the Hubble acceleration ΓH and the positive Hubble potential VH of the Space. So the proposed Hubble functions for the Space: H, rH , vH, ΓH and VH result higher than those in a gravitational field. All of these Hubble functions act in the total Space expansion though, into the Physical Universe, ΓH is not perceived as it does, continuously, the opposed gravitational acceleration g. Otherwise, a revision is made of the Einstein equation for the c value as function of the gravitational potential φ. Additional proposals are made about the horizons definitions and parameters Ω, Ʌ and ɣ.

Cosmological constant

2018 ◽  
Author(s):  
Michael Kachelriess
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Accelerated Expansion ◽  
Vacuum Fluctuations ◽  
Present Epoch ◽  
Modify Gravity ◽  
Expansion Of The Universe ◽  
The Universe

The contribution of vacuum fluctuations to the cosmological constant is reconsidered studying the dependence on the used regularisation scheme. Then alternative explanations for the observed accelerated expansion of the universe in the present epoch are introduced which either modify gravity or add a new component of matter, dubbed dark energy. The chapter closes with some comments on attempts to quantise gravity.

scholarly journals Taxonomy of Dark Energy Models

Universe ◽  
2021 ◽  
Vol 7 (6) ◽  
pp. 163
Author(s):  
Verónica Motta ◽  
Miguel A. García-Aspeitia ◽  
Alberto Hernández-Almada ◽  
Juan Magaña ◽  
Tomás Verdugo
Keyword(s):  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Energy Component ◽  
The Past ◽  
Energy Models ◽  
The Status ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Unknown Component

The accelerated expansion of the Universe is one of the main discoveries of the past decades, indicating the presence of an unknown component: the dark energy. Evidence of its presence is being gathered by a succession of observational experiments with increasing precision in its measurements. However, the most accepted model for explaining the dynamic of our Universe, the so-called Lambda cold dark matter, faces several problems related to the nature of such energy component. This has led to a growing exploration of alternative models attempting to solve those drawbacks. In this review, we briefly summarize the characteristics of a (non-exhaustive) list of dark energy models as well as some of the most used cosmological samples. Next, we discuss how to constrain each model’s parameters using observational data. Finally, we summarize the status of dark energy modeling.

scholarly journals Physical Acceptability of the Renyi, Tsallis and Sharma-Mittal Holographic Dark Energy Models in the f(T,B) Gravity under Hubble’s Cutoff

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 67
Author(s):  
Salim Harun Shekh ◽  
Pedro H. R. S. Moraes ◽  
Pradyumn Kumar Sahoo
Keyword(s):  
Dark Energy ◽  
Holographic Dark Energy ◽  
Cosmological Parameters ◽  
Field Equations ◽  
Eos Parameter ◽  
Two Fluids ◽  
Gravitational Field Equations ◽  
Energy Models ◽  
Different Types ◽  
The Universe

In the present article, we investigate the physical acceptability of the spatially homogeneous and isotropic Friedmann–Lemâitre–Robertson–Walker line element filled with two fluids, with the first being pressureless matter and the second being different types of holographic dark energy. This geometric and material content is considered within the gravitational field equations of the f(T,B) (where T is the torsion scalar and the B is the boundary term) gravity in Hubble’s cut-off. The cosmological parameters, such as the Equation of State (EoS) parameter, during the cosmic evolution, are calculated. The models are stable throughout the universe expansion. The region in which the model is presented is dependent on the real parameter δ of holographic dark energies. For all δ≥4.5, the models vary from ΛCDM era to the quintessence era.

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 ANISOTROPIC COMPACT STARS WITH VARIABLE COSMOLOGICAL CONSTANT

2012 ◽  
Vol 21 (13) ◽  
pp. 1250088 ◽  
Author(s):  
SK. MONOWAR HOSSEIN ◽  
FAROOK RAHAMAN ◽  
JAYANTA NASKAR ◽  
MEHEDI KALAM ◽  
SAIBAL RAY
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Compact Star ◽  
Compact Stars ◽  
Radial Dependence ◽  
Regularity Conditions ◽  
Variable Cosmological Constant ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Surface Redshift

Recently, the small value of the cosmological constant and its ability to accelerate the expansion of the universe is of great interest. We discuss the possibility of forming of anisotropic compact stars from this cosmological constant as one of the competent candidates of dark energy. For this purpose, we consider the analytical solution of Krori and Barua metric. We take the radial dependence of cosmological constant and check all the regularity conditions, TOV equations, stability and surface redshift of the compact stars. It has been shown as conclusion that this model is valid for any compact star and we have cited 4U 1820-30 as a specific example of that kind of star.

scholarly journals From Quantum Unstable Systems to the Decaying Dark Energy: Cosmological Implications

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Aleksander Stachowski ◽  
Marek Szydłowski ◽  
Krzysztof Urbanowski
Keyword(s):  
Dark Energy ◽  
Time Reversal ◽  
Hubble Parameter ◽  
Decay Process ◽  
Time Dependent ◽  
Time Reversal Symmetry ◽  
Exponential Form ◽  
Cosmological Time ◽  
Evolution Of The Universe ◽  
The Universe

We consider a cosmology with decaying metastable dark energy and assume that a decay process of this metastable dark energy is a quantum decay process. Such an assumption implies among others that the evolution of the Universe is irreversible and violates the time reversal symmetry. We show that if we replace the cosmological time t appearing in the equation describing the evolution of the Universe by the Hubble cosmological scale time, then we obtain time dependent Λ(t) in the form of the series of even powers of the Hubble parameter H: Λ(t)=Λ(H). Our special attention is focused on radioactive-like exponential form of the decay process of the dark energy and on the consequences of this type decay.

Dark energy, cosmic coincidence and future singularity of the universe

2012 ◽  
Vol 45 (1) ◽  
pp. 53-62 ◽  
Author(s):  
Sanjay Sarkar ◽  
Chandra Rekha Mahanta
Keyword(s):  
Dark Energy ◽  
Future Singularity ◽  
The Universe

scholarly journals On The Symmetry of The Universe

2020 ◽  
Author(s):  
Engel Roza
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Thermodynamic Equilibrium ◽  
Vacuum Energy ◽  
Quantum Mechanical ◽  
Baryonic Matter ◽  
Time Uncertainty ◽  
Matter Effect ◽  
Mechanical Interpretation ◽  
The Universe

It is shown that the Lambda component in the cosmological Lambda-CDM model can be conceived as vacuum energy, consisting of gravitational particles subject to Heisenberg&rsquo;s energy-time uncertainty. These particles can be modelled as elementary polarisable Dirac-type dipoles (&ldquo;darks&rdquo;) in a fluidal space at thermodynamic equilibrium, with spins that are subject to the Bekenstein-Hawking entropy. Around the baryonic kernels, uniformly distributed in the universe, the spins are polarized, thereby invoking an increase of the effective gravitational strength of the kernels. It explains the dark matter effect to the extent that the numerical value of Milgrom&rsquo;s acceleration constant can be assessed by theory. Non-polarized vacuum particles beyond the baryonic kernels compose the dark energy. The result is a quantum mechanical interpretation of gravity in terms of quantitatively established shares in baryonic matter, dark matter and dark energy, which correspond with the values of the Lambda-CDM model..

GROWTH INDEX AND MODIFIED GRAVITY

2011 ◽  
Vol 01 ◽  
pp. 228-233
Author(s):  
YUNGUI GONG
Keyword(s):  
Growth Rate ◽  
Dark Energy ◽  
Modified Gravity ◽  
Growth Index ◽  
Accurate Approximation ◽  
Energy Models ◽  
Λcdm Model ◽  
The Universe ◽  
Matter Energy ◽  
Matter Perturbation

The growth rate of matter perturbation and the expansion rate of the Universe can be used to distinguish modified gravity and dark energy models. Remarkably, the growth rate can be approximated as Ωγ. We discuss the dependence of the growth index γ on the dimensionless matter energy density Ω for a more accurate approximation of the growth factor. The observational data are used to fit different models. The data strongly disfavor the Dvali-Gabadadze-Porrati model. For the ΛCDM model, we find that [Formula: see text]. For the Dvali-Gabadadze-Porrati model, we find that [Formula: see text].

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