scholarly journals CONSTRAINTS ON A NEW ALTERNATIVE MODEL TO DARK ENERGY

2005 ◽  
Vol 14 (09) ◽  
pp. 1495-1506 ◽  
Author(s):  
YUNGUI GONG ◽  
XI-MING CHEN
Keyword(s):  
Dark Energy ◽  
Alternative Model ◽  
Friedmann Equation ◽  
Recent Past ◽  
New Model ◽  
Type Ia Supernova ◽  
The Future ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

The recent type Ia supernova data suggest that the Universe is accelerating now and had decelerated in recent past. This may provide the evidence that the standard Friedmann equation needs to be modified. We analyze in detail a new model in the context of modified Friedmann equation using the supernova data published by the High-z Supernova Search Team and the Supernova Cosmology Project. The new model explains recent acceleration and past deceleration. Furthermore, the acceleration of the expansion of the Universe is almost zero in the future.

A NEW ALTERNATIVE MODEL TO DARK ENERGY

2004 ◽  
Vol 19 (25) ◽  
pp. 1933-1938 ◽  
Author(s):  
YUNGUI GONG ◽  
XI-MING CHEN ◽  
CHANG-KUI DUAN
Keyword(s):  
Alternative Model ◽  
Friedmann Equation ◽  
Matter Density ◽  
General Function ◽  
Recent Past ◽  
New Model ◽  
The Past ◽  
Type Ia ◽  
Ia Supernovae ◽  
The Universe

The recent observations of type Ia supernovae strongly support that the universe is accelerating now and decelerated in the recent past. This may be the evidence of the breakdown of the standard Friedmann equation. Instead of a linear function of the matter density, we consider a general function of the matter density to modify the Freidmann equation. We propose a new model which explains the recent acceleration and the past deceleration. Furthermore, the new model also gives a decelerated universe in the future. The new model gives Ω m 0=0.46 and z T =0.44.

The Mystery of the Dark Energy Based on Energy Materials

2012 ◽  
Vol 496 ◽  
pp. 523-526
Author(s):  
Jian Guo Lu ◽  
Ming Hu
Keyword(s):  
Dark Energy ◽  
Gamma Ray ◽  
Background Radiation ◽  
Accelerated Expansion ◽  
Energy Materials ◽  
Type Ia Supernova ◽  
Microwave Background Radiation ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

Recently the observations on the type Ia supernova has showed the accelerated expansion of the universe which can be used to illustrate by the “dark energy”. In order to understand the accelerated expansion of the universe and the dark energy, people study them based on two aspects: theoretical mechanism and cosmology observation restrictions. The simplest and the most frequently used models of the dark energy are the vacuum energy, cosmic constant model and quintessence model etc. The measurement of the universe can be used to identify the properties of the dark energy. The anisotropy of the type Ia supernova and cosmic microwave background radiation are the methods which commonly used to detect the dark energy, other methods are weak lensing, X ray gas group, high red shift gamma-ray burst and so on

scholarly journals "Doppler De-boosting" and the Observation of "Standard Candles" in Cosmology

2021 ◽  
Author(s):  
Mark Zilberman ◽  
Keyword(s):  
Dark Energy ◽  
Relativistic Effect ◽  
Accelerated Expansion ◽  
Light Sources ◽  
Relativistic Jets ◽  
Radiation Sources ◽  
Standard Candle ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

“Doppler boosting” is a well-known relativistic effect that alters the apparent luminosity of approaching radiation sources. “Doppler de-boosting” is the same relativistic effect observed but for receding light sources (e.g. relativistic jets of AGN and GRB). “Doppler boosting” alters the apparent luminosity of approaching light sources to appear brighter, while “Doppler de-boosting” alters the apparent luminosity of receding light sources to appear fainter. While “Doppler de-boosting” has been successfully accounted for and observed in relativistic jets of AGN, it was ignored in the establishment of Standard candles for cosmological distances. A Standard Candle adjustment of Z>0.1 is necessary for “Doppler de-boosting”, otherwise we would incorrectly assume that Standard Candles appear dimmer, not because of “Doppler de-boosting” but because of the excessive distance, which would affect the entire Standard Candles ladder at cosmological distances. The ratio between apparent (L) and intrinsic (Lo) luminosities as a function of the redshift Z and spectral index α is given by the formula ℳ(Z) = L/Lo=(Z+1)α -3 and for Type Ia supernova appears as ℳ(Z) = L/Lo=(Z+1)-2. “Doppler de-boosting” may also explain the anomalously low luminosity of objects with a high Z without the introduction of an accelerated expansion of the Universe and Dark Energy.

CPL effective dark energy from the backreaction effect

2019 ◽  
Vol 34 (21) ◽  
pp. 1950167
Author(s):  
Yan-Hong Yao ◽  
Xin-He Meng
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Perfect Fluid ◽  
Coming Out ◽  
Hubble Parameter ◽  
Small Scale ◽  
Type Ia Supernova ◽  
Type Ia ◽  
The Difference ◽  
The Universe

In this paper, we interpret the dark energy as an effect caused by small-scale inhomogeneities of the universe with the use of the spatial averaged approach of Buchert [Gen. Relat. Gravit. 32, 105 (2000); 33, 1381 (2001)]. The model considered here adopts the Chevallier–Polarski–Linder (CPL) parametrizations of the equation of state of the effective perfect fluid from the backreaction effect. Thanks to the effective geometry introduced by Larena et al. [Phys. Rev. D 79, 083011 (2009)] in their previous work, we confront such backreaction model with the latest type Ia supernova and Hubble parameter observations, coming out with the results that reveal the difference between the Friedmann–Lemaître–Robertson–Walker model and backreaction model.

scholarly journals “Pure” Supernovae and Dark Energy

2011 ◽  
Vol 7 (S281) ◽  
pp. 17-20
Author(s):  
M. V. Pruzhinskaya ◽  
E. S. Gorbovskoy ◽  
V. M. Lipunov
Keyword(s):  
Dark Energy ◽  
Chemical Evolution ◽  
Special Class ◽  
Accelerated Expansion ◽  
Type Ia Supernovae ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
Ia Supernovae ◽  
The Universe

AbstractA special class of Type Ia supernovae that is not subject to ordinary and additional intragalactic gray absorption and chemical evolution has been identified. Analysis of the Hubble diagrams constructed for these supernovae confirms the accelerated expansion of the Universe irrespective of the chemical evolution and possible gray absorption in galaxies.

scholarly journals Are Type Ia supernova powerful tool to detect anisotropic expansion of the Universe?

2020 ◽  
Vol 80 (8) ◽  
Author(s):  
A. Salehi ◽  
H. Farajollahi ◽  
M. Motahari ◽  
P. Pashamokhtari ◽  
M. Yarahmadi ◽  
...  
Keyword(s):  
Dark Energy ◽  
Statistical Analysis ◽  
Coordinate System ◽  
Teleparallel Gravity ◽  
Preferred Direction ◽  
Energy Models ◽  
Anisotropic Expansion ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

Abstract In this paper, we present a detailed analysis of the dark energy dipole using Union2, Pantheon and GRB dataset in Chameleon and Teleparallel dark energy models, in comparison with $$\Lambda $$ΛCDM. Both models are extensively studied in recent years and our result shows that with Union2 and Pantheon data, the preferred direction of the anisotropy in both models are very close to each other as well as with those obtained in some studies for $$\Lambda $$ΛCDM. However, when the models fitted with a combination of Union 2 and GRB, the statistical analysis slightly favors the Chameleon cosmology over Teleparallel gravity, with the maximum anisotropic direction of $$(l = 330^{+30}_{-28}$$(l=330-28+30, $$b = -15^{+23}_{-25})$$b=-15-25+23) in galactic coordinate system, comparable with $$\alpha $$α-dipole result in Keck-VLT data and LCDM.

scholarly journals Cosmology with an interacting van der Waals fluid

2018 ◽  
Vol 27 (04) ◽  
pp. 1850037 ◽  
Author(s):  
E. Elizalde ◽  
M. Khurshudyan
Keyword(s):  
Dark Energy ◽  
Finite Time ◽  
Van Der Waals ◽  
The Other ◽  
Van Der Waals Fluid ◽  
Type Iv ◽  
Other Hand ◽  
The Future ◽  
Expansion Of The Universe ◽  
The Universe

A model for the late-time accelerated expansion of the Universe is considered where a van der Waals fluid interacting with matter plays the role of dark energy. The transition towards this phase in the cosmic evolution history is discussed in detail and, moreover, a complete classification of the future finite-time singularities is obtained for six different possible forms of the nongravitational interaction between dark energy (the van der Waals fluid) and dark matter. This study shows, in particular, that a Universe with a noninteracting three-parameter van der Waals fluid can evolve into a Universe characterized by a type IV (generalized sudden) singularity. On the other hand, for certain values of the parameters, exit from the accelerated expanding phase is possible in the near future, what means that the expansion of the Universe in the future could become decelerated – to our knowledge, this interesting situation is not commonplace in the literature. On the other hand, our study shows that space can be divided into different regions. For some of them, in particular, the nongravitational interactions [Formula: see text], [Formula: see text] and [Formula: see text] may completely suppress future finite-time singularity formation, for sufficiently high values of [Formula: see text]. On the other hand, for some other regions of the parameter space, the mentioned interactions would not affect the singularity type, namely the type IV singularity generated in the case of the noninteracting model would be preserved. A similar conclusion has been archived for the cases of [Formula: see text], [Formula: see text] and [Formula: see text] nongravitational interactions, with only one difference: the [Formula: see text] interaction will change the type IV singularity of the noninteracting model into a type II (the sudden) singularity.

scholarly journals About the Origin of the Dark Energy and the Zero Mass/Energy Universe

2021 ◽  
pp. 1-7
Author(s):  
Guenter Frohberg
Keyword(s):  
Dark Energy ◽  
Energy Density ◽  
Total Energy ◽  
Average Energy ◽  
Friedmann Equation ◽  
Relativity Theory ◽  
Total Energy Density ◽  
Gravitational Fields ◽  
Expansion Of The Universe ◽  
The Universe

Based on the Gravito-Electro-Magnetic (GEM) equations as another form (for low fields) of Einstein's Equations of General Relativity Theory (GRT) an equation is derived for the total energy density in the universe, including the gravitational fields, the contribution thereof is always negative and so it seems to represents the Dark Energy (DE).  When calculating the total energy of the universe from this equation, the result is near to zero because of negative contributions from gravitational fields, depending a little on the available parameters of the universe as e.g. it's baryonic mass. Thus the assumption is given a high amount of probability, that the total energy (mass) in the universe is really zero and very likely is always zero. This  would mean, that the universe developed from empty space-time or from nothing (may be by quantum fluctuations). Looking on the development it could be  that the average energy density is zero for each sufficient large part of the universe at any time, except for very local deviations (e.g. galaxies, black holes etc.). As a consequence the expansion of the universe is probably not retarded by gravity (thus the Friedmann equation and others do not apply). The expansion of the universe can be considered as driven by the pressure of a gas-like medium with positive masses as by intergalactic gas, dust, stars and galaxies. Conclusions are drawn as to the interpretation of the formation of voids in the universe, flat space etc.

scholarly journals Dark Energy and Cosmological Constant

2018 ◽  
Vol 17 (1) ◽  
pp. 25-32
Author(s):  
Louise Rebecca ◽  
C Sivaram ◽  
Kenath Arun
Keyword(s):  
Dark Energy ◽  
Cosmological Constant ◽  
Mass Density ◽  
Critical Density ◽  
Accelerated Expansion ◽  
Microwave Background ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
Ia Supernovae ◽  
The Universe

One of the unresolved problems in cosmology is that the measured mass density of the universe has revealed a value that was about 30% of the critical density. Since the universe is very nearly spatially flat, as is indicated by measurements of the cosmic microwave background, about 70% of the energy density of the universe was left unaccounted for. Another observation seems to be connected to this mystery. Generally one would expect the rate of expansion to slow down once the universe started expanding. The measurements of Type Ia supernovae have revealed that the expansion of the universe is actually accelerating. This accelerated expansion is attributed to the so-called dark energy (DE).Here we give a brief overview on the observational basis for DE hypothesis and how cosmological constant, initially proposed by Einstein to obtain a static universe, can play the role of dark energy.

scholarly journals Universe opacity and Type Ia supernova dimming

2019 ◽  
Vol 489 (1) ◽  
pp. L63-L68 ◽  
Author(s):  
Václav Vavryčuk
Keyword(s):  
Cold Dark Matter ◽  
Hubble Constant ◽  
Light Extinction ◽  
Universe Model ◽  
Type Ia Supernova ◽  
Accelerating Expansion ◽  
Λcdm Model ◽  
Type Ia ◽  
Expansion Of The Universe ◽  
The Universe

ABSTRACT In this paper, I revoke a debate about an origin of Type Ia supernova (SN Ia) dimming. I argue that except for a commonly accepted accelerating expansion of the Universe, a conceivable alternative for explaining this observation is universe opacity caused by light extinction by intergalactic dust, even though it is commonly assumed that this effect is negligible. Using data of the Union2.1 SN Ia compilation, I find that the standard Λ cold dark matter (ΛCDM) model and the opaque universe model fit the SN Ia measurements at redshifts z < 1.4 comparably well. The optimum solution for the opaque universe model is characterized by the B-band intergalactic opacity $\lambda _{B} = 0.10 \pm 0.03 \, \mathrm{Gpc}^{-1}$ and the Hubble constant $H_0 = 68.0 \pm 2.5 \, \mathrm{km\, s^{-1}\, Mpc^{-1}}$. The intergalactic opacity is higher than that obtained from independent observations but still within acceptable limits. This result emphasizes that the issue of the accelerating expansion of the Universe as the origin of the SN Ia dimming is not yet definitely resolved. Obviously, the opaque universe model as an alternative to the ΛCDM model is attractive, because it avoids puzzles and controversies associated with dark energy and the accelerating expansion.

Sign in / Sign up

Export Citation Format

Share Document