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 "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.

scholarly journals Unified Description of Dark Energy and Dark Matter within the Generalized Hybrid Metric-Palatini Theory of Gravity

Universe ◽  
2020 ◽  
Vol 6 (6) ◽  
pp. 78 ◽  
Author(s):  
Paulo M. Sá
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Fields ◽  
Accelerated Expansion ◽  
Late Time ◽  
Intermediate Phases ◽  
Expansion Of The Universe ◽  
Theory Of Gravity ◽  
The Universe ◽  
Unified Description

The generalized hybrid metric-Palatini theory of gravity admits a scalar-tensor representation in terms of two interacting scalar fields. We show that, upon an appropriate choice of the interaction potential, one of the scalar fields behaves like dark energy, inducing a late-time accelerated expansion of the universe, while the other scalar field behaves like pressureless dark matter that, together with ordinary baryonic matter, dominates the intermediate phases of cosmic evolution. This unified description of dark energy and dark matter gives rise to viable cosmological solutions, which reproduce the main features of the evolution of the universe.

scholarly journals COSMOGRAPHY OF INTERACTING GENERALIZED QCD GHOST DARK ENERGY

2013 ◽  
Vol 22 (14) ◽  
pp. 1350084 ◽  
Author(s):  
MOHAMMAD MALEKJANI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Accelerated Expansion ◽  
Model Parameter ◽  
Ghost Dark Energy ◽  
Evolutionary Trajectories ◽  
Expansion Of The Universe ◽  
Qcd Ghost Dark Energy ◽  
The Universe ◽  
Friedmann Robertson Walker

Exploring the accelerated expansion of the universe, we investigate the generalized ghost dark energy (GGDE) model from the statefinder diagnostic analysis in a flat Friedmann–Robertson–Walker universe. First, we calculate the cosmological evolution and statefinder trajectories for noninteracting case and then extend this work by considering the interaction between dark matter and dark energy components. We show that in the noninteracting case the phantom line cannot be crossed and also the evolutionary trajectories of model in s - r plane cannot be discriminated. It has been shown that the present location of model in s - r plane would be close to observational value for negative values of the model parameter. In the presence of interaction between dark matter and dark energy, the phantom regime is achieved, the accelerated phase of expansion occurs sooner compared with the noninteracting case. The GGDE model is also discussed from the viewpoint of perturbation theory by calculating the adiabatic sound speed of the model. Finally, unlike the noninteracting case, the evolutionary trajectories in s - r plane can be discriminated in the interacting model. Like the noninteracting model, in the interacting case the present location of GGDE model is closer to observational value for negative values of the model parameter.

scholarly journals The Influence of Evolving Dark Energy on Cosmology

2005 ◽  
Vol 22 (4) ◽  
pp. 315-325 ◽  
Author(s):  
Luke Barnes ◽  
Matthew J. Francis ◽  
Geraint F. Lewis ◽  
Eric V. Linder
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Constant ◽  
Energy Exchange ◽  
Observational Evidence ◽  
Cosmological Models ◽  
Observational Constraints ◽  
Expansion Of The Universe ◽  
The Universe

AbstractObservational evidence indicating that the expansion of the universe is accelerating has surprised cosmologists in recent years. Cosmological models have sought to explain this acceleration by incorporating ‘dark energy’, of which the traditional cosmological constant is just one possible candidate. Several cosmological models involving an evolving equation of state of the dark energy have been proposed, as well as possible energy exchange to other components, such as dark matter. This paper summarizes the forms of the most prominent models and discusses their implications for cosmology and astrophysics. Finally, this paper examines the current and future observational constraints on the nature of dark energy.

scholarly journals Quantum Space and the Evolution of the Dark Universe

2017 ◽  
Author(s):  
Carlos A. Melendres
Keyword(s):  
Phase Diagram ◽  
Dark Matter ◽  
Dark Energy ◽  
State Parameter ◽  
Big Bang ◽  
Accelerated Expansion ◽  
Quantum Space ◽  
Fundamental Particles ◽  
Expansion Of The Universe ◽  
The Universe

We present a model of space that considers it to be a quantized dynamical entity which is a component of the universe along with matter and radiation. The theory is used together with  thermodynamic data  to provide a new view of cosmic  evolution  and an insight into the nature of dark energy and dark matter.           Space is made up of energy quanta. The universe started from an atomic size volume at very high  temperature and pressure near the Planck epoch. Upon expansion  and  cooling, phase transitions occurred  resulting in the formation of radiation,  fundamental particles, and matter. These  nucleate and grow into stars, galaxies, and clusters. From a phase diagram of cosmic  composition,  we  obtained  a correlation between   dark energy  and the energy of space. Using  the Friedmann  equations, data from WMAP studies of  the composition of the universe  at 3.0 x 105 (a=5.25 x 10-2) years  and at present (a=1), are well fitted by our  model with an equation of state parameter, w= -0.7.  The accelerated expansion of the universe, starting at about 7  billion years, determined by  BOSS measurements,  also correlates well with the dominance of dark energy  at 7.25 x 109 years ( a= 0.65). The expansion  can be  attributed to Quintessence with a  space force  arising from a quantum space field.  From our phase diagram, we also find a correlation suggesting  that  dark matter is a plasma form of matter similar to that  which existed during the photon epoch  immediately prior to recombination.         Our Quantum Space  Model leads to a  universe which  is  homogeneous and isotropic without the need for inflation. The thermodynamics of expansion is consistent with  BOSS data  that  show the process  to be  adiabatic and the rate of expansion  decelerating  during  the first  6  billion years after the Big Bang.  However, it  became non-adiabatic and accelerating thereafter. This  implies  an influx  of energy from a source outside the universe; it warrants consideration as a possible factor  in  the accelerated expansion of the universe.  

scholarly journals A Thermodynamic Approach towards Understanding the Dark Universe

2018 ◽  
Author(s):  
Carlos A. Melendres
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cooling Curve ◽  
Accelerated Expansion ◽  
Thermodynamic Approach ◽  
Quantum Space ◽  
Conservation Of Energy ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Model Fits

We present a thermodynamic approach in modeling the evolution of the universe based on a theory that space consists of energy quanta and is the cosmic fluid component of the universe. It provides an insight on the nature of dark energy and dark matter, as well as a rationale for the accelerated expansion of the universe. The universe started from an atomic size volume of an ideal gas at very high temperature and pressure. Upon expansion and cooling, phase transitions occurred resulting in the formation of fundamental particles, and matter. These nucleate and grow into stars, galaxies, and clusters with the aid of gravity. From the cooling curve of the universe we constructed a thermodynamic phase diagram of cosmic composition, from which we obtained a correlation between dark energy and the energy of space. Using Friedmann’s equations, our model fits well the WMAP data on cosmic composition with an equation of state parameter, w = −0.7. The dominance of dark energy started at 7.25 × 109 years, in good agreement with BOSS measurements. The expansion of space is attributed to Quintessence associated with a quantum space field. Dark Matter is identified as a plasma form of matter similar to that which existed during the photon epoch, prior to recombination. The thermodynamics of expansion of the universe was adiabatic and decelerating during the first 7 billion years after the Big Bang; it became non-adiabatic and accelerating thereafter. The latter maybe due to an influx of energy from a source outside the universe, if it is open. If it is closed, thermodynamics requires that the pressure of space be negative. Said pressure would cause the accelerated expansion of the universe in accordance with the theory of General Relativity, and the law of conservation of energy. We provide a mechanism to explain this. The acceleration should not be interpreted as due to a repulsive form of gravity. Our Quantum Space model fits well the behavior of the observable universe.

Interacting new holographic dark energy model with varying G in nonflat universe

2013 ◽  
Vol 91 (12) ◽  
pp. 1090-1092
Author(s):  
V. Fayaz ◽  
F. Felegary ◽  
H. Hossienkhani
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Dark Energy Model ◽  
Holographic Dark Energy ◽  
Energy Model ◽  
Accelerated Expansion ◽  
Late Time ◽  
Holographic Dark Energy Model ◽  
Expansion Of The Universe ◽  
The Universe

Motivated by the work of Karami and Fehri (Phys. Lett. B, 684, 61 (2010)). We generalize their work with varying G. We investigate the new holographic dark energy model with varying G. We consider a spatially nonflat universe containing interacting new holographic dark energy with pressureless dark matter. We obtain the equation of state and the deceleration parameters. Also we reconstruct ωA for a = a0tn and H = [β/(α − 1)](1/t) in the late time universe. We also obtain q for a = a0tn and H = [β/(α − 1)](1/t) in the present time universe, which describes accelerated expansion of the universe.

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.

The accelerating universe and dark energy

2014 ◽  
Vol 23 (06) ◽  
pp. 1430012 ◽  
Author(s):  
Charles Baltay
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmological Parameters ◽  
Accelerating Universe ◽  
Heavy Particles ◽  
Familiar World ◽  
Acceleration Of The Universe ◽  
Expansion Of The Universe ◽  
The Universe ◽  
Present Understanding

The recent discovery by Riess et al.1 and Perlmutter et al.2 that the expansion of the universe is accelerating is one of the most significant discoveries in cosmology in the last few decades. To explain this acceleration a mysterious new component of the universe, dark energy, was hypothesized. Using general relativity (GR), the measured rate of acceleration translates to the present understanding that the baryonic matter, of which the familiar world is made of, is a mere 4% of the total mass-energy of the universe, with nonbaryonic dark matter making up 24% and dark energy making up the majority 72%. Dark matter, by definition, has attractive gravity, and even though we presently do not know what it is, it could be made of the next heavy particles discovered by particle physicists. Dark energy, however, is much more mysterious, in that even though we do not know what it is, it must have some kind of repulsive gravity and negative pressure, very unusual properties that are not part of the present understanding of physics. Investigating the nature of dark energy is therefore one of the most important areas of cosmology. In this review, the cosmology of an expanding universe, based on GR, is discussed. The methods of studying the acceleration of the universe, and the nature of dark energy, are presented. A large amount of experimentation on this topic has taken place in the decade since the discovery of the acceleration. These are discussed and the present state of knowledge of the cosmological parameters is summarized in Table 7 below. A vigorous program to further these studies is under way. These are presented and the expected results are summarized in Table 10 below. The hope is that at the end of this program, it would be possible to tell whether dark energy is due to Einstein's cosmological constant or is some other new constituent of the universe, or alternately the apparent acceleration is due to some modification of GR.

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