scholarly journals On dark matter and dark energy

2020 ◽  
pp. 166-168
Author(s):  
V. Yu. Stetsenko ◽  
A. V. Stetsenko
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cosmic Time ◽  
Accelerated Expansion ◽  
Stellar Clusters ◽  
Intergalactic Gas ◽  
Huge Amount ◽  
Absorption Of Light ◽  
Space Objects ◽  
Spectral Redshift

The dark matter hypothesis was created to explain the reason for the preservation of stellar clusters from dispersion. The weak point of this hypothesis is the great age of space, which is 13.8 billion years. Based on experimental data, it is shown that the age of space does not exceed 10 thousand years. In this case, the hypothesis of dark matter is not needed, since stellar clusters cannot scatter in such short cosmic time. The dark energy hypothesis was created to explain the reason for the accelerated expansion of space. The basis for this phenomenon is a large amount of spectral redshift of distant luminous space objects. It is shown that this value is mainly determined by the significant absorption of light energy of distant space objects by a huge amount of intergalactic gas, and not by the movement of these objects. In this case, the hypothesis of dark energy is not needed, and space should not rapidly expand and scatter in space.

scholarly journals FORMATION OF DARK MATTER HALOES IN A HOMOGENEOUS DARK ENERGY UNIVERSE

2010 ◽  
Vol 19 (08n10) ◽  
pp. 1397-1403
Author(s):  
L. MARASSI
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Large Scale ◽  
State Parameter ◽  
Mass Function ◽  
Accelerated Expansion ◽  
X Ray ◽  
Energy Models ◽  
Dark Energy Component ◽  
Standard Press

Several independent cosmological tests have shown evidences that the energy density of the universe is dominated by a dark energy component, which causes the present accelerated expansion. The large scale structure formation can be used to probe dark energy models, and the mass function of dark matter haloes is one of the best statistical tools to perform this study. We present here a statistical analysis of mass functions of galaxies under a homogeneous dark energy model, proposed in the work of Percival (2005), using an observational flux-limited X-ray cluster survey, and CMB data from WMAP. We compare, in our analysis, the standard Press–Schechter (PS) approach (where a Gaussian distribution is used to describe the primordial density fluctuation field of the mass function), and the PL (power–law) mass function (where we apply a non-extensive q-statistical distribution to the primordial density field). We conclude that the PS mass function cannot explain at the same time the X-ray and the CMB data (even at 99% confidence level), and the PS best fit dark energy equation of state parameter is ω = -0.58, which is distant from the cosmological constant case. The PL mass function provides better fits to the HIFLUGCS X-ray galaxy data and the CMB data; we also note that the ω parameter is very sensible to modifications in the PL free parameter, q, suggesting that the PL mass function could be a powerful tool to constrain dark energy models.

Pilgrim dark energy models in fractal universe

2016 ◽  
Vol 26 (06) ◽  
pp. 1750049 ◽  
Author(s):  
Abdul Jawad ◽  
Shamaila Rani ◽  
Ines G. Salako ◽  
Faiza Gulshan
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Cold Dark Matter ◽  
Accelerated Expansion ◽  
Freezing And Thawing ◽  
Eos Parameter ◽  
Pilgrim Dark Energy ◽  
Energy Models ◽  
Expansion Behavior ◽  
The Universe

We discuss the cosmological implications of interacting pilgrim dark energy (PDE) models (with Hubble, Granda–Oliveros and generalized ghost cutoffs) with cold dark matter ([Formula: see text]CDM) in fractal cosmology by assuming the flat universe. We observe that the Hubble parameter lies within observational suggested ranges while deceleration parameter represents the accelerated expansion behavior of the universe. The equation of state (EoS) parameter ([Formula: see text]) corresponds to the quintessence region and phantom region for different cases of [Formula: see text]. Further, we can see that [Formula: see text]–[Formula: see text] (where prime indicates the derivative with respect to natural logarithmic of scale factor) plane describes the freezing and thawing regions and also corresponds to [Formula: see text] limit for some cases of [Formula: see text] (PDE parameter). It is also noted that the [Formula: see text]–[Formula: see text] (state-finder parameters) plane corresponds to [Formula: see text] limit and also shows the Chaplygin as well as phantom/quintessence behavior. It is observed that pilgrim dark energy models in fractal cosmology expressed the consistent behavior with recent observational schemes.

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 Dual Cosmic Horizon Radius of Spacetime Curvature of a Multi-Path Connected Cosmic Topology

2020 ◽  
Author(s):  
Mohammed B. Al-Fadhli
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
High Speed ◽  
Initial Conditions ◽  
Large Angle ◽  
Big Bang ◽  
Accelerated Expansion ◽  
Horizon Radius ◽  
Spacetime Curvature ◽  
The Universe

The necessity of the dark energy and dark matter in the present universe could be a consequence of the antimatter elimination assumption in the early universe. In this research, I derive a new model to obtain the cosmic horizon radius and the potential cosmic topology utilising a new construal of space geometry inspired by large-angle correlations of the cosmic microwave background (CMB). A version of the Big Bounce theory is utilised to avoid the Big Bang singularity and inflationary constraints, and to tune the initial conditions of the curvature density. The mathematical derivation of a positively curved universe governed by only gravity revealed two cosmic horizon solutions. Although the positive horizon is conventionally associated with the evolution of the matter universe, the negative horizon solution could imply additional evolution in the opposite direction. This possibly suggests that the matter and antimatter could be evolving in opposite directions as distinct sides of the universe, as in the visualised Sloan Digital Sky Survey. The cosmic horizon radius is found to be accountable for the universal space curvature. By implementing this model, we find a decelerated stage of expansion during the first 10 Gyr, which is followed by a second stage of an accelerated expansion; potentially matching the tension in Hubble parameter measurements. In addition, the model predicts a final time-reversal stage of spatial contraction leading to the Big Crunch of a cyclic universe. The predicted density is 1.14. Other predictions are (1) a calculable flow rate of the matter side towards the antimatter side at the accelerated stage; conceivably explaining the dark flow observation, (2) a time-dependent spacetime curvature over horizon evolution, which could influence the galactic rotational speed; possibly explaining the high speed of stars, and (3) evolvable spacetime internal voids at the accelerated stage, which could contribute in continuously increasing the matter and antimatter densities elsewhere in both sides respectively. These findings may indicate the existence of the antimatter as a distinct side, which influences the evolution of the universe instead of the dark energy or dark matter.

scholarly journals Cosmography and Large Scale Structure by -Gravity: New Results

2009 ◽  
Vol 2009 ◽  
pp. 1-34 ◽  
Author(s):  
Salvatore Capozziello ◽  
Vincenzo Salzano
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Large Scale ◽  
Galaxy Cluster ◽  
Weak Field ◽  
Accelerated Expansion ◽  
Final Theory ◽  
Weak Field Limit ◽  
Expansion Of The Universe ◽  
Analytic Models

The so-called -gravity has recently attracted a lot of interest since it could be, in principle, able to explain the accelerated expansion of the Universe without adding unknown forms of dark energy/dark matter but, more simply, extending the General Relativity by generic functions of the Ricci scalar. However, apart several phenomenological models, there is no final -theory capable of fitting all the observations and addressing all the issues related to the presence of dark energy and dark matter. An alternative approach could be to “reconstruct” the form of starting from data without imposing particular classes of model. Besides, adopting the same philosophy, we take into account the possibility that galaxy cluster masses, estimated at X-ray wavelengths, could be explained, without dark matter, reconstructing the weak-field limit of analytic models. The corrected gravitational potential, obtained in this approximation, is used to estimate the total mass of a sample of 12 well-shaped clusters of galaxies.

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 Astromechanics of Dual Universe: A New Possible Explanation for the Universe Unsolved Problems

2020 ◽  
Author(s):  
Mohammed B. Al-Fadhli
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Hubble Parameter ◽  
Polar Coordinates ◽  
Accelerated Expansion ◽  
Dark Side ◽  
Second Phase ◽  
Spatial Curvature ◽  
Evolution Of The Universe ◽  
The Universe

The necessity of the dark energy and dark matter in the present universe could be a consequence of the antimatter elimination assumption in the early universe. Current cosmological models that rely on the dark side have left many unsolved mysteries, remarkably: tension in Hubble parameter measurements, the accelerated expansion, the fast orbital speed of stars, the dark flow observations, cosmic horizon, space flatness, absent of the antimatter, etc. On the other hand, General Relativity (GR) has relied on the spacetime to demonstrate the movement of matter due to a local curvature caused by the presence of matter. Founded on this, I trace the evolution of the spacetime worldlines based on the evolution of the universe spatial scale factor and its evolution time in polar coordinates in order to construct a potential spatial curvature over the temporal dimension or a global spacetime curvature. The mathematical derivations of a positively curved universe governed by only gravity revealed two opposite solutions of the worldline evolution. This possibly implies that the matter and antimatter could be evolving in opposite directions as distinct sides of the universe. By implementing the derived model, we find a decelerated phase of spatial expansion during the first 10 Gyr, that is followed by a second phase of an accelerated expansion; potentially matching the tension in Hubble parameter measurements. In addition, the model predicts a final time-reversal phase of spatial contraction, due to rapid surge in density i.e. reversal entropy, leading to a Big Crunch of a cyclic universe. The predicted density is 1.14. Other predictions are (1) an evolvable curved spacetime at the decelerated phase that is transformed to flatness at the accelerated phase with internal voids which could continuously increase the matter and antimatter densities elsewhere in both sides. (2) the spatial curvature through time dimension along spacetime worldlines was found to increase galaxy orbital speed and (3) a calculable flow rate of the matter side towards the antimatter side at the accelerated phase; conceivably explaining the dark flow observation. These findings may indicate the existence of the antimatter as a distinct side, which influences the evolution of the universe instead of the dark energy or dark matter. These theoretical outcomes and predictions are promising, which can be verified, fine-tuned or disproved using astrometric data in future works.

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 Macroscopic Theory of Dark Sector

2014 ◽  
Vol 2014 ◽  
pp. 1-23 ◽  
Author(s):  
Boris E. Meierovich
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Vector Field ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Accelerated Expansion ◽  
Kinetic Term ◽  
Dark Sector ◽  
Macroscopic Theory ◽  
Oscillating Solutions

A simple Lagrangian with squared covariant divergence of a vector field as a kinetic term turned out to be an adequate tool for macroscopic description of the dark sector. The zero-mass field acts as the dark energy. Its energy-momentum tensor is a simple additive to the cosmological constant. Massive fields describe two different forms of dark matter. The space-like massive vector field is attractive. It is responsible for the observed plateau in galaxy rotation curves. The time-like massive field displays repulsive elasticity. In balance with dark energy and ordinary matter it provides a four-parametric diversity of regular solutions of the Einstein equations describing different possible cosmological and oscillating nonsingular scenarios of evolution of the Universe. In particular, the singular big bang turns into a regular inflation-like transition from contraction to expansion with the accelerated expansion at late times. The fine-tuned Friedman-Robertson-Walker singular solution is a particular limiting case at the lower boundary of existence of regular oscillating solutions in the absence of vector fields. The simplicity of the general covariant expression for the energy-momentum tensor allows displaying the main properties of the dark sector analytically. Although the physical nature of dark sector is still unknown, the macroscopic theory can help analyze the role of dark matter in astrophysical phenomena without resorting to artificial model assumptions.

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