scholarly journals Constraints on Dark Energy from Supernovae, Gamma‐Ray Bursts, Acoustic Oscillations, Nucleosynthesis, Large‐Scale Structure, and the Hubble Constant

2007 ◽  
Vol 664 (2) ◽  
pp. 633-639 ◽  
Author(s):  
E. L. Wright
Keyword(s):  
Dark Energy ◽  
Large Scale ◽  
Gamma Ray ◽  
Hubble Constant ◽  
Large Scale Structure ◽  
Gamma Ray Bursts ◽  
Scale Structure ◽  
Acoustic Oscillations

scholarly journals Model-independent calibrations of gamma-ray bursts using machine learning

2021 ◽  
Vol 503 (3) ◽  
pp. 4581-4600
Author(s):  
Orlando Luongo ◽  
Marco Muccino
Keyword(s):  
Machine Learning ◽  
Dark Energy ◽  
Gamma Ray ◽  
Gamma Ray Bursts ◽  
Bayesian Regression ◽  
Machine Learning Techniques ◽  
Acoustic Oscillations ◽  
Chi Square ◽  
Model Independent ◽  
Chi Square Analysis

ABSTRACT We alleviate the circularity problem, whereby gamma-ray bursts are not perfect distance indicators, by means of a new model-independent technique based on Bézier polynomials. We use the well consolidate Amati and Combo correlations. We consider improved calibrated catalogues of mock data from differential Hubble rate points. To get our mock data, we use those machine learning scenarios that well adapt to gamma-ray bursts, discussing in detail how we handle small amounts of data from our machine learning techniques. We explore only three machine learning treatments, i.e. linear regression, neural network, and random forest, emphasizing quantitative statistical motivations behind these choices. Our calibration strategy consists in taking Hubble’s data, creating the mock compilation using machine learning and calibrating the aforementioned correlations through Bézier polynomials with a standard chi-square analysis first and then by means of a hierarchical Bayesian regression procedure. The corresponding catalogues, built up from the two correlations, have been used to constrain dark energy scenarios. We thus employ Markov chain Monte Carlo numerical analyses based on the most recent Pantheon supernova data, baryonic acoustic oscillations, and our gamma-ray burst data. We test the standard ΛCDM model and the Chevallier–Polarski–Linder parametrization. We discuss the recent H0 tension in view of our results. Moreover, we highlight a further severe tension over Ωm and we conclude that a slight evolving dark energy model is possible.

scholarly journals X-ray Cluster Large Scale Structure and Cosmology

2005 ◽  
Vol 216 ◽  
pp. 373-380
Author(s):  
Marguerite Pierre
Keyword(s):  
Dark Energy ◽  
Galaxy Clusters ◽  
Large Scale ◽  
Scaling Law ◽  
Large Scale Structure ◽  
Short Review ◽  
Scale Structure ◽  
X Ray ◽  
Recent Advances

We outline the main arguments in favor of cosmological X-ray surveys of galaxy clusters. We summarize recent advances in our understanding of cluster physics. After a short review of past surveys, we present the scientific motivations of the XMM Large Scale Structure survey. We further illustrate how such a survey can help constrain the nature of the dark energy as well as cluster scaling law evolution, i.e. non-gravitational physics.

scholarly journals The Fractal Turbulence and the Origin of Large Scale Structure

1988 ◽  
Vol 130 ◽  
pp. 553-553
Author(s):  
Y.-Z. Liu ◽  
Z.-G. Deng
Keyword(s):  
Early Universe ◽  
Large Scale ◽  
Hubble Constant ◽  
Large Scale Structure ◽  
Thomson Scattering ◽  
Scale Structure ◽  
Scale Free ◽  
Density Perturbations ◽  
Reynold’S Number ◽  
The Universe

We have suggested a scenario of fractal turbulence which might explain the origin of galaxies and the observed large scale structure of the universe (Liu and Deng, 1987). Under the condition of the early universe, the cosmic fluid can be regarded as incompressible. If we assume that the density perturbations in the early universe are adiabatic and have the scale-free Zeldovich spectrum, we may obtain the spectrum of the velocity perturbations. Perturbations with scales less than horizon will undergo dissipative process by Thomson scattering. So, the cosmic fluid can be considered as a viscous fluid (Peebles, 1971). We can find the largest and smallest scale of the perturbations in the cosmic fluid by taking account of the Reynold's number on given scale and the scale of horizon. Using the present values of Hubble constant and the mean density of matter, we have found that on the scale of horizon the Reynold's number is just the order of 102. This result shows that perturbations with scale a little smaller than horizon may produce Karman vortices before recombination and the vortices might form fractal turbulence due to Thomson drag.

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