scholarly journals Cosmological Parameter Inference with Bayesian Statistics

Universe ◽  
2021 ◽  
Vol 7 (7) ◽  
pp. 213
Author(s):  
Luis E. Padilla ◽  
Luis O. Tellez ◽  
Luis A. Escamilla ◽  
Jose Alberto Vazquez
Keyword(s):  
Bayesian Statistics ◽  
Model Comparison ◽  
General Description ◽  
Inference Procedure ◽  
Parameter Inference ◽  
Mcmc Algorithms ◽  
Cosmological Observations ◽  
Numerical Tools ◽  
Standard Cosmological Model ◽  
The Universe

Bayesian statistics and Markov Chain Monte Carlo (MCMC) algorithms have found their place in the field of Cosmology. They have become important mathematical and numerical tools, especially in parameter estimation and model comparison. In this paper, we review some fundamental concepts to understand Bayesian statistics and then introduce MCMC algorithms and samplers that allow us to perform the parameter inference procedure. We also introduce a general description of the standard cosmological model, known as the ΛCDM model, along with several alternatives, and current datasets coming from astrophysical and cosmological observations. Finally, with the tools acquired, we use an MCMC algorithm implemented in python to test several cosmological models and find out the combination of parameters that best describes the Universe.

scholarly journals Hunting for Gravitational Quantum Spikes

Universe ◽  
2021 ◽  
Vol 7 (3) ◽  
pp. 49
Author(s):  
Andrzej Góźdź ◽  
Włodzimierz Piechocki ◽  
Grzegorz Plewa ◽  
Tomasz Trześniewski
Keyword(s):  
Initial Data ◽  
Fundamental Importance ◽  
Quantum Structures ◽  
Subtle Effect ◽  
Gravitational Systems ◽  
Numerical Tools ◽  
The Universe

We present the result of our examination of quantum structures called quantum spikes. The classical spikes that are known in gravitational systems, occur in the evolution of the inhomogeneous spacetimes. A different kind of spikes, which we name strange spikes, can be seen in the dynamics of the homogeneous sector of the Belinski–Khalatnikov–Lifshitz scenario. They can be made visible if the so-called inhomogeneous initial data are used. The question to be explored is whether the strange spikes may survive quantization. The answer is in the affirmative. However, this is rather a subtle effect that needs further examination using sophisticated analytical and numerical tools. The spikes seem to be of fundamental importance, both at classical and quantum levels, as they may serve as seeds of real structures in the universe.

scholarly journals LARGE SCALE ANISOTROPY DUE TO PRE-INFLATIONARY PHASE OF COSMIC EVOLUTION

2012 ◽  
Vol 27 (04) ◽  
pp. 1250014 ◽  
Author(s):  
PAVAN K. ALURI ◽  
PANKAJ JAIN
Keyword(s):  
Large Scale ◽  
Cosmological Evolution ◽  
Cosmic Evolution ◽  
Cosmological Observations ◽  
Inflationary Phase ◽  
The Universe ◽  
Dipole Modulation

We show that perturbations generated during the anisotropic pre-inflationary stage of cosmic evolution may affect cosmological observations today for a certain range of parameters. Due to the anisotropic nature of the universe during such early times, it might explain some of the observed signals of large scale anisotropy. In particular, we argue that the alignment of CMB quadrupole and octopole may be explained by the Sachs–Wolfe effect due to the large scale anisotropic modes from very early times of cosmological evolution. We also comment on how the observed dipole modulation of CMB power may be explained within this framework.

scholarly journals O UNIVERSO VIVO

2012 ◽  
Vol 19 (1.2) ◽  
Author(s):  
Francisco César de Sá Barreto ◽  
Luiz Paulo Ribeiro Vaz ◽  
Gabriel Armando Pellegatti Franco
Keyword(s):  
Cosmological Model ◽  
Chemical Elements ◽  
Big Bang ◽  
Living System ◽  
Irreversible Processes ◽  
Thermodynamics Of Irreversible Processes ◽  
Protons And Neutrons ◽  
Standard Cosmological Model ◽  
The Big Bang ◽  
The Universe

The standard cosmological model suggests that after the “Big Bang”, 14 billion of years ago, the universe entered a period of expansion and cooling. In the first one millionth of a second appear quarks, glúons, electrons and neutrinos, followed by the appearance of protons and neutrons. In this paper, we describe the “cosmic battle” between gravitation and energy, responsible for the lighter chemical elements and the formation of the stars. We describe the thermodynamics of irreversible processes of systems which are far away from equilibrium, a route that is followed by the universe, seen as a living system.

scholarly journals The Perturbation of Material Density in f(R) Modified Gravity of Polynormal Exponential Form

10.29007/xqpk ◽  
2020 ◽  
Author(s):  
Van On Vo
Keyword(s):  
Cosmological Model ◽  
Modified Gravity ◽  
Linear Perturbation ◽  
Exponential Form ◽  
Material Density ◽  
Gravitational Model ◽  
Standard Cosmological Model ◽  
The Difference ◽  
Evolutionary Aspects ◽  
The Universe

In this paper, we investigate the linear perturbation of the material density of the universe in f(R) modified gravity of polynomial exponential form on the scale of distance below the cosmic horizon (sub-horizon). The results show that the model for the evolutionary aspects of the universe is slightly different from that in the standard cosmological model of ΛCDM. They can be used to show the difference between this modified gravitational model with the standard cosmological model of ΛCMD and other cosmological models. We also investigate the ration Ψ/ Φ and Geff / GN in the model and show that they are within allowable limits of experiments.

Unlocking the Universe with Astroinformatics

2017 ◽  
Vol 14 (S339) ◽  
pp. 201-201
Author(s):  
M. Lochner
Keyword(s):  
Machine Learning ◽  
Data Mining ◽  
Bayesian Statistics ◽  
Time Domain ◽  
Meaningful Information ◽  
Broad Field ◽  
Near Future ◽  
The Universe

AbstractIn the last decade Astronomy has been transformed by a deluge of data that will grow exponentially when near-future telescopes such as LSST and the SKA begin routine observing. Astroinformatics, a broad field encompassing many techniques in statistics, machine learning and data mining, is the key to extracting meaningful information from large amounts of data. This talk outlined Astroinformatics as a field, and gave a few examples of the use of machine learning and Bayesian statistics from my own work in survey Astronomy. The era of massive surveys in which we now find ourselves has the potential to revolutionise completely many fields, including time-domain Astronomy, but only if coupled with the powerful tools of Astroinformatics.

Which is the Best Model of the Universe?

2016 ◽  
Vol 4 (1) ◽  
pp. 152-169
Author(s):  
Martin Sahlén
Keyword(s):  
Scientific Knowledge ◽  
Model Comparison ◽  
Value Judgments ◽  
Statistical Framework ◽  
Philosophy Of Cosmology ◽  
Ultimate Explanation ◽  
Proposed Model ◽  
Framework Model ◽  
Fertile Ground ◽  
The Universe

Modern scientific cosmology pushes the boundaries of knowledge and the knowable. This is prompting questions on the nature of scientific knowledge, and the emergence of the new field “Philosophy of Cosmology.” One central issue is what defines a “good” model. I discuss how “good” models are conventionally chosen, and how those methods operate in data-sparse situations: enabling the implicit introduction of value judgments, which can determine inference and lead to inferential polarization, e.g., on the question of ultimate explanation. Additional dimensions for comparing models are needed. A three-legged comparison is proposed: evidence, elegance and beneficence. This explicitly considers the categories of criteria that are always at least implicitly used. A tentative path to an implementation of the proposed model comparison framework is presented. This extends the Bayesian statistical framework. Model comparison methodology is fertile ground for dialogue between the sciences and the humanities. The proposed framework might facilitate such a dialogue.

scholarly journals The investigation of detectability of the relic gravitational waves based on the WMAP-9 and Planck

2017 ◽  
Vol 26 (02) ◽  
pp. 1750003 ◽  
Author(s):  
Basem Ghayour
Keyword(s):  
Scalar Field ◽  
Gravitational Waves ◽  
Crucial Role ◽  
Planck Data ◽  
Evolution Of The Universe ◽  
Cosmological Observations ◽  
Relic Gravitational Waves ◽  
The Waves ◽  
The Universe ◽  
General Range

The generated relic gravitational waves underwent several stages of evolution of the universe such as inflation and reheating. These stages were affected on the shape of spectrum of the waves. As well known, at the end of inflation, the scalar field [Formula: see text] oscillates quickly around some point where potential [Formula: see text] has a minimum. The end of inflation stage played a crucial role on the further evolution stages of the universe because particles were created and collisions of the created particles were responsible for reheating the universe. There is a general range for the frequency of the spectrum [Formula: see text])[Formula: see text]Hz. It is shown that the reheating temperature can affect on the frequency of the spectrum as well. There is constraint on the temperature from cosmological observations based on WMAP-9 and Planck. Therefore, it is interesting to estimate allowed value of frequencies of the spectrum based on general range of reheating temperature like few MeV [Formula: see text] GeV, WMAP-9 and Planck data then compare the spectrum with sensitivity of future detectors such as LISA, BBO and ultimate-DECIGIO. The obtained results of this comparison give us some more chance for detection of the relic gravitational waves.

scholarly journals Applications of light speed expansion and gravitational self-energy density in black hole cosmology

2015 ◽  
Vol 3 (2) ◽  
pp. 123
Author(s):  
Satya Seshavatharam UV ◽  
Terry Tatum E ◽  
Lakshminarayana S
Keyword(s):  
Black Hole ◽  
Energy Density ◽  
Thermal Energy ◽  
Planck Scale ◽  
Cosmic Inflation ◽  
Self Energy ◽  
Light Speed ◽  
Cosmological Observations ◽  
The Universe ◽  
Matter Energy

<p>From the beginning of Planck scale to the scale of the current Hubble radius: 1) Considering the relation, subjects of black holes and cosmology, both can be integrated into evolving black hole cosmology and cosmic horizon problem can be relinquished. 2) Considering ‘continuous light speed expansion’ of the cosmic black hole horizon, attributed results of cosmic inflation can be re-addressed completely. If ‘nature’ of the universe is to expand with light speed, then there is no need to think about the existence of currently believed ‘Lambda term’. In addition, ‘light speed expanding cosmic space’ can be called as ‘flat space’. 3) Considering the ratio of gravitational self-energy density and thermal energy density to be  (where  is the Planck scale temperature, and is cosmic temperature at any time). Quantum gravity can be implemented in low energy scale current cosmological observations. Considering the above concepts, currently believed dark matter energy density and visible matter energy density both can be accurately fitted with the ratio of current gravitational self-energy density and current thermal energy density. To proceed further, the authors would like to highlight the following three points: 1) Deep-space red shift non-linearity can be expected to be connected with cosmological gravitational and relativistic effects and cannot be considered as a major criterion of cosmic evolution. 2) Until one finds solid applications of super luminal speeds and super luminal expansions in other areas of physics like astrophysics and nuclear astrophysics, currently believed ‘cosmic inflation’ cannot be considered as a real physical model and alternative proposals of inflation can be given a chance in exploring the evolving history of the universe. 3) Implementing Planck scale in current paradigm of cosmological observations and standard cosmology is very challenging and is inevitable.</p>

scholarly journals Computing Bayes factors for evidence-accumulation models using Warp-III bridge sampling

2019 ◽  
Vol 52 (2) ◽  
pp. 918-937
Author(s):  
Quentin F. Gronau ◽  
Andrew Heathcote ◽  
Dora Matzke
Keyword(s):  
Bayesian Estimation ◽  
Model Comparison ◽  
Bayes Factor ◽  
Parameter Inference ◽  
Bayesian Hierarchical ◽  
Practical Applications ◽  
Evidence Accumulation ◽  
Bridge Sampling ◽  
Linear Ballistic Accumulator ◽  
Complex Models

AbstractOver the last decade, the Bayesian estimation of evidence-accumulation models has gained popularity, largely due to the advantages afforded by the Bayesian hierarchical framework. Despite recent advances in the Bayesian estimation of evidence-accumulation models, model comparison continues to rely on suboptimal procedures, such as posterior parameter inference and model selection criteria known to favor overly complex models. In this paper, we advocate model comparison for evidence-accumulation models based on the Bayes factor obtained via Warp-III bridge sampling. We demonstrate, using the linear ballistic accumulator (LBA), that Warp-III sampling provides a powerful and flexible approach that can be applied to both nested and non-nested model comparisons, even in complex and high-dimensional hierarchical instantiations of the LBA. We provide an easy-to-use software implementation of the Warp-III sampler and outline a series of recommendations aimed at facilitating the use of Warp-III sampling in practical applications.

scholarly journals CLOSING THE UNIVERSE BY RELAXING THE COSMOLOGICAL CONSTANT

1994 ◽  
Vol 09 (30) ◽  
pp. 2755-2760 ◽  
Author(s):  
JORGE L. LOPEZ ◽  
D. V. NANOPOULOS
Keyword(s):  
Higgs Boson ◽  
String Theory ◽  
Cosmological Constant ◽  
Parameter Space ◽  
Vacuum Energy ◽  
Positive Contribution ◽  
Negative Contribution ◽  
Cosmological Observations ◽  
The Universe

We consider a string-inspired no-scale SU (5) × U (1) supergravity model. In this model there is a negative contribution to the vacuum energy, which may be suitably canceled by a positive contribution typically present in string theory. One may then end up with a vacuum energy which brings many cosmological observations into better agreement with theoretical expectations, and a fixed value for the present abundance of neutralinos. We delineate the regions of parameter space allowed in this scenario, and study the ensuing predictions for the sparticle and Higgs-boson masses in this model.

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