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28213 results in Astrophysics

Page 58 of 1411

A Course in Cosmology
  • From Theory to Practice
  • Dragan Huterer
  • Published online:
    31 March 2023
    Print publication:
    09 March 2023
  • This new graduate textbook adopts a pedagogical approach to contemporary cosmology that enables readers to build an intuitive understanding of theory and data, and of how they interact, which is where the greatest advances in the field are currently being made. Using analogies, intuitive explanations of complex topics, worked examples and computational problems, the book begins with the physics of the early universe, and goes on to cover key concepts such as inflation, dark matter and dark energy, large‑scale structure, and cosmic microwave background. Computational and data analysis techniques, and statistics, are integrated throughout the text, particularly in the chapters on late-universe cosmology, while another chapter is entirely devoted to the basics of statistical methods. A solutions manual for end-of-chapter problems is available to instructors, and suggested syllabi, based on different course lengths and emphasis, can be found in the Preface. Online computer code and datasets enhance the student learning experience.

  • Bayesian evidence-driven likelihood selection for sky-averaged 21-cm signal extraction

  • K. H. Scheutwinkel, W. Handley, E. de Lera Acedo
  • Journal:
    Publications of the Astronomical Society of Australia / Volume 40 / 2023
    Published online by Cambridge University Press:
    24 March 2023, e016
    • Article
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  • We demonstrate that the Bayesian evidence can be used to find a good approximation of the ground truth likelihood function of a dataset, a goal of the likelihood-free inference (LFI) paradigm. As a concrete example, we use forward modelled sky-averaged 21-cm signal antenna temperature datasets where we artificially inject noise structures of various physically motivated forms. We find that the Gaussian likelihood performs poorly when the noise distribution deviates from the Gaussian case, for example, heteroscedastic radiometric or heavy-tailed noise. For these non-Gaussian noise structures, we show that the generalised normal likelihood is on a similar Bayesian evidence scale with comparable sky-averaged 21-cm signal recovery as the ground truth likelihood function of our injected noise. We therefore propose the generalised normal likelihood function as a good approximation of the true likelihood function if the noise structure is a priori unknown.

Supermassive Black Holes
  • Andrew King
  • Published online:
    23 March 2023
    Print publication:
    30 March 2023
  • Written by an international leader in the field, this is a coherent and accessible account of the concepts that are now vital for understanding cutting-edge work on supermassive black holes. These include accretion disc misalignment, disc breaking and tearing, chaotic accretion, the merging of binary supermassive holes, the demographics of supermassive black holes, and the defining effects of feedback on their host galaxies. The treatment is largely analytic and gives in-depth discussions of the underlying physics, including gas dynamics, ideal and non-ideal magnetohydrodynamics, force-free electrodynamics, accretion disc physics, and the properties of the Kerr metric. It stresses aspects where conventional assumptions may be inappropriate and encourages the reader to think critically about current models. This volume will be useful for graduate or Masters courses in astrophysics, and as a handbook for active researchers in the field. eBook formats include colour figures while print formats are greyscale only.

  • 8 - Inflation

  • from Part II - The Early Universe
  • Dragan Huterer, University of Michigan, Ann Arbor
  • Book:
    A Course in Cosmology
    Published online:
    31 March 2023
    Print publication:
    09 March 2023, pp 136-172

  • Summary

    Here we discuss inflation, a period of accelerated expansion that occurred in the very early history of the universe. We motivate inflation by describing the flatness and horizon problems, then explain how inflation resolves them. We describe the early history of inflationary ideas, then move on to modern work where we outline the standard scalar-field model for inflation, and define the slow-roll parameters that phenomenologically describe the dynamics of inflation. We briefly outline how inflation leads to the generation of density fluctuations in the universe; we mathematically describe the spectrum of these fluctuations, and confront it with modern observations. We end by discussing more speculative ideas in this area, including eternal inflation and multiverse.

Page 58 of 1411