Annihilation From Above
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Collected Works (volume 4): Unpublished Papers
The motivation for the research that is described in these volumes is the wish to explain things in terms of their underlying causes, rather than merely being satisfied with phenomenological descriptions. When this reductionist approach is applied to information processing it allows the internal structure of information to be analysed, so information processing algorithms can then be derived from first principles. One of the simplest examples of this approach is the diagonalisation of a data covariance matrix – there are many variants of this basic approach, such as singular value decomposition – in which the assumed independent components of high-dimensional data are identified and extracted. The main limitation of this type of information analysis approach is that it is based on linear algebra applied globally to the data space, so it is unable to preserve information about any local data structure in the data space. For instance, if the data lives on a low-dimensional curved manifold embedded in the data space, then only the global properties of this manifold would be preserved by global linear algebra methods. In practice, data whose high-dimensional structure is non-trivial typically lives on a noisy version of a curved manifold, so techniques for analysing such data must automatically handle this type of structure. For instance, a blurred image of a point source is described by its underlying degrees of freedom – i.e. the position of the source – and as the source moves about it generates a curved manifold that lives in the high-dimensional space of pixel values of the sampled image. The basic problem is then to deduce the internal properties of this manifold by analysing examples of such images. A more challenging problem would be to extend this analysis to images that contain several overlapping blurred images of point sources, and so on. There is no limit to the complexity of the types of high-dimensional data that one might want to analyse. These methods then need to be automated so that they do not rely on human intervention, which would then allow them to be inserted as “components” into information processing networks. The purpose of the research that is described in these volumes is to develop principled information processing methods that can be used for such analysis. Self-organising information processing networks arise naturally in this context, in which ways of cutting up the original manifold into simpler pieces emerge automatically.
Introduction to Quantum Electrodynamics and Particle Physics
Author: Deep Chandra Joshi
language: en
Publisher: Techsar Pvt. Ltd.
Release Date: 2022-03-02
Apart from updating the existing text of 1st edition two new chapters, namely, Mandelstam Variables and Symmetries of Scattering Amplitude and Regge Poles have been included in this edition. The former, that constitutes the seventh chapter of the book, introduces Mandelstam variables and describes at length the s-channel, t-channel and the u-channel processes for both the equal and unequal masses of participating particles. The conditions for the occurrence of these channel processes have been made explicit through the Mandelstam plot. Introducing scattering amplitude as the matrix element of S-matrix, the crossing and Bose symmetries of scattering amplitudes for s-, t-, u-channel scatterings have been explained and the analyticity of scattering amplitude has been elucidated through examples. The topic Regge poles, describes the study of resonances and Regge poles that can be undertaken through the scattering process. Due to the significant role of partial waves in the chapter, the scattering process has been explained through the partial wave analysis and the scattering cross section has been expressed in terms of scattering amplitude and by the optical theorem. Assignments have been given at the end of each chapter, which contain descriptive questions as well as problems. A new feature of the book is that it has a substantial number of objective type questions to help aspirants of GATE, NET and related examinations. Most of the topics forming the model syllabus of University Grants Commission for Post Graduate Particle Physics (III Semester), Nuclear and Particle Physics (IV Semester, Strong, Weak and Electromagnetic Interactions) and Quantum Electrodynamics have been covered in the book. The topics have been developed in a pedagogical manner by providing all possible algebraic details.
Astrophysics with Radioactive Isotopes
Dealing with astrophysics derived from the radiation emitted by radioactive atomic nuclei, this book describes the different methods used to measure cosmic radio-isotopes. It demonstrates how this astronomical window has contributed to the understanding of the sources and the chemical evolution of cosmic gas. Reference materials and explanations are included for students in advanced stages of their education. Nuclear reactions in different sites across the universe lead to the production of stable and unstable nuclei. Their abundances can be measured through different methods, allowing to study the various nuclear processes taking place in cosmic environments. Nucleosynthesis is the cosmic formation of new nuclear species, starting from hydrogen and helium resulting from the big bang origins. Stars create and eject synthesized nuclei during their evolution and explosions. Incorporation of the new interstellar composition into next-generation stars characterises the compositional (chemical) evolution of cosmic gas in and between galaxies. Radioactive species have unique messages about how this occurs. Since the first Edition of this book published in 2011 with the title Astronomy with Radioactivities, long-awaited new direct observations of supernova radioactivity have been made and are now addressed in two updated chapters dealing with supernovae. In this second Edition, the advances of recent years beyond one-dimensional treatments of stellar structure and stellar explosions towards 3-dimensional models have been included, and led to significant re-writings in Chapters 3-5. The sections on the Solar System origins have been re-written to account for new insights into the evolution of giant molecular clouds. The chapter on diffuse radioactivities now also includes material measurements of radioactivities in the current solar system, and their interpretations for recent nucleosynthesis activity in our Galaxy. Significant new results on gamma-rays from positron annihilations have been accounted for in that chapter, and led to new links with nucleosynthesis sources as well as interstellar transport processes. A new chapter now provides a description of interstellar processes often called 'chemical evolution', thus linking the creation of new nuclei to their abundance observations in gas and stars. The experimental / instrumental chapters on nuclear reaction measurements, on gamma-ray telescopes, and pre-solar grain laboratories have been updated. Moreover, new windows of astronomy that have been opened up in recent years have been included in the discussions of the multi-messenger approach that broadens the basis for astrophysical insights.