Gravity as a Gauge Theory of Translations

The Poincar\'e group can be interpreted as the group of isometries of a minkowskian space. This point of view suggests to consider the group of isometries of a given space as the suitable group to construct a gauge theory of gravity. We extend these ideas to the case of maximally symmetric spaces to reach a realistic theory including the presence of a cosmological constant. Introducing the concept of "minimal tetrads" we deduce Einstein gravity in the vacuum as a gauge theory of translations.Comment: 14 pages. LaTeX 2

Harry Lehmann and the analyticity unitarity programme

I try to describe the extremely fruitful interaction I had with Harry Lehmann and the results which came out of the analyticity unitarity programme, especially the proof of the Froissart bound, which, with recent and future measurements of total cross-sections and real parts, remains topical.Comment: (10 pages, latex

History of Spin and Statistics

These lectures were given in the framework of the ``Dixi\`eme s\'eminaire rhodanien de physique'' entitled ``Le spin en physique'', given at Villa Gualino, Turin, March 2002. We have shown how the difficulties of interpretation of atomic spectra led to the Pauli exclusion principle and to the notion of spin, and then described the following steps: the Pauli spin with 2$\times$2 matrices after the birth of "new" quantum mechanics, the Dirac equation and the magnetic moment of the electron, the spins and magnetic moments of other particles, proton, neutron and hyperons. Finally, we show the crucial role of statistics in the stability of the world.Comment: latex file, 7 figures, 3 table

Commentary

published or submitted for publicatio

Ethan A. Nadelmann, Cops Across Borders: The Internationalization of U.S. Criminal Law Enforcement

This book review asserts that Cops Across Borders: The Internationalization of U.S. Criminal Law Enforcement ( Cops Across Borders ) is the first book to attempt a systematic analysis of the role that the United States has played in the field of international law enforcement. For that reason, the book represents a major step forward in understanding this rapidly evolving area. While many people have examined different aspects of international law enforcement, such as extraterritorial jurisdiction, extradition, and international evidence gathering, not until this book has the entire field been subjected to historical and scholarly research. Mr. Nadelmann\u27s book has forged a new road in this rapidly growing, but often confusing, area. The book is not without defects, however. The basic problem with Cops Across Borders is that the general theme of international law enforcement is not strong enough to hold together the different chapters to form a cohesive whole. Each chapter is a self-contained study of a particular facet of law enforcement, and the reader is left with the feeling that Mr. Nadelmann has forced the parts together to form a single text. Given the importance of his endeavor, however, the effort can be readily defended as the exercise of justifiable force. Indeed, the sections of the book are well-suited to use in an academic setting as the basis for an extended study of the issues raised

Extending the Coordination of Cognitive and Social Perspectives

Cognitive analyses are typically used to study individuals, whereas social analyses are typically used to study groups. In this article, I make a distinction between what one is looking with?one’s theoretical lens?and what one is looking at?e.g., an individual or a group?. By emphasizing the former, I discuss social analyses of individuals and cognitive analyses of groups, additional analyses that can enhance mathematics education research. I give examples of each and raise questions about the appropriateness of such analyses