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Preface to the Second Edition

This second edition of the book grew out of requests, by students and colleagues alike from all over the world, to include a wide range of related interesting topics. However, it was not at all practical to accommodate all the topics that were requested since the first edition of the book already had about 775 pages. I have only been able to fulfill only a few of the requests which, I believed, would fit in nicely with the logic of the earlier edition. There are two new chapters as well as two appendices in this new edition and that has enlarged the book by about 150 pages. One of the two chapters added discusses Nielsen identities which addresses questions of gauge independence of physical parameters such as mass of a particle as well as other physical parameters derived from the effective potential which itself is gauge dependent. The other chapter discusses global supersymmetry which is a very important idea and which was requested by many readers. One of the two appendices discusses fermions in arbitrary dimensions (as well as in four dimensions). In particular, it investigates the number of space-time dimensions where Majorana, Weyl and Majorana-Weyl fermions can exist. The second appendix discusses the question of gauge invariant (gauge) potentials in detail as well as the Fock-Schwinger gauge as an implementable, complete and ghost free gauge which is widely used in nonperturbative calculations of condensates. In addition, the material of the earlier edition of the book has also been revised and expanded wherever necessary to make explanations simpler and easier.

I would like to thank Dr. Pushpa Kalauni for going through the material carefully and Dave Munson for all the technical help with LaTex.

Ashok Das,

Rochester