The review is devoted to an investigation of the physical vacuum properties of quantum electrodynamics (QED), relying on the perturbative effective action approach. By probing the vacuum with external perturbations, its response is analyzed after averaging over the high-energy degrees of freedom. The book is written for scientists active in the field as well as for students who want to become familiar with the more advanced computational strategies of external-field problems which are partly outlined in great detail. Schwinger's proper-time method is the backbone of the book. Many recent...

This book is devoted to an investigation of the vacuum of quantum elec trodynamics (QED), relying on the perturbative effective action approach. If the vacuum is probed with external perturbations, the response of the system can be analyzed after averaging over the high energy degrees of freedom. This results in an effective description of the properties of the vacuum, which are comparable to the properties of a classical medium. We concentrate primarily on the physics of slowly varying fields or soft photons by integrating out the high energy degrees of freedom, i.e. the elec trons,...

This is a collection of lectures and seminars delivered at the "Symposi um on Particles and Fields" held at TUbingen University, West Germany, th from June 20 to July Pt, 1977, on the occasion of the University's sooth anniversary. We were very fortunate that so many excellent colleagues from Europe and the U. S. contributed their ideas to this meeting, whose main pur pose ist was to cover a brod spectrum of the various aspects in the current development of particles and fields, rahter than to focus on a single subject. It was interesting to see source-, quark-, and string people side by side...