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, employing Schwinger's proper time method. We derive a new represen tation of the one loop photon polarization tensor, coupling to all orders to an arbitrary constant electromagnetic field, fully maintaining the dependence on the complete set of invariants. On the basis of effective Lagrangians, we derive the light cone condition for low frequency photons propagating in strong fields. Our formalism can be extended to various external perturbations, such as temperature and Casimir situations. We give a proof of the "unified formula" for low energy phenom ena that describes the refractive indices of various perturbed quantum vacua. In the high energy domain, we observe similarities between a vacuum with a superstrong magnetic field and a magnetized plasma. The question of mea surability of the various effects is addressed; a violation of causality is not found.

Up-to-date overview of the physical vacuum properties of quantum electrodynamics Important topic in theoretical physics of elementary particles Access to recent literature Available online in LINK http://link.springer.de/series/stmp/ Includes supplementary material: sn.pub/extras

Autorentext

Prof. Dr. Walter Dittrich was head of the quantum electrodynamics group at the University of Tübingen before his retirement in 2001 and is still actively publishing papers and books in classical and quantum physics. He received his doctorate under Prof. Heinz Mitter at Heisenberg's institute in Munich and continued pre- and postdoc work at Brown University, Harvard and MIT. He profited immensely from lectures by and discussions with Profs. Herb Fried, Ken Johnson, Steve Weinberg, Julian Schwinger and, later on, at the Institute for Advanced Study (IAS) in Princeton, Steve Adler and David Gross at Princeton University. He started his work on gauge theories and QED in collaboration with Schwinger in the late 1960s. He was visiting professor at UCLA, Berkeley, Stanford and the IAS. He has over 30 years of teaching experience and is one of the key scientists in developing the theoretical framework of quantum electrodynamics.

Inhalt
Nonlinear Electrodynamics: Quantum Theory.- Nonlinear Electrodynamics: Effective-Action Approach.- QED in Two Spatial Dimensions.- Scattering of Light by Light.