Quantum Electrodynamics: with Unstable Vacuum(Springer Series in Nuclear and Particle Physics)

This book contains a systematic analysis of the formalisms of quantum electro­ dynamics in the presence of an intense external field able to create pairs from the vacuum, and thereby violate the stability of the latter. The approach developed is not specific to quantum electrodynamics, and can equally well be applied to any quantum field theory with an unstable vacuum. It should be noted that only macroscopic external fields are considered, whereas problems associated with the superstrong Coulomb (micro) field are not treated. As a rule, the discussion is confined to those details of the formalism and calculations that are specific to the instability property. For instance, renormalization is not discussed here since, in practical calculations, it is carried out according to standard methods. The presentation is based mainly on original research undertaken by the authors. Chapter 1 contains a general introduction to the problem. It also presents some standard information on quantum electrodynamics, which will be used later in the text. In addition, an interpretation of the concept of an external field is given, and the problems that arise when one tries to keep the interaction with the external field exactly are discussed. In Chapter 2, the perturbation expansion in powers of the radiative interac­ tion is developed for the matrix elements of transition processes, taking the arbitrary external field into account exactly.

Table of Contents:
1 Introduction.- 1.1 General Introduction and Definition of Notation.- 1.2 Quantum Electrodynamics with an External Field.- 2 Scattering Processes in Which Interactions with the External Field are Taken into Account Exactly.- 2.1 The Quantized Charged Field in an External Electromagnetic Field.- 2.2 Perturbation Expansion in the Radiative Interaction in QED with an External Field.- 2.3 Green’s Functions. The Generating Functional.- 2.4 Appendix. Extension of the Normal-Ordering Process to Theories with an Unstable Vacuum.- 3 Expectation Values.- 3.1 Green’s Functions for the Calculation of Expectation Values.- 3.2 Perturbations in Powers of Radiative Interaction for Expectation Values.- 3.3 Equation for the Average Electromagnetic Field. Effective Action.- 3.4 Density Matrix of Particles Created by an External Field.- 4 Total Probabilities of Radiative Processes in an External Field.- 4.1 Total Irradiation Probability.- 4.2 Unitarity Relation and the Optical Theorem.- 4.3 Generating Functional for the Total Probabilities of Radiation Processes.- 4.4 Decay Probability of States.- 5 Calculations of Zero-Order Processes in External Electromagnetic Fields.- 5.1 Processes in an Electric Field.- 5.2 A Constant Field Combined with that of a Plane Wave.- 5.3 Creation of Particles from the Vacuum in Coherent States.- 5.4 Calculation of the Density Matrix for Particles Created in an External Field.- 6 Propagators of Particles in External Electromagnetic Fields.- 6.1 Introduction.- 6.2 Determination of Propagators by Summing Solutions of the Relativistic Wave Equations.- 6.3 Schwinger’s Proper-Time Method.- 6.4 Calculation of the Green’s Functions by the Functional Integration Method.- 7 Calculations of Radiative Processes in External Electromagnetic Fields.- 7.1 EffectiveAction in the One-Loop Approximation.- 7.2 Vacuum Processes.- 7.3 Processes with an Electron in the Initial State. Mass Operator.- 7.4 Radiative Processes with a Photon in the Initial State. Polarization Operator.- 8 Green’s Function in Non-Abelian Theories.- 8.1 Introduction.- 8.2 Calculation of Green’s Functions by the Functional Integration Method.- 8.3 Calculation of Green’s Functions in an Abelian-like External Field.- References.