Quantum electrodynamics of strong fields

Abstract

In atomic physics if the electromagnetic coupling constant becomes sufficiently large bound electron states can join the negative-energy continuum of the Dirac equations. The resulting possibility of spontaneous positron production and the new concept of a charged electron-positron vacuum is discussed. The autoionisation model and the exact overcritical solutions of the single-particle Dirac equation are contrasted with a quantum-field-theoretical approach. Vacuum polarisation and the self-screening of extremely strong electric charges are treated explicitly. Adiabatic collisions of heavy ions leading to the transient formation of quasi-molecular electron orbitals are suggested as a means for an experimental test of the special features of strong-field QED.