Loops and loop clouds - a numerical approach to the worldline formalism in QED -

Abstract

A numerical technique for calculating effective actions of electromagnetic backgrounds is proposed, which is based on the string-inspired worldline formalism. As examples, we consider scalar electrodynamics in three and four dimensions to one-loop order. Beyond the constant-magnetic-field case, we analyze a step-function-like magnetic field exhibiting a nonlocal and nonperturbative phenomenon: ``magnetic-field diffusion''. Finally, generalizations to fermionic loops and systems at finite temperature are discussed.

Comments: 11 pages, 5 figures, talk given by H.G. at the Fifth Workshop on Quantum Field Theory under the Influence of External Conditions, Leipzig, Germany, September, 2001