2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/47950Table of Contents 1. One-loop effective Lagrangian in spinor QED. 2. Dispersion effects for low-frequency photons. 3. Vacuum birefringence in magnetic fields. 4. Light cone condition, effective Lagrangian approach.18pp., 3 figures, LaTeX, uses heronb.sty, Talk given at Workshop on Frontier Tests of Quantum Electrodynamics and Physics of the Vacuum, Sandansky, Bulgaria, June 9-15, 1998High Energy Physics - Phenomenologytext