2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/179700The QED effective action at finite temperature and density is calculated to all orders in an external homogeneous and time-independent magnetic field in the weak coupling limit. The free energy, obtained explicitly, exhibit the expected de\ Haas -- van\ Alphen oscillations. An effective coupling at finite temperature and density is derived in a closed form and is compared with renormalization group results.10 pages, Latex, NORDITA-93/35 P, Goteborg ITP 92-22High Energy Physics - Theorytext