DERIVATIVE EXPANSION FOR THE ONE-LOOP EFFECTIVE LAGRANGIAN IN OED

The derivative expansion of the one-loop effective Lagrangian in QED(4 ) is considered. The first term in such an expansion is the famous Sch winger result for a constant electromagnetic field. In this paper we g ive an explicit expression for the next term containing two derivative s of the field strength F-mu v. The results are presented for both fer mion and scalar electrodynamics. Some possible applications of an inho mogeneous external field are pointed out.