On the physical interpretation of effective actions using Schwinger's   formula
  We show explicitly that Schwinger's formula for one-loop effective actions corresponds to the summation of energies associated with the zero-point oscillations of the fields. We begin with a formal proof, and after that we confirm it using a regularization prescription. 
L. C. de Albuquerque, C. Farina, Silvio J. Rabello and Arvind N.   Vaidya