
 QFT SchwingerDyson  Wikibooks, collection of opencontent textbooks 
  In quantum field theory, if the action is given by the functional S of field configurations (which only depends locally on the fields), then the time ordered vacuum expectation value of polynomially bounded functional F, , is given by 
  If J (called the source field) is an element of the dual space of the field configurations (which has at least an affine structure because of the assumption of the translational invariance for the functional measure), then, the generating functional Z of the source fields is defined to be: 
  is viewed as a functional distribution (this shouldn't be taken too literally as an interpretation of QFT, unlike it's Wick rotated statistical mechanics analogue, because we have time ordering complications here!), then 
 en.wikibooks.org /wiki/QFT_SchwingerDyson (765 words) 
