Schwinger-Dyson Equation in Minkowski Space beyond the IE Approximation
  We investigate the properties of fermion mass functions in quantum electrodynamics calculated by the Schwinger-Dyson equation in the strong coupling region, in which the loop integration is performed in Minkowski space. The calculated results without the instantaneous exchange approximation are compared with those obtained by integration in Euclidean space. 
Shuji Sasagawa and Hidekazu Tanaka
hep-ph