Gauge and Lorentz Covariant Schwinger-Dyson Equation for Fermion   Propagator in Arbitrary External Gauge Field
  A formalism of gauge and Lorentz covariant Schwinger-Dyson equation is built up for fermion propagator in presence of arbitrary external gauge field within ladder approximation. Different type external electromagnetic field dependent trial solutions are investigated which spontaneously breaking chiral symmetry. 
Xiang Chen, Ying Zhang, Fa-Min Chen, Qing Wang