Massless Pseudoscalar Fields and Solution of the Federbush Model
  The formal Heisenberg equations of the Federbush model are linearized and then are directly integrated applying the method of dynamical mappings. The fundamental role of two-dimensional free massless pseudo-scalar fields is revealed for this procedure together with their locality condition taken into account. Thus the better insight into solvability of this model is obtained together with the additional phase factor for its general solution, and the meaning of the Schwinger terms is elucidated. 
S.E.Korenblit, V.V.Semenov