Theta-Vacuum of the Bosonized Massive Light-Front Schwinger Model
  The massive Schwinger model in bosonic representation is quantized on the light front using the Dirac--Bergmann method. The non-perturbative theta- vacuum in terms of coherent states of the gauge-field zero mode is derived and found to coincide with the massless case. On the other hand, the mass term becomes highly non-linear due to the constrained zero mode of the scalar field. A non-trivial mixing between the normal-mode and zero-mode sectors of the model is crucial for the correct calculation of the theta-dependence of the leading order mass correction to the chiral condensate. 
Lubomir Martinovic (1) and James P. Vary (2) ((1) Inst. of Physics,   Bratislava, (2) Iowa St. Univ., Ames)