Theta vacuum effects on the chiral condensation and the eta^prime meson   correlators in the two-flavor massive QED_2 on the lattice
  We study the scalar and pseudoscalar condensations and the eta^prime meson correlators of the two-flavor massive Schwinger model in the non-zero theta vacuum. Exploiting our new method which was developed to investigate topological effects in the previous work, we find that the pseudoscalar condensation is non-zero and there exists a long-range correlation of the eta^prime meson. This phenomenon is well described by the clustering property. We also find that even in theta=0 case the cancellation of the long-range correlation is nontrivial and requires accurate contributions from higher topological sectors. Our results imply that the fluctuation of the ``disconnected'' diagram originates from the pseudoscalar condensation in each topological sector. 
Hidenori Fukaya and Tetsuya Onogi