The three-boson bound state in massive QED2

We derive the (matrix-valued) Feynman rules of mass perturbation theory of the massive Schwinger model for non-zero vacuum angleϑ. Further, we discuss the properties of the three-boson bound state and compute — by a partial resummation of the mass perturbation series — its mass and its partial decay widths. This work was supported by a research stipendium of the Vienna University.