Nonperturbative Study of Generalized Ladder Graphs in aϕ2χTheory

Abstract
The Feynman-Schwinger representation is used to construct scalar-scalar bound states for the set of all ladder and crossed-ladder graphs in a ϕ2χ theory in 3+1 dimensions. The results are compared to those of the usual Bethe-Salpeter equation in the ladder approximation and of several quasipotential equations. Particularly for large couplings, the ladder predictions are seen to underestimate the binding energy significantly as compared to the generalized ladder case, whereas the solutions of the quasipotential equations provide a better correspondence. Results for the calculated bound state wave functions are also presented.
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