Abstract:

The Bethe-Salpeter formalism is used to study two-body bound 
states within a scalar theory: two scalar fields interacting 
via the exchange of a third massless scalar field.  The 
Schwinger-Dyson equation is derived using functional and 
diagrammatic techniques, and the Bethe-Salpeter equation is 
obtained in an analagous way, showing it to be a two-particle 
generalization of the Schwinger-Dyson equation.  We also 
present a numerical method for solving the Bethe-Salpeter 
equation without three-dimensional reduction.  The ground and 
first excited state masses and wavefunctions are computed 
within the ladder approximation and space-like form factors 
are calculated.