  Recently, an instantaneous approximation to the Bethe-Salpeter formalism for
the analysis of bound states in quantum field theory has been proposed which
retains, in contrast to the Salpeter equation, as far as possible the exact
propagators of the bound-state constituents, extracted nonperturbatively from
Dyson-Schwinger equations or lattice gauge theory. The implications of this
improvement for the solutions of this bound-state equation, that is, the
spectrum of the mass eigenvalues of its bound states and the corresponding wave
functions, when considering the quark propagators arising in quantum
chromodynamics are explored.
