Bound states in Galilean-invariant quantum field theory

We consider the nonrelativistic quantum mechanics of a model of two spinless fermions interacting via a two-body potential. The introduce quantum fields associated with the two particles as well as the expansion of these fields in asymptotic ''in'' and ''out'' fields, including such fields for bound states, in principle. We limit our explicit discussion to a two-body bound state. In this context we discuss the implications of the Galilean invariance of the model and, in particular, show how to include bound states in a strictly Galilean-invariant quantum field theory. (C) 1997 American Institute of Physics.