We prove the convergence in certain weighted spaces in momentum space of
eigenfunctions of H = T-lambda*V as the energy goes to an energy threshold. We
do this for three choices of kinetic energy T, namely the non-relativistic
Schr"odinger operator, the pseudorelativistc operator sqrt{-\Delta+m^2}-m, and
the Dirac operator.Comment: 15 pages; references and comments added (e.g., Remark 3
