Perturbation theory for a systematic account of the bound-state motion

We derive a perturbation theory (PT) for the Lorentz boost operator in the space of two-nucleon wave functions. The latter is expressed in terms of the nucleon-nucleon ($NN$) potentials, developed so far in great detail for their use in the $NN$ scattering studies. The PT is designed to take into account the boost relativistic corrections in a systematic way and, as such, it is the only missing part in the corresponding approaches developed up to now in the low-energy effective field theories.