Nucleon-Nucleon Potential: Drift Effects
  In the rest frame of a many-body system, used in the calculation of its static and scattering properties, the center of mass of a two-body subsystem is allowed to drift. We show, in a model independent way, that drift corrections to the nucleon-nucleon potential are relatively large and arise from both one- and two-pion exchange processes. As far as chiral symmetry is concerned, corrections to these processes begin respectively at $\cO(q^2)$ and $\cO(q^4)$. The two-pion exchange interaction also yields a new spin structure, that promotes the presence of $P$ waves in trinuclei and is associated with profile functions which do not coincide with neither central nor spin-orbit ones. In principle, the new spin terms should be smaller than the $\cO(q^3)$ spin-orbit components. However, in the isospin even channel, a large contribution reverts this expectation and gives rise to the prediction of important drift effects. 
M. R. Robilotta