exchange. One principal idea is the need for a separation of momentum or length scales. One explicitly includes the exchange of mesons lighter (and hence more long-ranged) than some scale separation point. All short ranged effects are either incorporated in phenomenologically determined vertex functions or by some other purely phenomenological means. The physical picture underlying this philosophy is that the nucleon has a three-quark core which cannot be described efficiently in terms of mesons, while at longer distances the nucleon structure is dominated by a meson cloud.

To some extent, the fact that short ranged effects are handled as pure phenomenology is of little importance in most low energy nuclear physics applications. Because of repulsion at short distances, nuclear wave functions have strong short distance correlations which prevent the system from feeling the truly short range part of the potential. Moreover, at very short distances the concept of an NN potential becomes particularly inappropriate. Typically, in meson exchange potentials this scale separation point, which we will call $\Lambda_s$, is taken to be of order 1 GeV so that $\rho$ and $\omega$ mesons are explicitly included while heavier vector mesons are not. It is worth observing, however, that this does not 