Off-shell effects in nuclear matter from an EFT point of view

摘要

Effective field theory requires all observables to be independent of the representation used for the quantum field operators. Off-shell parts of the in-medium vertex functions depend on the partucular representation so that off-shell properties of the interactions should not lead to any observable effects. We analyse this issue in the context of many-body approaches to nuclear matter, where it should be possible to shift into three-body force the contributions from purely off-shell two-body interactions. We show that none of the commonly used truncations of the two-body scattering amplitude such as the ladder, Brueckner-Hartree-Fock or parquet approximations respect this requirement.