Local projections of low-momentum potentials

Nuclear interactions evolved via renormalization group methods to lower resolution become increasingly nonlocal (off-diagonal in coordinate space) as they are softened. This inhibits both the development of intuition about the interactions and their use with some methods for solving the quantum many-body problem. By applying local projections, a softened interaction can be reduced to a local effective interaction plus a nonlocal residual interaction. At the two-body level, a local projection after similarity renormalization group (SRG) evolution manifests the elimination of short-range repulsive cores and the flow toward universal low-momentum interactions. The SRG residual interaction is found to be relatively weak at low energy, which motivates a perturbative treatment.