I examine the evolution of nuclear forces under the similarity renormalization group (SRG) using traces of the many-body configuration-space Hamiltonian. While SRG is often said to “soften” the nuclear interaction, I provide numerical examples which paint a complementary point of view: the primary effect of SRG, using the kinetic energy as the generator of the evolution, is to shift downward the diagonal matrix elements in the model space, while the off-diagonal elements undergo significantly smaller changes. By employing traces, I argue that this is a very natural outcome as one diagonalizes a matrix, and helps one to understand the success of SRG.
Johnson, C. W. (2017). Tracing the evolution of nuclear forces under the similarity renormalization group. Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 774, 465–469. https://doi.org/10.1016/j.physletb.2017.10.011