Similarity-Transformed Chiral NN+3N Interactions for the Ab Initio Description of 12-C and 16-O

Abstract

We present first ab initio no-core shell model (NCSM) calculations using similarity renormalization group (SRG) transformed chiral two-nucleon (NN) plus three-nucleon (3N) interactions for nuclei throughout the p-shell, particularly 12-C and 16-O. By introducing an adaptive importance truncation for the NCSM model space and an efficient JT-coupling scheme for the 3N matrix elements, we are able to surpass previous NCSM studies including 3N interactions regarding, both, particle number and model-space size. We present ground and excited states in 12-C and 16-O for model spaces up to N_max=12 including full 3N interactions, which is sufficient to obtain converged results for soft SRG-transformed interactions. We analyze the contributions of induced and initial 3N interactions and probe induced 4N terms through the sensitivity of the energies on the SRG flow parameter. Unlike for light p-shell nuclei, SRG-induced 4N contributions originating from the long-range two-pion terms of the chiral 3N interaction are sizable in 12-C and 16-O.