In-medium similarity renormalization group with three-body operators

Over the past decade in-medium similarity renormalization group (IMSRG) approach has proven to be a powerful and versatile ab initio many-body method for studying medium-mass nuclei. So far, IMSRG was limited approximation in which only up two-body operators are incorporated flow, referred as IMSRG(2). In this work, we extend IMSRG(2) fully include three-body yielding IMSRG(3) approximation. We use perturbative scaling analysis estimate importance of individual terms introduce truncations that aim approximate at lower computational cost. The is systematically benchmarked different nuclear Hamiltonians ${}^{4}\text{He}$ ${}^{16}\text{O}$ small model spaces. improves over relative exact results. Approximate constructed based on cost able reproduce much systematic improvement offered by full IMSRG(3). also find behave consistently with expectations from our analysis, indicating strategy may used