Non-perturbative calculations of nuclear matter using in-medium similarity renormalization group

The non-perturbative {\it ab initio} calculations of infinite nuclear matter using In-Medium Similarity Renormalization Group (IMSRG) method is developed in this work, which enables calculations with chiral two and three-nucleon forces at N$^2$LO and N$^3$LO. Results from the many-body perturbation theory at different orders and coupled-cluster theory are also presented for comparison. It is shown that different many-body approaches lead to obvious discrepancies with a harder nuclear interaction for both pure neutron matter and symmetric nuclear matter. This work provides a novel alternative infrastructure for future studies of dense nuclear matter and strongly-correlated many-body systems.