Medium-Mass and Heavy Open-Shell Nuclei from First Principles

The reach of ab initio many-body techniques has increased tremendously in recent years, owing to new developments in many-body theory as well as advances in their numerical implementation. Configuration-space methods like Coupled Cluster, Self-Consistent Green's Function, and In-Medium Similarity Renormalization Group (IM-SRG) are routinely applied to isotopes in the A ~ 100 region. Moreover, these techniques have been extended to tackle open-shell nuclei, either directly or through the auxiliary step of deriving valence-space interactions for use with existing Shell Model technology. One of the most powerful aspects of ab initio methods is their capability to provide results for energies and other observables with systematic uncertainties. Together with new accurate nuclear forces (and operators) derived from Chiral Effective Field Theory, they provide a consistent framework --- and a road map --- for a predictive description of nuclei. This will have a critical impact on important scientific endeavours like the search for the limits of nuclear existence or tests of fundamental symmetries (e.g., through the exploration of neutrinoless double beta decay). Using the Multi-Reference IM-SRG as an example, I will discuss successes and failures in the ab initio description of ground- and excited-state properties and the insights they provide into the underlying chiral forces, as well as upcoming developments like the construction of consistent ab initio transition operators.