A Novel Many-Body Method for the Description of Open-Shell Nuclei From First Principles

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This project seeks to find answers to a number of key questions in nuclear theory: How does subatomic matter organize itself, and what patterns emerge? Are the fundamental interactions that govern the structure of matter understood? These are two of the major questions that drive the research efforts in the field of nuclear physics in years to come. The experimental push towards exotic neutron-rich nuclei has already forced us to revise our understanding of nuclear physics, and facilities like FRIB, the Facility for Rare Isotope Beams, will provide a wealth of new data from isotopes that could not be studied under laboratory conditions before. In these nuclei, structural changes are driven by a complex interplay of nuclear forces, the continuum, and strong many-body correlations which signal the breakdown of traditional single-reference models of nuclear structure. This has far-reaching implications, e.g., on the half lives of key nuclei for astrophysical processes, or the limits of nuclear existence, explaining why O-24 rather than O-28 is the heaviest oxygen isotope found in nature. As its name suggests, the Multi-Reference In-Medium Similarity Renormalization Group MR-IM-SRG) developed by the PI is a novel many-body method that can be applied to nuclei (or other many-body systems) for which single-reference based descriptions are no longer an appropriate starting point. Under the current award, the MR-IM-SRG will be extended to the computation of excited state properties in medium-mass and heavy open-shell nuclei, including electromagnetic and weak transition rates. Using state-of-the-art interactions and currents from Chiral Effective Field Theory (EFT) the PI and his students will investigate the erosion and emergence of the so-called magic numbers, compute masses and decay rates relevant for nuclear astrophysics, and study effects like the formation of neutron skins that constrain the nuclear equation of state. The systematic improvability of the MR-IM-SRG and the inputs from Chiral EFT will allows us to control and quantify the theoretical uncertainties of these results. These efforts will help to identify potential issues in the theoretical framework through the confrontation with experimental data, and guide experimental efforts at the National Superconducting Cyclotron Laboratory (NSCL) and FRIB, as well as other facilities worldwide. The project will provide partial support for one graduate student, who will participate in research at the forefront of nuclear physics, and receive training in high-performance computing.