Nuclear Structure from the In-Medium Similarity Renormalization Group

TL;DR

This paper reviews the In-Medium Similarity Renormalization Group (IMSRG) method for nuclear structure, highlighting its ability to evolve nuclear Hamiltonians efficiently and its applications to medium-mass nuclei, bridging theory and experimental data.

Contribution

It introduces the IMSRG method, detailing its implementation, applications to open-shell and deformed nuclei, and potential integration with other many-body techniques for comprehensive nuclear modeling.

Findings

IMSRG effectively decouples energy scales in nuclear Hamiltonians.

Successful application to open-shell and deformed nuclei.

Potential for combined methods to improve nuclear structure predictions.

Abstract

Efforts to describe nuclear structure and dynamics from first principles have advanced significantly in recent years. Exact methods for light nuclei are now able to include continuum degrees of freedom and treat structure and reactions on the same footing, and multiple approximate, computationally efficient many-body methods have been developed that can be routinely applied for medium-mass nuclei. This has made it possible to confront modern nuclear interactions from Chiral Effective Field Theory, that are rooted in Quantum Chromodynamics with a wealth of experimental data. Here, we discuss one of these efficient new many-body methods, the In-Medium Similarity Renormalization Group (IMSRG), and its applications in modern nuclear structure theory. The IMSRG evolves the nuclear many-body Hamiltonian in second-quantized form through continuous unitary transformations that can be implemented with polynomial computational effort. Through suitably chosen generators, we drive the matrix representation of the Hamiltonian in configuration space to specific shapes, e.g., to implement a decoupling of low- and high-energy scales, or to extract energy eigenvalues for a given nucleus. We present selected results from Multireference IMSRG (MR-IMSRG) calculations of open-shell nuclei, as well as proof-of-principle applications for intrinsically deformed medium-mass nuclei. We discuss the successes and prospects of merging the (MR-)IMSRG with many-body methods ranging from Configuration Interaction to the Density Matrix Renormalization Group, with the goal of achieving an efficient simultaneous description of dynamic and static correlations in atomic nuclei.