Degree
Doctor of Philosophy (PhD)
Department
Physics and Astronomy
Document Type
Dissertation
Abstract
The importance of collective motion in atomic nuclei has been well-established for many decades. Even before the advent of the nuclear shell model and its much-needed answers to surprising empirical phenomena, collectivity and surface deformation have played a vital role in broadening our knowledge. Reconciling the collective and single-particle camps into a unified description required tremendous strides in the application of group theory and advances in high-performance supercomputing, and thanks to these efforts the symmetry-adapted no-core shell model, or SA-NCSM, has developed into a reliable model for the study of deformed light and medium-mass nuclei. State-of-the-art calculations reveal remarkably simple patterns within the complex collective structures of nuclei, and overwhelmingly support the increasingly inescapable conclusion that most nuclei are deformed. When combined with “realistic” inter-nucleon interactions firmly tied to ab initio considerations, and which precisely reproduce few-nucleon scatterings experiments, the SA-NCSM provides robust predictions for challenging nuclear properties with rigorously quantified uncertainties, a key ingredient in the design and analysis of experiments involving exotic isotopes.
Despite this remarkable progress, the exact mechanism by which deformation emerges from nuclear forces remains elusive. In this work, I utilize the SA-NCSM with chiral effective interactions to demonstrate that the parameters tying these interactions to the symmetry patterns of QCD induce large uncertainties in the quadrupole moments of 6Li and 12C, by exerting subtle but critical impacts on the dominant nuclear shapes driving this collective observable. The deformed snapshots comprising the shapes vary tremendously, even though the sum of their probabilities remain nearly constant, while global sensitivity analysis reveals that most of the quadrupole variance originates from two parameters describing the S-wave scattering of two nucleons in close contact. Larger deformation is achieved through a re-balancing of specific symmetry-preserving excitations that lower the overall kinetic energy of the nucleus, mediated by the S-wave parameters, which partially explains Nature’s preference for prolate deformation. I further combine the SA-NCSM with Bayesian analysis to deduce an effective alpha-deuteron scattering potential with fully propagated statistical method uncertainties, a first step towards the complete accounting of theoretical ab initio errors and empirical uncertainties considering both structure and reaction properties.
Date
9-1-2025
Recommended Citation
Becker, Kevin, "How the Inter-Nucleon Force Shapes Emergent Collectivity and Imparts Uncertainties in Ab Initio Nuclear Observables" (2025). LSU Doctoral Dissertations. 6902.
https://repository.lsu.edu/gradschool_dissertations/6902
Committee Chair
Launey, Kristina D.