Abstract
An innovative symmetry-guided concept, which capitalizes on partial as well as exact symmetries that underpin the structure of nuclei, is discussed. Within this framework, ab initio applications of the theory to light nuclei reveal the origin of collective modes and the emergence a simple orderly pattern from first principles. This provides a strategy for determining the nature of bound states of nuclei in terms of a relatively small fraction of the complete shell-model space, which, in turn, can be used to explore ultra-large model spaces for a description of alpha-cluster and highly deformed structures together with the associated rotations. We find that by using only a fraction of the model space extended far beyond current no-core shell-model limits and a long-range interaction that respects the symmetries in play, the outcome reproduces characteristic features of the low-lying 0+ states in 12 C (including the elusive Hoyle state and its 2+ excitation) and agrees with ab initio results in smaller spaces. This is achieved by selecting those particle configurations and components of the interaction found to be foremost responsible for the primary physics governing clustering phenomena and large spatial deformation in the ground-state and Hoyle-state rotational bands of 12 C. For these states, we offer a novel perspective emerging out of no-core shell-model considerations, including a discussion of associated nuclear deformation, matter radii, and density distribution. The framework we find is also extensible to negative-parity states (e.g., the 3−1 state in 12C) and beyond, namely, to the low-lying 0+ states of 8Be as well as the ground-state rotational band of Ne, Mg, and Si isotopes. The findings inform key features of the nuclear interaction and point to a new insight into the formation of highly-organized simple patterns in nuclear dynamics.
Highlights
Approximate symmetries in atomic nuclei that favor large deformation in nuclear dynamics have been long recognized [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], and only recently confirmed in the ab initio symmetry-adapted no-core shell model (SA-NCSM) [11]
We show the emergence – in the framework of the SA-NCSM from first principles – of orderly patterns that favor large deformation/low spin in nuclear wavefunctions [11]
The ab initio Nmax = 8 SA-NCSM results with the bare N3LO realistic interaction for the 8Be 0+ ground state (g.st.) and its rotational band reveal the dominance of the 0 Ω component with the foremost contribution coming from the leading (4 0) S = 0 irrep (Fig. 1a)
Summary
Approximate symmetries in atomic nuclei that favor large deformation in nuclear dynamics have been long recognized [1, 2, 3, 4, 5, 6, 7, 8, 9, 10], and only recently confirmed in the ab initio symmetry-adapted no-core shell model (SA-NCSM) [11]. The ab initio Nmax = 8 SA-NCSM results with the bare N3LO (for JISP16) realistic interaction for the 8Be 0+ ground state (g.st.) and its rotational band reveal the dominance of the 0 Ω component with the foremost contribution coming from the leading (4 0) S = 0 irrep (Fig. 1a).
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