Efficacy of the symmetry-adapted basis for ab initio nucleon-nucleus interactions for light- and intermediate-mass nuclei

Abstract

We study the efficacy of a new ab initio framework that combines the symmetry-adapted (SA) no-core shell-model approach with the resonating group method (RGM) for unified descriptions of nuclear structure and reactions. We obtain ab initio neutron-nucleus interactions for 4 He, 16 O, and 20 Ne targets, starting with realistic nucleon-nucleon potentials. We discuss the effect of increasing model space sizes and symmetry-based selections on the SA-RGM norm and direct potential kernels, as well as on phase shifts, which are the input to calculations of cross sections. We demonstrate the efficacy of the SA basis and its scalability with particle numbers and model space dimensions, with a view toward ab initio descriptions of nucleon scattering and capture reactions up through the medium-mass region. I. INTRODUCTIONAb initio descriptions of spherical and deformed nuclei up through the calcium region are now possible within a no-core shell-model framework, by utilizing emerging symplectic symmetry in nuclei. In particular, the symmetry-adapted no-core shell-model (SA-NCSM) [1, 2] uses a physically relevant symmetry-adapted (SA) basis that can achieve significantly reduced model spaces compared to the corresponding complete ultra-large model spaces, without compromising the accuracy of results for various observables [1,3,4]. This enables the SA-NCSM to accommodate contributions from more shells and to describe heavier nuclei, such as 20 Ne [2], 21 Mg [5], 22 Mg [6], 28 Mg [7], as well as 32 Ne and 48 Ti [8,9]. The access to higher-lying shells makes the SA basis suitable for describing nuclear reactions [9], the processes that are typically studied in experiments and govern stellar evolution. Remarkable progress has been made in firstprinciple descriptions to scattering and nuclear reactions for light nuclei (for an overview, see [10,11]), including studies of elastic scattering [12][13][14][15][16][17][18], photoabsorption [19], transfer [20] and capture reactions [21], α widths [22,23] and resonant states [24], as well as thermonuclear fusion [25]. In this paper, we show that expanding the reach of ab initio reactions to deformed and heavier targets is now feasible with the SA basis.