Xiang-Xiang Sun

We make \textit{ab initio} predictions of charge form factors (FFs) and radii for the isoscalar nuclei $^6$Li and $^8$Be using the Jacobi-coordinate No-Core Shell Model. The calculations employ chiral semilocal momentum-space regularized two- and three-nucleon interactions, together with consistently regularized one- and two-nucleon electromagnetic charge operators. With the short-range charge density fixed to the $^4$He charge radius, the predicted FFs and the $^6$Li radius show good agreement with available experimental data. We find that two-nucleon charge density contributions are essential for describing the FFs, particularly at intermediate and large momentum transfers. Although their influence on the charge radii is limited, these contributions remain crucial for attaining accurate predictions. The present results highlight the importance of two-nucleon charge operators in addressing the long-standing underestimation of nuclear charge radii in \textit{ab initio} calculations based on modern chiral interactions.

Modern advanced nuclear ab initio approaches with the similarity renormalization group (SRG) softened interactions miss high-momentum information, thus rendering them less suitable for characterizing nucleon-nucleon short-range physics. We introduce a novel framework to construct SRG-independent nuclear wave functions from No-Core Shell Model calculations. Applying our method to densities obtained with semilocal momentum-space-regularized chiral NN and NNN forces, we show key universalities of short-range behavior: (1) The two-body density ratio in the np S=1 channel, relative to the deuteron (d), is remarkably insensitive to interaction details. (2) More strikingly, while the ratio of total two-body densities to the deuteron exhibits cutoff dependence, the same ratio to the $α$-particle (4-He) is almost independent of the interactions.

Accurately determining the size of the atomic nucleus with realistic nuclear forces is a long-outstanding issue of nuclear physics. The no-core shell model (NCSM), one of the powerful methods for nuclear structure, can achieve accurate energies of light nuclei. The extraction of converged radii is more difficult. In this work, we present a novel method to effectively extract the radius of light nuclei by restoring the long-range behavior of densities from NCSM calculations. The correct large distance asymptotics of two-body relative densities are deduced based on the NCSM densities in limited basis size. The resulting radii using the corrected densities show a nice convergence. The root-mean-square matter and charge radii of He 4 , 6 , 8 and Li 6 , 7 , 8 can be accurately obtained based on Jacobi-NCSM calculations with the high-precision chiral two-nucleon and three-nucleon forces combined with this new method. Our method can be straightforwardly extended to other calculations, potentially providing a better description of nuclear sizes with realistic nuclear forces.

1985 年晕核 11Li 的发现开启了奇特原子核的研究。迄今为止，已观测到的晕核有 6He、11Li、11,14Be、 8,17,19B、15,19,22C、17,29F、17,29,31Ne 和 37Mg。对晕核的研究有助于理解核力以及极端丰中子或丰质子原子核的 性质。形状是原子核最重要的特征之一，大多数原子核是变形的。早在 1997 年就有形变晕核的探索。2010 年， 包含连续谱贡献的变形相对论 Hartree-Bogoliubov 理论 (deformed relativistic Hartree-Bogoliubiv theory in continuum, DRHBc)实现了对奇特原子核在考虑形变、连续谱、弱束缚及其它们之间的相互耦合的微观描述。 DRHBc 理论最早应用于研究氖和镁同位素中的形变晕结构，并预测了 36Ne 和 44Mg 中的形变晕。特别地，该 理论预言形变晕核的核芯和晕具有不同形状，这种效应称为形状退耦合。最近，该理论广泛应用于预测或描述 许多形变系统中的晕结构，其结果与实验分析相符。在碳同位素的晕研究中，揭示了 15,22C 中的形变晕，并指 出形变对晕结构的影响，进而解决了 22C 中价中子的半径和晕组态之谜。新观测到的 17,19B 晕也通过 DRHBc 理论得到了很好的理解，所得变形晕结构组态与实验结果一致，表明形变对晕的重要性。通过基于 DRHBc 理 论发展角动量投影，研究了形变晕的旋转激发，表明变形晕及其形状退耦合效应在形变晕核的低激发旋转态中 仍然存在。本文总结这些最新进展，展示形变效应与晕结构的相互关联。

Accurately determining the size of the atomic nucleus with realistic nuclear forces is a long outstanding issue of nuclear physics. The no-core shell model (NCSM), one of the powerful ab initio methods for nuclear structure, can achieve accurate energies of light nuclei. The extraction of converged radii is more difficult. In this work, we present a novel method to effectively extract the radius of light nuclei by restoring the long-range behavior of densities from NCSM calculations. The correct large distance asymptotic of two-body relative densities are deduced based on the NCSM densities in limited basis size. The resulting radii using the corrected densities show a nice convergence. The root-mean-square matter and charge radii of $^{4,6,8}$He and $^{6,7,8}$Li can be accurately obtained based on Jacobi-NCSM calculations with the high-precision chiral two-nucleon and three-nucleon forces combined with this new method. Our method can be straightforwardly extended to other ab initio calculations, potentially providing a better description of nuclear sizes with realistic nuclear forces.