Nuclear Theory·nucl-th

Wednesday·December 25, 2024

10 papers—5 primary·5 cross-listed

01
Emulation of the final r-process abundance pattern with a neural network
Yukiya Saito · Iris Dillmann · Reiner Krücken · Matthew R. Mumpower · Rebecca Surman
This work explores the construction of a fast emulator for the calculation of the final pattern of nucleosynthesis in the rapid neutron capture process (the $r$ -process). An emulator is built using a feed-forward artificial neural network (ANN). We train the ANN with nuclear data and relative abundance patterns. We take as input the $β$ -decay half-lives and the one-neutron separation energy of the nuclei in the rare-earth region. The output is the final isotopic abundance pattern. In this work, we focus on the nuclear data and abundance patterns in the rare-earth region to reduce the dimension of the input and output space. We show that the ANN can capture the effect of the changes in the nuclear physics inputs on the final $r$ -process abundance pattern in the adopted astrophysical conditions. We employ the deep ensemble method to quantify the prediction uncertainty of the neutal network emulator. The emulator achieves a speed-up by a factor of about 20,000 in obtaining a final abundance pattern in the rare-earth region. The emulator may be utilized in statistical analyses such as uncertainty quantification, inverse problems, and sensitivity analysis.
nucl-thnucl-exJ.Phys.G(2025)·2 citations
02
Alpha-Particle Monopole Form Factors with Ab Initio No-Core Shell Model
P. Yin · A. M. Shirokov · H. Li · B. Zhou · X. Zhao · S. Bacca · J. P. Vary
The state-of-the-art ab initio nuclear many-body approaches with modern nuclear forces are challenged by the recent experimental measurement of the monopole form factor of the $0_{1}^{+} \to 0_{2}^{+}$ transition in the $α$ particle [Kegel et al., Phys. Rev. Lett. 130, 152502 (2023)]. We investigate the elastic and inelastic $0_{1}^{+} \to 0_{2}^{+}$ transition form factors using the ab initio no-core shell model (NCSM). We observe a good convergence of both form factors with respect to the basis size employing the Daejeon16 nucleon-nucleon ( $N N$ ) interaction. Our NCSM results are very close to the effective interaction hyperspherical harmonic calculations using $N N$ plus three-nucleon interactions based on the chiral effective field theory which take into account the continuum effects via the Lorentz integral transform. The significant difference between the ab initio results with various modern nuclear interactions and of some of them with the recent experimental data provides motivations for deeper investigation of this observable.
nucl-thnucl-exPRC(2025)·3 citations
03
Chirality in $(p, 2 p)$ reactions induced by proton helicity
Tomoatsu Edagawa🇯🇵 · Kazuki Yoshida🇯🇵 · Shoichiro Kawase🇯🇵 · Kazuyuki Ogata🇯🇵 · Masaki Sasano🇯🇵
It is shown that longitudinally polarized protons can be used to induce chirality in the final states of the $(p, pN)$ reaction at intermediate energies, when there exist three final-state particles with non-coplanar momentum vectors. The analyzing power $A_{z}$ is proposed as a measure of this effect. Theoretical descriptions to obtain $A_{z}$ based on an intuitive picture as well as a distorted wave impulse approximation are presented, showing that the helicity of incident protons is coupled to the chirality of the orbital motion of a single-particle wave function, resulting in the chirality of the final states and a large $A_{z}$ value.
nucl-thnucl-exPRC(2026)·0 citations
04
Fermionic equations of motion in strongly-correlated media: applications to the nuclear many-body problem
Elena Litvinova🇺🇸
These notes summarise the lectures given at the International School of Physics "Enrico Fermi" in Summer 2024 in Varenna (Italy) about the strongly coupled quantum many-body theory and its applications to nuclear structure. The lectures present a rather short overview of the subject with an emphasis on the analytical aspects of the nuclear many-body problem, aiming at a deep understanding of the complexity of strongly coupled nucleonic states and emergent collective phenomena. The major pedagogical focus is recognizing how all the models describing nuclear dynamics follow from a unified model-independent framework formulated in the universal language of quantum field theory. In particular, connections between the classes of ab initio, density functional theory, and beyond mean-field approaches are made accessible. Approximations of varying complexity are discussed in applications to excited states of medium-heavy nuclei.
nucl-thnucl-ex0 citations
05
Global analysis of the non-uniformity of nucleon density distributions
Shuichiro Ebata · Wataru Horiuchi
Background: Saturation of nuclear density is a fundamental property of atomic nuclei but in reality, the nuclear internal density distribution is not uniform, e.g., some nuclei are known to have the so-called bubble structure, in which the central density is depressed. Purpose: We aim to unveil the emergent mechanism of the non-uniformity of the nucleon density distributions for whole nuclear mass regions, not only for a typical bubble structure. Method: We systematically investigate the nucleon density distributions using the Skyrme Hartree-Fock plus Bardeen-Cooper-Schrieffer calculation represented in the three-dimensional Cartesian coordinate space. The ground states of 1,389 even-even nuclei are generated. To quantify the nonuniformity of these density distributions, a ``generalized bubble parameter" is introduced. Results: We find that the bubble structure appears around the magic numbers, which correspond to the regions where the s orbit appears near the Fermi surface. The nuclear deformation and pairing correlations strongly affect the occupation probability, but the robust bubble structure of a medium mass nucleus, $^{100}$ Sn, is found. We confirm that the Coulomb force enhances the bubble degree in the superheavy region. The nuclear non-uniformity is further generalized by the ``multi-layered" bubble structure, which exhibits some density depression in the internal regions of the density distributions. Conclusion: The non-uniformity of the internal density distribution occurs due to the deficiency of the specific single-particle orbits: the nodal $s$ , $p$ , and $d$ orbits. This is certainly reflected in the density distribution near the nuclear surface, which can be deduced from proton-elastic scattering.
nucl-thPRC(2025)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE

Emulation of the final r-process abundance pattern with a neural network

Alpha-Particle Monopole Form Factors with Ab Initio No-Core Shell Model

Chirality in (p​,2p) reactions induced by proton helicity

Fermionic equations of motion in strongly-correlated media: applications to the nuclear many-body problem

Global analysis of the non-uniformity of nucleon density distributions

Affiliations

Chirality in $(p, 2 p)$ reactions induced by proton helicity