Nuclear Theory·nucl-th

Thursday·April 18, 2024

8 papers—6 primary·2 cross-listed

01
Vector meson production in ultraperipheral heavy ion collisions
Björn Schenke🇺🇸 · Heikki Mäntysaari🇫🇮 · Farid Salazar🇺🇸 · Chun Shen🇺🇸 · Wenbin Zhao🇺🇸
We review model calculations of exclusive vector meson production in ultraperipheral heavy ion collisions. We highlight differences and similarities between different dipole models and leading twist shadowing calculations. Recent color glass condensate calculations are presented with focus on effects from nuclear structure and azimuthal anisotropies driven by interference effects.
nucl-thhep-phnucl-exPhys.Proc.UPC(2024)·7 citations
02
Sizes of the Nucleon
Norbert Kaiser🇩🇪 · Wolfram Weise🇩🇪
Evidences are updated and strengthened for the two-scales picture of low-energy nucleon structure as a compact `hard' valence quark core surrounded by a `soft' cloud of quark-antiquark pairs (the meson cloud). These considerations are quantified by a spectral analysis of the mean-squared radii associated with the isoscalar and isovector electric form factors of the nucleon. Further supporting arguments come from corresponding studies of the axial and mass form factors and their inferred radii. Separating low-mass (mesonic) and high-mass (short-range) contributions in the spectral representations of each of these form factors, we conclude that a central core with an r.m.s. radius of about 1/2 fm results consistently as the common feature in all cases. Implications are discussed for baryonic matter at densities beyond that of equilibrium nuclear matter.
nucl-thPRC(2024)·22 citations
03
Momentum dependent nucleon-nucleon contact interactions and their effect on p-d scattering observables
E. Filandri🇮🇹 · L. Girlanda🇮🇹 · A. Kievsky🇮🇹 · L. E. Marcucci🇮🇹 · M. Viviani🇮🇹
Starting from a complete set of relativistic nucleon-nucleon contact operators up to order $O (p^{4})$ of the expansion in the soft (relative or nucleon) momentum $p$ , we show that non-relativistic expansions of relativistic operators involve twenty-six independent combinations, two starting at $O (p^{0})$ , seven at order $O (p^{2})$ and seventeen at order $O (p^{4})$ . This demonstrates the existence of two low-energy free constants that parameterize interactions dependent on the total momentum of the pair of nucleons $P$ . The latter, through the use of a unitary transformation, can be removed in the two-nucleon fourth-order contact interaction of the Chiral Effective Field Theory, generating a three-nucleon interaction at the same order. Within a hybrid approach in which this interaction is considered together with the phenomenological potential AV18, we show that the LECs involved can be used to fit very accurate data on the polarization observables of the low-energy $p - d$ scattering, in particular the $A_{y}$ asymmetry.
nucl-thFew Body Syst.(2024)·1 citation
04
Discovering Nuclear Models from Symbolic Machine Learning
Jose M. Munoz · Silviu M. Udrescu · Ronald F. Garcia Ruiz
Numerous phenomenological nuclear models have been proposed to describe specific observables within different regions of the nuclear chart. However, developing a unified model that describes the complex behavior of all nuclei remains an open challenge. Here, we explore whether novel symbolic Machine Learning (ML) can rediscover traditional nuclear physics models or identify alternatives with improved simplicity, fidelity, and predictive power. To address this challenge, we developed a Multi-objective Iterated Symbolic Regression approach that handles symbolic regressions over multiple target observables, accounts for experimental uncertainties and is robust against high-dimensional problems. As a proof of principle, we applied this method to describe the nuclear binding energies and charge radii of light and medium mass nuclei. Our approach identified simple analytical relationships based on the number of protons and neutrons, providing interpretable models with precision comparable to state-of-the-art nuclear models. Additionally, we integrated this ML-discovered model with an existing complementary model to estimate the limits of nuclear stability. These results highlight the potential of symbolic ML to develop accurate nuclear models and guide our description of complex many-body problems.
nucl-thcs.AIcs.LGnucl-exCommun.Phys.(2025)·9 citations
05
Uncertainty estimation and anomaly detection in chiral effective field theory studies of key nuclear electroweak processes
Bijaya Acharya🇺🇸
Chiral effective field theory ( $χ$ EFT) is a powerful tool for studying electroweak processes in nuclei. I discuss $χ$ EFT calculations of three key nuclear electroweak processes: primordial deuterium production, proton-proton fusion, and magnetic dipole excitations of $^{48} Ca$ . This article showcases $χ$ EFT's ability to quantify theory uncertainties at the appropriate level of rigor for addressing the different precision demands of these three processes.
nucl-thFew Body Syst.(2024)·1 citation
06
Emulators for scarce and noisy data: application to auxiliary field diffusion Monte Carlo for the deuteron
Rahul Somasundaram · Cassandra L. Armstrong · Pablo Giuliani · Kyle Godbey · Stefano Gandolfi · Ingo Tews
The validation, verification, and uncertainty quantification of computationally expensive theoretical models of quantum many-body systems require the construction of fast and accurate emulators. In this work, we develop emulators for auxiliary field diffusion Monte Carlo (AFDMC), a powerful many-body method for nuclear systems. We introduce a reduced-basis method (RBM) emulator for AFDMC and study it in the simple case of the deuteron. Furthermore, we compare our RBM emulator with the recently proposed parametric matrix model (PMM) that combines elements of RBMs with machine learning. We contrast these two approaches with a traditional Gaussian Process emulator. All three emulators constructed here are based on a very limited set of 5 training points, as expected for realistic AFDMC calculations, but validated against $O (1 0^{3})$ exact solutions. We find that the PMM, with emulator errors of only $\approx 0.1%$ and speed-up factors of $\approx 1 0^{7}$ , outperforms our implementation of the other two emulators when applied to AFDMC.
nucl-thPLB(2025)·24 citations

Affiliations

first authorsco-authorsvia INSPIRE

Vector meson production in ultraperipheral heavy ion collisions

Sizes of the Nucleon

Momentum dependent nucleon-nucleon contact interactions and their effect on p-d scattering observables

Discovering Nuclear Models from Symbolic Machine Learning

Uncertainty estimation and anomaly detection in chiral effective field theory studies of key nuclear electroweak processes

Emulators for scarce and noisy data: application to auxiliary field diffusion Monte Carlo for the deuteron

Affiliations