Nuclear Theory·nucl-th

Wednesday·April 1, 2026

14 papers—7 primary·7 cross-listed

01
Dimer Effective Field Theory
Cullen Gantenberg🇺🇸 · David B. Kaplan🇺🇸
While chiral perturbation theory for mesons is characterized by a momentum expansion in $Q / Λ_{χ}$ with $Λ_{χ} \sim 1$ GeV, existing formulations of effective theory for nucleon-nucleon scattering deviate from data at $Q \sim 300$ MeV or lower. We offer heuristic evidence that unsuspected nonanalytic structure exists in the complex momentum plane obstructing the effective field theory expansion in the spin-triplet channels, associated with the peak of the angular momentum barrier whose energy in low partial waves satisfies $k = M E \sim 300$ MeV. With this motivation, we construct a meromorphic function of $k^{2}$ we call the $C$ -matrix, for which the radius of convergence of its Taylor expansion in $k^{2}$ is equivalent to that of the momentum expansion of the effective field theory. Thus the range of validity of the effective theory is directly related to the pole structure of the $C$ -matrix. We uncover that pole structure and confirm that it is the source of the obstruction. The systematic inclusion of dimer fields as propagating degrees of freedom in the effective theory to account for those poles results in cut-off insensitive fits at order $Q^{0}$ to most of the lower partial wave phase shifts up to the pion production threshold, using only the one pion exchange part of the long-range nucleon-nucleon interaction. Our theory should be applicable to the singular potentials regularly found in atomic physics as well.
nucl-thphysics.atom-ph2 citations
02
Ab initio optical potentials for magnesium isotopes at intermediate energies: from stability to the island of inversion
G.H. Sargsyan · J. I. Fuentealba Bustamente · K. Beyer · Ch. Elster
We present the first calculations of ab initio nonlocal optical potentials for $^{24, 26, 28}$ Mg and $^{32}$ Mg isotopes using the leading-order term of the spectator expansion of multiple-scattering theory. We use the structure input from the ab initio symmetry-adapted no-core shell model (SA-NCSM), which provides translationally invariant, off-shell scalar and spin-projected densities so that structure and reaction inputs are treated on equal footing with no adjustable parameters. This leading-order potential reproduces $^{24}$ Mg neutron total, reaction, and elastic-scattering data at energies between 65 and 250 MeV and provides predictions for $^{26, 28}$ Mg and $^{32}$ Mg. We compare our prediction with those from uncertainty-quantified Koning-Delaroche (KDUQ) and Weppner-Penney global optical potentials, and with the ENDF nuclear data evaluations. These comparisons highlight some of the limitations of the global models, while also validating their use in reaction modeling near the N=20 island of inversion.
nucl-thnucl-exJ.Phys.G(2026)·0 citations
03
Multi-task deep neural network for predicting both nuclear fission yields and their experimental errors in peak-shaped data
Maomi Ueno · Enbo Zhang · Kazuma Fuchimoto · Satoshi Chiba · Jingde Chen · Chikako Ishizuka
The fission product yield (FPY) is crucially important information for numerous nuclear applications. However, the peak-shaped characteristics of FPY data present important challenges for predicting unobservable FPY data. To address these challenges, after applying Multi-task learning models to fission product yield data and their experimental error estimates, we introduce a novel loss function along with incorporation of the odd even effect. Our approach is intended to predict unknown fission yields and the associated experimental error. To demonstrate the effectiveness of our proposed method, we compared our proposed method with conventional methods that learn each dataset independently. Our findings demonstrate that the proposed methods can predict peak shaped data with experimental error estimates more effectively than earlier methods can.
nucl-th0 citations
04
Time evolution formalism in the complex scaling method: Application to the E1 response of $^{6}$ He
Yuma Kikuchi · Kiyoshi Katō · Takayuki Myo
Background: The complex scaling method (CSM) has been successfully used to describe many-body resonances as eigenvalues of the complex-scaled Hamiltonian in an appropriate $L^{2}$ basis representation. Its scope has subsequently been extended to many-body continuum states, strength functions, and scattering observables. However, a general framework that incorporates time evolution within the same CSM framework has not yet been established. Purpose: We formulate a time-evolution formalism as a natural extension of the CSM based on the extended completeness relation (ECR), and apply it to the electric dipole (E1) excitation of $^{6}$ He in order to clarify how an initially correlated three-body configuration evolves into continuum states. Methods: Time evolution is described by a complex-scaled time-evolution operator represented with the ECR. The formalism is first tested in a simple two-body model through comparison with a direct numerical solution of the time-dependent Schrödinger equation. It is then applied to the E1 excitation of $^{6}$ He in an $α + n + n$ three-body model, and the density distributions are analyzed in different Jacobi coordinate systems. Results: The present formalism reproduces the wave-packet evolution obtained in the direct time-dependent calculation. In the application to $^{6}$ He, the initial E1-excited state exhibits a correlated configuration and evolves into spatially extended continuum states. The time evolution of the density distributions indicates the coexistence of sequential decay through a core-neutron subsystem and direct breakup. Conclusions: The present formalism extends the scope of the CSM from spectral and scattering observables to real-time continuum dynamics, and provides a unified framework that connects initial-state correlations, continuum structure, and decay dynamics in weakly bound nuclei.
nucl-thPRC(2026)·0 citations
05
Nuclear shapes of Nb isotopes
Esperanza Maya-Barbecho · José-Enrique García-Ramos
The study of the structure of odd-mass nuclei in regions characterized by the interplay of multiple particle-hole configurations represents a major challenge in nuclear structure physics. The odd-mass niobium isotopes ( $Z = 41$ ), located near the $N = 60$ region, are of particular interest due to shape coexistence and quantum phase transitions. This work investigates the structure of the $^{93 - 103}$ Nb isotopes using the intrinsic-frame formalism of the interacting boson-fermion model with configuration mixing (IBFM-CM), aiming to determine nuclear shapes and explore shape coexistence, configuration crossing, and quantum phase transitions. We employ the intrinsic formalism of the IBFM-CM, including both 0p-0h (regular) and 2p-2h (intruder) configurations interacting with the unpaired nucleon, providing a self-consistent framework to study energy surfaces, shape coexistence, and intruder bands for both positive- and negative-parity states. A realistic Hamiltonian for niobium, determined in previous studies, is adopted. The formalism is applied to the $^{93 - 103}$ Nb isotopes for both positive- and negative-parity bands. A detailed analysis of the mean-field energy surfaces has been performed, including axial energy curves, triaxial energy surfaces in the $β - γ$ plane, and the corresponding equilibrium deformation parameters. The results reveal clear evidence of configuration coexistence and crossing along the isotopic chain. The existence of crossing configurations is demonstrated around $N = 60$ , corresponding to a quantum phase transition previously identified in the Sr and Zr isotopic chains. Furthermore, the presence of an unpaired nucleon in Nb influences the abruptness of the quantum phase transition, underscoring the sensitivity of the structural evolution to single-particle degrees of freedom.
nucl-thPRC(2026)·0 citations
06
Optimizing the description of the Delta region in the Ghent Hybrid model for single-pion production
M. Hooft🇧🇪 · A. Nikolakopoulos🇧🇪 · J. García-Marcos🇧🇪 · Y. De Backer🇧🇪 · T. Franco-Munoz🇧🇪 · K. Niewczas🇧🇪 · R. González-Jiménez🇪🇸 · N. Jachowicz🇧🇪
Single-pion production is an important contribution to the total neutrino-nucleus interaction cross section in accelerator-based neutrino oscillation experiments. The goal of this paper is to improve the Ghent model in the Delta resonance region by incorporating as many physical constraints as possible while keeping the number of fitted parameters as low as possible. A multipole decomposition of the model is performed allowing the use of $K$ -matrix theory to unitarize the background contributions. Watson's theorem is enforced by consistently modifying both the Delta and background contributions across all multipoles. Furthermore, the decay width and form factors of the Delta contribution are modified to ensure compliance with Watson's theorem, while the model is extended to include $ρ$ - and $ω$ -exchange diagrams. These adjustments are compared with other pion production models, as well as with CLAS pion electroproduction data on the nucleon. The results show considerable improvement in the description of the Delta peak region.
nucl-th1 citation
07
A systematic approach to Covariance matrix formulation in charged particle activation experiments
Tanmoy Bar
This work presents a detailed covariance and correlation matrix analysis for experimentally measured cross sections obtained using the activation technique. Both statistical and systematic contributions to the covariance matrix were explicitly calculated using sensitivity coefficients. The detector efficiency was determined by refitting standard source data with an exponential function, and the associated covariance matrix of the fitted parameters was propagated to estimate the uncertainty in efficiency at the relevant $γ$ -ray energy. The cross sections and the corresponding experimental parameters, such as beam flux, target thickness, $γ$ -ray intensity, and decay corrections, were taken from previously published measurements and are used here for the purpose of illustrating the covariance formalism. The resulting covariance and correlation matrices provide a comprehensive representation of uncertainties and their interdependencies. This formalism demonstrates the importance of including correlated uncertainties for reliable interpretation and comparison of experimental cross section data.
nucl-thnucl-exphysics.data-an0 citations

Affiliations

first authorsco-authorsvia INSPIRE

Dimer Effective Field Theory

Ab initio optical potentials for magnesium isotopes at intermediate energies: from stability to the island of inversion

Multi-task deep neural network for predicting both nuclear fission yields and their experimental errors in peak-shaped data

Time evolution formalism in the complex scaling method: Application to the E1 response of 6He

Nuclear shapes of Nb isotopes

Optimizing the description of the Delta region in the Ghent Hybrid model for single-pion production

A systematic approach to Covariance matrix formulation in charged particle activation experiments

Affiliations

Time evolution formalism in the complex scaling method: Application to the E1 response of $^{6}$ He