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Nuclear Theory·nucl-th

Thursday·June 4, 2026

11 papers—5 primary·6 cross-listed

All11Primary5Cross-lists6
  2. 02

    NuGNN: a Graph Neural Network for Nuclear Reaction Network Equations

    C. H. Kim · K. Y. Chae · S. Ko · M. R. Mumpower · M. S. Smith

    Nuclear reaction networks are a major computational bottleneck in astrophysical simulations when large isotope sets are required, because of the stiffness of the network equations and the repeated calls to Jacobian-based solvers required by implicit methods. In this work, we develop a deep learning surrogate solver for a large 690-isotope nuclear reaction network under general Type I X-ray burst conditions using a graph neural network, NuGNN. Unlike conventional fully connected or convolutional neural networks, NuGNN directly reflects the structure of the reaction network through heterogeneous isotope and reaction nodes and message-passing along reaction connections. The model is trained on data spanning many orders of magnitude in stellar temperature and density and in simulation time step size. We compare NuGNN with a Res-U-Net and fully connected neural network and find that NuGNN consistently achieves significantly better accuracy with errors of only a few percent. More importantly, when implemented in the network evolution code in place of the original solver, NuGNN successfully reproduces the final abundance patterns, whereas the other architectures fail to do so. We also show that the trained model can substantially improve computational speed, demonstrating its practical potential for large-scale simulations. These results show that graph neural networks provide a robust and promising framework for accurate surrogate modeling of large nuclear reaction networks.

    nucl-th0 citations
  3. 03

    Physics of many-body resonances with complex scaling and applications to light unstable nuclei

    Takayuki Myo

    We review the exotic phenomena in light unstable nuclei with a focus on many-body resonances, which can decay into more than two constituents, and are frequently observed in unstable nuclei above the three-body threshold energy. The complex scaling transformation of the Schrödinger equation is a powerful method for describing many-body resonances, because it separates the continuum spectra into resonant and non-resonant continuum ones. Since the asymptotic wave functions of the resonances are regularized in the complex scaling, many-body resonances are described using the basis functions in the eigenvalue problem. The properties of many-body resonances can then be discussed in the same way as those of the bound states. We apply the complex scaling to the system consisting of a stable nucleus and valence nucleons and investigate many-body resonances in neutron-rich and proton-rich light nuclei. Using the eigenstates obtained with the complex scaling, we construct the extended completeness relation and the Green's function. They are used to calculate the level densities and the general transition strengths into many-body unbound states. We also discuss the interpretation of the complex expectation values associated with resonances, which remains an open problem. We propose a possible scheme for it in terms of the complex-scaled Green's function.

    nucl-thnucl-exAAPPS Bull.(2026)·0 citations
  4. 04

    Analisys of excitations in O from inelastic scattering of polarized protons of intermediate energy

    M.S. Onegin

    Comparison of the calculation of inelastic proton scattering from O with excitation of levels with with accessible experimental data at different energies of incident protons is presented. The role of antisymmetrization in reaction formalism and the manifestation of the pion condensation in nuclear are discussed. To obtain more solid conclusions on these points more experimental data are needed.

    nucl-th0 citations
  5. 05

    Numerical study of the three-boson bound-state problem in partial-wave and vector-variable formulations

    Wolfgang Schadow · Mohammadreza R. Hadizadeh

    We present a systematic benchmark of the three-boson bound-state problem in momentum space, comparing one-dimensional (1D) spectator-amplitude, two-dimensional (2D) partial-wave, and three-dimensional (3D) vector-variable formulations. The benchmark controls the interaction representation by embedding the same finite partial-wave interaction space in each formulation, so that discrepancies reflect discretization, interpolation, and quadrature errors. This enables direct 1D--2D--3D comparisons for separable interactions, controlled 2D--3D tests for local interactions, and comparison with the full local interaction in the 3D vector-variable formulation. Binding energies agree at the ~MeV level for separable interactions and at the few- to ~MeV level for local interactions. The 2D and 3D equations are also solved in both -matrix-driven and bare-potential-driven forms, whose agreement validates the permutation geometry, quadrature, and interpolation. Fourier transforms to coordinate space yield consistent norm decompositions and spatial observables, providing an independent check of the momentum-space solutions.

    nucl-th0 citations

Affiliations

first authorsco-authorsvia INSPIRE