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Nuclear Theory·nucl-th

Friday·September 19, 2025

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 01

    [Submitted on 17 Sept 2025]

    An improved formula for Wigner function and spin polarization in a decoupling relativistic fluid at local thermodynamic equilibrium

    Xin-Li Sheng🇮🇹 · Francesco Becattini🇮🇹 · Daniele Roselli🇮🇹

    We present an upgraded formula for Wigner function and spin polarization of fermions emitted by a relativistic fluid at local thermodynamic equilibrium at the decoupling which improves the one obtained in refs. [1, 2] and used in numerical simulations of relativistic nuclear collisions. By using a new expansion method, applicable to decoupling hypersurfaces with arbitrary geometry, we reproduce the known term proportional to thermal vorticity and obtain an upgraded form of the spin-shear term which captures the dependence on the geometry. The new method also includes additional contributions whose physical nature is to be assessed. The new expression also naturally excludes contributions from space-time gradients in the normal direction of the hypersurface, providing a theoretical justification for the isothermal condition previously imposed a priori. This framework can be extended to particles with arbitrary spin.

    Comments:
    17 pages, 1 figure
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th)
    arXiv:
    2509.14301 [pdf]
    11 citations
  2. 02

    [Submitted on 18 Sept 2025]

    Secondary bow with ripples in C+C rainbow scattering

    S. Ohkubo · Y. Hirabayashi

    We report, {for the first time, the emergence of} a secondary bow with ripples in C+C nuclear rainbow scattering. This finding was achieved by studying the experimental angular distributions in C+C scattering at incident energies = 240 and 300 MeV, utilizing an extended double-folding model. This model accurately describes all diagonal and off-diagonal coupling potentials derived from the microscopic wave functions for C. Although the observed angular distributions of rainbow scattering at large angles (approaching ) are complicated by the symmetrization of two identical bosonic nuclei, the Airy minimum, associated with a dynamically generated secondary bow with ripples, is clearly identified at approximately 77 for 240 MeV in the fall-off region of the primary nuclear rainbow. This {finding}, along with previous findings in the O+C and C+C systems, {reinforces} the concept of a secondary bow in nuclear rainbow scattering.

    Comments:
    9 pages, 6 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2509.14535 [pdf]
    EPJA(2025)·2 citations
  3. 03

    [Submitted on 18 Sept 2025]

    Systematic Bayesian Evaluation of Resonance Parameters in 19Ne for the 15O(alpha,gamma)19Ne and 18F(p,alpha)15O Reactions

    S.H. Kim · K.Y. Chae · C.H. Kim · C.D. Nesaraja · M.S. Smith

    We present a comprehensive evaluation of the nuclear structure properties of 19Ne using a novel and rigorous Bayesian statistical framework. Precise characterization of 19Ne resonance parameters is critical for accurately determining reaction rates of the astrophysically significant 15O(alpha, gamma)19Ne and 18F(p, alpha)15O reactions, which govern breakout from the hot CNO cycle in X-ray bursts and influence gamma-ray emission in novae, respectively. By reconstructing likelihood functions from published experimental data, including asymmetric uncertainties and upper or lower limits, we derive posterior distributions for resonance energies, decay widths, and branching ratios. Our Bayesian approach systematically incorporates previously reported discrepancies among measurements, providing a statistically robust and consistent treatment of these uncertainties. The evaluated resonance parameters and associated uncertainties provide crucial input for stellar nucleosynthesis modeling, contributing to a refined understanding of explosive astrophysical phenomena.

    Subjects:
    Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)
    arXiv:
    2509.14570 [pdf]
    PRC(2025)·1 citation
  4. 04

    [Submitted on 18 Sept 2025]

    Learning Informed Prior Distributions with Normalizing Flows for Bayesian Analysis

    Hendrik Roch · Chun Shen

    We investigate the use of normalizing flow (NF) models as flexible priors in Bayesian inference via Markov Chain Monte Carlo (MCMC) sampling for iterative Bayesian calibration. Trained on posteriors from previous analyses, these models can be used as informative priors that capture non-trivial distributions and correlations in subsequent inference tasks. We compare different training strategies and loss functions, finding that training based on Kullback-Leibler (KL) divergence and unsupervised learning consistently yield the most accurate reproductions of reference distributions. We apply such a sequential Bayesian workflow to a high-energy nuclear physics problem; MCMC with NF-based priors reproduces the results of one-shot joint inference well, provided the target distributions are unimodal. In cases with pronounced multi-modality or dataset tension, distortions may arise, underscoring the need for caution in multi-stage Bayesian inference. A comparison between the pocoMC MCMC sampler and the standard emcee sampler further demonstrates the importance of advanced and robust algorithms for exploring the posterior space. Overall, our results establish NF-based priors as a practical and efficient tool for sequential Bayesian inference in high-dimensional parameter spaces.

    Comments:
    13 pages, 7 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    2509.14911 [pdf]
    PRC(2026)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE