PaperPanorama
FAQ

Nuclear Theory·nucl-th

Friday·June 5, 2026

13 papers—6 primary·7 cross-listed

All13Primary6Cross-lists7
  1. 01

    [Submitted on 4 Jun 2026]

    -exchange correction beyond the forward-angle limit in neutron decay

    Hui-Yun Cao🇨🇳 · Hai-Qing Zhou🇨🇳

    In this work, we discuss the -exchange contributions in neutron decay with an elastic intermediate state, beyond the forward-angle limit (FAL). By decomposing the one--exchange and -exchange amplitudes in terms of independent Pauli-spinor structures, we calculate the -exchange corrections to the relevant coefficients. Our numerical results show that the relative corrections to the Fermi Born term and the Gamow-Teller Born term are enhanced by about 8\% and 18\%, respectively. In particular, we find a non-zero contribution to from the axial-vector current, which is identically zero in the FAL. The corresponding effect on the extracted from the neutron lifetime is also analyzed, and we find the correction to be at the level.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2606.05643 [pdf]
    0 citations
  2. 02

    [Submitted on 4 Jun 2026]

    Seed-Robust PINN Determination of -Wave Bound States and Jost-Function-Based vertex constants in Pb

    J.T Tshipi🇿🇦 · A.S Cornell🇿🇦

    We investigate physics-informed neural networks (PINNs) for computing the -wave bound states of the hypernucleus Pb, modeled as a two-body system composed of a hyperon and a Pb core. The interaction is described by a Woods--Saxon potential without spin--orbit coupling. In the PINN formulation, the radial bound-state wave function is represented by an artificial neural network, and the eigenenergies are obtained from the Rayleigh--Ritz variational quotient. Because PINN eigenvalue calculations can depend on the residual-loss formulation and random-seed initialization, two residual losses are compared across four independent random seeds. Their performance is assessed using eigenvalue accuracy, coefficient of variation, signal-to-noise ratio, bias--variance decomposition, and Hermitian spectral-ordering consistency. The normalized residual loss gives the most stable and physically consistent bound-state spectrum for the four seeds considered. With this loss, the computed bound-state energies and root-mean-square radii are in very good agreement with the corresponding theoretical values. The resulting wave functions are used to construct the Jost functions through the Wronskian with incoming and outgoing Riccati--Hankel functions. From these Jost functions, the residue of the partial-wave -matrix at the bound-state pole, the Asymptotic Normalization and the Nuclear Vertex Constants are extracted. These quantities show reasonable agreement with theoretical values, although with larger standard deviations than those obtained for the eigenenergies and radii. The results indicate that the Rayleigh--Ritz formulation combined with a seed-robust normalized residual loss provides a stable PINN framework for bound-state and Jost-function-based calculations in hypernuclear two-body systems.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2606.05940 [pdf]
    EPJA(2026)·0 citations
  4. 04

    [Submitted on 4 Jun 2026]

    Equilibrium state of a Fermi system in the diffusion approximation of kinetic theory

    Sergiy V. Lukyanov

    A consistent transformation from momentum space to energy space is performed for the diffusion equation within kinetic theory, with particle-number conservation explicitly preserved. Under the assumption of a constant single-particle level density, the equation reduces to a one-dimensional diffusion equation in energy space with consistent kinetic coefficients. The equivalence of the definitions of the equilibrium temperature in momentum space and in energy space is demonstrated. It is established that the inclusion of the energy dependence of the kinetic coefficients leads to an energy-dependent equilibrium temperature and a modification of the distribution function. The obtained results may be used to analyze relaxation processes in atomic nuclei and nonequilibrium dynamics of Fermi systems.

    Comments:
    24 pages, 6 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2606.06321 [pdf]
    1 citation
  5. 05

    [Submitted on 4 Jun 2026]

    On the Possibility of a Strong First-Order Phase Transition in Neutron Stars

    Zheng Cao · Lie-Wen Chen🇨🇭

    Whether cold dense QCD matter undergoes a strong first-order phase transition remains an open question. In nature, neutron stars provide the most direct probe of cold dense QCD matter. Theoretically, chiral effective field theory constrains the equation of state of dense matter near nuclear saturation density, while perturbative QCD calculations constrain it at densities well beyond stable neutron-star interiors. We perform Bayesian inference with non-parametric Gaussian-process equation of state for -equilibrated neutron-star matter under the assumption with and without a strong first-order phase transition, using the tidal deformability from GW170817, the NICER mass--radius measurements of PSR~J07406620, PSR~J00300451, PSR~J04374715, PSR~J06143329, chiral effective field theory, and perturbative QCD. Within this Bayesian inference framework, the model comparison mildly to moderately favors a strong first-order phase transition, with its onset most likely lying \emph{above} the central density of the most massive neutron star. Such an onset reconciles the stiffness required to support massive neutron stars with the softening favored by perturbative QCD from asymptotically high density.

    Comments:
    11 pages, 3 figures, 2 tables. Presentation improved and discussions added. Accepted version to appear in ApJ
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    2606.06378 [pdf]
    2 citations
  6. 06

    [Submitted on 4 Jun 2026]

    When positive and negative pairs differ in femtoscopy: residual Coulomb and isospin effects

    Yevheniia Khyzhniak🇺🇸 · Michael Annan Lisa🇺🇸

    We study charge-dependent modifications of identical-pion and identical-kaon femtoscopic correlation functions from two sources: the residual Coulomb field of the charged source and isospin-related hadronic dynamics. The residual Coulomb effect is modeled with a modified Retiere--Lisa blast-wave source, where the same emitted particles are propagated with positive and negative charge signs through an effective residual field. The residual Coulomb field produces a small but systematic positive-to-negative splitting of the correlation functions, strongest at low and sensitive to the effective charge, spatial width, and expansion velocity of the residual source. It also modifies the height and shape of the correlation function, complicating interpretation of the fitted radii. UrQMD 3.4 cascade calculations for Au+Au collisions at show that charge-dependent splittings can also appear even without a residual Coulomb field. For pions, this difference is mainly driven by the initial isospin composition, while for kaons it is strongly affected by different and production mechanisms and subsequent hadronic evolution. These results show that residual Coulomb and isospin-related effects can compete, and neither can be interpreted reliably without constraining the other within the same model framework.

    Comments:
    25 pages, 16 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2606.06472 [pdf]
    0 citations

Affiliations

first authorsco-authorsvia INSPIRE