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Nuclear Theory·nucl-th

Monday·December 12, 2022

3 papers—2 primary·1 cross-listed

All3Primary2Cross-lists1
  1. 01

    [Submitted on 9 Dec 2022]

    The Gerasimov-Drell-Hearn sum-rule with nuclear targets

    Steven D. Bass🇦🇹 · Paolo Pedroni🇮🇹 · Andreas Thomas🇩🇪

    Hadron properties are modified when the hadron is embedded in a nuclear medium. Here we discuss the Gerasimov-Drell-Hearn, GDH, sum rule for polarised photoproduction from a polarised nucleon within a polarised nuclear target. Strong enhancement is expected with the suppression of the proton and nucleon resonance masses and enhancement of the proton's anomalous magnetic moment in medium. This could be tested in polarised photoproduction experiments with interesting targets being polarised deuterons, He, Li and Li. The largest contribution to the GDH sum rule comes from the resonance excitation. In existing data with polarised deuterons and He the excitation is shifted to slightly lower energy when compared to model predictions where the is treated with its free mass.

    Comments:
    10 pages, 3 Figures, to appear in the European Physical Journal A
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    2212.04795 [pdf]
    EPJA(2023)·4 citations
  2. 02

    [Submitted on 9 Dec 2022]

    BUQEYE Guide to Projection-Based Emulators in Nuclear Physics

    C. Drischler · J.A. Melendez · R.J. Furnstahl · A.J. Garcia · Xilin Zhang

    The BUQEYE collaboration (Bayesian Uncertainty Quantification: Errors in Your EFT) presents a pedagogical introduction to projection-based, reduced-order emulators for applications in low-energy nuclear physics. The term emulator refers here to a fast surrogate model capable of reliably approximating high-fidelity models. As the general tools employed by these emulators are not yet well-known in the nuclear physics community, we discuss variational and Galerkin projection methods, emphasize the benefits of offline-online decompositions, and explore how these concepts lead to emulators for bound and scattering systems that enable fast & accurate calculations using many different model parameter sets. We also point to future extensions and applications of these emulators for nuclear physics, guided by the mature field of model (order) reduction. All examples discussed here and more are available as interactive, open-source Python code so that practitioners can readily adapt projection-based emulators for their own work.

    Comments:
    31 pages, 10 figures, 1 table; invited contribution to the Research Topic "Uncertainty Quantification in Nuclear Physics" in Frontiers in Physics
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Data Analysis, Statistics and Probability (physics.data-an)
    arXiv:
    2212.04912 [pdf]
    Front.in Phys.(2022)·49 citations
  3. 03

    [Submitted on 9 Dec 2022] (cross-list from hep-ph)

    Axial coupling constant in a magnetic background

    Cristián Villavicencio🇨🇱

    The nucleon axial coupling constant is calculated in the presence of an external uniform magnetic field using finite energy sum rules. The correlation function of proton, neutron and axial-vector currents is calculated both the hadronic and the QCD sector. Once the axial contribution in the form factor is isolated, a double sum rule is considered, i.e., the usual QCD contour integration for the external moments of both the proton and neutron current. The effects of the external magnetic field come mainly through the in-medium current-nucleon coupling constants and the hadronic thresholds provided by the nucleon-nucleon correlators. As a result, the axial coupling constant decreases in the presence of the magnetic field.

    Comments:
    6 pages, 5 figures. The case of average flavor approximation was removed. Accepted for publication in PRD
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2212.04649 [pdf]
    PRD(2023)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE