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Nuclear Theory·nucl-th

Tuesday·May 28, 2024

9 papers—2 primary·7 cross-listed

All9Primary2Cross-lists7
  1. 03

    [Submitted on 25 May 2024] (cross-list from hep-ph)

    Pion gravitational form factors in the QCD instanton vacuum II

    Wei-Yang Liu🇺🇸 · Edward Shuryak🇺🇸 · Ismail Zahed🇺🇸

    We revisit the hard QCD contributions to the pion gravitational form factors (GFFs), in terms of the twist-2,3 pion distribution amplitudes (DA), including novel semi-hard contributions from the instantons. The pion DAs are evaluated in the QCD instanton vacuum, and then properly evolved to higher resolution. The results are compared to our recent results from the QCD instanton vacuum, as well as Bethe-Salpeter calculations and recent lattice data. The interpolated hard and soft contributions to the pion D-form-factor, are used to derive the (gravitational) pressure and shear within the pion, with a clear delineation of their range.

    Comments:
    14 pages, 6 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
    arXiv:
    2405.16269 [pdf]
    PRD(2024)·25 citations
  2. 04

    [Submitted on 25 May 2024] (cross-list from hep-ph)

    Magnetic field effect on hadron yield ratios and fluctuations in a hadron resonance gas

    Volodymyr Vovchenko🇺🇸

    This work studies the influence of an external magnetic field on hadron yields and fluctuations in a hadron resonance gas by performing calculations within an updated version of the open-source Thermal-FIST package. The presence of the magnetic field has a sizable influence on certain hadron yield ratios. Most notably, it leads to enhanced and suppressed ratios, which may serve as a magnetometer in heavy-ion collisions. By attributing the centrality dependence of the ratio in Pb-Pb collisions at 5.02~TeV measured by the ALICE Collaboration entirely to the magnetic field, its maximal strength at freeze-out is estimated to be ~GeV in peripheral collisions. The magnetic field also enhances various conserved charge susceptibilities, which is qualitatively consistent with recent lattice QCD data and is driven in the HRG model by the increase of hadron densities. However, the variances of hadrons do not show any enhancement when normalized by the means, therefore, measurements of second-order fluctuations in heavy-ion collisions appear to offer limited additional information about the magnetic field relative to mean multiplicities.

    Comments:
    11 pages, 7 figures, v3: published version, minor misprints corrected, v2: Fig. 7 added with the comparison between proton-charge correlator and proton/pion ratio
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2405.16306 [pdf]
    PRC(2024)·21 citations
  3. 05

    [Submitted on 26 May 2024] (cross-list from hep-ph)

    Nuclear deformation effects in photoproduction of mesons in ultraperipheral isobaric collisions

    Shuo Lin🇨🇳 · Jin-Yu Hu🇨🇳 · Hao-Jie Xu🇨🇳 · Shi Pu🇨🇳 · Qun Wang🇨🇳

    We have investigated the meson photoproduction in ultraperipheral isobaric collisions between and at GeV, employing the dipole model with the equivalent photon approximation. By implementing the Woods-Saxon distribution to represent the nuclear mass density, which is derived from density functional theory with an inclusion of nuclear deformation effects, we have calculated the transverse momentum spectra in isobaric collisions. We observe the characteristic dip behavior in these spectra, indicative of diffraction phenomena in high-energy physics. We notice that the deformation effects cause a nearly linear increase with for , aligning with experimental observations. We offer a simple explanation for the observed behavior in these spectra by introducing the effective width of the nuclei in the thickness function. We also extend our discussion on the meson photoproduction with the targets ,, and .

    Comments:
    9 pages, 5 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2405.16491 [pdf]
    PRD(2025)·12 citations
  4. 06

    [Submitted on 27 May 2024] (cross-list from nucl-ex)

    Jet substructure measurements in heavy-ion collisions

    Robert Vertesi (for the ATLAS, CMS, and ALICE Collaborations)🇭🇺

    Jet substructure in heavy-ion collisions is a rapidly evolving area with lots of intriguing new measurements. This contribution presents a selection of recent jet-substructure measurements from experiments at the LHC, in particular, soft-drop groomed radii of jets and reclustered large-radius jets from ATLAS, jet axis difference and generalized jet angularities from ALICE, as well as dijet shapes and b-jet shapes from the CMS experiment.

    Comments:
    Conference proceedings, 5 pages
    Subjects:
    Nuclear Experiment (nucl-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2405.16955 [pdf]
    Int.J.Mod.Phys.A(2025)·5 citations
  5. 07

    [Submitted on 27 May 2024] (cross-list from hep-ph)

    Electron form factors in Basis Light-front Quantization

    Lingdi Meng🇨🇳 · Shuo Tang🇺🇸 · Zhi Hu🇯🇵 · Guo-Li Wang🇨🇳 · Yang Li🇺🇸 · Xingbo Zhao🇨🇳 · James P. Vary🇺🇸

    In this paper, we evaluate the electromagnetic and gravitational form factors as well as the corresponding generalized parton distributions of the electron using the Basis Light-front Quantization approach to QED. We compare our results with those from light-front perturbation theory. We adopt a novel basis with its scale depending on the constituents' longitudinal momentum fraction. We show that this basis improves convergence of the form factors with increasing basis dimension, compared to that calculated in the original basis with fixed scale. These results both validate the BLFQ approach and provide guidance for its efficient implementation in solving light-front Hamiltonian mass eigenstates for more complex systems in QED and QCD.

    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2405.16995 [pdf]
    2 citations
  6. 08

    [Submitted on 27 May 2024] (cross-list from hep-lat)

    Thermodynamic Potential of the Polyakov Loop in SU(3) Quenched Lattice QCD

    Hideo Suganuma (Kyoto U.)🇯🇵 · Hiroki Ohata🇯🇵 · Masakiyo Kitazawa (YITP, Kyoto U.)🇯🇵

    Using SU(3) lattice QCD, we study for the first time the effective potential of the Polyakov loop at finite temperature, i.e., the thermodynamic potential, in the field-theoretical way. In the framework of the reweighting method in lattice QCD, we express the effective potential using the expectation value without a source term. In particular, we consider the most difficult and interesting case of vacuum coexistence at the critical temperature . We adopt SU(3) quenched lattice QCD on at = 5.89379, which corresponds exactly to the critical temperature of the deconfinement phase transition, and use 200,000 Monte Carlo configurations. After categorizing the gauge configurations into one -symmetric and three -broken vacua each, we perform a vacuum-associated reweighting method, using the gauge configurations around each vacuum separately. Finally, we obtain the Polyakov-loop effective potential, which is well depicted around the -symmetric and -broken vacua.

    Comments:
    11 pages, 4 figures, prepared for XIIth Int. Conf. on New Frontiers in Physics (ICNFP2023)
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
    arXiv:
    2405.17335 [pdf]
    Int.J.Mod.Phys.A(2024)·2 citations
  7. 09

    [Submitted on 27 May 2024] (cross-list from cs.LG)

    From Neurons to Neutrons: A Case Study in Interpretability

    Ouail Kitouni · Niklas Nolte · Víctor Samuel Pérez-Díaz · Sokratis Trifinopoulos · Mike Williams

    Mechanistic Interpretability (MI) promises a path toward fully understanding how neural networks make their predictions. Prior work demonstrates that even when trained to perform simple arithmetic, models can implement a variety of algorithms (sometimes concurrently) depending on initialization and hyperparameters. Does this mean neuron-level interpretability techniques have limited applicability? We argue that high-dimensional neural networks can learn low-dimensional representations of their training data that are useful beyond simply making good predictions. Such representations can be understood through the mechanistic interpretability lens and provide insights that are surprisingly faithful to human-derived domain knowledge. This indicates that such approaches to interpretability can be useful for deriving a new understanding of a problem from models trained to solve it. As a case study, we extract nuclear physics concepts by studying models trained to reproduce nuclear data.

    Comments:
    International Conference on Machine Learning (ICML) 2024
    Subjects:
    Machine Learning (cs.LG); Nuclear Theory (nucl-th)
    arXiv:
    2405.17425 [pdf]
    2 citations

Affiliations

first authorsco-authorsvia INSPIRE