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Nuclear Theory·nucl-th

Monday·April 7, 2025

11 papers—5 primary·6 cross-listed

All11Primary5Cross-lists6
  1. 06

    [Submitted on 4 Apr 2025] (cross-list from hep-ph)

    Optimal Observables for the Chiral Magnetic Effect from Machine Learning

    Yuji Hirono🇯🇵 · Kazuki Ikeda🇺🇸 · Dmitri E. Kharzeev🇺🇸 · Ziyi Liu🇨🇳 · Shuzhe Shi🇨🇳

    The detection of the Chiral Magnetic Effect (CME) in relativistic heavy-ion collisions remains challenging due to substantial background contributions that obscure the expected signal. In this Letter, we present a novel machine learning approach for constructing optimized observables that significantly enhance CME detection capabilities. By parameterizing generic observables constructed from flow harmonics and optimizing them to maximize the signal-to-background ratio, we systematically develop CME-sensitive measures that outperform conventional methods. Using simulated data from the Anomalous Viscous Fluid Dynamics framework, our machine learning observables demonstrate up to 90\% higher sensitivity to CME signals compared to traditional and correlators, while maintaining minimal background contamination. The constructed observables provide physical insight into optimal CME detection strategies, and offer a promising path forward for experimental searches of CME at RHIC and the LHC.

    Comments:
    4 pages, 1 figure
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2504.03248 [pdf]
    PRC(2025)·1 citation
  2. 07

    [Submitted on 4 Apr 2025] (cross-list from hep-ph)

    Relativistic dynamics of charmonia in strong magnetic fields

    Liuyuan Wen🇨🇳 · Meijian Li🇪🇸 · Yiyu Zhou🇮🇹 · Yang Li🇨🇳 · James P. Vary🇺🇸

    We investigate the properties of charmonium systems in strong external magnetic fields using a relativistic light-front Hamiltonian approach within the Basis Light-Front Quantization (BLFQ) framework. By solving the eigenvalue problem for the invariant mass squared operator with confinement potentials and one-gluon-exchange interactions, we obtain the mass spectrum and wave functions under varying magnetic fields. Our results reveal significant spectral modifications via the Zeeman effect, including - mixing and magnetic sublevel splitting. Momentum density analysis demonstrates wave function deformation, with transverse momentum broadening and longitudinal narrowing under strong fields, alongside structural shifts in parton distributions such as double-hump profiles in excited states. Relativistic corrections and center-of-mass coupling critically drive these dynamics, highlighting the necessity of a relativistic framework for QCD bound states in extreme magnetic environments.

    Comments:
    24 pages, 9 figures. Added the derivation of the quantum many-body Hamiltonian from the minimally coupled Lagrangian in Appendix A. To appear in Phys. Rev. D
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph)
    arXiv:
    2504.03294 [pdf]
    PRD(2025)·6 citations
  3. 08

    [Submitted on 4 Apr 2025] (cross-list from hep-ph)

    Hybrid framework of Fermi-Dirac spin hydrodynamics

    Zbigniew Drogosz🇵🇱

    We outline the hybrid framework of spin hydrodynamics, combining classical kinetic theory with the Israel-Stewart method of introducing dissipation. We obtain the local equilibrium expressions for the baryon current, the energy-momentum tensor, and the spin tensor of particles with spin 1/2 following the Fermi-Dirac statistics and compare them with the previously derived versions where the Boltzmann approximation was used. The expressions in the two cases have the same form, but the coefficients are governed by different functions. The relative differences between the tensor coefficients in the Fermi-Dirac and Boltzmann cases are found to grow exponentially with the baryon chemical potential. In the proposed formalism, nonequilibrium processes are studied including mathematically possible dissipative corrections. Standard conservation laws are applied, and the condition of positive entropy production allows for transfer between the spin and orbital parts of angular momentum.

    Comments:
    15 pages, 3 tables, 1 figure, proceedings of the 24th Zimanyi School Winter Workshop on Heavy Ion Physics, Budapest, Hungary, December 2-6, 2024
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2504.03396 [pdf]
    MDPI Physics(2025)·3 citations
  4. 09

    [Submitted on 4 Apr 2025] (cross-list from hep-ph)

    Exact Wigner function for chiral spirals

    Samapan Bhadury🇵🇱 · Wojciech Florkowski🇵🇱 · Sudip Kumar Kar🇵🇱 · Valeriya Mykhaylova🇵🇱

    The exact solution of the Dirac equation for fermions coupled to an external periodic chiral condensate (chiral spiral) is used to obtain the exact formula for the Wigner function (up to the quantum loop corrections). We find that the resulting expressions for various coefficients of the Wigner function exhibit properties that cannot be reproduced within the standard semiclassical expansion. The formula for the axial vector component of the Wigner function can be conveniently used to study spin polarization effects and illustrate connections between the spin density matrix and axial current. In particular, we find that during an adiabatic change of the periodic potential into a uniform one, the polarization vector is twisted from its original direction.

    Comments:
    28 pages, 3 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2504.03413 [pdf]
    PRD(2025)·1 citation
  5. 10

    [Submitted on 4 Apr 2025] (cross-list from hep-lat)

    Quenching through the QCD chiral phase transition

    Adrien Florio🇩🇪 · Eduardo Grossi🇮🇹 · Aleksas Mazeliauskas🇩🇪 · Alexander Soloviev🇸🇮 · Derek Teaney🇺🇸

    We present a detailed numerical and analytical study of the out-of-equilibrium dynamics of Model G, the dynamical universality class relevant to the chiral phase transition. We perform numerical 3D stochastic (Langevin) simulations of the critical point for large lattices in the chiral limit. We quench the system from the high-temperature unbroken phase to the broken phase and study the non-equilibrium dynamics of pion fields. Strikingly, the non-equilibrium evolution of the two-point functions exhibits a regime of growth, a parametrically large enhancement, and a subsequent slow relaxation to equilibrium. We analyze our numerical results using dynamic critical scaling and mean-field theory. The growth of the two point functions is determined by the non-linear dynamics of an ideal non-abelian superfluid, which is a limit of Model G that reflects the broken chiral symmetry. We also relate the non-equilibrium two-point functions to a long-lived parametric enhancement of soft pion yields relative to thermal equilibrium following a quench.

    Comments:
    45 pages, 11 figures; added quasi-particle description of pion waves; published version, see companion letter "Supercooled Goldstone Bosons at the QCD Chiral Phase Transition" arXiv:2504.03514
    Subjects:
    High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2504.03514 [pdf]
    PRD(2025)·9 citations
  6. 11

    [Submitted on 4 Apr 2025] (cross-list from hep-ph)

    Supercooled Goldstone Bosons at the QCD Chiral Phase Transition

    Adrien Florio🇩🇪 · Eduardo Grossi🇮🇹 · Aleksas Mazeliauskas🇩🇪 · Alexander Soloviev🇸🇮 · Derek Teaney🇺🇸

    We discuss a universal non-equilibrium enhancement of long-wavelength Goldstone bosons induced by quenches to the broken phase in Model G -- the dynamical universality class of an -antiferromagnet and the chiral phase transition in QCD. Scaling arguments for the coarsening dynamics describing the formation of the chiral condensate predict a parametric enhancement in the infrared spectra of Goldstones, a prediction confirmed by stochastic simulations of the transition. The details of the enhancement are determined by the non-linear dynamics of a superfluid effective theory, which is a limit of Model G reflecting the broken symmetry. Our results translate to a parametric enhancement of low-momentum pions in heavy-ion collisions at the LHC, which are underpredicted in current hydrodynamic models without critical dynamics.

    Comments:
    7 pages, 4 figures; published version, see the companion paper "Quenching through the QCD chiral phase transition" arXiv:2504.03514
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2504.03516 [pdf]
    PRL(2025)·14 citations

Affiliations

first authorsco-authorsvia INSPIRE