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Nuclear Theory·nucl-th

Wednesday·November 13, 2024

8 papers—6 primary·2 cross-listed

All8Primary6Cross-lists2
  1. 07

    [Submitted on 12 Nov 2024] (cross-list from hep-ph)

    Centrality definition in e+A collisions at the Electron-Ion Collider

    Mariam Hegazy🇪🇬 · Aliaa Rafaat🇪🇬 · Niseem Magdy🇺🇸 · Wenliang Li🇺🇸 · Abhay Deshpande🇺🇸 · A. M. H. Abdelhady🇪🇬 · A.Y.Ellithi🇪🇬

    In this work, we investigate the feasibility of defining centrality in electron-ion collisions at the Electron-Ion Collider (EIC) by examining the correlation between the impact parameter and several observables, including total energy, total transverse momentum, and total number of particles. Using the BeAGLE Monte Carlo generator, we simulate e+Au and e+Ru collisions at different energies and analyze the correlation between the impact parameter and these observables across different kinematic regions. Our findings indicate that the correlation is weak in the central rapidity region but becomes stronger in the forward and far-forward rapidity regions. However, the correlation is not sufficiently robust to allow for precise centrality determination. We conclude that defining centrality in electron-ion collisions is more challenging than in ion-ion collisions, necessitating further studies to develop a robust centrality definition for the EIC.

    Comments:
    9 pages, 9 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2411.07963 [pdf]
    J.Phys.G(2025)·0 citations
  2. 08

    [Submitted on 12 Nov 2024] (cross-list from hep-th)

    Schwinger-Keldysh effective action for hydrodynamics with approximate symmetries

    Masaru Hongo🇯🇵 · Noriyuki Sogabe🇺🇸 · Mikhail A. Stephanov🇺🇸 · Ho-Ung Yee🇺🇸

    We study the hydrodynamic theories with approximate symmetries in the recently developed effective action approach on the Schwinger-Keldysh (SK) contour. We employ the method of spurious symmetry transformation for small explicit symmetry-breaking parameters to systematically constrain symmetry-breaking effects in the non-equilibrium effective action for hydrodynamics. We apply our method to the hydrodynamic theory of chiral symmetry in Quantum Chromodynamics (QCD) at finite temperature and density and its explicit breaking by quark masses. We show that the spurious symmetry and the Kubo-Martin-Schwinger (KMS) relation dictate that the Ward-Takahashi identity for the axial symmetry, i.e., the partial conservation of axial vector current (PCAC) relation, contains a relaxational term proportional to the axial chemical potential, whose kinetic coefficient is at least of the second order in the quark mass. In the phase where the chiral symmetry is spontaneously broken, and the pseudo-Nambu-Goldstone pions appear as hydrodynamic variables, this relaxation effect is subleading compared to the conventional pion mass term in the PCAC relation, which is of the first order in the quark mass. On the other hand, in the chiral symmetry-restored phase, we show that our relaxation term, which is of the second order in the quark mass, becomes the leading contribution to the axial charge relaxation. Therefore, the leading axial charge relaxation mechanism is parametrically different in the quark mass across a chiral phase transition.

    Comments:
    34 pages, 0 figures
    Subjects:
    High Energy Physics — Theory (hep-th); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2411.08016 [pdf]
    PRD(2026)·15 citations

Affiliations

first authorsco-authorsvia INSPIRE