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Nuclear Theory·nucl-th

Thursday·September 22, 2022

10 papers—7 primary·3 cross-listed

All10Primary7Cross-lists3
  1. 08

    [Submitted on 20 Sept 2022] (cross-list from hep-ph)

    Theoretical discrepancies in the nucleon spin structure and the hyperfine splitting of muonic hydrogen

    Vladimir Pascalutsa (JGU)🇩🇪 · Franziska Hagelstein (JGU & PSI)🇩🇪 · Vadim Lensky (JGU)🇩🇪

    Two groups, ours (Mainz) and Bochum, have recently been re-evaluating the spin polarizabilities and spin structure functions at low , using the baryon chiral perturbation theory (BPT), the manifestly-covariant counterpart of the heavy-baryon chiral perturbation theory (HBPT). Whilst the two groups agree that the BPT framework works better than HBPT in this sector, their quantitative results disagree in some of the quantities; most notably, the proton spin polarizabilities and . These discrepancies are especially intriguing in light of new experimental data coming from the Jefferson Lab "Spin Physics Program". The preliminary data on the proton are reported by Karl Slifer in a plenary session of this workshop. Another theoretical discrepancy is emerging in the proton-polarizability contribution to the hyperfine splitting (hfs) in hydrogen and muonic hydrogen. Our BPT calculation shows a significantly smaller effect than the state-of-the-art data-driven evaluations based on empirical spin structure functions. The smaller polarizability contribution leads to a smaller Zemach radius of the proton. This discrepancy could be relevant for the planned first-ever measurement of the ground-state hfs in muonic hydrogen.

    Comments:
    10 pages, 5 figures, to appear in the proceedings of the 10th International Workshop on Chiral Dynamics - CD2021, 15-19 November 2021, Beijing, China (Online)
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2209.09995 [pdf]
    PoS(2024)·2 citations
  2. 09

    [Submitted on 21 Sept 2022] (cross-list from hep-ph)

    Unified Balance Functions

    Claude Pruneau🇺🇸 · Victor Gonzales🇺🇸 · Brian Hanley🇺🇸 · Ana Marin🇩🇪 · Sumit Basu🇸🇪

    The use of charge balance functions in heavy-ion collision studies was initially proposed as a probe of delayed hadronization and two-stage quark production in these collisions. It later emerged that general balance functions can also serve as a probe of the diffusivity of light quarks as well as the evolution of the systems formed in heavy-ion collisions. In this work, we reexamine the formulation of general balance functions and consider how to best define and measure these correlation functions in terms of differences of conditional densities of unlike-sign and like-sign particle pairs. We define general balance functions in terms of associated particle functions and show these obey a simple sum rule. We additionally proceed to distinguish between balance functions expressed as differences of conditional densities valid irrespective of experimental acceptance boundaries and bound balance functions that explicitly account for the limited acceptance of experiments. General balance functions are additionally extended to accommodate strange, baryon, as well as charm and bottom quantum numbers based on the densities of these quantum numbers.

    Comments:
    19 pages. 3 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2209.10420 [pdf]
    PRC(2023)·16 citations
  3. 10

    [Submitted on 21 Sept 2022] (cross-list from hep-ph)

    Far-off-equilibrium expansion trajectories in the QCD phase diagram

    Chandrodoy Chattopadhyay (North Carolina State University)🇺🇸 · Ulrich Heinz (Ohio State University)🇺🇸 · Thomas Schaefer (North Carolina State University)🇺🇸

    We consider the hydrodynamic evolution of a quark-gluon gas with non-zero quark masses and net baryon number in its phase diagram. For far-off-equilibrium initial conditions the expansion trajectories appear to violate simple rules based on the second law of thermodynamics that were previously established for ideal or weakly dissipative fluids. For Bjorken flow we present a detailed analysis within kinetic theory that provides a full microscopic understanding of these macroscopic phenomena and establishes their thermodynamic consistency. We point out that, for certain far-off-equilibrium initial conditions, the well-known phenomenon of "viscous heating" turns into "viscous cooling" where, driven by dissipative effects, the temperature decreases faster than in adiabatic expansion.

    Comments:
    25 pages, 14 figures (manuscript now in PRC format, added references)
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2209.10483 [pdf]
    PRC(2023)·17 citations

Affiliations

first authorsco-authorsvia INSPIRE