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Nuclear Theory·nucl-th

Wednesday·July 24, 2024

9 papers—4 primary·5 cross-listed

All9Primary4Cross-lists5
  1. 01

    [Submitted on 23 Jul 2024]

    Bulk Viscosity in Dense Nuclear Matter

    Steven P. Harris

    In this chapter, I describe bulk viscosity as a general concept, and then focus on bulk viscosity in the dense matter present in compact objects. While this review is focused on bulk viscosity in the conditions present in neutron star mergers, I present a history of bulk viscosity research in dense matter, from its role in damping radial oscillations in neutron stars through its current applications in neutron star mergers. The majority of the chapter consists of calculations of the bulk viscosity from Urca processes in generic neutron-proton-electron () matter, and then in dense matter containing muons ( matter) as well. I make several approximations in these calculations to keep the focus on the concepts. More precise calculations exist in the literature, to which I refer the reader. One concept I attempt to elucidate is the thermodynamic behavior of a fluid element throughout an oscillation and how that leads to bulk-viscous dissipation. I conclude with a discussion of the recent research into the role of weak interactions and bulk viscosity in neutron star mergers.

    Comments:
    Preprint version of chapter 8 in the book "Nuclear Theory in the Age of Multimessenger Astronomy" (CRC Press 2024). The writing was finished in July 2023, so references beyond that date are not included
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE)
    arXiv:
    2407.16157 [pdf]
    8 citations
  2. 02

    [Submitted on 23 Jul 2024]

    Equation of state of nuclear matter from collective flows and stopping in intermediate energy heavy-ion collisions

    Dan Cozma (IFIN-HH, Bucharest)🇷🇴

    The equation of state of nuclear matter, momentum dependence of the effective interaction and in-medium modification of elastic nucleon-nucleon cross-sections are studied by comparing theoretical predictions for stopping, directed and elliptic flows of protons and light clusters in intermediate energy heavy-ion collisions of beam energy between 150 and 800 MeV/nucleon to experimental data gathered by the FOPI Collaboration. A multivariate analysis that takes into account systematic uncertainties induced on model predictions by the coalescence afterburner leads to the following constraint for the equation of state at 68 percent confidence level: compressibility modulus of isospin symmetric matter MeV and slope of the symmetry energy MeV. The momentum dependence of the isoscalar potential is found to be similar to that of the empirical optical potential, with an effective isoscalar mass . The isovector potential displays a momentum dependence corresponding to a positive neutron-proton effective mass difference , close to the world average for this quantity. A suppression of elastic nucleon-nucleon cross-sections in symmetric nuclear matter at saturation by about 60 relative to vacuum values is deduced, in qualitative agreement with microscopical results. A strong dependence of the suppression factor on isospin asymmetry is evidenced, experimental data for isospin symmetric systems proving crucial for this last conclusion.

    Comments:
    28 pages, 22 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2407.16411 [pdf]
    PRC(2024)·16 citations
  3. 03

    [Submitted on 23 Jul 2024]

    Phase transitions in N = 40, 60 and 90 nuclei

    A. Prášek🇨🇿 · P. Alexa🇨🇿 · D. Bonatsos🇬🇷 · G. Thiamová🇫🇷 · D. Petrellis🇨🇿 · P. Veselý🇨🇿

    In this paper we focus on three mass regions where first-order phase transitions occur, namely for , 60 and 90. We investigate four isotopic chains (Se, Zr, Mo and Nd) in the framework of microscopic Skyrme-Hartree-Fock + Bardeen-Cooper-Schrieffer calculations for 15 different parametrizations. The microscopic calculations show the typical behavior expected for first-order phase transitions. To find the best candidate for the critical point phase transition we propose new microscopic position and occupation indices calculated for positive-parity and negative-parity proton and neutron single-quasiparticle states around the Fermi level. The microscopic calculations are completed by macroscopic calculations within the Algebraic Collective Model (ACM), and compared to the experimental data for Se, Mo and Nd, considered to be the best candidates for the critical point nuclei.

    Comments:
    accepted in Phys. Rev. C
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2407.16428 [pdf]
    PRC(2024)·4 citations
  4. 04

    [Submitted on 23 Jul 2024]

    The Hidden Variables: Harnessing Half-Shell Potentials for Enhanced Precision in Nuclear Reaction Calculations

    Hao Liu · Jin Lei · Zhongzhou Ren

    We explore the impact of half-shell components on nuclear reaction calculations, focusing on nonelastic breakup cross sections within the Ichimura-Austern-Vincent (IAV) model. By advocating for the use of a consistent Single Folding Model (SFM) for all optical potentials in IAV calculations, we aim to reduce the uncertainties associated with half-shell components and enhance agreement with experimental data. We present results from deuteron-induced reactions on Ni and Pb, which serve as surrogate targets for neutron-induced reactions on short-lived nuclei. The application of consistent optical potentials derived from the SFM shows improved alignment with experimental data compared to traditional global phenomenological potentials. Furthermore, we investigate the Co(Li,) reaction, which reveals that the half-shell -matrix plays a pivotal role in accurately modeling nuclear reactions. Our findings suggest that a unified approach to optical potentials, accounting for half-shell effects, is critical for a precise understanding of complex nuclear reactions. This work highlights the significance of the internal dynamics of the wave function, particularly in lighter targets, and underscores the importance of the half-shell -matrix as a previously underappreciated variable in reaction calculations.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2407.16452 [pdf]
    0 citations

Affiliations

first authorsco-authorsvia INSPIRE