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Nuclear Theory·nucl-th

Tuesday·June 15, 2021

10 papers—7 primary·3 cross-listed

All10Primary7Cross-lists3
  1. 01

    [Submitted on 12 Jun 2021]

    Stiffening of matter in quark-hadron continuity

    Toru Kojo🇨🇳

    We discuss stiffening of matter in quark-hadron continuity. We introduce a model that relates quark wave functions in a baryon and the occupation probability of states for baryons and quarks in dense matter. In a dilute regime, the confined quarks contribute to the energy density through the masses of baryons, but do not directly contribute to the pressure; hence, the equations of state are very soft. This dilute regime continues until the low momentum states for quarks get saturated; this may happen even before baryons fully overlap, possibly at density slightly above the nuclear saturation density. After the saturation the pressure grows rapidly while changes in energy density are modest, producing a peak in the speed of sound. If we use baryonic descriptions for quark distributions near the Fermi surface, we reach a description similar to the quarkyonic matter model of McLerran and Reddy. With a simple adjustment of quark interactions to get the nucleon mass, our model becomes consistent with the constraints from 1.4-solar mass neutron stars, but the high density part is too soft to account for two-solar mass neutron stars. We delineate the relation between the saturation effects and short range interactions of quarks, suggesting interactions that leave low density equations of state unchanged but stiffen the high density part.

    Comments:
    14 pages, 14 figures; v2) 15 pages, 16 figures; v3) published in PRD
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th)
    arXiv:
    2106.06687 [pdf]
    PRD(2021)·85 citations
  2. 02

    [Submitted on 12 Jun 2021]

    The Angular Correlations in the Decay of Excited States in 8Be

    A.C Hayes🇺🇸 · J.L. Friar🇺🇸 · GM. Hale🇺🇸 · GT. Garvey🇺🇸

    Motivated by the recent observation of anomalous electron-positron angular correlations in the decay of the 18.15 MeV 1+ excited states in 8Be, we reexamine in detail the Standard Model expectations for these angular correlations. The 18.15 MeV state is above particle threshold, and several multipoles can contribute to its decay. We present the general theoretical expressions for angular distributions for nuclear decay by C0, C1, C2 M1, E1, and E2 multipoles, and we examine their relative contribution to the decay of 8Be at 18.15 MeV. We find that this resonance is dominated by M1 and E1 decay, and that the ratio of M1 to E1 strength is a strong function of energy. This is in contract to the original analysis of the angular distributions, where the M1/E1 ratio was assumed to be a constant over the energy region Ep = 0:8-1:2 MeV. We find that the existence of a `bump' in the measured angular distribution is strongly dependent on the assumed M1/E1 ratio, with the present analysis finding the measured large-angle contributions to the angular distribution to be lower than expectation. Thus, in the current analysis we find no evidence for axion decay in the 18.15 MeV resonance region of 8Be.

    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    2106.06834 [pdf]
    PRC(2022)·20 citations
  3. 03

    [Submitted on 12 Jun 2021]

    Axial meson contribution to proton form factors

    Nikolai Korchagin🇨🇳 · Andrey Radzhabov🇷🇺

    The effect of axial meson exchange on extraction of proton electromagnetic form factors in scattering is calculated. Taking as an example meson exchange, it is quantitatively shown how it affects Rosenbluth and polarization transfer methods. The contribution of an axial meson is negligible in comparison with the traditional box-type two photon exchange and could not be responsible for difference of form factors extracted by different techniques. However, results support the idea that meson exchange could explain deviation of individual polarizations.

    Comments:
    21 pages, 9 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    2106.06883 [pdf]
    1 citation
  4. 04

    [Submitted on 13 Jun 2021]

    Hybrid neutron stars in the mass-radius diagram

    Mateusz Cierniak🇵🇱 · David Blaschke🇵🇱

    We present a systematic investigation of the possible locations for the special point (SP), a unique feature of hybrid neutron stars in the mass-radius. The study is performed within the two-phase approach where the high-density (quark matter) phase is described by the constant-sound-speed (CSS) equation of state (EoS) and the nuclear matter phase around saturation density is varied from very soft (APR) to stiff (DD2 with excluded nucleon volume. Different construction schemes for the deconfinement transition are applied: Maxwell construction, mixed phase construction and parabolic interpolation. We demonstrate for the first time that the SP is invariant not only against changing the nuclear matter EoS, but also against variation of the construction schemes for the phase transition. Since the SP serves as a proxy for the maximum mass and accessible radii of massive hybrid stars, we draw conclusions for the limiting masses and radii of hybrid neutron stars.

    Comments:
    7 pages, 5 figures, 1 table, accepted for publication in Astronomische Nachrichten
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    2106.06986 [pdf]
    Astron.Nachr.(2021)·30 citations
  5. 05

    [Submitted on 14 Jun 2021]

    Interplay between pairing and triaxial shape degrees of freedom in Os and Pt nuclei

    K. Nomura · D. Vretenar · Z. P. Li · J. Xiang

    The effect of coupling between pairing and quadrupole triaxial shape vibrations on the low-energy collective states of -soft nuclei is investigated using a model based on the framework of nuclear energy density functionals (EDFs). Employing a constrained self-consistent mean-field (SCMF) method that uses universal EDFs and pairing interactions, potential energy surfaces of characteristic -soft Os and Pt nuclei with are calculated as functions of the pairing and triaxial quadrupole deformations. Collective spectroscopic properties are computed using a number-nonconserving interacting boson model (IBM) Hamiltonian, with parameters determined by mapping the SCMF energy surface onto the expectation value of the Hamiltonian in the boson condensate state. It is shown that, by simultaneously considering both the shape and pairing collective degrees of freedom, the EDF-based IBM successfully reproduces data on collective structures based on low-energy states, as well as -vibrational bands.

    Comments:
    18 pages, 14 figures, 6 tables
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2106.07145 [pdf]
    PRC(2021)·11 citations
  6. 06

    [Submitted on 14 Jun 2021]

    Comparative study of He -decay based on different similarity-renormalization-group evolved chiral interactions

    A. Gnech · L.E. Marcucci · R. Schiavilla · M. Viviani

    We report on a study of the Gamow-Teller matrix element contributing to He -decay with similarity renormalization group (SRG) versions of momentum- and configuration-space two-nucleon interactions. These interactions are derived from two different formulations of chiral effective field theory (EFT) -- without and with the explicit inclusion of -isobars. We consider evolution parameters in the range between 1.2 and 2.0 fm and, for the -less case, also the unevolved (bare) interaction. The axial current contains one- and two-body terms, consistently derived at tree level (no loops) in the two distinct EFT formulations we have adopted here. The He and Li ground-state wave functions are obtained from hyperspherical-harmonics (HH) solutions of the nuclear many-body problem. In = systems, the HH method is limited at present to treat only two-body interactions and non-SRG evolved currents. Our results exhibit a significant dependence on of the contributions associated with two-body currents, suggesting that a consistent SRG-evolution of these is needed in order to obtain reliable estimates. We also show that the contributions from one-pion-exchange currents depend strongly on the model (chiral) interactions and on the momentum- or configuration-space cutoffs used to regularize them. These results might prove helpful in clarifying the origin of the sign difference recently found in No-Core-Shell-Model and Quantum Monte Carlo calculations of the He Gamow-Teller matrix element.

    Comments:
    16 pages, 4 figures, accepted for publication on Phys. Rev. C
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2106.07439 [pdf]
    PRC(2021)·11 citations
  7. 07

    [Submitted on 14 Jun 2021]

    Scaling in the short-time approximation

    S. Pastore · J. Carlson · S. Gandolfi · R. Schiavilla · R. B. Wiringa

    We briefly review the concept of scaling and how it occurs in quasielastic electron and neutrino scattering from nuclei, and then the particular approach to scaling in the short-time approximation. We show that, while two-nucleon currents do significantly enhance the transverse electromagnetic response, they do not spoil scaling, but in fact enhance it. We provide scaling results obtained in the short-time approximation that verify this claim. The enhanced scaling is not ``accidental'' -- as claimed in Ref.~\cite{Benhar:2020jye} -- but rather reflects the dominant role played by pion exchange interactions and currents in the quasielastic regime.

    Comments:
    2 figures, 4 pages
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2106.07584 [pdf]
    0 citations

Affiliations

first authorsco-authorsvia INSPIRE