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Nuclear Theory·nucl-th

Friday·December 18, 2020

6 papers—3 primary·3 cross-listed

All6Primary3Cross-lists3
  1. 01

    [Submitted on 17 Dec 2020]

    Probing the boundary of phase transition of nuclear matter using proton flows in heavy-ion collisions at 2-8 GeV/nucleon

    Ya-Fei Guo🇨🇳 · Gao-Chan Yong🇨🇳

    Based on the relativistic transport model ART with the hadronic equation of state extended to have a phase transition via the use of the MIT bag model, properties of phase transition of dense nuclear matter formed in relativistic heavy-ion collisions are investigated. Proton sideward and directed flows are calculated with different equation of states in Au + Au collisions at beam energies of 2, 4, 6 and 8 GeV/nucleon. Compared with AGS experimental data in existence, the boundary of first-order phase transition is roughly confined, i.e., in the range of 2.5-4 times saturation density with temperature about 64-94 MeV. Such constraints are useful for ongoing RHIC Beam Energy Scan-II program to study the QCD matter phase diagram.

    Comments:
    5 pages, 5 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    2012.09471 [pdf]
    PLB(2021)·8 citations
  2. 02

    [Submitted on 17 Dec 2020]

    The nucleon-pair approximation for nuclei from spherical to deformed regions

    G. J. Fu · Calvin W. Johnson

    In this paper we model low-lying states of atomic nuclei in the nucleon-pair approximation of the shell model, using three approaches to select collective nucleon pairs: the generalized seniority scheme, the conjugate gradient method, and the Hartree-Fock approach. We find the collective pairs obtained from the generalized seniority scheme provides a good description for nearly spherical nuclei, and those from the conjugate gradient method or the Hartree-Fock approach work well for transitional and deformed nuclei. Our NPA calculations using collective pairs with angular momenta 0, 2, and 4 (denoted by pairs) reproduce the nuclear shape evolution in the isotones, Ca, Ti, Cr, and Fe, and yield good agreement with full configuration-interaction calculations of low-lying states in medium-heavy transitional and deformed nuclei: Ti, Cr, Cr, Fe, Zn, Ge, Mo, and Xe. Finally, using the -pair approximation we describe low-lying states of Ba, cases difficult to reach by conventional configuration-interaction methods.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2012.09560 [pdf]
    PRC(2021)·14 citations
  3. 03

    [Submitted on 17 Dec 2020]

    Quantum statistics effects and fluctuations of particle numbers near the critical point of nuclear matter

    S.N. Fedotkin · A.G. Magner · U.V. Grygoriev

    Equation of state with quantum statistics corrections is derived for a multi-component gas of particles interacting through the repulsive and attractive van der Waals (vdW) forces up to first few orders over a small parameter , where and are the particle number density and temperature, and the particle mass and degeneracy factor. The parameter corresponds to the vdW excluded volume. For interacting system of Fermi nucleon and Bose particles, a small impurity of particles to the nucleon system at leading first order in both particle and nucleon small parameters does not change much the basic results for the symmetric nuclear matter. The particle number fluctuations determined by the isothermal in-compressibility can be obtained analytically at the same first order quantum-statistics approximation for symmetric nucleon matter. Our approximate analytical results appear to be in good agreement with the accurate numerical calculations.

    Comments:
    12 pages, 5 figures, 2 tables
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2012.09695 [pdf]
    3 citations
  4. 04

    [Submitted on 17 Dec 2020] (cross-list from hep-ph)

    Leading-order QED radiative corrections to timelike Compton scattering on the proton

    Matthias Heller🇩🇪 · Niklas Keil🇩🇪 · Marc Vanderhaeghen🇩🇪

    We evaluate the leading-order QED radiative corrections to the timelike Compton scattering (TCS) process . We study these corrections in two energy regimes using different models for the TCS amplitude. In the low-energy regime we calculate the contribution due to the proton and its lowest-energy excitation, the resonance. In the high-energy near-forward kinematical regime we calculate the TCS amplitude in a handbag approach in terms of Generalized Parton Distributions (GPDs). On the level of cross sections we find the QED radiative corrections to be in the range in the low-energy regime and around in the high-energy regime. We show that in both the di-lepton forward-backward asymmetry as well as in the photon beam helicity asymmetry these corrections nearly cancel out, making them gold-plated observables to extract the real and imaginary parts of the TCS amplitude. We demonstrate in particular the sensitivity of these asymmetries on GPD parameterizations for a recent CLAS12@JLab TCS experiment.

    Comments:
    16 pages, 13 figures
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    2012.09565 [pdf]
    PRD(2021)·6 citations
  5. 05

    [Submitted on 17 Dec 2020] (cross-list from astro-ph.HE)

    Probing the nuclear equation of state from the existence of a neutron star: the GW190814 puzzle

    A. Kanakis-Pegios🇬🇷 · P.S. Koliogiannis🇬🇷 · Ch.C. Moustakidis🇬🇷

    On August 14, 2019, the LIGO/Virgo collaboration observed a compact object with mass , as a component of a system where the main companion was a black hole with mass . A scientific debate initiated concerning the identification of the low mass component, as it falls into the neutron star - black hole mass gap. The understanding of the nature of GW190814 event will offer rich information concerning open issues, the speed of sound and the possible phase transition into other degrees of freedom. In the present work, we made an effort to probe the nuclear equation of state along with the GW190814 event. Firstly, we examine possible constraints on the nuclear equation of state inferred from the consideration that the low mass companion is a slow or rapidly rotating neutron star. In this case, the role of the upper bounds on the speed of sound is revealed, in connection with the dense nuclear matter properties. Secondly, we systematically study the tidal deformability of a possible high mass candidate existing as an individual star or as a component one in a binary neutron star system. As the tidal deformability and radius are quantities very sensitive on the neutron star equation of state, they are excellent counters on dense matter properties. We conjecture that similar isolated neutron stars or systems may exist in the Universe and their possible future observation will shed light on the maximum neutron star mass problem.

    Comments:
    v1: 18 pages, 8 figures, 2 tables. v2: 23 pages, 9 figures, 3 tables; accepted for publication in Symmetry
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
    arXiv:
    2012.09580 [pdf]
    Symmetry(2021)·54 citations
  6. 06

    [Submitted on 17 Dec 2020] (cross-list from hep-ph)

    Searching for Lepton Flavour (Universality) Violation and Collider Signals from a Singly-Charged Scalar Singlet

    Andreas Crivellin🇨🇭 · Fiona Kirk🇨🇭 · Claudio Andrea Manzari🇨🇭 · Luca Panizzi🇸🇪

    In recent years, evidence for lepton flavour universality violation beyond the Standard Model has been accumulated. In this context, a singly charged singlet scalar () is very interesting, as it can only have flavour off-diagonal couplings to neutrinos and charged leptons, therefore necessarily violating lepton flavour (universality). In fact, it gives a (necessarily constructive) tree-level effect in processes, while contributing to charged lepton flavour violating only at the loop-level. Therefore, it can provide a common explanation of the hints for new physics in and of the Cabibbo Angle Anomaly. Such an explanation predicts to be of the order of a few times while can be of the order of for order one couplings and therefore in the reach of forthcoming experiments. Furthermore, we derive a {novel} coupling-independent lower limit on the scalar mass of GeV by recasting LHC slepton searches. In the scenario preferred by low energy precision data, the lower limit is even strengthened to GeV, showing the complementary between LHC searches and flavour observables. Furthermore, we point out that this model can be tested by reinterpreting DM mono-photon searches at future colliders.

    Comments:
    8 pages, 4 figures, matches version published in PRD
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    2012.09845 [pdf]
    PRD(2021)·66 citations

Affiliations

first authorsco-authorsvia INSPIRE