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Nuclear Theory·nucl-th

Tuesday·June 22, 2021

19 papers—6 primary·13 cross-listed

All19Primary6Cross-lists13
  1. 01

    [Submitted on 18 Jun 2021]

    Hidden variables in angular correlations of the particles emitted in fission

    F. F. Karpeshin

    A comparative analysis of experiments on studying the (n, f), on one hand, and (n, n), on the other hand, angular correlations in fission is carried out, based on the model proposed by muonic conversion in fragments of prompt fission of 238U with negative muons. Their fundamental difference is shown in the sense of the information that can be inferred from them. Historically, the situation resembles the EPR paradox. An experimental check of the empirical relation between the alignment and polarization parameters, the former is twice as small as the latter one.

    Comments:
    A talk paper delivered at ISINN-28 Workshop
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2106.10371 [pdf]
    0 citations
  2. 02

    [Submitted on 18 Jun 2021]

    A model-agnostic analysis of hybrid stars with reactive interfaces

    Germán Lugones🇧🇷 · Mauro Mariani🇦🇷 · Ignacio F. Ranea-Sandoval🇦🇷

    We study hybrid stars considering the effects on stellar stability of the hadron-quark conversion speed at the sharp interface. The equation of state is constructed by combining a model-agnostic hadronic description with a constant speed of sound model for quark matter. We show that current LIGO/Virgo, NICER, low-density nuclear and high-density perturbative QCD constraints can be satisfied in two scenarios, with low and high transition pressures. If the conversion speed at the interface is slow, a new class of dynamically stable hybrid objects is possible and very stiff hadronic equations of state cannot be discarded. Densities tens of times larger than the nuclear saturation density are possible at the center of these objects. We discuss possible formation mechanisms for the new class of hybrid stars and smoking guns for their observational identification.

    Comments:
    17 pages, 7 figures, accepted for publication in JCAP
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    2106.10380 [pdf]
    JCAP(2023)·38 citations
  3. 03

    [Submitted on 19 Jun 2021]

    On attractor and fixed points in Bjorken flows

    Jean-Paul Blaizot🇫🇷 · Li Yan🇨🇳

    We consider a plasma of massless particles undergoing Bjorken expansion, mimicking the matter created in ultra-relativistic heavy ion collisions. We study the transition to hydrodynamics using kinetic theory in the relaxation time approximation. By allowing the relaxation time to depend on time, we can monitor the speed of the transition from the collisionless regime to hydrodynamics. By using a special set of moments of the momentum distribution, we reduce the kinetic equation to a coupled mode problem which encompasses all versions of second order viscous hydrodynamics for Bjorken flows. This coupled mode problem is analysed first using techniques of linear algebra. Then we transform this two mode problem into a single non linear differential equation and proceed to a fixed point analysis. We identify an attractor solution as the particular solution of this non linear equation that joins two fixed points: one corresponding to the collisionless, early time regime, the other corresponding to late time hydrodynamics. We exploit the analytic solution of this equation in order to test several approximations and to identify generic features of the transition to hydrodynamics. We argue that extending the accuracy of hydrodynamics to early time, i.e. to the region of large gradients, amounts essentially to improve the accuracy of the location of the collisionless fixed point. This is demonstrated by showing that a simple renormalisation of a second order transport coefficient puts the free streaming fixed point at the right location, and allows us to reproduce accurately the full solution of the kinetic equation within second order viscous hydrodynamics, even in regimes far from local equilibrium.

    Comments:
    53 pages and 12 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    2106.10508 [pdf]
    PRC(2021)·53 citations
  4. 04

    [Submitted on 21 Jun 2021]

    Multi-messenger heavy-ion collision physics

    Charles Gale🇨🇦 · Jean-François Paquet🇺🇸 · Björn Schenke🇺🇸 · Chun Shen🇺🇸

    This work studies the production of direct photons in relativistic nuclear collisions, along with the production of hadrons. Radiation from the very first instants to the final moments of the evolution is included. The hybrid model used here describes all stages of relativistic heavy-ion collisions. Chronologically, those are an initial state reflecting the collision of nuclei described within the Color Glass Condensate effective theory; a pre-equilibrium phase based on non-equilibrium linear response; relativistic viscous hydrodynamics, and a hadronic afterburner. The effect of the pre-equilibrium phase on both photonic and hadronic observables is highlighted for the first time. The potential of photon observables -- spectrum, differential elliptic and triangular flow -- to reveal the chemical equilibration time is studied. Finally, we consider "small collision systems", including proton+nucleus collisions and collisions of light nuclei, as probed by hadronic and electromagnetic observables. We demonstrate how photon production can signal the formation of quark-gluon plasma in such small systems.

    Comments:
    15 pages, 20 figures. Version updated to match published version (including title modification)
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    2106.11216 [pdf]
    PRC(2022)·122 citations
  5. 05

    [Submitted on 21 Jun 2021]

    Unraveling the Flux-Averaged Neutrino-Nucleus Cross Section

    Omar Benhar🇮🇹

    The interpretation of the nuclear cross sections measured using accelerator neutrino beams involve severe difficulties, arising primarily from the average over the incoming neutrino flux. The broad energy distribution of the beam particles hampers the determination of the energy transfer to the nuclear target, the knowledge of which is needed to pin down the dominant reaction mechanism. Overcoming this problem requires the development of a theoretical approach suitable to describe neutrino interactions at energies ranging from hundreds of MeV to few GeV. In this paper, it is argued that the approach based on the factorisation of the nuclear cross section provides a consistent framework for the calculation of neutrino-nucleus interactions in both the quasi elastic and inelastic channels. The near-degeneracy between theoretical models based on different assumptions, and the use of electron scattering data to advance the understanding of neutrino-nucleus cross sections are also discussed.

    Comments:
    Submittted to EPJ Special Topics. arXiv admin note: substantial text overlap with arXiv:1612.01473
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    2106.11228 [pdf]
    Eur.Phys.J.ST(2021)·0 citations
  6. 06

    [Submitted on 21 Jun 2021]

    Analysis of the neutron matter equation of state and the symmetry energy up to fourth order of chiral effective field theory

    Francesca Sammarruca🇺🇸 · Randy Millerson🇺🇸

    We present predictions for the neutron matter equation of state, from leading to fourth order of chiral effective field theory, using recently developed, accurate chiral nucleon-nucleon potentials. We find the impact of subleading three-neutron forces to be mild and attractive. We also show order-by-order predictions for the symmetry energy, and discuss its density dependence in relation to empirical constraints.

    Comments:
    9 pages, 7 figures
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    2106.11282 [pdf]
    PRC(2021)·20 citations

Affiliations

first authorsco-authorsvia INSPIRE