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Nuclear Theory·nucl-th

Friday·April 29, 2016

8 papers—6 primary·2 cross-listed

All8Primary6Cross-lists2
  1. 01

    [Submitted on 28 Apr 2016]

    Relation between (e,e') sum rules in 6,7Li and 4He nuclei.Experiment and cluster model

    V. D. Efros · I. S. Timchenko · A. Yu. Buki

    The sums over (e,e') spectra of 6Li and 7Li nuclei which correspond to the longitudinal sum rule are studied. It is suggested that due to the cluster structure of the lithium isotopes these sums may approximately be expressed in terms of such a sum pertaining to the alpha-particle. Calculation of these sums is performed in the framework of cluster models with antisymmetrization done with respect to all the nucleons. At momentum transfers higher than 0.8 fm^{-1} the relations expressing the A=6 or 7 sum in terms of the A=4 sum prove to be valid with rather high accuracy. In the region of momentum transfers around 1 fm^{-1} the longitudinal correlation functions of 6Li and 7Li nuclei are found to be close to that of the alpha-particle. The experimental longitudinal sums in the range between 0.450 and 1.625 fm^{-1} are employed to perform comparison with those calculated in the framework of cluster models. Out of the mentioned experimental sums, those in the range between 0.750 and 1.000 fm^{-1} in the 6Li case and between 0.750 and 1.125 fm^{-1} in the 7Li case are obtained in the present work. In the 6Li case a complete agreement is found while in the 7Li case an agreement only at a qualitative level is observed.

    Comments:
    8 pages, 2 figures. Small additions and improvements of the presentation. Additional references
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1604.08408 [pdf]
    EPJA(2016)·0 citations
  2. 02

    [Submitted on 28 Apr 2016]

    Relativistic model of 2p-2h meson exchange currents in (anti)neutrino scattering

    I. Ruiz Simo🇪🇸 · J.E. Amaro🇪🇸 · M.B. Barbaro🇮🇹 · A. De Pace🇮🇹 · J.A. Caballero🇪🇸 · T.W. Donnelly🇺🇸

    We develop a model of relativistic, charged meson-exchange currents (MEC) for neutrino-nucleus interactions. The two-body current is the sum of seagull, pion-in-flight, pion-pole and -pole operators. These operators are obtained from the weak pion-production amplitudes for the nucleon derived in the non-linear -model together with weak excitation of the resonance and its subsequent decay into . With these currents we compute the five 2p-2h response functions contributing to and reactions in the relativistic Fermi gas model. The total current is the sum of vector and axial two-body currents. The vector current is related to the electromagnetic MEC operator that contributes to electron scattering. This allows one to check our model by comparison with the results of De Pace {\em et al.,} Nuclear Physics A 726 (2003) 303. Thus our model is a natural extension of that model to the weak sector with the addition of the axial MEC operator. The dependences of the response functions on several ingredients of the approach are analyzed. Specifically we discuss relativistic effects, quantify the size of the direct-exchange interferences, and the relative importance of the axial versus vector current.

    Comments:
    17 pages, 11 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1604.08423 [pdf]
    J.Phys.G(2017)·121 citations
  3. 03

    [Submitted on 28 Apr 2016]

    Critical endpoint in the presence of a chiral chemical potential

    Zhu-Fang Cui🇨🇳 · Ian C. Cloet🇺🇸 · Ya Lu🇨🇳 · Craig D. Roberts🇺🇸 · Sebastian M. Schmidt🇩🇪 · Shu-Sheng Xu🇨🇳 · Hong-Shi Zong🇨🇳

    A class of Polyakov-loop-modified Nambu--Jona-Lasinio (PNJL) models have been used to support a conjecture that numerical simulations of lattice-regularized quantum chromodynamics (QCD) defined with a chiral chemical potential can provide information about the existence and location of a critical endpoint in the QCD phase diagram drawn in the plane spanned by baryon chemical potential and temperature. That conjecture is challenged by conflicts between the model results and analyses of the same problem using simulations of lattice-regularized QCD (lQCD) and well-constrained Dyson-Schwinger equation (DSE) studies. We find the conflict is resolved in favor of the lQCD and DSE predictions when both a physically-motivated regularization is employed to suppress the contribution of high-momentum quark modes in the definition of the effective potential connected with the PNJL models and the four-fermion coupling in those models does not react strongly to changes in the mean-field that is assumed to mock-up Polyakov loop dynamics. With the lQCD and DSE predictions thus confirmed, it seems unlikely that simulations of lQCD with can shed any light on a critical endpoint in the regular QCD phase diagram.

    Comments:
    6 pages, 5 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1604.08454 [pdf]
    PRD(2016)·53 citations
  4. 04

    [Submitted on 28 Apr 2016]

    Asymptotics of three-body bound state radial wave functions of halo nuclei involving two charged particles

    R. Yarmukhamedov

    Asymptotic expressions for the radial and full wave functions of a three{body bound halo nuclear system with two charged particles in relative coordinates are obtained in explicit form, when the relative distance between two particles tends to infinity. The obtained asymptotic forms are applied to the analysis of the asymptotic behavior of the three-body (pn?) wave functions for the halo ( MeV, , ) state of Li derived by D. Baye within the Lagrange-mesh method for two forms of the -potential. The agreement between the calculated wave function and the asymptotic formula is excellent for distances up to 30 fm. Information about the values of the three-body asymptotic normalization functions is extracted. It is shown that the extracted values of the three-body asymptotic normalization function are sensitive to the form of the -potential. The mirror symmetry is revealed for the three-body asymptotic normalization functions derived for the isobaric (He, Li) pair.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1604.08495 [pdf]
    NPA(2017)·0 citations
  5. 05

    [Submitted on 28 Apr 2016]

    High Baryon Densities in Heavy Ion Collisions at Energies Attainable at the BNL Relativistic Heavy Ion Collider and the CERN Large Hadron Collider

    Ming Li🇺🇸 · Joseph I. Kapusta🇺🇸

    In very high energy collisions nuclei are practically transparent to each other but produce very hot, nearly baryon-free, matter in the so-called central rapidity region. The energy in the central rapidity region comes from the kinetic energy of the colliding nuclei. We calculate the energy and rapidity loss of the nuclei using the color glass condensate model. This model also predicts the excitation energy of the nuclear fragments. Using a space-time picture of the collision we calculate the baryon and energy densities of the receding baryonic fireballs. For central collisions of gold nuclei at the highest energy attainable at the Relativistic Heavy Ion Collider, for example, we find baryon densities more than ten times that of atomic nuclei over a large volume.

    Comments:
    5 pages, 7 figures. This version incorporates changes in response to the referee reports
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1604.08525 [pdf]
    PRC(2017)·23 citations
  6. 06

    [Submitted on 28 Apr 2016]

    Universal symmetry energy contribution to the neutron star equation of state

    D. Blaschke🇵🇱 · D. E. Alvarez-Castillo🇷🇺 · T. Klahn🇵🇱

    We discuss the observation that under neutron star conditions of charge neutrality and equilibrium the contribution from the symmetry energy to the equation of state (EoS) follows a universal behaviour. We call this behaviour the conjecture of a Universal Symmetry Energy Contribution (USEC). We find that an USEC holds provided the density dependence of the symmetry energy follows a behaviour that limits the proton fraction to values below the threshold for the direct Urca (DU) cooling process. The absence of DU cooling in typical mass neutron stars appears to be supported by the phenomenology of neutron star cooling data and allows to constrain the behaviour of at high densities. Two classes of symmetry energy functions are investigated more in detail to elucidate the USEC. We derive an analytic formula for the USEC to the neutron star EoS based on the result for the symmetry energy extracted from isobaric analog states of nuclei.

    Comments:
    12 pages, 12 figures, one figure (Fig. 6) and descriptive text added
    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1604.08575 [pdf]
    17 citations

Affiliations

first authorsco-authorsvia INSPIRE