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Nuclear Theory·nucl-th

Wednesday·June 6, 2018

12 papers—8 primary·4 cross-listed

All12Primary8Cross-lists4
  1. 01

    [Submitted on 4 Jun 2018]

    Proton tensor charges from a Poincaré-covariant Faddeev equation

    Qing-Wu Wang🇨🇳 · Si-Xue Qin🇨🇳 · Craig D. Roberts🇺🇸 · Sebastian M. Schmidt🇩🇪

    The proton's tensor charges are calculated at leading order in a symmetry-preserving truncation of all matter-sector equations relevant to the associated bound-state and scattering problems. In particular, the nucleon three-body bound-state equation is solved without using a diquark approximation of the two-body scattering kernel. The computed charges are similar to those obtained in contemporary simulations of lattice-regularised quantum chromodynamics, an outcome which increases the tension between theory and phenomenology. Curiously, the theoretical calculations produce a value of the scale-invariant ratio which matches that obtained in simple quark models, even though the individual charges are themselves different. The proton's tensor charges can be used to constrain extensions of the Standard Model using empirical limits on nucleon electric dipole moments.

    Comments:
    10 pages, 9 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1806.01287 [pdf]
    PRD(2018)·54 citations
  2. 02

    [Submitted on 4 Jun 2018]

    Estimation of the freeze-out parameters reachable in the AFTER@LHC project

    Viktor Begun🇵🇱 · Daniel Kikoła🇵🇱 · Volodymyr Vovchenko🇩🇪 · Daniel Wielanek🇵🇱

    Estimation of the freeze-out parameters as the function of rapidity in Pb+Pb collisions at GeV in the AFTER@LHC project is performed. The conventional hadron resonance gas model is used for the analysis of the events generated by the UrQMD model. The results indicate that one may obtain at least times increase of baryon chemical potential in the forward rapidity range as compared to the mid-rapidity. The values in the rapidity range of for AFTER@LHC are comparable to that covered by the RHIC Beam Energy Scan program. Thus, a rapidity scan in the AFTER@LHC project provides a complementary approach to study the QCD phase diagram.

    Comments:
    6 pages, 4 figures
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Experiment (hep-ex); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
    arXiv:
    1806.01303 [pdf]
    PRC(2018)·17 citations
  3. 03

    [Submitted on 4 Jun 2018]

    Beam Spin Asymmetry in Electroproduction of Pseudoscalar or Scalar Meson Production off the Scalar Target

    Chueng-Ryong Ji🇺🇸 · Ho-Meoyng Choi🇰🇷 · Andrew Lundeen🇺🇸 · Bernard L. G. Bakker🇳🇱

    We discuss the electroproduction of pseudoscalar () or scalar () meson production off the scalar target. The most general formulation of the differential cross section for the or meson production process involves only one or two hadronic form factors, respectively, on a scalar target. The Rosenbluth-type separation of the differential cross section provides the explicit relation between the hadronic form factors and the different parts of the differential cross section in a completely model-independent manner. The absence of the beam spin asymmetry for the pseudoscalar meson production provides a benchmark for the experimental data analysis. The measurement of the beam spin asymmetry for the scalar meson production may also provide a unique opportunity not only to explore the imaginary part of the hadronic amplitude in the general formulation but also to examine the significance of the chiral-odd generalized parton distribution (GPD) contribution in the leading-twist GPD formulation.

    Comments:
    8 pages, 1 figure
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1806.01379 [pdf]
    PRD(2019)·4 citations
  4. 04

    [Submitted on 4 Jun 2018]

    Coupling charge-exchange vibrations to nucleons in a relativistic framework: effect on Gamow-Teller transitions and beta-decay half-lives

    Caroline Robin · Elena Litvinova

    The nuclear response theory for isospin-transfer modes in the relativistic particle-vibration coupling framework is extended to include coupling of single nucleons to isospin-flip (charge-exchange) phonons, in addition to the usual neutral vibrations. This new coupling introduces dynamical pion and rho-meson exchange, beyond the Hartree-Fock approximation, up to infinite order. We investigate the impact of this new mechanism on the Gamow-Teller response of a few doubly-magic neutron-rich nuclei, namely Ca, Ni, Sn and Pb. It is found that the coupling to isospin-flip vibrations can have a non negligible impact on the strength distribution and quenching of the giant resonance, globally improving the agreement with the experimental data. The corresponding beta-decay half-lives of Ni and Sn are also calculated, and found to be decreased by a factor by the inclusion of the new phonons.

    Comments:
    6 pages, 5 figures, v2: accepted version
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1806.01409 [pdf]
    PRC(2018)·38 citations
  5. 05

    [Submitted on 5 Jun 2018]

    The Effect of Multiplicity Cut on Particle Ratios at 7 TeV Proton-Proton Collisions

    Ehab Abbas🇪🇬

    The final state hadronic composition of proton-proton collisions at 7 TeV as a function of charged particle multiplicity density is studied. The thermal model is adjusted to match the experimental conditions in order to understand the effect of the experimental cuts on rapidity and multiplicity. This study indicates that the measured hadronic composition under a simultaneous cut on rapidity and multiplicity does not coincide with the fireball hadronic composition. Excluding proton to pion ratio, the adjusted model can explain the measured particle ratios. Therefore, the observed strangeness enhancement as a function of charged particle multiplicity density could be an effect of the experimental cuts.

    Comments:
    12 page , 4 figures Typo, minor corrections and additions
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1806.01459 [pdf]
    0 citations
  6. 06

    [Submitted on 5 Jun 2018]

    Realistic shell-model calculations for p-shell nuclei including contributions of a chiral three-body force

    T. Fukui · L. De Angelis · Y. Z. Ma · L. Coraggio · A. Gargano · N. Itaco · F. R. Xu

    In this paper we present an evolution of our derivation of the shell-model effective Hamiltonian, namely introducing effects of three-body contributions. More precisely, we consider a three-body potential at next-to-next-to-leading order in chiral perturbation theory, and the induced three-body forces that arise from many-body correlations among valence nucleons. The first one is included, in the derivation of the effective Hamiltonian for one- and two-valence nucleon-systems, at first order in the many-body perturbation theory. Namely, we include only the three-body interaction between one or two valence nucleons and those belonging to the core. For nuclei with more than two valence particles, both induced - turned on by the two-body potential - and genuine three-body forces come into play. Since it is difficult to perform shell-model calculations with three-body forces, these contributions are estimated for the ground-state energy only. In order to establish the reliability of our approximations, we focus attention on nuclei belonging to the p shell, aiming to benchmark our calculations against those performed with the ab initio no-core shell-model. The obtained results are satisfactory, and pave the way to the application of our approach to nuclear systems with heavier masses.

    Comments:
    10 pages, 15 figures, to be published on Physical Review C
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1806.01573 [pdf]
    PRC(2018)·50 citations
  7. 07

    [Submitted on 5 Jun 2018]

    QCD sum rules for the isobar in neutron matter

    Jesuel Marques L.🇧🇷 · Su Houng Lee🇰🇷 · Aaron Park🇰🇷 · R. D. Matheus🇧🇷 · Kie Sang Jeong🇰🇷

    We study the properties of the isobar in the symmetric and asymmetric nuclear matter using the QCD sum rules approach based on the energy dispersion relation. Allowing for different continuum thresholds for the polarization tensors with different dimensions, we find stable masses for the in both the vacuum and the medium. Compared to the nucleon case, we find that the vector repulsion is smaller for the while the scalar attraction is similar (75 MeV vector repulsion and 150 MeV scalar attraction in the symmetric matter). The smaller vector repulsion can be understood using the Pauli principle and a constituent quark model. Also the isospin dependence of the quasiparticle energy, which mainly comes from the vector self energy, is quite weak. We also allow for an explicit continuum contribution to the polarization function, but find its effect to be minimal. Phenomenological consequences of our results are discussed.

    Comments:
    18 pages, 6 figure, Updated version as revised in the publication
    Subjects:
    Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1806.01668 [pdf]
    PRC(2018)·7 citations
  8. 08

    [Submitted on 5 Jun 2018]

    Semiclassical calculations of complete and incomplete fusion in collisions of weakly bound nuclei

    G.D. Kolinger · L.F. Canto · R. Donangelo · S.R. Souza

    We use an improved version of the semiclassical method described in Refs. [1,2,3] to evaluate fusion cross sections in collisions of weakly bound nuclei. This version takes into account the static effects of the low breakup threshold, uses better bin states in the discretization of the continuum and avoids the excitation of closed channels. The population of these channels is a consequence of the violation of energy conservation, which is inherent in the semiclassical method. The method is employed to evaluate complete fusion and total fusion cross section in collisions of the weakly bound 6,7Li projectiles with 159Tb and 197Au targets, for which data is available. The overall agreement between theory and experiment is fairly good.

    Comments:
    12 pages, 3 figures
    Subjects:
    Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
    arXiv:
    1806.01679 [pdf]
    PRC(2018)·18 citations
  9. 09

    [Submitted on 5 Jun 2018] (cross-list from astro-ph.HE)

    Glitch Behavior of Pulsars and Contribution from Neutron Star Crust

    Avishek Basu · Prasanta Char · Rana Nandi · Bhal Chandra Joshi · Debades Bandyopadhyay

    Pulsars are highly magnetized rotating neutron stars with a very stable rotation speed. Irrespective of their stable rotation rate, many pulsars have been observed with the sudden jump in the rotation rate, which is known as pulsar glitch. The glitch phenomena are considered to be an exhibit of superfluidity of neutron matter inside the neutron star's crustal region. The magnitude of such rapid change in rotation rate relative to their stable rotation frequency can quantify the moment of inertia of the crustal region to the total moment of inertia of the star called as the fractional moment of inertia (FMI). In this paper, we have calculated FMI for different masses of the star using six different representative unified equations of state (EoS) constructed under Relativistic Mean Field (RMF) framework. We have performed an event-wise comparison of FMI obtained from data with that of theoretically calculated values with and without considering the entrainment effect. It is found that larger glitches can't be explained by crustal FMI alone, even without the entrainment.

    Comments:
    9 pages, 3 figures, 1 table, revised, accepted for publication in ApJ
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
    arXiv:
    1806.01521 [pdf]
    ApJ(2018)·27 citations
  10. 10

    [Submitted on 5 Jun 2018] (cross-list from hep-ph)

    Two-photon exchange correction in elastic lepton-proton scattering

    Oleksandr Tomalak🇩🇪

    We present the dispersion relation approach based on unitarity and analyticity to evaluate the two-photon exchange contribution to elastic electron-proton scattering. The leading elastic and first inelastic intermediate state contributions are accounted for in the region of small momentum transfer based on the available data input. The novel methods of analytical continuation allow us to exploit the MAMI form factor data and the MAID parameterization for the pion electroproduction amplitudes as input in the calculation. The results are compared to the recent CLAS, VEPP-3 and OLYMPUS data as well as to the full two-photon exchange correction in the near-forward approximation, which is based on the Christy and Bosted unpolarized structure functions fit. Additionally, predictions are given for a forthcoming muon-proton scattering experiment.

    Comments:
    12 pages, 8 figures, version published in Few-Body Syst. 59, 87 (2018)
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
    arXiv:
    1806.01627 [pdf]
    Few Body Syst.(2018)·15 citations
  11. 11

    [Submitted on 5 Jun 2018] (cross-list from astro-ph.HE)

    Cosmological Constant Effects on the Properties of Mass Twin Compact Stars

    Noshad Khosravi Largani🇮🇷 · David E. Alvarez-Castillo🇷🇺

    We present a systematic investigation of the cosmological constant effects in compact stars interiors in the framework of Einstein's gravity. Consideration of a cosmological constant in compact stars is motivated by the mechanism of acceleration of the observable universe, where is usually related to the dark energy. In particular, we consider compact star mass twins, hybrid neutron stars that populate both the second and third branch of the mass-radius diagram. For those models, the need of consideration of excluded volume effects in the equation of state, resulting from the finite size volume of nucleons, leads to a stiffening of matter causing compact stars to acquire higher mass and radius values. We demonstrate that certain values of the cosmological constant can also modify the compact star properties but in an opposite way. In addition, we find that the inclusion of can have a similar effect to the existence of pasta phases at the hadron-quark interface.

    Comments:
    5 pages, 1 figure, Proceedings of The XXII International Scientific Conference of Young Scientists and Specialists (AYSS-2018), Dubna, April 23-27, 2018; references added, typos corrected
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1806.01698 [pdf]
    EPJ Web Conf.(2019)·6 citations
  12. 12

    [Submitted on 5 Jun 2018] (cross-list from hep-lat)

    Phase Unwrapping and One-Dimensional Sign Problems

    William Detmold🇺🇸 · Gurtej Kanwar🇺🇸 · Michael L. Wagman🇺🇸

    Sign problems in path integrals arise when different field configurations contribute with different signs or phases. Phase unwrapping describes a family of signal processing techniques in which phase differences between elements of a time series are integrated to construct non-compact unwrapped phase differences. By combining phase unwrapping with a cumulant expansion, path integrals with sign problems arising from phase fluctuations can be systematically approximated as linear combinations of path integrals without sign problems. This work explores phase unwrapping in zero-plus-one-dimensional complex scalar field theory. Results with improved signal-to-noise ratios for the spectrum of scalar field theory can be obtained from unwrapped phases, but the size of cumulant expansion truncation errors is found to be undesirably sensitive to the parameters of the phase unwrapping algorithm employed. It is argued that this numerical sensitivity arises from discretization artifacts that become large when phases fluctuate close to singularities of a complex logarithm in the definition of the unwrapped phase.

    Comments:
    42 pages, 16 figures. Journal version
    Subjects:
    High Energy Physics — Lattice (hep-lat); Statistical Mechanics (cond-mat.stat-mech); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
    arXiv:
    1806.01832 [pdf]
    PRD(2018)·16 citations

Affiliations

first authorsco-authorsvia INSPIRE