Nuclear Theory·nucl-th

Tuesday·August 22, 2017

13 papers—7 primary·6 cross-listed

01
[Submitted on 19 Aug 2017]
Fluctuations of electromagnetic fields in heavy ion collisions
B.G. Zakharov🇷🇺
We perform quantum calculations of fluctuations of the electromagnetic fields in $AA$ collisions at RHIC and LHC energies. We find that in the quantum picture the field fluctuations are much smaller than predictions of the classical Monte-Carlo simulation with the Woods-Saxon nuclear density.
Comments:
4 pages, 2 figures, proceedings for QCD Moriond 2017
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1708.05882 [pdf]
3 citations
02
[Submitted on 20 Aug 2017]
Neutron-proton pairing and double-beta decay in the interacting boson model
P. Van Isacker🇫🇷 · J. Engel🇺🇸 · K. Nomura🇫🇷
Background: The interacting boson model (IBM) has been used extensively to calculate the matrix elements governing neutrinoless double-beta decay. Studies within other models indicate that a good description of neutron-proton pairing is essential for accurate calculations of those matrix elements. The usual interacting boson model is based only on like-particle pairs, however, and the extent to which it captures neutron-proton pairing is not clear. Purpose: To determine whether neutron-proton pairing should be explicitly included as neutron-proton bosons in IBM calculations of neutrinoless double-beta decay matrix elements. Method: An isospin-invariant version of the nucleon-pair shell model is applied to carry out shell-model calculations in a large space and in a collective subspace, and to define effective operators in the latter. A democratic mapping is then used to define corresponding boson operators for the IBM, with and without an isoscalar neutron-proton pair boson. Results: IBM calculations with and without the isoscalar boson are carried out for nuclei near the beginning of the $p f$ shell, with a realistic shell-model Hamiltonian and neutrinoless double-beta-decay operator as the starting point. Energy spectra and double-beta matrix elements are compared to those obtained in the underlying shell model. Conclusions: The isoscalar boson does not improve energy spectra but does improve double-beta matrix elements. To be useful at the level of precision we need, the mapping procedure must be further developed to better determine the dependence of the boson Hamiltonian and decay operator on particle number and isospin. But the benefits provided by the isoscalar boson suggest that through an appropriate combination of mappings and fitting, it would make IBM matrix elements more accurate for the heavier nuclei used in experiments.
Comments:
17 pages, 8 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1708.05925 [pdf]
PRC(2017)·18 citations
03
[Submitted on 21 Aug 2017]
Yrast band of 109Ag described by tilted axis cranking covariant density functional theory with a separable pairing force
Yakun Wang
A separable form of the Gogny pairing force is implemented in tilted axis cranking covariant density functional theory for the description of rotational bands in open shell nuclei. The developed method is used to investigate the yrast sequence of 109Ag for an example. The experimental energy spectrum, angular momenta, and electromagnetic transition probabilities are well reproduced by taking into account pairing correlations with the separable pairing force. An abrupt transition of the rotational axis from the long-intermediate plane to the long-short one is obtained and discussed in detail.
Comments:
9 pages, 8 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1708.06117 [pdf]
PRC(2017)·31 citations
04
[Submitted on 21 Aug 2017]
Gamow-Teller and double-beta decays of heavy nuclei within an effective theory
Eduardo Antonio Coello Pérez · Javier Menéndez · Achim Schwenk
We study $β$ decays within an effective theory that treats nuclei as a spherical collective core with an even number of neutrons and protons that can couple to an additional neutron and/or proton. First we explore Gamow-Teller $β$ decays of parent odd-odd nuclei into low-lying ground-, one-, and two-phonon states of the daughter even-even system. The low-energy constants of the effective theory are adjusted to data on $β$ decays to ground states or Gamow-Teller strengths. The corresponding theoretical uncertainty is estimated based on the power counting of the effective theory. For a variety of medium-mass and heavy isotopes the theoretical matrix elements are in good agreement with experiment within the theoretical uncertainties. We then study the two-neutrino double- $β$ decay into ground and excited states. The results are remarkably consistent with experiment within theoretical uncertainties, without the necessity to adjust any low-energy constants.
Comments:
17 pages, 5 figures, results extended to two-neutrino double beta-minus decays and two-neutrino double electron-capture decays to excited 2+ states, matches published version
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1708.06140 [pdf]
PRC(2018)·25 citations
05
[Submitted on 21 Aug 2017]
Neutron-star radii based on realistic nuclear interactions
Y. Yamamoto · H. Togashi · T. Tamagawa · T. Furumoto · N. Yasutake · Th.A. Rijken
The existence of neutron stars with $2 M_{⊙}$ requires the strong stiffness of the equation of state (EoS) of neutron-star matter. We introduce a multi-pomeron exchange potential (MPP) working universally among 3- and 4-baryons to stiffen the EoS. Its strength is restricted by analyzing the nucleus-nucleus scattering with the G-matrix folding model. The EoSs are derived using the Brueckner-Hartree-Fock (BHF) and the cluster variational method (CVM) with the nuclear interactions ESC and AV18. The mass-radius relations are derived by solving the Tolmann-Oppenheimer-Volkoff (TOV) equation, where the maximum masses over $2 M_{⊙}$ are obtained on the basis of the terrestrial data. Neutron-star radii $R$ at a typical mass $1.5 M_{⊙}$ are predicted to be $12.3 \sim 13.0$ km. The uncertainty of calculated radii is mainly from the ratio of 3- and 4-pomeron coupling constants, which cannot be fixed by any terrestrial experiment. Though values of $R (1.5 M_{⊙})$ are not influenced by hyperon-mixing effects, finely-observed values for them indicate degrees of EoS softening by hyperon mixing in the region of $M \sim 2 M_{⊙}$ . If $R (1.5 M_{⊙})$ is less than about 12.4 km, the softening of EoS by hyperon mixing has to be weak. Useful information can be expected by the space mission NICER offering precise measurements for neutron-star radii within $\pm 5%$ .
Comments:
8 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th); Solar and Stellar Astrophysics (astro-ph.SR)
arXiv:
1708.06163 [pdf]
PRC(2017)·29 citations
06
[Submitted on 21 Aug 2017]
Calculations of antiproton-nucleus quasi-bound states using the Paris $N ˉ N$ potential
Jaroslava Hrtánková🇨🇿 · Jiří Mareš🇨🇿
An optical potential constructed using the $p ˉ N$ scattering amplitudes derived from the 2009 version of the Paris $N ˉ N$ potential is applied in calculations of $p ˉ$ quasi-bound states in selected nuclei across the periodic table. A proper self-consistent procedure for treating energy dependence of the amplitudes in a nucleus appears crucial for evaluating $p ˉ$ binding energies and widths. Particular attention is paid to the role of $P$ -wave amplitudes. While the $P$ -wave potential nearly does not affect calculated $p ˉ$ binding energies, it reduces considerably the corresponding widths. The Paris $S$ -wave potential supplemented by a phenomenological $P$ -wave term yields in dynamical calculations $p ˉ$ binding energies $B_{p ˉ} \approx 200$ MeV and widths $Γ_{p ˉ} \sim 200 - 230$ MeV, which is very close to the values obtained within the RMF model consistent with $p ˉ$ -atom data.
Comments:
19 pages, 10 figures, 2 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1708.06204 [pdf]
NPA(2018)·7 citations
07
[Submitted on 21 Aug 2017]
Partial dynamical symmetries and shape coexistence in nuclei
A. Leviatan · N. Gavrielov
We present a symmetry-based approach for shape coexistence in nuclei, founded on the concept of partial dynamical symmetry (PDS). The latter corresponds to a situation when only selected states (or bands of states) of the coexisting configurations preserve the symmetry while other states are mixed. We construct explicitly critical-point Hamiltonians with two or three PDSs of the type U(5), SU(3), $SU (3)$ and SO(6), appropriate to double or triple coexistence of spherical, prolate, oblate and $γ$ -soft deformed shapes, respectively. In each case, we analyze the topology of the energy surface with multiple minima and corresponding normal modes. Characteristic features and symmetry attributes of the quantum spectra and wave functions are discussed. Analytic expressions for quadrupole moments and $E 2$ rates involving the remaining solvable states are derived and isomeric states are identified by means of selection rules.
Comments:
25 pages, 14 figures, accepted for publication as a Special Issue on "Shapes and Symmetries in Nuclei: From Experiment to Theory" in Physica Scripta
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex); Quantum Physics (quant-ph)
arXiv:
1708.06321 [pdf]
Phys.Scripta(2017)·17 citations
08
[Submitted on 18 Aug 2017] (cross-list from nucl-ex)
Photoproduction prospects at the EIC
Heikki Mäntysaari🇺🇸
We discuss how photoproduction and electroproduction processes will provide a precise tool to study nuclear structure in the small- $x$ region in the future Electron-Ion Collider. In particular, we emphasize how exclusive vector meson production at the EIC can be used to accurately map the gluonic density profile of nuclei, including its event-by-event fluctuations. In addition, we show how measurements of the total diffractive cross section will be sensitive to saturation effects.
Comments:
5 pages, 6 figures. Invited talk at the Photon 2017 conference
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1708.05756 [pdf]
CERN Proc.(2018)·1 citation
09
[Submitted on 18 Aug 2017] (cross-list from hep-ph)
On the absorption and production cross sections of $K$ and $K^{*}$
A. Martinez Torres🇧🇷 · K. P. Khemchandani🇧🇷 · L. M. Abreu🇧🇷 · F. S. Navarra🇧🇷 · M. Nielsen🇧🇷
We have computed the isospin and spin averaged cross sections of the processes $π K^{*} \to ρ K$ and $ρ K^{*} \to π K$ , which are crucial in the determination of the abundances of $K^{*}$ and $K$ in heavy ion collisions. Improving previous calculations, we have considered several mechanisms which were missing, such as the exchange of axial and vector resonances ( $K_{1} (1270)$ , $K_{2}^{*} (1430)$ , $h_{1} (1170)$ , etc...) and also other processes such as $π K^{*} \to ω K, ϕ K$ and $ω K^{*}, ϕ K^{*} \to π K$ . We find that some of these mechanisms give important contributions to the cross section. Our results also suggest that, in a hadron gas, $K^{*}$ production might be more important than its absorption.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1708.05784 [pdf]
PRD(2018)·10 citations
10
[Submitted on 19 Aug 2017] (cross-list from hep-ph)
Dependencies of Lepton Angular Distribution Coefficients on the Transverse Momentum and Rapidity of $Z$ Bosons Produced in $pp$ Collisions at LHC
Wen-Chen Chang🇹🇼 · Randall Evan McClellan🇺🇸 · Jen-Chieh Peng🇺🇸 · Oleg Teryaev🇷🇺
High precision data of lepton angular distributions for $γ^{*} / Z$ production in $pp$ collisions at the LHC, covering broad ranges of dilepton transverse momenta ( $q_{T}$ ) and rapidity ( $y$ ), were recently reported. Strong $q_{T}$ dependencies were observed for several angular distribution coefficients, $A_{i}$ , including $A_{0} - A_{4}$ . Significant $y$ dependencies were also found for the coefficients $A_{1}$ , $A_{3}$ and $A_{4}$ , while $A_{0}$ and $A_{2}$ exhibit very weak rapidity dependence. Using an intuitive geometric picture we show that the $q_{T}$ and $y$ dependencies of the angular distributions coefficients can be well described.
Comments:
9 pages, 9 figures, some typos corrected
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1708.05807 [pdf]
PRD(2017)·17 citations
11
[Submitted on 20 Aug 2017] (cross-list from gr-qc)
Non-radial Oscillation Modes of Compact Stars with a Crust
C. Vasquez Flores🇧🇷 · Zack B. Hall II🇺🇸 · Prashanth Jaikumar🇺🇸
Oscillation modes of isolated compact stars can, in principle, be a fingerprint of the equation of state (EoS) of dense matter. We study the non-radial high-frequency l=2 spheroidal modes of neutron stars and strange quark stars, adopting a two-component model (core and crust) for these two types of stars. Using perturbed fluid equations in the relativistic Cowling approximation, we explore the effect of a strangelet or hadronic crust on the oscillation modes of strange stars. The results differ from the case of neutron stars with a crust. In comparison to fluid-only configurations, we find that a solid crust on top of a neutron star increases the p-mode frequency slightly with little effect on the f-mode frequency, whereas for strange stars, a strangelet crust on top of a quark core significantly increases the f-mode frequency with little effect on the p-mode frequency.
Comments:
10 pages, 6 figures
Subjects:
General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
1708.05985 [pdf]
PRC(2017)·50 citations
12
[Submitted on 20 Aug 2017] (cross-list from hep-ph)
Fermi Liquid Model for Hadrons in Medium
A. Bhattacharya🇮🇳 · S. Pal🇮🇳 · R. Ghosh🇮🇳 · B.Chakrabarti🇮🇳
A Fermi liquid model for hadrons has been suggested for the hadrons in medium. The hadrons are supposed to behave like quasi particle as Fermi excitation while in the medium and the effective mass of the hadrons have been estimated using Fermi liquid model. Considering a momentum dependent potential inside the medium to describe the interaction, the effective masses of the hadrons are estimated. The temperature dependence of effective masses has also been studied. The possibility of describing masses of the quarks as Fermi excitation has been investigated. Compressibility, specific heats, density of states in medium has been studied. The potential depth for light and singly heavy baryons in medium has been extracted. The results are found to be very interesting and compared with the other studies available in literature.
Comments:
18 pages, 14 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1708.05995 [pdf]
0 citations
13
[Submitted on 18 Aug 2017] (cross-list from gr-qc)
Causality and existence of solutions of relativistic viscous fluid dynamics with gravity
Fabio S. Bemfica (Rio Grande do Norte U.)🇧🇷 · Marcelo M. Disconzi (Vanderbilt U.)🇺🇸 · Jorge Noronha (Sao Paulo U.)🇧🇷
A new approach is described to help improve the foundations of relativistic viscous fluid dynamics and its coupling to general relativity. Focusing on neutral conformal fluids constructed solely in terms of hydrodynamic variables, we derive the most general viscous energy-momentum tensor yielding equations of motion of second order in the derivatives, which is shown to provide a novel type of generalization of the relativistic Navier-Stokes equations for which causality holds. We show how this energy-momentum tensor may be derived from conformal kinetic theory. We rigorously prove existence, uniqueness, and causality of solutions of this theory (in the full nonlinear regime) both in a Minkowski background and also when the fluid is dynamically coupled to Einstein's equations. Linearized disturbances around equilibrium in Minkowski spacetime are stable in this causal theory. A numerical study reveals the presence of an out-of-equilibrium hydrodynamic attractor for a rapidly expanding fluid. Further properties are also studied and a brief discussion of how this approach can be generalized to non-conformal fluids is presented.
Comments:
33 pages, 5 figures. Substantial improvements were made: the new conformal tensor is now derived from kinetic theory; the causality and well-posedness theorems now hold under more general conditions on the transport coefficients; further discussion and applications have also been included; new references were added
Subjects:
General Relativity and Quantum Cosmology (gr-qc); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Mathematical Physics (math-ph); math.MP (math.MP); Nuclear Theory (nucl-th)
arXiv:
1708.06255 [pdf]
PRD(2018)·285 citations

Affiliations

first authorsco-authorsvia INSPIRE