Nuclear Theory·nucl-th

Monday·November 25, 2019

8 papers—4 primary·4 cross-listed

01
Low-energy isoscalar dipole response of heavy nuclei within kinetic model
V.I.Abrosimov · O.I.Davydovska
The low-energy isoscalar dipole response of heavy spherical nuclei is studied by using a semiclassical model, based on the solution of the linearized Vlasov kinetic equation for finite Fermi systems. In this translation-invariant model the excitations of the center of mass motion are exactly separated from the internal ones. The low-energy dipole strength function displays three resonance structures in the energy region up to 15 MeV. Calculations of the velocity fields associated with the resonance structures at the centroid energies show a vortex (toroidal) character of two overlying resonances, while the origin of the lowest isoscalar dipole resonance structure is related to the dipole single-particle excitations. Its centroid energy is close to the minimum energy of the dipole single-particle spectrum. The main toroidal resonance gives a qualitative description of the low-energy isoscalar dipole resonance observed in heavy spherical nuclei.
nucl-th0 citations
02
Quenching factor of Gamow-Teller and spin dipole giant resonances
Li-Gang Cao · Shi-Sheng Zhang · H. Sagawa
Gamow-Teller (GT) and spin-dipole (SD) strength distributions of four doubly magic nuclei $^{48}$ Ca, $^{90}$ Zr, $^{132}$ Sn and $^{208}$ Pb are studied by the self-consistent Hartree-Fock plus random phase approximation (RPA) method. The Skyrme forces SAMi and SAMi-T without/with tensor interactions are adopted in our calculations. The calculated strengths are compared with available experimental data. The RPA results of GT and SD strengths of all four nuclei show fine agreement with observed GT and SD resonances in energy. A small GT peak below the main GT resonance is better described by the Skyrme interaction SAMi-T with the tensor terms. The quenching factors for GT and SD are extracted from the comparisons between RPA results and experimental strengths. It is pointed out that the quenching effect on experimental SD peaks is somewhat modest compared with that on GT peaks in the four nuclei.
nucl-thPRC(2019)·15 citations
03
An approximation to the Woods-Saxon potential based on a contact interaction
C. Romaniega🇪🇸 · M. Gadella🇪🇸 · R. M. Id Betan🇦🇷 · L. M. Nieto🇪🇸
We study a non-relativistic particle subject to a three-dimensional spherical potential consisting of a finite well and a radial $δ$ - $δ^{'}$ contact interaction at the well edge. This contact potential is defined by appropriate matching conditions for the radial functions, thereby fixing a self adjoint extension of the non-singular Hamiltonian. Since this model admits exact solutions for the wave function, we are able to characterize and calculate the number of bound states. We also extend some well-known properties of certain spherically symmetric potentials and describe the resonances, defined as unstable quantum states. Based on the Woods-Saxon potential, this configuration is implemented as a first approximation for a mean-field nuclear model. The results derived are tested with experimental and numerical data in the double magic nuclei $^{132}$ Sn and $^{208}$ Pb with an extra neutron.
nucl-thquant-phEur.Phys.J.Plus(2020)·8 citations
04
Influence of resonances on the $^{11}$ B(n,gamma) $^{12}$ B capture reaction rate. III. Capture to the 2nd, 3rd and 4th excited state of $^{12}$ B
S.B. Dubovichenko · N.A. Burkova · A.V. Dzhazairov-Kakhramanov
Within the framework of the modified potential cluster model with a classification of orbital states according to Young diagrams, the possibility of data description of the radiative neutron capture on 11B to the second excited state of 12B at 1.67365 MeV (2-) and prediction absentee of experimental data for the total cross sections to the third and fourth excited state of 12B at 2.6208 MeV (1-) and 2.723 MeV (0+) for reaction energy of 10 meV (1 meV = 10-3 eV) to 7 MeV was considered. The reaction rate in the temperature range of 0.01 to 10.0 T9 is calculated on the basis of obtained cross sections, which take into account resonances up to 5 MeV. It is shown, that low-lying resonances exercise a significant influence to the capture reaction rate. The approximation of the calculation reaction rate is carried out by the simple analytic formula.
nucl-th1 citation
05
Spectral swaps in a two-dimensional neutrino ring model
Joshua D. Martin🇺🇸 · J. Carlson🇺🇸 · Huaiyu Duan🇺🇸
Neutrinos emitted deep within a supernova explosion experience a self-induced index of refraction. In the stationary, one-dimensional (1D) supernova "bulb model", this self-induced refraction can lead to a collective flavor transformation which is coherent among different neutrino momentum modes. Such collective oscillations can produce partial swaps of the energy spectra of different neutrino species as the neutrinos stream away from the proto-neutron star. However, it has been demonstrated that the spatial symmetries (such as the spherical symmetry in the bulb model) can be broken spontaneously by collective neutrino oscillations in multi-dimensional models. Using a stationary, 2D neutrino ring model we demonstrate that there exist two limiting scenarios where collective oscillations may occur. In one limit, the collective flavor transformation begins at a radius with relatively high neutrino densities and develops small-scale flavor structures. The loss of the spatial correlation in the neutrino flavor field results in similar (average) energy spectra for the anti-neutrinos of almost all energies and the neutrinos of relatively high energies. In the other limit, the flavor transformation starts at a radius where the neutrino densities are smaller (e.g., due to the suppression of the high matter density near the proto-neutron star). Although the spatial symmetry is broken initially, it is restored as the neutrino densities decrease, and the neutrinos of different flavors partially swap their energy spectra as in the 1D bulb model. This finding may have interesting ramifications in other aspects of supernova physics.
↳ hep-phastro-ph.HEnucl-thPRD(2020)·22 citations
06
Quark fluctuations and anisotropic confinement in magnetic fields
Gaoqing Cao🇨🇳 · Toru Kojo🇨🇳
We study the string tension $σ$ of quantum chromodynamics (QCD) in external magnetic fields $B$ by combining the quasi-particle treatments for quarks with the collective treatments for gluons. We utilize the 1/Nc-expansion (Nc: number of colors) and the framework of Wilson's strong coupling expansion at long distance, and compare the resulting string tensions with the lattice data. The effects of magnetic fields are taken into account through the dielectric functions, which are evaluated from the one-loop polarization due to light flavor quarks with $B$ -dependent effective masses $M_{f} (B) (f = u, d, s)$ . All Landau levels are adopted in the calculations so that we can explore the string tensions from weak to strong magnetic fields. For the effective quark masses, we use a simple parameterization: $M_{f} (B) = M_{f} (0) + C_{B} ∣ q_{f} B ∣^{1/2}$ with $q_{f}$ the electric charge of a given flavor and $C_{B}$ an adaptive parameter. We find that the parameter $C_{B}$ needs to be small, $C_{B} ≲ 0.05$ , to qualitatively reproduce the trends of lattice QCD results for $0 \leq ∣ e B ∣ ≲ 1.5 GeV^{2}$ . The quantitative agreement is found for $C_{B} ≃ 0$ and the strong coupling $α_{S} ≃ 5$ in the infrared.
↳ hep-phhep-lathep-thnucl-th3 citations
07
Tetraquark mixing framework to explain two light-meson nonets
Hungchong Kim🇰🇷
In this talk, we summarize our recent works on the tetraquark mixing framework for the two light-meson nonets in the $J^{P C} = 0^{++}$ channel, the light nonet [ $a_{0} (980)$ , $K_{0}^{*} (700)$ , $f_{0} (500)$ , $f_{0} (980)$ ] and the heavy nonet [ $a_{0} (1450)$ , $K_{0}^{*} (1430)$ , $f_{0} (1370)$ , $f_{0} (1500)$ ]. We briefly explain this mixing framework and present various phenomenological signatures to support this picture.
↳ hep-phhep-exnucl-th3 citations
08
Anisotropic electrical conductivity of magnetized hot quark matter
Sabyasachi Ghosh🇮🇳 · Aritra Bandyopadhyay🇧🇷 · Ricardo L. S. Farias🇧🇷 · Jayanta Dey🇮🇳 · Gastão Krein🇧🇷
We studied the effect of a strong magnetic field ( $B$ ) on the electrical conductivity of hot quark matter. The electrical conductivity is a key transport coefficient determining the time dependence and strength of magnetic fields generated in a relativistic heavy-ion collision. A~magnetic field induces Hall anisotropic conduction, phase-space Landau-level quantization and, if sufficiently strong, interferes with prominent QCD phenomena such as dynamical quark mass generation, likely affecting the quark matter electrical conductivity, which depends strongly on the quark masses. To address these issues, we used a quasi-particle description of quark matter in which the electric charge carriers are constituent quarks with temperature- and magnetic-field-dependent masses predicted by a Nambu--Jona-Lasinio model. The model accurately describes recent lattice QCD results showing magnetic catalysis at low temperatures and inverse magnetic catalysis at temperatures close to the pseudo-critical temperature ( $T_{pc}$ ) of the QCD phase transition. We found that the magnetic field increases the conductivity component parallel to it and decreases the transverse component, in qualitative agreement with recent lattice QCD results. In addition, we found that: (1)~the space anisotropy of the conductivity increases with~ $B$ , (2)~the longitudinal conductivity increases due to phase-space Landau-level quantization, (3)~a lowest Landau level approximation behaves poorly for temperatures close to $T_{pc}$ , and (5)~inverse magnetic catalysis leaves a distinctive signal in all components of the conductivity, a prominent peak at $T_{pc}$ . Our study adds to the existing body of work on the hot quark matter electrical conductivity by incorporating nontrivial temperature and magnetic field effects on dynamical mass generation.
↳ hep-phnucl-thPRD(2020)·49 citations

Affiliations

first authorsco-authorsvia INSPIRE