Nuclear Theory·nucl-th

Tuesday·October 10, 2017

20 papers—11 primary·9 cross-listed

01
$^{6}$ Li in a Three-Body Model with Realistic Forces: Separable vs. Non-separable Approach
L. Hlophe🇺🇸 · Jin Lei🇺🇸 · Ch. Elster🇺🇸 · A. Nogga🇩🇪 · F.M. Nunes🇺🇸
{\bf Background:} Deuteron induced reactions are widely used to probe nuclear structure and astrophysical information. Those (d,p) reactions may be viewed as three-body reactions and described with Faddeev techniques. {\bf Purpose:} Faddeev equations in momentum space have a long tradition of utilizing separable interactions in order to arrive at sets of coupled integral equations in one variable. However, it needs to be demonstrated that their solution based on separable interactions agrees exactly with solutions based on non-separable forces. {\bf Results:} The ground state of $^{6}$ Li is calculated via momentum space Faddeev equations using the CD-Bonn neutron-proton force and a Woods-Saxon type neutron(proton)- $^{4}$ He force. For the latter the Pauli-forbidden $S$ -wave bound state is projected out. This result is compared to a calculation in which the interactions in the two-body subsystems are represented by separable interactions derived in the Ernst-Shakin-Thaler framework. {\bf Conclusions:} We find that calculations based on the separable representation of the interactions and the original interactions give results that agree to four significant figures for the binding energy, provided an off-shell extension of the EST representation is employed in both subsystems. The momentum distributions computed in both approaches also fully agree with each other.
nucl-thPRC(2017)·14 citations
02
$α$ -cluster states in $^{46, 54}$ Cr from double-folding potentials
Peter Mohr
$α$ --cluster states in $^{46}$ Cr and $^{54}$ Cr are investigated in the double-folding model. This study complements a recent similar work of Souza and Miyake \cite{Sou17} which was based on a specially shaped potential. Excitation energies, reduced widths, intercluster separations, and intra-band transition strengths are calculated and compared to experimental values for the ground state bands in $^{46}$ Cr and $^{54}$ Cr. The $α$ -cluster potential is also applied to elastic scattering at low and intermediate energies. Here, as a byproduct, a larger radial extent of the neutron density in $^{50}$ Ti is found.
nucl-thEPJA(2017)·14 citations
03
The ratios between the moments of inertia of triaxial nuclei: Comment on the Physical Review C 95, 064315 (2017)
S. Frauendorf
The instability of transverse wobbling claim is disputed.
nucl-th1 citation
04
Nuclear Axial Currents from Scale-Chiral Effective Field Theory
Yan-Ling Li🇨🇳 · Yong-Liang Ma🇨🇳 · Mannque Rho🇫🇷
By incorporating hidden scale symmetry and hidden local symmetry in nuclear effective field theory, combined with double soft-pion theorem, we predict that the Gamow-Teller operator coming from the space component of the axial current should remain unaffected by the QCD vacuum change caused by baryonic density whereas the first forbidden beta transition operator coming from the time component should be strongly enhanced. While the latter has been confirmed since some time, the former is given a support by a powerful recent {\it ab initio} quantum Monte Carlo calculation in light nuclei, also confirming the old "chiral filter hypothesis." Formulated in terms of Fermi-liquid fixed point structure of strong-coupled nuclear interactions, we offer an extremely simple resolution to the long-standing puzzle of "quenched $g_{A}$ ", $g_{A}^{eff} \approx 1$ ~\cite{quenched}, in nuclear Gamow-Teller beta transitions, giant Gamow-Teller resonances and double beta decays.
nucl-thhep-phCPC(2018)·13 citations
05
Level density of the $s d$ -nuclei $-$ statistical shell-model predictions
S. Karampagia · R. A. Senkov · V. Zelevinsky
Accurate knowledge of the nuclear level density is important both from a theoretical viewpoint as a powerful instrument for studying nuclear structure and for numerous applications. For example, astrophysical reactions responsible for the nucleosynthesis in the universe can be understood only if we know the nuclear level density. We use the configuration-interaction nuclear shell model to predict nuclear level density for all nuclei in the $s d$ -shell, both total and for individual spins (only with positive parity). To avoid the diagonalization in large model spaces we use the moments method based on statistical properties of nuclear many-body systems. In the cases where the diagonalization is possible, the results of the moments method practically coincide with those from the shell-model calculations. Using the computed level densities, we fit the parameters of the Constant Temperature phenomenological model, which can be used by practitioners in their studies of nuclear reactions at excitation energies appropriate for the $s d$ -shell nuclei.
nucl-thAtom.Data Nucl.Data Tabl.(2018)·13 citations
06
Green's function method for the single-particle resonances in a deformed Dirac equation
T.-T. Sun · L. Qian · C. Chen · P. Ring · Z. P. Li
Single-particle resonances are crucial for exotic nuclei near and beyond the drip lines. Since the majority of nuclei are deformed, the interplay between deformation and orbital structure near threshold becomes very important and can lead to an improved description of exotic nuclei. In this work, the Green's function (GF) method is applied to solve the coupled-channel Dirac equation with quadrupole-deformed Woods-Saxon potentials for the first time. The detailed formalism for the partial-wave expansion of the Green's function is presented. A new approach getting exact values for energies and widths of resonant states by the GF method is proposed. Numerical checks are carried out by comparing with our previous implementation of the spherical GF method and the results from the deformed complex momentum representation~(CMR), the analytical continuation of the coupling constant (ACCC), and the scattering phase shift (SPS) methods, and it is proved that the GF method is very effective and reliably for describing resonance states, no matter they are narrow or broad, spherical or deformed. Finally, Nilsson levels for bound and resonant orbitals in the halo candidate nucleus $^{37}$ Mg are calculated from the deformed GF method over a wide range of deformations and some decisive hints of $p$ -wave halo formation are shown in this nucleus, namely, the crossing between the configurations $1/2 [321]$ and $5/2 [312]$ at deformation parameter $β > 0.5$ may enhance the probability to occupy the $1/2 [321]$ orbital that is originated from the $2 p_{3/2}$ shell.
nucl-thPRC(2020)·32 citations
07
$α$ decay properties of nucleus $^{297}$ Og within two-potential approach
Jun-Gang Deng · Jun-Hao Cheng · Bo Zheng · Xiao-Hua Li
The $α$ decay half-life of unknown nucleus $^{297}$ Og is predicted within two-potential approach, and $α$ preformation probabilities of 64 odd- $A$ nuclei in the region of proton numbers $82 < Z < 126$ and neutron numbers $152 < N < 184$ from $^{251}$ Cf to $^{295}$ Og are extracted. In addition, based on the latest experimental data, a new set of parameters for $α$ preformation probabilities considering the shell effect and proton-neutron interaction are obtained. The predicted $α$ decay half-life of $^{297}$ Og is 0.16 ms within a factor of 4.97 as well as the spin and parity of ground states for nuclei $^{269}$ Sg, $^{285}$ Fl and $^{293}$ Lv are $3/ 2^{+}$ , $3/ 2^{+}$ and $5/ 2^{+}$ , respectively.
nucl-thnucl-exCPC(2017)·26 citations
08
Effects of initial-state dynamics on collective flow within a coupled transport and viscous hydrodynamic approach
Chandrodoy Chattopadhyay🇮🇳 · Rajeev S. Bhalerao🇮🇳 · Jean-Yves Ollitrault🇫🇷 · Subrata Pal🇮🇳
We evaluate the effects of preequilibrium dynamics on observables in ultrarelativistic heavy-ion collisions. We simulate the initial nonequilibrium phase within A MultiPhase Transport (AMPT) model, while the subsequent near-equilibrium evolution is modeled using (2+1)-dimensional relativistic viscous hydrodynamics. We match the two stages of evolution carefully by calculating the full energy-momentum tensor from AMPT and using it as input for the hydrodynamic evolution. We find that when the preequilibrium evolution is taken into account, final-state observables are insensitive to the switching time from AMPT to hydrodynamics. Unlike some earlier treatments of preequilibrium dynamics, we do not find the initial shear viscous tensor to be large. With a shear viscosity to entropy density ratio of $0.12$ , our model describes quantitatively a large set of experimental data on Pb+Pb collisions at the Large Hadron Collider(LHC) over a wide range of centrality: differential anisotropic flow $v_{n} (p_{T}) (n = 2 - 6)$ , event-plane correlations, correlation between $v_{2}$ and $v_{3}$ , and cumulant ratio $v_{2} {4} / v_{2} {2}$ .
nucl-thhep-phnucl-exPRC(2018)·21 citations
09
Importance of isobar density distributions on the chiral magnetic effect search
Hao-jie Xu🇨🇳 · Xiaobao Wang🇨🇳 · Hanlin Li🇨🇳 · Jie Zhao🇺🇸 · Zi-Wei Lin🇺🇸 · Caiwan Shen🇨🇳 · Fuqiang Wang🇨🇳
Under the approximate chiral symmetry restoration, quark interactions with topological gluon fields in quantum chromodynamics can induce chirality imbalance and parity violation in local domains. An electric charge separation ({\sc cs}) could be generated along the direction of a strong magnetic field ({\bf B}), a phenomenon called the chiral magnetic effect ({\sc cme}). {\sc cs} measurements by azimuthal correlators are contaminated by a major background from elliptic flow anisotropy ( $v_{2}$ ). Isobaric $_{44}^{96}$ Ru+ $_{44}^{96}$ Ru and $_{40}^{96}$ Zr+ $_{40}^{96}$ Zr collisions have been proposed to identify the {\sc cme} (expected to differ between the two systems) out of the background (expected to be almost the same). We show, by using the density-functional calculated proton and neutron distributions, that these expectations may not hold as originally anticipated, because the two systems may have sizable differences in eccentricity and $v_{2}$ and because their difference in {\bf B} may suffer from large uncertainties.
nucl-thnucl-exPRL(2018)·110 citations
10
Hubbard-Stratonovich-like Transformations for Few-Body Interactions
Christopher Körber · Evan Berkowitz · Thomas Luu
Through the development of many-body methodology and algorithms, it has become possible to describe quantum systems composed of a large number of particles with great accuracy. Essential to all these methods is the application of auxiliary fields via the Hubbard-Stratonovich transformation. This transformation effectively reduces two-body interactions to interactions of one particle with the auxiliary field, thereby improving the computational scaling of the respective algorithms. The relevance of collective phenomena and interactions grows with the number of particles. For many theories, e.g. Chiral Perturbation Theory, the inclusion of three-body forces has become essential in order to further increase the accuracy on the many-body level. In this proceeding, the analytical framework for establishing a Hubbard-Stratonovich-like transformation, which allows for the systematic and controlled inclusion of contact three- and more-body interactions, is presented.
nucl-thEPJ Web Conf.(2018)·2 citations
11
Transition sum rules in the shell model
Yi Lu · Calvin W. Johnson
An important characterization of electromagnetic and weak transitions in atomic nuclei are sum rules. We focus on the non-energy-weighted sum rule (NEWSR), or total strength, and the energy-weighted sum rule (EWSR); the ratio of the EWSR to the NEWSR is the centroid or average energy of transition strengths from an nuclear initial state to all allowed final states. These sum rules can be expressed as expectation values of operators, in the case of the EWSR a double commutator. While most prior applications of the double-commutator have been to special cases, we derive general formulas for matrix elements of both operators in a shell model framework (occupation space), given the input matrix elements for the nuclear Hamiltonian and for the transition operator. With these new formulas, we easily evaluate centroids of transition strength functions, with no need to calculate daughter states. We apply this simple tool to a number of nuclides, and demonstrate the sum rules follow smooth secular behavior as a function of initial energy, as well as compare the electric dipole (E1) sum rule against the famous Thomas-Reiche-Kuhn version. We also find surprising systematic behaviors for ground state electric quadrupole (E2) centroids in the $s d$ -shell.
nucl-thPRC(2018)·16 citations

Affiliations

first authorsco-authorsvia INSPIRE