Tensor Force Research Articles

Current-induced shuttlecock-like movement of non-axisymmetric chiral skyrmions

Current-induced motion of non-axisymmetric skyrmions within tilted ferromagnetic phases of polar helimagnets with the easy plane anisotropy is studied by micromagnetic simulations. Such non-axisymmetric skyrmions consist of a circular core and a crescent-shaped domain-wall region formed with respect to the tilted surrounding state. Current-driven motion of non-axisymmetric skyrmions exhibits two distinct time regimes: initially the skyrmions rotate towards the current flow direction and subsequently move along the current with the skyrmionic crescent first. According to the Thiele equation, the asymmetric distribution of the topological charge and the dissipative force tensor play an important role for giving the different velocities for the circular and the crescent-shaped constituent parts of the skyrmion what underlies such a shuttlecock-like movement. Moreover, the current-velocity relation depends on the angle of the tilted ferromagnetic phase what makes in particular the transverse velocity of skyrmions sensitive to their field-driven configurational transformation. We also argue the possibility of magnetic racetrack waveguides based on complex interplay of robust asymmetric skyrmions with multiple twisted edge states.

Sensitivity of nuclear matrix elements of 0νββ of Ca48 to different components of the two-nucleon interaction

In the present work, we examine the sensitivity of nuclear matrix elements (NMEs) for light neutrino-exchange mechanism of neutrinoless double beta decay ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) of $^{48}\mathrm{Ca}$ to the central, spin-orbit, and tensor components of two-nucleon interaction. The NMEs are calculated in the nuclear shell-model framework in $fp$-model space using frequently used GXPF1A interaction and a new effective interaction named GX1R of $pf$ shell. The decomposition of the shell-model two-nucleon interactions into their individual components is performed using spin-tensor decomposition. The NMEs are calculated in closure approximation by using optimal value of the closure energy. The results shows that the total NMEs calculated with the central component of the interactions are of positive sign. By adding spin-orbit part to central part of the interactions, sign of the total NMEs gets change, and in absolute value, NMEs decreases by about $15\text{--}18%$. Sign change in total NMEs are again seen by adding tensor part to the $\text{central}+\text{spin}\ensuremath{-}\text{orbit}$ part of the interactions. Similar trends of sign change are also observed for Fermi, Gamow-Teller, and tensor matrix elements. Thus we infer that SO and T part mostly cancel the effects of each other in NMEs calculations. For both the interactions, the total NMEs calculated with the C part is found to be $20%$ enhanced as compared to the NMEs calculated with the total interactions. With new GX1R interaction, there is about $1\text{--}3%$ increments in the total NMEs as compared to NMEs with GXPF1A interaction. This increments comes from the modifications of isospin $T=1$ tensor force two-nucleon matrix elements to bring the characteristic properties of tensor force into the GX1R interaction.

Breakdown of the tensor component in the Skyrme energy density functional

The tensor force, as an important component of strong nuclear force, generates a variety of intriguing effects ranging from few-body systems to neutron stars. It is responsible for the nucleon-nucleon correlation beyond mean-field approximation, and is accordingly proved to play no role in the standard Skyrme energy density functionals in the present work. Therefore, the Skyrme's original tensor interaction that is extensively-employed presently is invalid. As an alternative strategy, we introduced a central interaction, i.e., the $\bm{\sigma }_{1}\cdot \bm{\sigma }_{2}$ term, to improve the description of experimental single-particle structure, and to address its effect, we established two Skyrme interactions IMP1 and IMP2 complemented by the calibrated charge-violating interactions. The central $\bm{\sigma }_{1}\cdot \bm{\sigma }_{2}$ interaction turns out to substantially improve the description of shell evolution in Sn isotopes and $N=82$ isotones.

Properties of exotic nuclei and their linkage to the nucleonic interaction

The structure of exotic nuclei sheds new light on the linkage of the nuclear structure to the nucleonic interaction. The self-consistent mean-field (SCMF) theories are useful to investigate this linkage, which are applicable to many nuclei covering almost the whole range of the nuclear chart without artificial truncation of model space. For this purpose, it is desired to develop effective interaction for the SCMF calculations well connected to the bare nucleonic interaction. Focusing on ground-state properties, I show the results of SCMF calculations primarily with the Michigan-three-range-Yukawa (M3Y)-type semi-realistic interaction, M3Y-P6 and M3Y-P6a to be precise, and discuss in detail how the nucleonic interaction affects the structure of nuclei including those far off the [Formula: see text]-stability. The central channels of the effective interaction are examined by the properties of the infinite nuclear matter up to the spin dependence and the isospin dependence. While experimental information of the infinite matter is obtained by extrapolating systematic data on finite nuclei in principle, it is not easy to constrain the spin dependence and the isospin dependence without connection to the bare nucleonic interaction. The noncentral channels play important roles in the shell structure of the finite nuclei. The tensor force is demonstrated to affect [Formula: see text]- or [Formula: see text]-dependence of the shell structure and the magic numbers, on which the spin–isospin channel in the central force often acts cooperatively. By using the M3Y-P6 interaction, the prediction of magic numbers is given in a wide range of the nuclear chart, which is consistent with almost all the available data. In relation to the erosion of magic numbers in unstable nuclei, effects of the tensor force on the nuclear deformation are also argued, being opposite between nuclei at the [Formula: see text]- and the [Formula: see text]-closed magicities. Qualitatively consistent with the [Formula: see text]-force effect on the [Formula: see text]-splitting suggested from the chiral effective field theory, the density-dependent LS channel, which is newly introduced in M3Y-P6a, reproduces the observed kinks in the differential charge radii at the [Formula: see text]-closed magic numbers and predicts anti-kinks at the [Formula: see text]-closed magic numbers. The pairing correlation has significant effects on the halos near the neutron drip line. A new mechanism called “unpaired-particle haloing” is disclosed.

Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure

Study of the Shell Evolution Effect on the Nuclei around the 78Ni Core Structure

Strength of tensor forces from neutron drops in ab initio relativistic Brueckner-Hartree-Fock theory

CITATION: Wang, S., et al. 2019. Strength of tensor forces from neutron drops in ab initio relativistic Brueckner-Hartree-Fock theory. Physical Review C, 100(6):064319, doi:10.1103/PhysRevC.100.064319.

Electrohydrodynamics and boiling: Experiments, numerical calculation and modeling of Maxwell stress tensor and electric force acting on bubbles

Boiling dynamics on earth is heavily affected by gravity. The purpose of this work is to investigate the feasibility of a replacement of gravity when it lacks: an external electric field can promote an efficient and reliable bubble removal system for space applications. To this intent, different experiments running in normal gravity, reverse gravity and microgravity (via parabolic flights) have been performed. The experiments were executed in adiabatic conditions (injecting air through an orifice) and in quasi-static conditions. This option was chosen in order to investigate only the dynamics terms of momentum balance, neglecting, at this stage, all the terms involving heat and mass transfer (which are in turn promoted by the electric field, i.e.: electroconvection). An experimental electric force has been calculated, as the unbalanced component of the force balance, and, thanks to the FEM software COMSOL Multiphysics, compared to the numerical integration of Maxwell stress tensor. Furthermore, a simple model based on the electrohydrodynamics of an oblate ellipsoid (Landau and Lifšitz 1984) has been compared to the results of the three sets of experiments.

Influence of the tensor interaction on heavy-ion fusion cross sections

[Background] While the tensor interaction has been shown to significantly affect the nuclear structure of exotic nuclei, its influence on nuclear reactions has only recently been investigated. The primary reason for this neglect is the fact that most studies of nuclear dynamics do not include the tensor force at all in their models. Indeed, only a few Skyrme parametrizations consider the tensor interaction in parameter determination. With modern research facilities extending our ability to probe exotic nuclei, a correct description of nuclear dynamics and heavy-ion fusion is vital to both supporting and leading experimental efforts. [Method] Fusion cross sections are calculated using ion-ion potentials generated by the fully microscopic density-constrained time-dependent Hartree-Fock (DC-TDHF) method with the complete Skyrme tensor interaction. [Results] For light nuclei, the tensor force only slightly changes the sub-barrier fusion cross sections at very low energies. Heavier nuclei, however, begin to exhibit a substantial hindrance effect in the sub-barrier region. This effect is strongest in spin-unsaturated systems, though can manifest in other configurations as well. Static, ground state deformation effects of the tensor force can also affect cross sections by shifting the fusion barrier. [Conclusions] The tensor interaction has a measurable effect on the fusion cross sections of nuclei spanning the nuclear chart. The effect comes from both static effects present in the ground state and dynamic processes arising from the time evolution of the system. This motivates the development of a modern Skyrme parameter set that includes all time-odd and tensor terms and that studies moving forward should include the tensor force to ensure a more robust and complete description of nuclei.

Microscopic Characteristics of Field Compaction of Asphalt Mixture Using Discrete Element Method

Abstract To investigate microscopic characteristics of the field compaction of asphalt pavement, a three-dimensional (3D) compaction model of asphalt pavement considering morphological characteristics of aggregate and temperature effect was established by distributed load and time equivalence principles using Particle Flow Code in Three Dimensions (PFC3D). The microscopic parameters of hot asphalt mixture were determined with a dynamic modulus test based on the time–temperature superposition principle. Aggregate motion, contact force, and the evolutional mechanism of energy were monitored during the virtual compaction process. This indicated that the motion displacement, angle, and stress are positively associated with load direction. It is necessary to select the proper plane angle with the load direction to evaluate the 3D motion of the aggregate with the two-dimensional (2D) plane angle. During the compaction process, the contact compressive force is mainly produced between aggregates, and the evolution laws of contact force and stress tensor can be used to reasonably interpret the aggregate motion within the asphalt mixture. Additionally, the work of external force, kinetic energy, and strain energy can be employed to precisely demonstrate energy conversion for the developed compaction model. Indexes including motion displacement and angle, contact force, and energy can reflect the microscopic characteristics of asphalt mixture during field compaction. It is rational and feasible to analyze microscopic behavior of asphalt pavement with the proposed pavement compaction model using the discrete element method (DEM). The DEM is a significant tool of investigation of microscopic characteristics of asphalt pavement.

The structure of neutron-rich calcium isotopes studied by the shell model with realistic effective interactions * * Supported by National Natural Science Foundation of China (U1732138, 11605054,11505056, 11305108, 11790325, 11847315)

We study the structure of neutron-rich calcium isotopes in the shell model with realistic interactions. The CD-Bonn and Kuo-Brown (KB) interactions are used. As these interactions do not include the three-body force, their direct use leads to poor results. We tested whether the adjustment of the single particle energies (SPEs) would be sufficient to include the three-body correlations empirically. It turns out that the CD-Bonn interaction, after the adjustment of SPEs, gives good agreement with the experimental data for the energies and spectroscopy. For the KB interaction, both the SPEs and monopole terms require adjustments. Thus, the monopole problem is less serious for modern realistic interactions which include perturbations up to the third order. We also tested the effect of the non-central force on the shell structure. It is found that the effect of the tensor force in the CD-Bonn interaction is weaker than in the KB interaction.

The charge-dependent Bonn potentials with pseudovector pion-nucleon coupling * * Supported by National Natural Science Foundation of China (11775119, 11405116, 11675083)

In order to use high-precision realistic nucleon-nucleon (NN) potentials in relativistic many-body problems, new versions of the charge-dependent Bonn (CD-Bonn) NN potential are constructed with pseudovector pion-nucleon coupling, instead of pseudoscalar coupling used in the original CD-Bonn potential as given by Machleidt . To describe precisely the charge dependence in the NN scattering data, two effective scalar mesons are introduced, whose coupling constants with nucleons are independently determined for each partial wave and for the total angular momentum . The coupling constants between the vector and pseudovector mesons and a nucleon are identical in all channels. Three revised CD-Bonn potentials with the pseudovector pion-nucleon coupling (pvCD-Bonn) are generated by fitting the Nijmegen PWA phase shift data and the deuteron binding energy with different pion-nucleon coupling strengths. The potentials reproduce the phase shifts in the spin-single channels and the low-energyNNscattering parameters very well, but result in significantly different mixing parameters in the spin-triplet channels. The D-state probabilities for the deuteron range from 4.22% to 6.05%, demonstrating that the potentials contain different components of the tensor force, which is useful when considering the role of the tensor force in nuclear few- and many-body systems.

Tensor force effect on the exotic structure of neutron-rich Ca isotopes * * Supported by the National Natural Science Foundation of China (U1832120, 11675265), the State Scholarship Fund of China Scholarship Council (201708130035) and the Natural Science Foundation for Outstanding Young Scholars of Hebei Province of China (A2018210146)

The structure of neutron-rich Ca isotopes is studied in the spherical Skyrme-Hartree-Fock-Bogoliubov (SHFB) approach with SLy5, SLy5+T, and 36 sets of TIJ parametrizations. The calculated results are compared with the available experimental data for the average binding energies, two-neutron separation energies and charge radii. It is found that the SLy5+T, T31, and T32 parametrizations reproduce best the experimental properties, especially the neutron shell effects at N = 20, 28 and 32, and the recently measured two-neutron separation energy of 56Ca. The calculations with the SLy5+T and T31 parametrizations are extended to isotopes near the neutron drip line. The neutron giant halo structure in the very neutron-rich Ca isotopes is not seen with these two interactions. However, depleted neutron central densities are found in these nuclei. By analyzing the neutron mean-potential, the reason for the bubble-like structure formation is given.

Proton-neutron force and proton single-particle strength in Sc, F, and Li isotopes

In the present work, the effect of proton-neutron interaction and its different components, i.e., central, spin-orbit, and tensor force, on proton shell-structure of odd-$A$ Sc, F, and Li isotopes is studied within the nuclear shell model framework. It has been observed that the central force possesses strong-orbital node $(nl)$ and weak-spin $(j)$ dependency, and plays a key role in producing changes in proton shell-structure. The integrated effect of proton shell-structure and proton single-particle strength in building the level structure of $^{49,53,55}\mathrm{Sc}$, $^{23,25}\mathrm{F}$, and $^{9}\mathrm{Li}$ isotopes are also discussed. Proton single-particle strength in the level structure of above-mentioned nuclei is studied using proton-transfer spectroscopic factors. It has been particularly discerned that the low energy of the ${\frac{3}{2}}_{1}^{\ensuremath{-}}$ state of $^{55}\mathrm{Sc}$ is caused by the weakening of the $N=34$ semimagic gap, the high energy of the ${\frac{1}{2}}_{1}^{+}$ state of $^{23}\mathrm{F}$ is originated from an increase in the energy gap between orbitals $\ensuremath{\pi}1{s}_{1/2}$ and $\ensuremath{\pi}0{d}_{5/2}$ at $N=14$, and the high energy of the ${\frac{1}{2}}_{1}^{\ensuremath{-}}$ state of $^{9}\mathrm{Li}$ is originated from the large energy gap between $\ensuremath{\pi}0{p}_{1/2}$ and $\ensuremath{\pi}0{p}_{3/2}$ orbitals which remained nearly constant from $^{5}\mathrm{Li}$ to $^{9}\mathrm{Li}$.

Restoration of pseudo-spin symmetry in N = 32 and N = 34 isotonesdescribed by relativistic Hartree-Fock theory * * Supported by National Natural Science Foundation of China (11675065, 11711540016)

The restoration of pseudo-spin symmetry (PSS) along the and N = isotonic chains and the physics behind are studied by applying the relativistic Hartree-Fock theory with the effective Lagrangian PKA1. Taking the proton pseudo-spin partners as candidates, the systematic restoration of PSS along both isotonic chains is found from sulphur (S) to nickel (Ni), while an obvious PSS violation from silicon (Si) to sulphur is discovered near the drip lines. The effects of the tensor force components are investigated, introduced naturally by the Fock terms, which can only partially interpret the systematics from calcium to nickel, whereas they fail for the overall trends. Further analysis following the Schrödinger-like equation of the lower component of Dirac spinor shows that contributions from the Hartree terms dominate the overall systematics of the PSS restoration. Such effects can be self-consistently interpreted by the evolution of the proton central density profiles along both isotonic chains. In particular, the PSS violation is found to tightly relate to the dramatic changes from the bubble-like density profiles in silicon to the central-bumped ones in sulphur.

Proton Shell Evolution below Sn132 : First Measurement of Low-Lying β -Emitting Isomers in Ag123,125

The β-delayed γ-ray spectroscopy of neutron-rich ^{123,125}Ag isotopes is investigated at the Radioactive Isotope Beam Factory of RIKEN, and the long-predicted 1/2^{-} β-emitting isomers in ^{123,125}Ag are identified for the first time. With the new experimental results, the systematic trend of energy spacing between the lowest 9/2^{+} and 1/2^{-} levels is extended in Ag isotopes up to N=78, providing a clear signal for the reduction of the Z=40 subshell gap in Ag towards N=82. Shell-model calculations with the state-of-the-art V_{MU} plus M3Y spin-orbit interaction give a satisfactory description of the low-lying states in ^{123,125}Ag. The tensor force is found to play a crucial role in the evolution of the size of the Z=40 subshell gap. The observed inversion of the single-particle levels around ^{123}Ag can be well interpreted in terms of the monopole shift of the π1g_{9/2} orbitals mainly caused by the increasing occupation of ν1h_{11/2} orbitals.

Current-induced motion of twisted skyrmions

Twisted skyrmions, whose helicity angles are different from those of Bloch and Néel skyrmions, have recently been demonstrated in experiments. In this work, we first discuss the origin and the topological properties of twisted skyrmions. Following that, we investigate the current-induced motion of twisted skyrmions by using micromagnetic simulations. It is found that the skyrmion Hall angle of twisted skyrmions driven by the spin Hall effect (SHE) varies continuously with the helicity, which means that the skyrmion Hall angle depends significantly upon the helicity in addition to the dissipative force tensor and the Gilbert damping. More importantly, we demonstrate that the trajectory of the twisted skyrmion can be controlled in a two-dimensional plane with a Gilbert damping gradient, which makes it possible to achieve the SHE-induced motion of twisted skyrmions with zero skyrmion Hall angle. At last, the simulation results demonstrate that the dynamics of twisted skyrmions driven by the spin transfer torque can be described by Thiele's equation, and they are essentially identical to the dynamics of Bloch and Néel skyrmions. Our results provide an understanding of the current-induced motion of twisted skyrmions, which may contribute to the applications of skyrmion-based racetrack memories.

Heavy baryon-antibaryon molecules in effective field theory

We discuss the effective field theory description of bound states composed of a heavy baryon and antibaryon. This framework is a variation of the ones already developed for heavy meson-antimeson states to describe the $X(3872)$ or the $Z_c$ and $Z_b$ resonances. We consider the case of heavy baryons for which the light quark pair is in S-wave and we explore how heavy quark spin symmetry constrains the heavy baryon-antibaryon potential. The one pion exchange potential mediates the low energy dynamics of this system. We determine the relative importance of pion exchanges, in particular the tensor force. We find that in general pion exchanges are probably non-perturbative for the $\Sigma_Q \bar{\Sigma}_Q$, $\Sigma_Q^* \bar{\Sigma}_Q$ and $\Sigma_Q^* \bar{\Sigma}_Q^*$ systems, while for the $\Xi_Q' \bar{\Xi}_Q'$, $\Xi_Q^* \bar{\Xi}_Q'$ and $\Xi_Q^* \bar{\Xi}_Q^*$ cases they are perturbative If we assume that the contact-range couplings of the effective field theory are saturated by the exchange of vector mesons, we can estimate for which quantum numbers it is more probable to find a heavy baryonium state. The most probable candidates to form bound states are the isoscalar $\Lambda_Q \bar{\Lambda}_Q$, $\Sigma_Q \bar{\Sigma}_Q$, $\Sigma_Q^* \bar{\Sigma}_Q$ and $\Sigma_Q^* \bar{\Sigma}_Q^*$ and the isovector $\Lambda_Q \bar{\Sigma}_Q$ and $\Lambda_Q \bar{\Sigma}_Q^*$ systems, both in the hidden-charm and hidden-bottom sectors. Their doubly-charmed and -bottom counterparts ($\Lambda_Q {\Lambda}_Q$, $\Lambda_Q {\Sigma}_Q^{(*)}$, $\Sigma_Q^{(*)} {\Sigma}_Q^{(*)}$) are also good candidates for binding.

Charge density distributions and electron scattering form factors of 19F, 27Al and 25Mg nuclei

An effective two-body density operator for point nucleon system folded with two-body correlation functions, which take account of the effect of the strong short range repulsion and the strong tensor force in the nucleon-nucleon forces, is produced and used to derive an explicit form for ground state two-body charge density distributions (2BCDD's) and elastic electron scattering form factors F (q) for 19F, 27Al and 25Mg nuclei. It is found that the inclusion of the two-body short range correlations (SRC) has the feature of reducing the central part of the 2BCDD's significantly and increasing the tail part of them slightly, i.e. it tends to increase the probability of transferring the protons from the central region of the nucleus towards its surface and to increase the root mean square charge radius ˂ r 2˃ 1/2 of the nucleus and then makes the nucleus to be less rigid than the case when there is no (SRC). It is also found that the effects of two body tensor correlations (TCs) on 2BCDD's and ˂ r 2˃ 1/2 are in opposite direction to those of (SRC).

Evolution of nuclear spin-orbit splittings with Skyrme functional SAMi-T

A new Skyrme functional has been developed with tensor term guided by ab initio relativistic Brueckner-Hartree-Fock (RBHF) studies on neutron-proton drops. Instead of extracting information on the tensor force from experimental single-particle energy splittings, the RBHF calculations do not contain beyond mean-field effects such as particle-vibration coupling and therefore the information on the tensor force can be obtained without ambiguities. The new functional gives a good description of nuclear ground-state properties aswell as various giant resonances. The description for the evolution of single-particle energy splittings is also improved by the new functional.

Nucleon form factors at threshold

The pp¯invariant mass spectra in the processes e+e−→ pp¯, e+e−→ nn¯, J/ψ → pp¯ω, J/ψ → pp¯ρ, and J/ψ → pp¯γ close to the pp¯is discussed. The optical potentials for NN¯pair in the superposition of S and D waves (due to tensor forces) at spin unity of the pair, as well as for NN¯pair in the S wave at spin zero of the pair, are proposed. The parameters of the potentials are obtained by fitting the cross sections of NN¯scattering together with the pp¯invariant mass spectra in e+e−→ pp¯annihilation and J/ψ decays. Good agreement with the available experimental data is achieved. Using our potential and the Green’s function approach we also describe the cross section of e+ e−→ 6π and the η’π+ π− invariant mass spectrum in the decay J/ψ → γη’π+π− in the energy region near the NN¯threshold.