Relations between electromagnetic form factors of baryons

The inclusion of two-body exchange currents in the constituent quark model leads to new relations between the electromagnetic properties of octet and decuplet baryons. In particular, the N → Δ quadrupole transition form factor can be expressed in terms of the neutron charge form factor.     

A relativistic calculation of the deuteron threshold electrodisintegration at backward angles

Deuteron threshold electrodisintegration at backward angles is studied with a relativistic Hamiltonian, including a relativistic one-pion-exchange potential with off-shell terms. Boost effects in bound and scattering states are considered. Full Lorentz structure of the electromagnetic current is retained, which includes one- and two-body terms. Pseudovector coupling of pions to nucleons is consistently used. Cross-section results show significant relativistic corrections, even for low momentum transfer. Calculations suggest the need for including additional two-body currents.     

Two-body Current Operators and Deuteron Form Factors Within the Light-Front Hamiltonian Dynamics

The deuteron electromagnetic properties are investigated within the Light-Front Hamiltonian dynamics using one-body and two-body currents. The dynamical nature of the latter is generated within a Yukawa model from an analysis of the Light-Front current that acts on the three-dimensional valence component and fulfills the Ward?CTakahashi identity. Preliminary results for the magnetic moment and the probability of the nonvalence component are shown.     

Bogolubov–Hartree–Fock Theory for Strongly Interacting Fermions in the Low Density Limit

We consider the Bogolubov–Hartree–Fock functional for a fermionic many-body system with two-body interactions. For suitable interaction potentials that have a strong enough attractive tail in order to allow for two-body bound states, but are otherwise sufficiently repulsive to guarantee stability of the system, we show that in the low-density limit the ground state of this model consists of a Bose–Einstein condensate of fermion pairs. The latter can be described by means of the Gross–Pitaevskii energy functional.     

Two-body deuteron photodisintegration above pion threshold with a dynamical treatment of δ degrees of freedom

The two-body photo break-up of the deuteron above pion threshold is calculated treating the final state interaction in a coupled channel approach with inclusion of Δ degrees of freedom. For the electromagnetic interaction nucleon, isobar and meson exchange currents are taken into account. Various observables (total and differential cross sections, γ-asymmetry and nucleon polarization) are influenced by the dynamical treatment of Δ degrees of freedom. Especially for the proton polarization it leads to an improved agreement with experiment. However, the situation for the shape of the differential cross section remains problematic.     

Chiral two-body currents in nuclei: Gamow-Teller transitions and neutrinoless double-beta decay

We show that chiral effective field theory (EFT) two-body currents provide important contributions to the quenching of low-momentum-transfer Gamow-Teller transitions, and use chiral EFT to predict the momentum-transfer dependence that is probed in neutrinoless double-beta (0νββ) decay. We then calculate for the first time the 0νββ decay operator based on chiral EFT currents and study the nuclear matrix elements at successive orders. The contributions from chiral two-body currents are significant and should be included in all calculations.     

Shell model structures in the N = 46 isotones 86Zr, 87Nb, 88Mo, 89Tc, 90Ru and 91Rh

The known level energies, electromagnetic moments and decay probabilities of high-spin states in the N = 46 isotones ⁸⁶Zr, ⁸⁷Nb, ⁸⁸Mo, ⁸⁹Tc, and ⁹⁰Ru are interpreted within the shell model. The single-particle space was truncated to the p _1/2 and g _9/2 orbits (relative to the ⁸⁸Sr core) and the single-particle energies and empirical two-body matrix elements derived by Gross and Frenkel were used in the calculations. Based on the generally good success of this approach, energies and decay properties of the yrast spectra in ⁹⁰Ru and ⁹¹Rh are predicted. Received: 31 July 2000 / Accepted: 18 December 2000     

Relaxation algorithm to hyperbolic states in Gross–Pitaevskii equation

A new version of the relaxation algorithm is proposed in order to obtain the stationary ground-state solutions of nonlinear Schrödinger-type equations, including the hyperbolic solutions. In a first example, the method is applied to the three-dimensional Gross–Pitaevskii equation, describing a condensed atomic system with attractive two-body interaction in a non-symmetrical trap, to obtain results for the unstable branch. Next, the approach is also shown to be very reliable and easy to be implemented in a non-symmetrical case that we have bifurcation, with nonlinear cubic and quintic terms.     

Commutators of second-class axial currents with normal weak currents and consequences for particle decays

Second-class weak axial currents are studied in the framework of normal weak and electromagnetic currents. Equal time commutators between normal and abnormal axial currents and the isoscalar electromagnetic current are postulated and their consequences are worked out. A number of predictions for masses, coupling constants and decay properties are derived and are compared to available data.     

Electromagnetic energies of nuclei and the nuclear compton amplitude

The electromagnetic energy of a nucleus is derived in perturbation theory, which relates this quantity to the amplitude for the forward scattering of virtual photons on a nucleus (nuclear Compton amplitude). Using the gauge invariance of this amplitude, the energy is separated into Coulomb and transverse components. Our formalism, although basically nonrelativistic, admits corrections of order ($\text{v}\text{c}$)² to the nuclear charge operator. The energy is further separated into one-body terms, related to the n-p mass difference, and two-body terms which lead to the Breit interaction and the nuclear Lamb shift. These results are then related to electron scattering sum rules in the manner of Cottingham. Mesonic contributions to the electromagnetic energy are also discussed.     

Nuclear charge-asymmetry effects from isotensor currents

Departures from mirror symmetry in γ- and β-decays of nuclear states are investigated by postulating the existence of isotensor components in electromagnetic and weak currents of hadrons. Their effects are described by means of two-body exchange current operators. These are found to exhibit simple properties which enable one to set useful bounds on the isotensor admixture. The consideration of resonance-exchange contributions in the processes γ (or β) + N → π + N suggests the N → Δ transition current as the most favorable candidate. We discuss a numerical application to M1 and Gamow-Teller transitions of the isoquartet of states in the isobars A = 13 (B, C, N, O). It is found that the test is reasonably model-independent but very insensitive. Therefore, low-energy phenomena may be not too promising. Results are also given for other isoquartets in the p-shell.     

基于压缩感知的一维海面与二维舰船复合后向电磁散射快速算法研究

矩量法作为数值方法中积分方程方法的代表, 具有计算精度高、所用格林函数自动满足辐射条件、无须额外设置边界条件等优点. 但是在舰船目标与海面复合后向电磁散射仿真中, 传统矩量法需针对每个入射角反复求解矩阵方程组, 导致其在处理后向散射问题时计算量大, 耗时长, 仿真效率低下. 为解决上述问题, 本文提出了一种基于压缩感知技术的矩量法的改进算法. 该算法在求解复合后向散射问题时, 首先利用观测矩阵与传统矩量法中的电压矩阵相乘, 得到一组新的低维度的电压矩阵; 其次通过求解新电压矩阵下的矩阵方程组, 获得电流矩阵的观测值; 最后利用恢复算法(本文采用正交匹配追踪算法)重构出所需的原始入射源照射下的电流系数. 通过与传统矩量法的计算结果对比, 表明本文所提算法能够在保证计算精度的前提下, 明显减少计算时间, 提高计算效率.     

Meson-retardation effects in deuteron photodisintegration below π-threshold

Mesor-retardation effects in photodisintegration of the deuteron below pion threshold are studied by constructing retarded one-boson-exchange potentials using time-dependent non-covariant perturbation theory. The corresponding retarded meson-exchange currents including retarded vertex currents are derived analogously by gauge-invariant minimal coupling. It is found that retardation effects in the wave functions and in the electromagnetic currents as well have a significant influence on total and differential cross sections.Supported by the Deutsche Forschungsgemeinschaft (SFB 201)     

Dynamic analysis of a BLDC motor with mechanical and electromagnetic interaction due to air gap variation

In this study, the dynamic behaviors of a BLDC motor are analyzed, when the motor undergoes mechanical and electromagnetic interaction due to an air gap variation between the stator and rotor. When considering the air gap variation caused by the translational motion of the rotor relative to the stator, the kinetic and potential energies, Rayleigh dissipation function, and the magnetic coenergy are expressed in terms of the rotor displacements and stator currents. With these energies and function, new equations of motion are derived using Lagrange’s equation. The equations for the proposed model are nonlinear equations in which the displacements and currents are coupled. The time responses for the displacements and currents are computed for the proposed and previous models. Furthermore, the effects of rotor eccentricity are also investigated. It is found that, when the air gap varies with time, the time responses for the proposed and previous models have small differences in the stator currents, electromagnetic torques, and rotating speeds. However, the time responses have large differences in the rotor displacements. Therefore, this paper claims that the proposed model describes the dynamic behaviors of the motor more accurately than the previous model. It is also shown that rotor eccentricity increases the stator current period and the electromagnetic torque, while it decreases the rotating speed of the rotor.     

Semi-leptonic weak and electromagnetic interactions in nuclei:: Parity violations in electron scattering and weak neutral currents

A general result for the difference in differential cross sections for electron scattering between any two nuclear levels with incident longitudinally polarized right- and left-handed electrons is derived. This difference must involve the parity-violating weak interaction at least linearly and can be used to study weak neutral currents as pointed out by Feinberg. A V — A structure for the weak neutral currents is assumed with a semi-leptonic current-current interaction, and the electromagnetic interaction is treated in the one-photon-exchange approximation. The result is expressed in terms of the same set of reduced matrix elements of the multipoles of the nuclear currents which govern all electromagnetic and weak transitions between these levels. A previously developed unified analysis of semi-leptonic weak and electromagnetic interactions in nuclei which determines one-body transition densities, including their spin and spatial dependences, through electron scattering provides nuclear transitions to serve as known analyzers in testing the structure of this part of the weak interaction. Examples are given using Weinberg's model of the weak neutral currents. Feinberg's result for elastic scattering from spin-0 nuclei is rederived and two new examples using previously determined one-body densities are discussed : the 1⁺0 → 0⁺1 (3.56 MeV) transition in ⁶Li and the 0⁺0 → 1⁺ 1(15.1 MeV) transition in ¹²C.     

Absorption von π-Mesonen durch Kerne

The quantized pion field in the presence of an external electromagnetic field is first treated. Then the propability of absorption of pions by nuclei, followed by the emission of two nucleons, is evaluated without introducing adjustable parameters or singular two-body forces (repulsive core) between nucleons. This calculation yields results whose order of magnitude agrees with the available data, and whose form corresponds to the semi-empirical formulae in use.     

On the angular momentum transferred during electromagnetic energy absorption and emission

In the framework of classical electrodynamics, the angular momentum transported into (and/or from) a volume bounded by a rotational surface is derived. The dependences of electromagnetic field on space and time, and also the electromagnetic properties of the interacting masses are arbitrary. The results may be useful for the theory of toroidal currents induced by high-frequency heating of plasmas. A connection with the Manley-Rowe equations is given.     

A Remark on the Mean-Field Dynamics of Many-Body Bosonic Systems with Random Interactions and in a Random Potential

The mean-field limit for the dynamics of bosons with random two-body interactions and in the presence of a random external potential is rigorously studied, both for the Hartree dynamics and the Gross–Pitaevskii dynamics. First, it is shown that, for interactions and potentials that are almost surely bounded, the many-body quantum evolution can be replaced in the mean-field limit by a single particle nonlinear evolution that is described by the Hartree equation. This is an Egorov-type theorem for many-body quantum systems with random interactions. The analysis is then extended to derive the Gross–Pitaevskii equation with random interactions.