All the Fundamental Massless Fermion Fields in Superstring Theory: A Rigorous Analysis

A systematic rigorous analysis of both massless fermion fields in the mass spectra of superstring theory is carried out. Our interest is in dynamical aspects of these fields. An explicit novel expression for the propagator of the massless Rarita-Schwinger field (the gravitino), in the mass spectrum involving massless fermions in superstring theory in 10 dimensions, is derived. The analysis is carried in the presence of a non-constrained external source so that the full expression of the propagator emerges. The number of associated degrees of freedom is also obtained. We work in a Coulomb-like gauge. The massless Dirac field (the dilatino), the other massless fermion field in the mass spectra of superstring theory in 10 dimensions, is first investigated to this end.

Radiative Decay Bc → Ds*γ in the Technicolor with a Massless Scalar Doublet Model

Applying perturbative QCD, we study the process Bc → Dsγ in the technicolor with a massless scalar doublet model (TCMLSM). There are mainly two mechanisms contributing to the Bc → D*sγ process. One proceeds through the short distance b → sγ transition and the other through weak annihilation accompanied by a photon emission.We find that, compared with the standard model, the modification of Bc → D*sγ from πρ (the physical pions in the TCMLSM) is so small that can be neglected for the allowed mass ofπρ. The weak-annihilation contribution is found to be about one order larger than that of the electromagnetic penguin diagrams.

Complex frequencies of a massless scalar field in loop quantum black hole spacetime

Recently, considerable progress has been made in understanding the early universe by loop quantum cosmology. Modesto et al. investigated the loop quantum black hole （LQBH）using improved semiclassical analysis and they found that the LQBH has two horizons, an event horizon and a Cauchy horizon, just like the Reissner-NordstrSm black hole. This paper focuses on the dynamical evolution of a massless scalar wave in the LQBH background. By investigating the relation between the complex frequencies of the massless scalar field and the LQBH parameters using the numerical method, we find that the polymeric parameter P makes the massless scalar field decay more quickly and makes the ground scalar wave oscillate slowly. However, the polymeric parameter P causes the frequency of the high harmonic massless scalar wave to shift according to its value. We also find that the loop quantum gravity area gap parameter a0 causes the massless scalar field to decay more slowly and makes the period of the massless scalar field wave become longer. In the complex ω plane, the frequency curves move counterclockwise when the polymeric parameter P increases and this spiral effect is more obvious for a higher harmonic scalar wave.

Absorption of a massless scalar wave from a Schwarzschild black hole surrounded by quintessence

By using the partial wave method, we investigate the absorption of a massless scalar wave from a Schwarzschild black hole surrounded by quintessence. We obtained the expression of absorption cross sectionσabs（ω）=π/ω^2 ∑ t=0^∞ （2l＋1）｜Tωl（ω）｜^2=π/ω^2∑ t=0^∞（2l＋1）Гωl（ω）.Then we numerically carry out the absorption cross section and we find that the larger the angular momentum quantum number 1 is, the smaller the corresponding maximum value of the partial absorption cross section is, and that the total absorption cross section tends to the geometric-optical limit σhfabs≈ bc^2. We also find that higher value of ωq （state abs parameter of quintessence） corresponds to the higher value of absorption cross section gabs.

Thermodynamic properties of massless Dirac–Weyl fermions under the generalized uncertainty principle

The Dirac–Weyl equation characterized quasi-particles in the T3 lattice are studied under external magnetic field using the generalized uncertainty principle(GUP). The energy spectrum of the quasi-particles is found by the Nikiforov–Uvarov method. Based on the energy spectrum obtained, the thermodynamic properties are given, and the influence of the GUP on the statistical properties of systems is discussed. The results show that the energy and thermodynamic functions of massless Dirac–Weyl fermions in the T3 lattice depend on the variation of the GUP parameter.

Quasinormal Modes of a Noncommutative-Geometry-Inspired Schwarzschild Black Hole: Gravitational, Electromagnetic and Massless Dirac Perturbations

In our previous work [Chin. Phys. Lett. 35（2018） 010410], the quasinormal modes of massless scalar field perturbation in a noncommutative-geometry-inspired Schwarzschild black hole spacetime are studied using the third-order Wentzel–Kramers–Brillouin approximative approach. In this study, we extend the work to the cases of gravitational, electromagnetic and massless Dirac perturbations. The result further confirms that the noncommutative parameter plays an important role for the quasinormal frequencies.

Casimir Effect for a Massless Spin-3/2 Field in Minkowski Spacetime

The Casimir effect has been studied for various quantum fields in both fiat and curved spacetimes. As a further step along this line, we provide an explicit derivation of Casimlr effect for massless spin-3/2 field with periodic boundary condition imposed in four-dimensional Minkowski spacetime. The corresponding results with Dirichlet and Neumann boundary conditions are also discussed.

Massless Dirac perturbations of black holes in f(Q)gravity:quasinormal modes and a weak deflection angle

This article considers a static and spherical black hole(BH)in f(Q)gravity.f(Q)gravity is the extension of symmetric teleparallel general relativity,where both curvature and torsion are vanishing and gravity is described by nonmetricity.In this study,we investigate the possible implications of quasinormal mode(QNM)modified Hawking spectra and deflection angles generated by the model.The Wentzel–Kramers–Brillouin method is used to solve the equations of motion for massless Dirac perturbation fields and explore the impact of the nonmetricity parameter(Q_(0)).Based on the QNM computation,we can ensure that the BH is stable against massless Dirac perturbations and as Q_(0)increases the oscillatory frequency of the mode decreases.We then discuss the weak deflection angle in the weak field limit approximation.We compute the deflection angle up to the fourth order of approximation and show how the nonmetricity parameter affects it.We find that the Q_(0)parameter reduces the deflection angle.

Structure of Massive “Standard Model” Particles

The massive vector bosons Z o, W ± and the scalar Higgs-boson H o assumed in weak interaction theory, but also the six quarks required in strong interactions are well understood in an alternative quantum field theory of fermions and bosons: Z o and W ± as well as all quark-antiquark states (here only the tt¯state is discussed) are described by bound states with scalar coupling between their massless constituents and have a structure similar to leptons. However, the scalar Higgs-boson H o corresponds to a state with vector coupling between the elementary constituents. Similar scalar states are expected also in the mass region of the mesons ω (0.782 GeV) - Υ ( 9.46 GeV). The underlying calculations can be run on line using the Web-address https://h2909473.stratoserver.net.

Gaupta-Bleuler triplet for massless spin-3/2 field in de Sitter space

Physicists have been interested in quantization of spinor and vector free fields in 4-dimensional de Sitter space-time, in ambient space notation. The Gupta-Bleuler formalism has been extensively applied to the quantization of gauge invariant theories. The field equation of the massless spin-3/2 fields is gauge invariant in de Sitter space. In this paper, we study the quantization of massless spin-3/2 gauge fields in de Sitter space-time by the Gupta-Bleuler formalism. This triplet carries an indecomposable representation of the de Sitter group.

Scattering of massless fermions by Schwarzschild and Reissner-Nordstrm black holes

We study the scattering of massless Dirac fermions by Schwarzschild and Reissner-Nordstrm black holes. This is done by applying partial wave analysis to the scattering modes obtained after solving the massless Dirac equation in the asymptotic regions of the two black hole geometries. We successfully obtain analytic phase shifts, with the help of which the scattering cross section is computed. The glory and spiral scattering phenomena are shown to be present, as in the case of massive fermion scattering by black holes.

Quasinormal modes and absorption of a massless scalar field for the magnetic Gauss-Bonnet black hole

We study the massless scalar quasinormal frequencies of an asymptotically flat static and spherically symmetric black hole with a nonzero magnetic charge in four-dimensional extended scalar-tensor-Gauss-Bonnet theory. The results show that the real part of the quasinormal frequency becomes larger and the imaginary part becomes smaller with increasing the magnetic charge or the angular harmonic index. The existence of magnetic charges will reduce the damping of scalar perturbation, but increase the frequency. We also study the absorption crosssection of the scalar field in this black hole. We find that its curve will become lower as the magnetic charge increases, i.e. the magnetic charge will weaken the absorption capacity of the black hole. Meanwhile, the high-frequency limit of the total absorption cross-section is just the area of black hole shadow.

一种含铰链间隙机器人运动分析方法及其验证

针对六轴机器人铰链间隙,基于无质量杆建模方法,提出一种改进的无质量杆方法。由于六轴机器人各关节间隙所引起的误差将会在末端形成误差累积,因此各关节铰链间隙对机器人精度将产生较大影响。若采用较复杂的铰链间隙建模方式,将会使建模过于复杂,故选择无质量杆方法,并对其进行改进。此方法在无质量杆的基础上增加一滑块,反映铰链径向运动。最后通过仿真,分析改进无质量杆方法与实际数据之间的误差。研究表明,该方法在简化计算的同时,具有一定的精度。

深埋反应堆厂房土结相互作用下的楼层反应谱分析

埋深对核安全级厂房楼层反应谱的计算具有较大影响,尤其当埋深较大且周围的地基岩性较好时,其对厂房的约束作用不可忽略,土—结相互作用明显,国内鲜有对深埋结构采用三维整体分析法进行土—结相互作用分析的研究。利用ANSYS分别建立某反应堆厂房上部结构和其周围岩土体的三维有限元模型,两者之间采用接触单元进行真实模拟,采用无质量的三维地基模型进行楼层反应谱的计算,并同采用地基阻抗函数简化模型来考虑地基影响的ANSYS三维结构有限元模型所计算的楼层反应谱进行对比分析,以期为类似工程的楼层反应谱计算提供一些有用的参考和建议。

不同边界和地基条件的大型滑坡体动力响应分析

动力有限元计算结果的真实性与模型边界条件的设置和地震波输入高程的选择有着密切的关系。采用动力有限元时程分析法对不同边界和地基条件的大型滑坡体进行了数值计算,在此基础上分析了地基辐射阻尼和地震加速度输入高程对滑坡体动力响应的影响,以及大型滑坡体的地震响应规律。结果表明,上田镇大型滑坡体在动力作用下上部的位移响应值大,剪应力小,而下部则相反;黏弹性边界能有效地降低滑坡体的地震反应,而且地震输入高程的不同对滑坡体的地震响应会产生相当大的影响,地基辐射阻尼和地震波输入的模拟合理性直接影响滑坡体动力分析的客观性。

求解结构地震响应位移输入模型存在的问题及其AMCE实效对策

提出一种实效方法-刚性无质量束缚元AMCE(Appended Massless Constraint Element)法,以解决地震地面运动作用下求解结构响应的位移输入模型中容易而不容忽视的问题。首先对位移输入模型进行了详细分析,明确指出当前位移输入模型在理论上会导致计算结果具有不稳定性和不可靠性,进一步通过算例对此加以说明;针对此问题,提出了AMCE解决方法,并对本方法进行物理角度解释、理论分析和数值验证。结果表明,AMCE法不仅物理概念清晰、简单可行,而且具有足够的计算精度。

采用无质量地基模型时动力平衡方程的缩减

在求解坝与地基动力相互作用时 ,为了消除地基材料对地震运动的放大作用常常忽略地基质量。但在求解动力平衡方程时为了消除质量矩阵的病态 ,地基质量被赋以很小的值代表无质量地基。为了从动力平衡方程中消除零质量矩阵 ,用矩阵理论对其进行分块简化 ,从而大大缩减了方程的自由度和复杂度 ,并导出了地基对上部结构的耦合作用刚度矩阵 ,使地基刚度在相互作用方程式中显示化。结果表明 。

不同地基模型对拱坝动力响应的影响

在粘弹性人工边界理论基础上,结合波场分解法的地震动输入方法,应用ANSYS软件的参数化语言APDL,编制了模拟粘弹性人工边界和地震荷载输入的程序。针对某碾压混凝土拱坝建立了"库水-拱坝-地基"联合作用的有限元模型,采用施加粘弹性边界并输入相应地震动,讨论了无限地基辐射阻尼的影响,并与无质量地基模型的计算结果进行比较分析。研究结果表明,只有考虑辐射阻尼效应才会得到符合实际情况的坝体地震响应结果,因此实际工程抗震分析时对地基的模拟应该合理选取。

库水-重力坝-无限地基系统地震响应分析

为了分析库水以及无限地基辐射阻尼对库水-重力坝-无限地基系统的地震响应影响,通过比例边界有限元法、有限元法以及无限单元法计算了库水-重力坝-无限地基系统的响应.基于SBFEM计算上游坝面库水压力,利用无限单元法分析无限地基辐射阻尼的影响,以Koyna重力坝为研究对象,给出了重力坝在不同地基弹性模量条件下地震位移时程以及应力的响应,随着地基弹性模量的增加,坝体响应增加.与无质量地基模型的计算结果进行对比,考虑无限地基辐射阻尼的计算结果较小.

不同重力环境下间隙对机械臂末端轨迹的影响

以在轨服务高精度操控任务为背景,根据不同重力环境中机构的间隙界面运动特性,研究了地面装调及空间服役两种不同工况下的近似间隙等效模型。分析了不同重力环境下影响间隙形成的主要因素,并以二自由度空间机械臂为例,使用无质量轻杆法获取考虑铰间间隙的空间机械臂在重力及重力释放条件下的动力学解析解,进行了铰间间隙与重力对末端轨迹跟踪控制精度耦合影响的仿真研究。在此基础上,针对间隙等效模型造成的模型不确定性及干扰设计了间隙补偿控制器,并通过仿真验证了间隙补偿控制器的有效性。