Scalar Charged Particle in Weyl–Wigner–Moyal Phase Space. Constant Magnetic Field

A relativistic phase-space representation for a class of observables with matrix-valued Weyl symbols proportional to the identity matrix (charge-invariant observables) is proposed. We take into account the nontrivial charge structure of the position and momentum operators. The evolution equation coincides with its analog in relativistic quantum mechanics with nonlocal Hamiltonian under conditions where particle-pair creation does not take place (free particle and constant magnetic field). The differences in the equations are connected with the peculiarities of the constraints on the initial conditions. An effective increase in coherence between eigenstates of the Hamiltonian is found and possibilities of its experimental observation are discussed.     

Consistency of relativistic particle theories

While direct-interaction particle theories are generally thought to be incompatible with relativity in classical physics, such relativistic theories in quantum mechanics have recently attracted attention. The reasons for rejecting these theories in classical physics are based on the consideration of world lines, while relativistic quantum mechanics has no covariant position operator so that the classical refuting argument cannot be adapted.This paper discusses the consistency of relativistic particle theories with a finite number of degrees of freedom, without recourse to the position operator. A particle is described by a sub-algebra of observables at one time. Homogeneous transformations, including accelerations, must preserve the identity of particles, and therefore leave the sub-algebras invariant. It is shown that with this assumption only non-interacting particle theories are compatible with the principle of relativity, in quantum as well as classical mechanics.     

大入射能量范围内重离子输运过程的动力学性质研究

基于一个改进的微观动力学输运模型——极端相对论量子分子动力学（UrQMD）, 较为系统地研究了从SIS能区到AGS和SPS能区, 再到RHIC能区, 入射能量跨5个数量级的重离子核反应及多个人们感兴趣的实验观测量, 如粒子产额、 集体流、 核阻止以及两粒子HBT关联等。研究表明, 不论单粒子观测量, 还是两粒子关联观测量, 都能自洽地由同一个输运模型加以描述。Based on one updated microscopic transport model Ultra relativistic Quantum Molecular Dynamics (UrQMD) with modifications of both potentials and two body scattering cross sections, quite a few interesting observables, such as yields, collective flows, the nuclear stopping, and the HBT two particle interferometry, are systematically investigated for heavy ion collisions within a large beam energy regime of five orders of magnitude (from SIS, AGS, SPS up to RHIC). It is shown that a consistent explanation can be received from both single particle and two particle related observables.     

Separability,gauge invariance and nonsuperluminality in direct interaction dynamics

We discuss the classical mechanics of relativistic systems with direct interaction. We show that various desiderata can all be accommodated in the single time approach by restricting the observables to the gauge invariant variables. We show how such observables can be constructed in general. We explicitly construct position observables in a general system and show that they lead to separable, invariant world lines. Nonsuperluminality is explicitly demonstrated for two body systems interacting via central forces of semibounded magnitude provided they ensure timelike canonical momenta. For two particles, our results reproduce the usual solution in covariant equal-time gauge.     

Conformal Symmetry and Quantum Relativity

The relativistic conception of space and time is challenged by the quantum nature of physical observables. It has been known for a long time that Poincare symmetry of field theory can be extended to the larger conformal symmetry. We use these symmetries to define quantum observables associated with positions in space-time, in the spirit of Einstein theory of relativity. This conception of localization may be applied to massive as well as massless fields. Localization observables are defined as to obey Lorentz covariant commutation relations and in particular include a time observable conjugated to energy. While position components do not commute in the presence of a nonvanishing spin, they still satisfy quantum relations which generalize the differential laws of classical relativity. We also give of these observables a representation in terms of canonical spatial positions, canonical spin components, and a proper time operator conjugated to mass. These results plead for a new representation not only of space-time localization but also of motion.     

Constants of Motion for Several One-Dimensional Systems and Problems Associated with Getting Their Hamiltonians

The constants of motion of the following systems are deduced: a relativistic particle with linear dissipation; a no-relativistic particle with a time explicitly depending force; a no-relativistic particle with a constant force and time depending mass; and a relativistic particle under a conservative force with position depending mass. The Hamiltonian for these systems, which is determined by getting the velocity as a function of position and generalized linear momentum, can be found explicitly at first approximation for the first system. The Hamiltonians for the other systems are kept implicitly in their expressions for their constants of motion.     

“Simultaneous measurement” from the standpoint of quantum estimation theory

The purpose of the simultaneous measurement of noncommuting quantum observables can be viewed as the joint estimation of parameters of the density operator of the quantum system. Joint estimation involves the application of a multiply parameterized operator-valued measure. An example related to the simultaneous estimation of the position and velocity of a particle is given. Conceptual difficulties attending simultaneous measurement of noncommuting observables are avoided by this formation.     

Infinite invariant density determines statistics of time averages for weak chaos

Weakly chaotic nonlinear maps with marginal fixed points have an infinite invariant measure. Time averages of integrable and nonintegrable observables remain random even in the long time limit. Temporal averages of integrable observables are described by the Aaronson-Darling-Kac theorem. We find the distribution of time averages of nonintegrable observables, for example, the time average position of the particle, x[over ˉ]. We show how this distribution is related to the infinite invariant density. We establish four identities between amplitude ratios controlling the statistics of the problem.     

基于粒子模拟和并行遗传算法的高功率微波源优化设计

提出了基于粒子模拟和并行遗传算法的高功率微波源优化设计方法, 以全电磁粒子模拟软件UNIPIC模拟的高功率微波器件输出功率作为适应度函数, 采用浮点数编码的遗传算法对高功率微波源器件进行优化. 采用该算法, 对相对论返波管的布拉格反射器位置以及高度进行了浮点数编码,然后在巨型机上进行参数的全局优化, 获得了该返波管布拉格反射器的全局最优参数. 关键词： 并行遗传算法 相对论返波管 粒子模拟 高功率微波源     

Dilepton creation based on an analytic hydrodynamic solution

High-energy collisions of various nuclei, so called “Little Bangs” are observed in various experiments of heavy ion colliders. The time evolution of the strongly interacting quark-gluon plasma created in heavy ion collisions can be described by hydrodynamical models. After expansion and cooling, the hadrons are created in a freeze-out. Their distribution describes the final state of this medium. To investigate the time evolution one needs to analyze penetrating probes, such as direct photon or dilepton observables, as these particles are created throughout the evolution of the medium. In this paper we analyze an 1+3 dimensional analytic solution of relativistic hydrodynamics, and we calculate dilepton transverse momentum and invariant mass distributions. We investigate the dependence of dilepton production on time evolution parameters, such as emission duration and equation of state. Using parameters from earlier fits of this model to photon and hadron spectra, we compare our calculations to measurements as well. The most important feature of this work is that dilepton observables are calculated from an exact, analytic, 1+3D solution of relativistic hydrodynamics that is also compatible with hadronic and direct photon observables.     

Equations of motion for a relativistic wave packet

The time derivative of the position of a relativistic wave packet is evaluated. It is found that it is equal to the mean value of the momentum of the wave packet divided by the mass of the particle. The equation derived represents a relativistic version of the second Ehrenfest theorem.     

Relativistic particles on quantum space-time

We discuss alternatives to the usual quantization of a relativistic particle which result in discrete spectra for position and time operators.     

Analyses of Relativistic Optical Potential for Medium Energy Proton

The influence of the parameters of the relativistic optical potential on the nucleon scattering properties,such as cross sections,angular distributions and spin observables etc.,is studied based on a set of global Dirac phenomenological optical potentials.It is shown that,in contrast with the case at low energies.the total scattering cross sections vary slowly as the energy and weakly depend on the potentials at E_p<200MeV.The differential cross sections and spin observables depend not only on the volume integrals of the optical potentials,but also on their strengths and shapes.The applicability of the relativistic microscopic optical potentia based on Walecka model in the medium energy region is also discussed in this paper.     

Application of transition radiation in a small dihedral angle to detection of relativistic particles

The features of transition radiation excited by a relativistic particle in a dihedral angle with an opening comparable to the angular divergence of transition radiation are considered. It is shown that the radiation distribution in the dihedral angle is more sensitive to the direction of emitting particle motion and to the position of the surface intersection by the particle, than the radiation excited when a plane surface is intersected. It is indicated that the spectral radiation density in the small dihedral angle is higher than the density of radiation excited when a plane surface is intersected. These features offer additional opportunities to use transition radiation in systems for measuring particle parameters.     

Analysis of a relativistic ribbon-shaped beam of charged particles moving in crossed fields without allowance for the space charge

It is shown that, when placed in uniform crossed fields, a relativistic charged particle with an initial thermal velocity describes a prolate cycloid. Analytical formulas for the parameters of the relativistic ribbon-shaped beam (velocity straggling, oscillation amplitude, and spatial and time periods) forming in crossed fields are derived without allowance for space charge fields. All the desired parameters can be determined by presetting three initial parameters (beam velocity, magnetic field, and emitting surface area).     

Algorithms for accurate relativistic particle injection

In particle-in-cell plasma codes, the second-order leap-frog method is used to push the velocity and position of each particle in the main loop. Once a velocity distribution has been inverted for injection, time-centering of the position and velocity is necessary to maintain second-order accuracy. We have set up non-relativistic time-centering algorithms for particle injection in our PIC code. We further developed relativistic time-centering methods for injection and we added methods to calculate higher order accurate position. Also, the algorithms are expanded to find the position and velocity at any specific time from those at the initial discrete time, which can be used not only in the leap-frog method but also any other algorithms.     

Observables have No Value: A no-go Theorem for Position and Momentum Observables

The Bell–Kochen–Specker contradiction is presented using continuous observables in infinite dimensional Hilbert space. It is shown that the assumption of the existence of putative values for position and momentum observables for one single particle is incompatible with quantum mechanics.     

中能核反应中碰撞参数的确定

介绍了中高能核反应过程中与碰撞参数相关的可观测量.确定碰撞参数的各种方法 ,以及这些方法的适用范围和可靠性.这些方法包括约化线性动量转移、带电离子多重性、横向动量的方向性、横向动能和纵向动能的比 Erat、 Zbound和椭圆流参量. Observables that related to the impact parameters in intermediate and relativistic energy heavy ion reactions were introduced. These observables that related to the impact parameter include linear momentum transfer, multiplicities of charged particles, the ratio of transverse kinetic energy and longitudinal kinetic energy E rat , the transverse momentum directivity, Z bound , elliptic flow etc. Impact parameter determination for intermediate and relativistic energy heavy...