Gravitational waves and massive tensor particles in thef-g theory of gravity

Starting from the generally covariant version of the Pauli-Fierz mass term, it is stressed that the tensor fields representing spin-2 particles, eigenstates of strong and gravitational interactions, are linear combinations of one massive and one massless state. This implies that any hadronic reaction, in which massive tensor particles are produced, can be regarded, at least in principle, also as an effective source of gravitons which may become very important in the early stages of the universe; conversely, any process in which gravitational radiation of sufficiently high energy is emitted, should be a source of strongly interacting tensor particles which decay into photons and neutrinos. These two effects could be used for producing and detecting gravitational waves.This essay was awarded an honorable mention (1985) by the Gravity Research Foundation—Ed.     

Polarized radiation in Mössbauer spectroscopy

Mössbauer polarimetry is a spectroscopic technique sensitive to the orientations of hyperfine fields. The technique is particularly effective with monochromatic, polarized radiation: the measured spectra do not contain many additional transitions present when nonmonochromatic radiation is used. The paper reviews recent achievements in the construction of sources of polarized monochromatic radiation. Recently, filter techniques were adopted for achieving circularly and linearly polarized radiation from commercially available radioactive isotopes. A synchrotron source with nano-eV energy width, suitable for Mössbauer measurements was constructed. Applications are reviewed, in particular determination of the direction of the hyperfine magnetic field and the orientation of the electric field gradient. Special attention is paid to cases when the distributions of the hyperfine fields and mixed interactions result in poorly resolved spectra. Recent achievements in methodology are described. An explicit form of the intensity tensor is derived, which allows the transition probabilities to be calculated omitting the diagonalization of the Hamiltonian. The concept of the velocity moments is introduced. It is shown that some averages of the whole Mössbauer spectra relate to the averages of hyperfine fields and possess tensor properties.     

Particle Creation in the Effective Action Method

The effect of particle creation by nonstationary external fields is considered as a radiation effect in the expectation-value spacetime. The energy of created massless particles is calculated as the vacuum contribution in the energy-momentum tensor of the expectation value of the metric. The calculation is carried out for an arbitrary quantum field coupled to all external fields entering the general second-order equation. The result is obtained as a functional of the external fields. The paper gives a systematic derivation of this result on the basis of the nonlocal effective action. Although the derivation is quite involved and touches on many aspects of the theory, the result itself is remarkably simple. It brings the quantum problem of particle creation to the level of complexity of the classical radiation problem. For external fields like the electromagnetic or gravitational field there appears a quantity, the radiation moment, that governs both the classical radiation of waves and the quantum particle production. The vacuum radiation of an electrically charged source is considered as an example. The research is aimed at the problem of backreaction of the vacuum radiation.     

Spatial correlations and degree of polarization in homogeneous electromagnetic fields

We consider stationary electromagnetic fields modeled as superpositions of unpolarized and angularly uncorrelated plane waves and show that in anisotropic case the electric cross-spectral tensor is proportional to the imaginary part of the Green tensor. This is as for blackbody radiation, but here the field need not be in thermal equilibrium. We also evaluate the degree of polarization for a homogeneous but nonisotropic field for which the plane waves propagate within a cone of angles. The results are compared with the known polarization properties of blackbody radiation.     

Kerr-Schild metric cannot have an accelerating source

We give a simple proof that if the source of a vacuum electro-magnetic or purely gravitational Kerr-Schild metric is a world-line in the background Minkowski space-time then the 4-acceleration of the world-line must vanish.     

Charged dilaton,energy, momentum and angular-momentum in teleparallel theory equivalent to general relativity

We apply the energy-momentum tensor to calculate energy, momentum and angular-momentum of two different tetrad fields. This tensor is coordinate independent of the gravitational field established in the Hamiltonian structure of the teleparallel equivalent of general relativity (TEGR). The spacetime of these tetrad fields is the charged dilaton. Our results show that the energy associated with one of these tetrad fields is consistent, while the other one does not show this consistency. Therefore, we use the regularized expression of the gravitational energy-momentum tensor of the TEGR. We investigate the energy within the external event horizon using the definition of the gravitational energy-momentum. PACS 04.70.Bw; 04.50.+h; 04.20.-Jb     

基于有限元法的光子并矢格林函数重整化及其在自发辐射率和能级移动研究中的应用

任意微纳结构中量子点的自发辐射率和能级移动均可用并矢格林函数表达.当源点和场点在同一位置时,格林函数的实部是发散的.为解决这一发散问题,可采用重整化格林函数方法.本文提出一种计算重整化格林函数和散射格林函数的方法.该方法利用有限元,计算点电偶极子的辐射场,将其在量子点体积内做平均得到重整化的并矢格林函数,减去均匀空间中解析的重整化格林函数,得到重整化的散射格林函数.在均匀空间情况下,本方法所得数值结果与解析解一致.将该方法应用到银纳米球系统,以解析的散射格林函数作为参考,结果表明该方法能准确处理散射格林函数的重整化问题.将该方法应用到表面等离激元纳米腔中,发现有极大的自发辐射增强和能级移动,且该结果不依赖于量子点的体积.这些研究在光与物质相互作用领域具有积极的意义.     

Electromagnetic Fields of Non-Equilibrium Plasmas

A statistical treatment of the electromagnetic fields of a fully ionized plasma shows that there are two types of radiation. One of the radiation fields is determined by the time change of the distribution function and is characteristic of such plasmas. When the time change is due to the many-body couplings of the charges in the plasma, the radiation can be related to the nonequilibrium stress tensor. In particular, for large distances the radiation is determined by the total internal pressure in a way similar to the classical Larmor formula for a point charge.     

Special-purpose radiation sources based on the Siberia-2 storage ring

Synchrotron radiation (SR) generated by homogeneous magnetic fields of bending magnets is now employed at the Siberia-2 electron storage ring. It is planned that, in the near future, most of the storage ring’s free straight sections will be equipped with insertion devices (undulators and wigglers). Two projects of specialized radiation sources based on the Siberia-2 stor age ring are discussed. The first source is a vacuum milliundulator intended for generation of extremely bright X-ray beams. An X-ray source with vertically limited diffraction is shown to be feasible when the vertical emittance of an electron beam is equal to the diffraction emittance of photons with an energy of 2 keV. The second source uses edge radiation (ER) generated at the ends of bending magnets of the storage ring. Calculations show that, in the infrared and ultraviolet spectral regions, the ER intensity must exceed the intensity of standard SR formed by the homogeneous field of a bending magnet.     

A Non-geometric Relativistic Theory of Gravitation

A non-geometric relativistic theory of gravitation is developed by defining a semi-metric to replace the metric tensor as gravitational vector potential. The theory show that the energy-momentum tensor of the gravitational field belong to the gravitational source, gravitational radiation is contained in Einstein’s field equations that including the contribution of gravitational field, the real physical singularity in the gravitational field can be eliminated, and the dark matter in the universe is interpreted as the matter of pure gravitational field.     

Gravitational energy from a quadratic Lagrangian with torsion

Gravitation is considered as a gauge field within the formalism of Utiyama and Kibble. In empty space-time a Lagrangian density, quadratic in Riemann's curvature tensor and in Cartan's torsion tensor, is introduced. The equations of motion are coupled differential equations for the curvature and torsion tensors. The spin of the torsion field behaves as a curvature source and the energy of both fields acts as a torsion source. Each field has an energy tensor, similar to the Maxwell tensor of electrodynamics, vanishing in a torsionless space. It thus appears that the torsion of space-time is a geometric property that makes possible the propagation of gravitational energy in the absence of matter.A summary of this work was presented to the first Marcel Grossmann meeting on the recent progress of the fundamentals of general relativity (Trieste, July 1975).     

Hamiltonian Structure for Dispersive and Dissipative Dynamical Systems

We develop a Hamiltonian theory of a time dispersive and dissipative inhomogeneous medium, as described by a linear response equation respecting causality and power dissipation. The proposed Hamiltonian couples the given system to auxiliary fields, in the universal form of a so-called canonical heat bath. After integrating out the heat bath the original dissipative evolution is exactly reproduced. Furthermore, we show that the dynamics associated to a minimal Hamiltonian are essentially unique, up to a natural class of isomorphisms. Using this formalism, we obtain closed form expressions for the energy density, energy flux, momentum density, and stress tensor involving the auxiliary fields, from which we derive an approximate, “Brillouin-type,” formula for the time averaged energy density and stress tensor associated to an almost mono-chromatic wave.     

The velocity-dependent source function in radiative transfer theory

We consider the effect of velocity fields upon the transfer of line radiation by two-level atoms. We show that a simultaneous solution of the radiation transfer equation and the time-dependent rate equations leads to an equation for the source function which contains the Lagrangian derivative. We discuss a physical interpretation of the derivative term and present a method for solving this type of problem.We exhibit calculations which show that, for quite reasonable velocity fields, large errors can be produced if the derivative terms in the rate equations are neglected.     

Stress-energy connection and cosmological constant problem

We study gravitational properties of vacuum energy by erecting a geometry on the stress-energy tensor of vacuum, matter and radiation. Postulating that the gravitational effects of matter and radiation can be formulated by an appropriate modification of the spacetime connection, we obtain varied geometrodynamical equations which properly comprise the usual gravitational field equations with, however, Planck-suppressed, non-local, higher-dimensional additional terms. The prime novelty brought about by the formalism is that, the vacuum energy does act not as the cosmological constant but as the source of the gravitational constant. The formalism thus deafens the cosmological constant problem by channeling vacuum energy to gravitational constant. Nevertheless, quantum gravitational effects, if any, restore the problem via the graviton and graviton-matter loops, and the mechanism proposed here falls short of taming such contributions to cosmological constant.     

Energy conditions and classical scalar fields

Attention has been recently called upon the fact that the weak and null energy conditions are violated in wormhole solutions of Einstein's theory with classical, nonminimally coupled, scalar fields as material source. It is shown that the discussion is only meaningful when ambiguities in the definitions of stress-energy tensor and energy density of a nonminimally coupled scalar are resolved. The three possible approaches are discussed with emphasis on the positivity of the respective energy densities and covariant conservation laws. The root of the ambiguities is traced to the energy localization problem for the gravitational field.     

Helical Cerenkov effect, a novel radiation source

The observability of the helical Cerenkov effect as a novel radiation source is discussed. Depending on the value of the index of refraction of the medium, the strength of the uniform magnetic field, and the electron beam energy, helical Cerenkov radiation can occur in the same spectral regions as the ordinary Cerenkov effect, that is, from microwave to visible wavelengths. From the kinematics point of view, I argue that for a microwave wavelength of 10^-1cm this effect should be observable in a medium with an index of refraction of 1.4, with a beam energy of 3 MeV, and a uniform magnetic field of 4 T. On the specific level, however, for the sake of simplicity, I discuss the observability of this effect for visible light with the central wavelength of 5×10^-5 cm which can be achieved with 2 MeV in beam energy, silica aerogel as a medium (with an index of refraction of 1.075), and uniform magnetic fields from 5 to 10 T. For a 10-T magnetic field, I calculate that in the visible region of 250 to 750 nm an electron will produce a photon per 10 cm of traveled length. As to the stimulated helical Cerenkov emission, I estimate that respectable gains are possible even if the beam passes close to the dielectric rather than through it. In addition to being potentially a new radiation source, the helical Cerenkov effect could possibly be used as a detector of radiation by energetic electrons that are trapped in a medium by strong magnetic fields     

Modelling background radiation in isotropic cosmologies

Using explicit perturbations of isotropic cosmological models which describe simple gravitational waves, an isotropic tensor having the algebraic symmetries of the Bel–Robinson tensor is derived as a model of cosmic background gravitational radiation and this is used to provide an answer to the question: in what sense can an energy–momentum–stress tensor similar to that describing the cosmic microwave background radiation (neglecting anisotropies) be associated with an isotropic background of gravitational radiation?     

A Monte-Carlo generator for statistical hadronization in high energy e+e− collisions

We extend some previous attempts to explain the origin and evolution of primordial magnetic fields during inflation induced from a 5D vacuum. We show that the usual quantum fluctuations of a generalized 5D electromagnetic field cannot provide us with the desired magnetic seeds. We show that special fields without propagation on the extra non-compact dimension are needed to arrive at appreciable magnetic strengths. We also identify a new magnetic tensor field B _ij in this kind of extra dimensional theory. Our results are in very good agreement with observational requirements, in particular from TeV blazars and CMB radiation limits we see that primordial cosmological magnetic fields should be close to scale invariance.     

冲击脉冲辐射天线辐射场计算及应用

根据由张量法得到的任意线天线电场计算公式,利用镜像法推导,得到冲击脉冲辐射天线辐射电场的时域解析表达式。应用该表达式计算冲击脉冲辐射天线应用于辐射波电磁脉冲模拟器的时域辐射场,并与数值计算进行比较,结果表明:解析计算得到的辐射场波形与数值计算结果吻合较好,因此,利用解析表达式可以方便地观察天线结构参数对天线辐射场波形的影响,从而选取合适的参数以产生符合标准要求的天线场波形。     

非平衡辐射烧蚀对内爆中子产额的影响

 利用1维多群非平衡辐射输运RDMG程序,对不同能谱分布的辐射场驱动的靶丸的辐射烧蚀过程及中子产额进行了模拟计算,并与实验测量结果进行了初步比较。结果发现,辐射驱动源的能谱平衡性,特别是高能金M带成分对内爆靶丸产生预热效应,降低核燃料区压缩度,电子及离子温度,从而显著降低了中子产额。计算结果表明：中子产额随CH壳厚增加而下降,该变化规律与实验结果基本符合。