Electromagnetic interpretation of the massless spin-1 field equation in curved space-time

The source-free Maxwell equations associated to the massless spin-1 free field equation are considered in curved space-time. The gauge invariance of the theory is discussed by using as starting point the notion of the spinor potential. The structure of the electromagnetic field in the case of the Robertson-Walker space-time is discussed by using the solutions of the massless spin-1 equations previously determined. The flat-universe case of the standard cosmology is studied exactly and considered in some limiting physical situations.     

Effect of internal waves on the intensity and interference structure of the sound field in a shelf zone

Experimental data obtained by studying the effect of internal waves with known space-time parameters on the propagation of a 240-Hz tone signal and on the space-time interference structure of the sound field generated by a noiselike sound source are presented.     

Simple linear technique for the measurement of space-time coupling in ultrashort optical pulses

We demonstrate a simple sensitive linear technique that quantifies the spatiotemporal coupling in the electric field of an ultrashort optical pulse. The space-time uniformity of the field can be determined with only time-stationary filters and square-law integrating detectors, even if it is impossible to measure the temporal electric field in this way. A degree of spatiotemporal uniformity is defined and can be used with the demonstrated diagnostic to quantify space-time coupling. Experimental measurements of space-time coupling due to linear and nonlinear focusing, refraction, and diffraction are presented.     

The structure of groups of motions admitted by Einstein-Maxwell space-times

The known symmetry of the non-null electromagnetic field, which acts as the source of a four-dimensional space-time satisfying the Einstein-Maxwell equations, is used to show that when such a space-time admits a group of motions, generated by a Killing vector, the structure constants for the group must satisfy an additional relation to the known relations of group theory.     

Gauge Gravitational Field in a Fractal Space-Time

Considering the fractal structure of space-time, the scale relativity theory in the topological dimension D_T=2 is built. In such a conjecture, the geodesics of this space-time imply the hydrodynamic model of the quantum mechanics. Subsequently, the gauge gravitational field on a fractal space-time is given. Then, the gauge group, the gauge-covariant derivative, the strength tensor of the gauge field, the gauge-invariant Lagrangean, the field equations of the gauge potentials and the gauge energy-momentum tensor are determined. Finally, using this model, a Reissner-Nordström type metric is obtained.     

External fields as intrinsic geometry

There is an interesting dichotomy between a space-time metric considered as external field in a flat background and the same considered as an intrinsic part of the geometry of space-time. We shall describe and compare two other external fields which can be absorbed into an appropriate redefinition of the geometry, this time a noncommutative one. We shall also recall some previous incidences of the same phenomena involving bosonic field theories. It is known that some such theories on the commutative geometry of space-time can be re-expressed as abelian-gauge theory in an appropriate noncommutative geometry. The noncommutative structure can be considered as containing extra modes all of whose dynamics are given by the one abelian action. Received: 1 December 2000 / Published online: 23 January 2001     

Spinor fields at spacelike infinity

The concept of a spinor structure at spacelike infinity is introduced for space-times which are asymptotically flat. It is shown how zero-rest-mass fields on space-time acquire smooth limits on this structure and that these limits satisfy certain differential equations characterized by the helicity and regularity of the field. The geometry of the limits of twistor fields is also discussed, and it seems possible that one can define the momentum and angular momentum of an asymptotically flat space-time in terms of a twistor space at spacelike infinity.     

Quantum Fields in the Spacetime Tangent Bundle

Maximal-acceleration invariant quantum fields are formulated in terms of the differential geometric structure of the spacetime tangent bundle. The simple special case is considered of a flat Minkowski space-time for which the bundle is also flat. The field is shown to have a physically based Planck-scale effective regularization and a spectral cutoff at the Planck mass.     

Space-time sound field interference in the horizontal plane in a coastal slope region

The nonstationary interference structure formed in the horizontal plane in the field of a point source in a coastal slope region is analyzed on the basis of the space-time horizontal ray concept. For a model that includes the typical bathymetry and sound velocity profile, the space, time, and frequency dependences of the sound field are considered for different waveguide modes. The characteristic scales of the field variability in space and time are estimated. The frequency-time diagram is analyzed for the region of the interference of direct and reflected waves. The variability of the field interference structure in the presence of mesoscale perturbations is considered.     

旋翼尾流时空发展二维速度场的实验研究

旋翼作为直升机的主要升力和操纵部件, 具有复杂的流场结构, 如非定常性, 桨-涡干扰和桨尖涡等, 导致旋翼流场研究十分困难. 针对这一问题, 结合锁相技术和粒子图像测速(particle image velocimetry, PIV)技术开展了悬停状态下旋翼流场的实验研究, 并通过本征正交分解(proper orthogonal decomposition, POD)提取主要含能模态, 刻画流场时空演化. 结果显示, 旋翼尾流发展过程中向旋转轴靠近, 二维流场结构呈现倒三角结构, 即扩展到三维流动中会呈现倒锥型结构的特性; 通过POD进行含能模态分析, 旋翼尾流中对湍动能贡献最大的为桨叶涡结构, 其次是桨尖涡结构.      

Intensity and space-time characteristics of the sound field in the underwater sound channel of the Black Sea

Experimental data are presented on the intensity and space-time characteristics of the sound field generated by explosions in underwater and surface sound channels of the Black Sea. The fine field structure is studied as a function of distance and positions of the source and the receiver. The discreteness of the field structure governed by the deterministic nature of the waveguide is revealed, and the destruction of this structure under the effect of the instability of the waveguide parameters is demonstrated. The effect of the rough sea surface on the sound field in the surface channel is studied, and the diffraction-caused propagation loss is estimated. The mechanism of the forerunner formation is considered. The experimentally observed sound field features are compared with the calculations. A possibility for solving the inverse problem is indicated, and the main parameters that are used in the ray method of determining the source coordinates in the underwater channel (i.e., the method earlier proposed by the author on the basis of the intrinsic structure of the sound field) are pointed out.     

Relativistic Nonlinear Optical Phenomena in the Field of Subterawatt Laser Pulses

Experiments on the generation of high optical harmonics demonstrating that relativistic regimes of interaction of radiation with matter can be implemented in the field of mid-infrared laser pulses with a peak power of 0.3 TW have been reported. The observation of relativistic phenomena at such extraordinary low peak powers of the laser field becomes possible because of the formation of a high-quality space-time mode of the laser field with an exactly specified polarization state. Such a field structure ensures a high intensity of radiation in the focus of the beam and the effective acceleration of electrons by a low-frequency electromagnetic field of a high-contrast laser pulse with an exactly specified polarization at the extremely sharp vacuum-solid interface.

     

On the Goldstonic gravitation theory

The physical specificity of gravity as a Goldstone-type field responsible for spontaneous breaking of space-time symmetries is investigated and extended up to supergravity. Problems of the Higgs gravitation vacuum and its matter sources are discussed. A particular “dislocation” structure of a space-time due to Poincaré translation gauge fields and the corresponding modification of Newton’s gravitational potential are predicted.     

A contribution to the Rainich theory of the neutrino field

The neutrino-gravitational field is divided into fourteen distinct classes. This classification is shown also to determine the class of the space-time. Then for four particular classes of space-time, necessary and sufficient conditions on the concomitants of the Ricci tensor are given for it to admit a neutrino field. It is further shown that for three of these classes the neutrino field is determined uniquely by the metric of space-time.     

The effect of temperature on the nonlinear dynamics of charge in a semiconductor superlattice in the presence of a magnetic field

The space-time dynamics of electron domains in a semiconductor superlattice is studied in a tilted magnetic field with regard to the effect of temperature. It is shown that an increase in temperature substantially changes the space-time dynamics of the system. This leads to a decrease in the frequency and amplitude of oscillations of a current flowing through the semiconductor superlattice. The quenching of oscillations is observed, which is attributed to the change in the drift velocity as a function of electric-field strength under the variation of temperature.     

Manifestation of external field effect in time-resolved photo-dissociation dynamics of LiF

The photo-dissociation dynamics of LiF is investigated with newly constructed accurate ab initio potential energy curves (PECs) using the time-dependent quantum wave packet method. The oscillations and decay of the wave packet on the adiabats as a function of time are given, which can be compared with the femtosecond transition-state (FTS) spectroscopy. The photo-absorption spectra and the kinetic-energy distribution of the dissociation fragments, which can exhibit the vibration-level structure and the dispersion of the wave packet, respectively, are also obtained. The investigation shows a blue shift of the band center for the photo-absorption spectrum and multiple peaks in the kinetic-energy spectrum with increasing laser intensity, which can be attributed to external field effects. By analyzing the oscillations of the wave packet evolving on the upper adiabat, an approximate inversion scheme is devised to roughly deduce its shape.     

Spatial control of recollision wave packets with attosecond precision

We propose orthogonally polarized two-color laser pulses to steer tunneling electrons with attosecond precision around the ion core. We numerically demonstrate that the angles of birth and recollision, the recollision energy, and the temporal structure of the recolliding wave packet can be controlled without stabilization of the carrier-envelope phase of the laser, and that the wave packet's properties can be described by classical relations for a point charge. This establishes unique mapping between parameters of the laser field and attributes of the recolliding wave packet. The method is capable of probing ionic wave packet dynamics with attosecond resolution from an adjustable direction and might be used as an alternative to aligning molecules. Shaping the properties of the recollision wave packet by controlling the laser field may also provide new routes for improvement of attosecond pulse generation via high harmonic radiation.     

Null surface quantization and quantum theory of massless fields in asymptotically flat space-time

The quantum theory of massless fields in an asymptotically simple space-time is developed. The Schwinger dynamical principle and the Penrose conformal technique are exploited to derive the commutation relations on proper null surfaces in a curved space-time and on null infinities. The explicit expression for theS matrix in an asymptotically simple space-time is presented. The general expression for a density matrix describing particles created in an external field is also given and its possible applications are discussed briefly.