Form-factor measurements on chromium with high-energy synchrotron radiation

Results of high-energy magnetic X-ray diffraction on pure antiferromagnetic chromium are presented. The temperature dependence of the propagation vector of the spin-density wave (SDW) and the strain-wave (SW) could be reproduced. The temperature dependence of the magnetic integrated intensity could be measured in the transversally as well as in the longitudinally polarised SDW phase. The magnetic form-factor has been determined in the transversally polarised SDW phase with five magnetic satellites. For the first time a spin-orbit separation has been performed by comparing X-ray to neutron data. The small orbital contribution to the magnetisation density turns out to be negligible, in agreement to our relativistic band-structure calculations. In addition, measurements of strain-wave reflections have been undertaken, and the results complement previous studies. Received 17 August 1998 and Received in final form 10 August 1999     

On the hadron contributions to high-energy quantum electrodynamics

Without taking into account the electromagnetic structure, caused by the strong interactions, all charged particles contribute with nearly the same weight to the electromagnetic vacuum polarization at very high energy. The structure effects come in via the form factors at timelike momentum transfer. By making use of the strong asymptotic decrease of the nucleon form factors for spacelike argument, it is inferred from an unsubtracted dispersion relation that the nucleon contribution to vacuum polarization can be neglected asymptotically, compared to the contribution of the unstructured leptons.     

Terahertz radiation from carbon nanorings in external collinear constant and varying electric fields

We consider the response of a quasi-one-dimensional ballistic carbon ring to the field of an electromagnetic wave propagating along the normal to the ring plane in the presence of a constant electric field collinear to the field of the wave. The dipole moment and the radiation intensity of the ring are calculated for the ballistic motion of a conduction electron. The possibility of implementation of regular periodic and chaotic regimes of ring emission under the action of external fields is demonstrated. The radiation spectrum of the ring is analyzed, and the dependence of the scattering cross section for an electromagnetic wave incident on the ring on its frequency and amplitude is calculated.     

Interactions of high-energy cosmic rays with extragalactic infrared radiation background

We consider the modification of the extragalactic cosmic-ray spectrum caused by cosmic-ray interactions with infrared background photons which are present in extragalactic space together with relic photons. It is assumed that cosmic-ray spectrum at superhigh energies has extragalactic origin and is proton dominated. The text was submitted by the authors in English.     

The HERO project for the study of high-energy primary cosmic radiation

Proposals for the High-Energy Ray Observatory (HERO) comprising scientific equipment with increased power availability are presented. Under the long exposure (>7 years), it is proposed to investigate the spectrum and charge composition of cosmic-ray nuclei up to E ₀ ～ 10¹⁶ eV and to determine the behavior of the energy spectrum in the energy regions >100 GeV for cosmic-ray electrons and >50 GeV for γ radiation. The geometrical factor of the apparatus is 6.0–9.0 m² sr depending on the type of particles.     

Inhomogeneous lens antenna design with fan-beam radiation pattern

This Letter presents an original technique to design and synthesize an inhomogeneous asymmetrical lens resulting in a special fan-beam radiation pattern in a wide frequency bandwidth. The vertical and horizontal planes of the fan-beam radiation pattern can be determined separately. Wide angle search and detection are achievable by using this type of lens antenna because of its suitable radiation pattern. The proposed relative index profile is validated by the means of commercial CST software and an FDTD scheme.     

The early high-energy afterglow emission from short GRBs

We calculate the high energy afterglow emission from short Gamma-Ray Bursts (SGRBs) in the external shock model. There are two possible components contributing to the high energy afterglow: electron synchrotron emission and synchrotron self-Compton (SSC) emission. We find that for typical parameter values of SGRBs, the early high-energy afterglow emission in 10 MeV-10 GeV is dominated by synchrotron emission. For a burst occurring at redshift z = 0.1, the high-energy emission can be detectable by Fermi LAT if the blast wave has energy E ⩾ 10⁵¹ ergs and the fraction of electron energy ɛ _e ⩾ 0.1. This provides a possible explanation for the high energy tail of SGRB 081024B.

     

Photo-protons from high-energy bremsstrahlung

Recent results on the yields of high-energy photo-protons from both bremsstrahlung and monochromatic photons incident mainly on carbon are compared with calculations using the Gabriel-Alsmiller model of high-energy photo-induced reactions. Good agreement is found for photons of energies up to 600 MeV.     

Control of pattern formation by time-delay feedback with global and local contributions

We consider the suppression of spatiotemporal chaos in the complex Ginzburg-Landau equation by a combined global and local time-delay feedback. Feedback terms are implemented as a control scheme, i.e., they are proportional to the difference between the time-delayed state of the system and its current state. We perform a linear stability analysis of uniform oscillations with respect to space-dependent perturbations and compare with numerical simulations. Similarly, for the fixed-point solution that corresponds to amplitude death in the spatially extended system, a linear stability analysis with respect to space-dependent perturbations is performed and complemented by numerical simulations.     

LEED Kikuchi pattern: Phonon and plasmon contributions

Detailed properties of LEED Kikuchi patterns for MgO and Al are studied experimentally and theoretically. The Kikuchi line disappearance, the intensity change of various Kikuchi bands, the temperature dependence of Kikuchi band intensity etc. are studied experimentally with an energy analyser, and the results are interpreted theoretically by phonon and plasmon excitations.     

Coherent and incoherent radiation from high-energy electron and the LPM effect in oriented single crystal

The process of radiation from high-energy electron in oriented single crystal is considered using the method which permits inseparable consideration of both coherent and incoherent mechanisms of photon emission. The total intensity of radiation is calculated. The theory, where the energy loss of projectile has to be taken into account, agrees quite satisfactory with available CERN data. It is shown that the influence of multiple scattering on radiation process is suppressed due to action of crystal field.     

Structuring of material parameters in lithium niobate crystals with low-mass, high-energy ion radiation

Ferroelectric lithium niobate crystals offer a great potential for applications in modern optics. To provide powerful optical components, tailoring of key material parameters, especially of the refractive index n and the ferroelectric domain landscape, is required. Irradiation of lithium niobate crystals with accelerated ions causes strong structured modifications in the material. The effects induced by low-mass, high-energy ions (such as ³He with 41?MeV, which are not implanted, but transmit through the entire crystal volume) are reviewed. Irradiation yields large changes of the refractive index ??n, improved domain engineering capability within the material along the ion track, and waveguiding structures. The periodic modification of ??n as well as the formation of periodically poled lithium niobate (PPLN) (supported by radiation damage) is described. Two-step knock-on displacement processes, ³He??Nb and ³He??O causing thermal spikes, are identified as origin for the material modifications.     

Energy characteristics of planar-channeling radiation for high-energy electrons in diamond

γ-ray spectra have been measured for (110) and (111) planar channeling of 600–900 MeV electrons in a diamond crystal. It is shown that in the case of (111) crystallographic planes the influence of molecular-type motion on the formation of the spectra is predominant.     

SrTiO3同质外延过程中的反射高能电子衍射图案分析

在激光分子束外延实验中,用RHEED原位监测了SrTiO3基片初始、退火以及同质外延过程中的表面形态.通过对RHEED图案分析,获取了表面面内的晶格常数振荡与衍射条纹的半高宽振荡现象,前者是由退火重构表面与薄膜之间的界面造成的,后者与二维岛边界的弛豫相关.另外还观察到了等离子体对入射电子束的影响而导致的RHEED强度振荡行为的相位移现象.     

Muons from high-energy cosmic photino

Summary The muon production at photino-nucleon interaction for high-energy photino (E⊂)10⁴GeV) is studied. The production of muons is the result of the creation and the subsequent decay of charmed hadrons. The quark subprocess considered is . In the calculation the chains of reactions and c→D→μ are taken into account. The main contribution to a muon flux is given by the production of -quark. Muon fluxes from high-energy cosmic photino absorbed in water (ground) and atmosphere are calculated. For muon energy above −2.10³GeV the ration of equilibrium underground muon flux to photino flux decreases with a rise of energyE because of nuclear interactions of D-mesons at decay length, and at energy −2·10⁵GeV the vertical muon flux created in the atmosphere becomes comparable with underground equilibrium flux. The production of muons by photino is less effective than by neutrino: the ratio is higher than for all energies. On the other hand, the cross-section at superhigh energies is by a factor of −10² larger than the cross-section. This fact gives some signature of photino flux from source in case of combined observations by sea-level EAS arrays and underground detectors: large EAS flux and relatively small flux of underground high-energy muons.

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Riassunto Si studia la produzione di muoni nell'interazione fra il fotino e il nucleone per il fotino ad alta energia (E>-10⁴GeV). La produzione dei muoni è il risultato della creazione e del conseguente decadimento di adroni con charm. Il subprocesso dei quark considerato è . Nel calcolo sono considerate le catene di reazioni e c→D→μ. Il contributo principale al flusso dei muoni è dato dalla produzione del quark . Si calcolano i flussi dei muoni dal fotino cosmico ad alta energia assorbito nell'acqua (terra) e nell'atmosfera. Per un'energia dei muoni sopra ≈2·10³GeV il rapporto tra il flusso dei muoni sotterranei in equilibrio e il flusso dei fotini diminuisce al crescere dell'energiaE a causa delle interazioni dei mesoni D a lunghezza di decadimento, e ad un'energia ∼2·10⁵GeV il flusso dei muoni verticale creato nell'atmosfera diventa paragonabile al flusso in equilibrio sotterraneo. La produzione di muoni da parte del fotino è meno efficace di quella causata dal neutrino: il rapporto è maggiore di per tutte le energie. D'altra parte, la sezione d'urto ad energie super alte è maggiore della sezione d'urto di un fattore di ∼10². Essa dà un qualche segno del flusso dei fotini dalla sorgente in caso di osservazioni combinate da schiere EAS a livello del mare e rilevatori sotterranei: un alto flusso EAS e uno relativamente ridotto di muoni sotterranei ad alta energia.

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Реэуме Исспедется роздение муонов ири взаямцеиствиях фотино с нуклонами ири энергиях фотино (E>=10⁴ ГэВ). Роздение муонов ирецтавляет реэултат обраэования и поцледыюшего раццада ачарованных адронов. Рааццматqrиваетця кварковыи цубпроцецц . При вычициениях учитываутця кварковыи реакций и c→D→μ. Оцновной вклац в мюнный поток опредчтця рождением -кварка. Вычицяютця потокоцмичецнмх фотино, поглощенные в воде (эемле) и в атмосфере. Для мюонов с энергиями выще ∼ 2·10³ ГэВ отнощение равновесного потока мюонов поц эемлей к пооку фотино уменящается с ростом энерпии Э иэ-эа ядерных бэаимодействий Д-меэонов на длине распада, и при энергии ∼2·10⁵ ГэВ вертикальный поток мюнов, образованных в атмосфере, становится сравнимым с равновесным потоком под землей. Рождение мюонов фотино оказывается менее эффективным, чем рождение мюонов нейтрино: отношение выше, чем для всех энергиях. С другой стороны, поперечное сечение при супервысоких энергиях оказывается примерно в 10² раз больше, чем сечение. В работе приводятся некоторые сигнатуры для потока фотино от источника в случае комбинированных наблюдений с помощью антенн широких атмосферных ливней на уровне моря и с помщью подземных детекторов: большой поток широких атмосферных ливней и относительно малый поток подземных мюонов высоких энергий.

     

The high-energy quark-quark scattering: from Minkowskian to Euclidean theory

In this paper we consider some analytic properties of the high-energy quark-quark scattering amplitude, which, as is well known, can be described by the expectation value of two lightlike Wilson lines, running along the classical trajectories of the two colliding particles. We will show that the expectation value of two infinite Wilson lines, forming a certain hyperbolic angle in Minkowski space-time, and the expectation value of two infinite Euclidean Wilson lines, forming a certain angle in Euclidean four-space, are connected by an analytic continuation in the angular variables: the proof is given for an Abelian gauge theory (QED) in the so-called quenched approximation and for a non-Abelian gauge theory (QCD) up to the fourth order in the renormalized coupling constant in perturbation theory. This could open the possibility of evaluating the high-energy scattering amplitude directly on the lattice or using the stochastic vacuum model.     

Synthesis of current on a strip from a given realizable radiation pattern

A theory of synthesis of current on a strip from a given realizable radiation pattern is developed. The theory chooses the space of currents from the condition that the near-zone field is limited. The space of patterns is defined as the image of the space of currents due to current-to-pattern mapping. For these spaces, the Hilbert structure is introduced and the basis is constructed. As a result, the problem of synthesizing current from a given pattern is reduced to expansion over the basis. A numerical example is considered.     

The directivity pattern of an interferometer for measuring thermal acoustic radiation

The directivity patterns of a pair of piezoelectric transducers for measuring the spatial correlation function of sound pressures produced by sources of thermal acoustic radiation in the megahertz frequency range are calculated. Sources in the form of a heated plane or strip are considered. The signal detection by two circular or rectangular piezoelectric transducers and by focusing transducers is studied. It is demonstrated that, for measuring the correlation function, the piezoelectric transducers must partially overlap. To determine the directivity pattern with a strong dependence on the distance between the heated object and the pair of piezoelectric transducers, focusing piezoelectric transducers should be used. The results obtained offer possibilities for a noninvasive measurement of the absorption coefficient of a medium and also for the realization of the previously proposed [20] passive acoustic thermotomograph, which does not use a priori information on the absorption coefficient of the medium.     

Investigations of ultrafast phenomena in high-energy density physics using X-ray FEL radiation

The advent of highly intense and ultrashort pulses of short-wavelength radiation in the vacuum-ultraviolet to X-ray regime provides for the first time the possibility to study plasmas at the time scale of equilibration or even electron thermalization. The emerging radiation sources are free-electron lasers (FEL) based on high-energy electron accelerators. FELs provide a peak brilliance nine orders of magnitude higher than the best performing X-rays sources today. The FEL radiation parameters will enable the creation of high-energy density states of matter and the development of new diagnostics tools to investigate dense plasmas. As the first of the new sources the VUV-FEL at DESY, Hamburg becomes operational for high-energy density physics experiments during 2005.