References14

Newest

Abstract Transmission electron microscopy of single-cryatal non-stoichiometric spinel (MgO. 3–5 A12O3) deformed in compression at 1500°C have revealed dislocation networks in which the ½〈110〉 dislocations are extended by climb into ¼〈110〉 collinear partials. Dislocation nodes of two types are found, both of the form ½[110] + ½[101] + ½[110] = 0. One configuration (type I) forms by climb dissociation and contains two partial modes of the form ¼[110] + ¼[101] + ¼[101] = 0, while the second (type I...

Tabulations are presented of relativistic Hartree‐Fock atomic form factors F (x,Z), for values of x (=sin(ϑ/2)/λ from 0.01 to 109 A−1, for all elements Z=1 to 100. For Z=1, F (x,Z) is given by the exact expression of Pirenne. For Z=2 to 98, x=0.01 to 2.0 A−1, the tabulated values are those of Cromer and Waber given in the International Tables for X−Ray Crystallography (Vol. IV, 1974), based in part on the work of Doyle and Turner. For Z=21 to 92, x=2.2 to 6.0 A−1, the present tables are based on...

Atomic form factors for momentum transfers between 0.1mec and infinity are given for the neutral atoms 3Li through 19K and for 22Ti.

Atomic form factors are calculated for momentum transfers between 0.1mec and infinity. The calculation is based on electron charge densities obtained from a relativistic self-consistent-field program with exchange represented essentially by the Gaspar-Kohn-Sham equivalent potential. Form factors are tabulated in the range 0.1mec≲q≲2mec for 18 atoms ranging from20Ca to92U. For higherq, the form factor for each atom is given as a simple 3-parameter form, multiplying the Bethe-Levinger relativistic...

Abstract Photon splitting in a Coulomb field cross-section has been found and compared with recent DESY experiment. The theoretical cross-section is approximately two order of magnitude lower than experimental one. A possible origin of the discrepance is discussed.

The differential cross section for Delbruck scattering has been measured at photon energies between 1 and 7 GeV and scattering angles between 1 and 3 mrad on copper, silver, gold, and uranium targets. The results confirm the predictions of quantum electrodynamics, if the exchange of a very large number of photons with the nucleus (Coulomb correction) is taken into account. At momentum transfers of a few MeV/c, the Coulomb correction for uranium results in a reduction of the cross section by a fa...

The fourth-rank vacuum polarization tensor, which is related to the lowest-order nonlinear interaction between four electromagnetic fields in quantum electrodynamics, is exactly calculated in terms of rational, logarithm and dilogarithm functions when two of the four electromagnetic fields describe photons off the mass shell. This task has been accomplished by a not exccedingly laborious effort with the aid of double dispersion relations which proved to be a very convenient tool for the treatmen...

The cross-section for the splitting of a photon into two photons in the Coulomb field of a nucleus is determined with the standard techniques of the quantum electrodynamics for the case in which the energy of the incident photon is smaller than two electron masses. Numerical evaluations for some values of the variables are made in this energy range.

The cross section for photon splitting in a nuclear electric field is derived, using the Feynman formulation of quantum electrodynamics. A closed form for the cross section is obtained and numerical values for interesting cases are calculated.

Cited By7

Newest

Probing and possible application of the QED vacuum with micro-bubble implosions induced by ultra-intense laser pulses

The interaction of micro-bubbles with ultra-intense laser pulses has been shown to generate ultra-high proton densities and correspondingly high electric fields. We investigate the possibility of using such a combination to study the fundamental physical phenomenon of vacuum polarization. With current or near-future laser systems, measurement of vacuum polarization via the bending of gamma rays that pass near imploded micro-bubbles may be possible. Since it is independent of photon energy to wit...

In the last years the Lorentz Violation scheme was implemented in QFT, in special in standard model of particle physics, in an attempt to explain our actual open problems. In this work we analyze non-minimal couplings between a Lorentz-violating 4-vector and the photon field and the leptonic current of QED. The 1-loop contribution of the elastic photon-photon scattering is showed and the novel characteristics which arose are pointed out.

Abstract Photon splitting due to vacuum polarization in the electric field of an atom is considered. We survey different theoretical approaches to the description of this nonlinear QED process and several attempts of its experimental observation. We present the results of the lowest-order perturbation theory as well as those obtained within the quasiclassical approximation being exact in the external field strength. The experiment where photon splitting was really observed for the first time is ...

Various differential cross sections of high-energy photon splitting in the electric fields of heavy atoms are calculated exactly in the parameter \al. The consideration is based on the quasiclassical approach applicable for small angles between all photon momenta. The expressions obtained are valid for arbitrary transverse momenta of final photons . The detailed investigation of the process is performed taking into account the effect of screening . The exact cross section turns out to be noticea...

The helical splitting amplitudes of a high-energy photon in an external Coulomb field are found exactly with respect to Zα. Both screened and unscreened potentials are investigated. The treatment is carried out within the semiclassical approach, which is valid for small angles between the momenta of all photons. A new representation is used for the semiclassical electronic Green’s function. The resulting expressions are analyzed in detail for the case of transverse components of the momenta of t...

The splitting of one photon into two in the electric field of a nucleus is discussed in lowest order perturbation theory. Various aspects of photon splitting cross sections that are of interest for an experimental detection of the process are presented. The behaviour of the differential cross section and a partially integrated cross section, summing over one splitting photon, are explained in detail. Useful approximate scale transformation formulas are presented and a fit to the partially integr...