Pair Photoproduction in Constant and Homogeneous Electromagnetic Fields

The process of pair creation by a photon in a constant and homogeneous electromagnetic field of an arbitrary configuration is investigating. At high energy the correction to the standard quasiclassical approximation (SQA) has been calculated. In the region of intermediate photon energies where SQA is inapplicable the new approximation, developed recently by authors, is used. The influence of weak electric field on the process in a magnetic field is considered. In particular, in the presence of electric field the root divergence in the probability of pair creation on the Landau energy levels is vanished. For smaller photon energies the low energy approximation is used. The found probability describes the absorption of soft photon by particles created by field. At low photon energy the electric field action dominates and the influence of magnetic field on the process is connected with the interaction of it and the magnetic moment of creating particles.Comment: 11 page

Beam-size effect in Bremsstrahlung

The smallness of the transverse dimensions of the colliding beams leads to suppression of bremsstrahlung cross section. This beam-size effect was discovered and investigated at INP, Novosibirsk. Different mechanisms of radiation are discussed. Separation of coherent and incoherent radiation is analyzed in detail. For linear collider this suppression affects the whole radiation spectrum. It is shown that objections to the subtraction procedure in \cite{BK2} are groundless.Comment: Plenary talk at the Workshop "Quantum Aspects of Beam Physics", Hiroshima, Japan, January 7-11, 2003. To be pulished in the Proceedings (World Scientific, Singapore

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.Comment: 15 pages, 3 figure