Channeling and radiation of the 855 MeV electrons enhanced by the re-channeling in a periodically bent diamond crystal

Channeling properties and radiation spectra are studied on the grounds of numerical simulations for the 855 MeV electrons in a periodically bent diamond crystal. The bent crystalline profiles are shown to enhance the re-channeling of the projectiles and to produce distinct lines in the radiation spectra. The results obtained are analyzed and contrasted to the properties of the planar channeling and of the channeling in uniformly bent crystals.Comment: 8 pages, 5 figure

Bound states of negatively charged ions induced by a magnetic field

We analyse the bound states of negatively charged ions which were predicted to exist because of the presence of a magnetic field by Avron et al. We confirm that the number of such states is infinite in the approximation of an infinitely heavy nucleus and provide insight into the underlying physical picture by means of a combined adiabatic and perturbation theoretical approach. We also calculate the corresponding binding energies which are qualitatively different for the states with vanishing and non-vanishing angular momentum. An outlook on the case of including center of mass effects is presented.Comment: 14 pages, 2 figure

Neutrino-electron processes in a dense maqnetized plasma

The neutrino-electron processes in a dense strongly degenerate magnetized plasma are analyzed in the framework of the Standard Model. The total probability and the mean values of the neutrino energy and momentum losses are calculated. It is shown that neutrino scattering on the excited electrons with Landau level number conservation dominates under the conditions "mu^2 > eB >> mu T" but does not give a contribution into the neutrino force acting on plasma along the magnetic field.Comment: 7 pages, LATEX, to appear in Modern Physics Letters

Once-ionized helium in superstrong magnetic fields

It is generally believed that magnetic fields of some neutron stars, the so-called magnetars, are enormously strong, up to 10^{14} - 10^{15} G. Recent investigations have shown that the atmospheres of magnetars are possibly composed of helium. We calculate the structure and bound-bound radiative transitions of the He^+ ion in superstrong fields, including the effects caused by the coupling of the ion's internal degrees of freedom to its center-of-mass motion. We show that He^+ in superstrong magnetic fields can produce spectral lines with energies of up to about 3 keV, and it may be responsible for absorption features detected recently in the soft X-ray spectra of several radio-quiet isolated neutron stars. Quantization of the ion's motion across a magnetic field results in a fine structure of spectral lines, with a typical spacing of tens electron-volts in magnetar-scale fields. It also gives rise to ion cyclotron transitions, whose energies and oscillator strengths depend on the state of the bound ion.Comment: 12 pages, including 3 figures. Submitted to ApJ Letters (revised version

Simulation of Ultra-Relativistic Electrons and Positrons Channeling in Crystals with MBN Explorer

A newly developed code, implemented as a part of the \MBNExplorer package \cite{MBN_ExplorerPaper,MBN_ExplorerSite} to simulate trajectories of an ultra-relativistic projectile in a crystalline medium, is presented. The motion of a projectile is treated classically by integrating the relativistic equations of motion with account for the interaction between the projectile and crystal atoms. The probabilistic element is introduced by a random choice of transverse coordinates and velocities of the projectile at the crystal entrance as well as by accounting for the random positions of the atoms due to thermal vibrations. The simulated trajectories are used for numerical analysis of the emitted radiation. Initial approbation and verification of the code have been carried out by simulating the trajectories and calculating the radiation emitted by \E=6.7 GeV and \E=855 MeV electrons and positrons in oriented Si(110) crystal and in amorphous silicon. The calculated spectra are compared with the experimental data and with predictions of the Bethe-Heitler theory for the amorphous environment.Comment: 41 pages, 11 figures. Initially submitted on Dec 29, 2012 to Phys. Rev.

Fine structure of the exciton absorption in semiconductor superlattices in crossed electric and magnetic fields

The exciton absorption coefficient is determined analytically for a semiconductor superlattice in crossed electric and magnetic fields, for the magnetic field being parallel and the electric field being perpendicular to the superlattice axis. Our investigation applies to the case where the magnetic length, while being much smaller than the exiton Bohr radius, considerably exceeds the superlattice period. The optical absorption in superlattices displays a spectral fine structure related to the sequences of exciton states bound whose energies are adjacent to the Landau energies of the charge carriers in the magnetic field. We study effects of external fields and of the centre-of-mass exciton motion on the fine structure peak positions and oscillator strengths. In particular, we find that the inversion of the orientation of the external fields and of the in-plane total exciton momentum notably affects the absorption spectrum. Conditions for the experimental observation of the exciton absorption are discussed