Real and virtual photons in an external constant electromagnetic field of most general form

The photon behavior in an arbitrary superposition of constant magnetic and electric fields is considered on most general grounds basing on the first principles like Lorentz- gauge- charge- and parity-invariance. We make model- and approximation-independent, but still rather informative, statements about the behavior that the requirement of causal propagation prescribes to massive and massless branches of dispersion curves, and describe the way the eigenmodes are polarized. We find, as a consequence of Hermiticity in the transparency domain, that adding a smaller electric field to a strong magnetic field in parallel to the latter causes enhancement of birefringence. We find the magnetic field produced by a point electric charge far from it (a manifestation of magneto-electric phenomenon). We establish degeneracies of the polarization tensor that (under special kinematic conditions) occur due to space-time symmetries of the vacuum left after the external field is imposed.Comment: 30 pages, 1 figure, 57 equations, reference list of 38 item

Precursors of gamma-ray bursts: a clue to the burster's nature

In relativistic strongly magnetized winds outflowing from the fast-rotating compact progenitors of gamma-ray bursts (GRBs) there are three regions where powerful high-frequency emission may be generated: (i) the thermal photosphere, (ii) the region of the internal wind instability and (iii) the region of the wind interaction with an ambient gas. This results in a multicomponent structure of GRBs. The emission from the thermal photosphere may be observed as a weak precursor to the main burst. The precursor should have a blackbody-like spectrum with the mean energy of photons of $\sim 1$ MeV, and its intensity should be tens to hundreds of times smaller than that of the main GRB emission. Observations of such precursors with future $\gamma$-ray missions like GLAST can clarify the nature of bursters.Comment: 5 pages, 3 postscript figures, submitted to ApJ Let

Bethe-Salpeter approach for relativistic positronium in a strong magnetic field

We study the electron-positron system in a strong magnetic field using the differential Bethe-Salpeter equation in the ladder approximation. We derive the fully relativistic two-dimensional form that the four-dimensional Bethe-Salpeter equation takes in the limit of asymptotically strong constant and homogeneous magnetic field. An ultimate value for the magnetic field is determined, which provides the full compensation of the positronium rest mass by the binding energy in the maximum symmetry state and vanishing of the energy gap separating the electron-positron system from the vacuum. The compensation becomes possible owing to the falling to the center phenomenon that occurs in a strong magnetic field because of the dimensional reduction. The solution of the Bethe-Salpeter equation corresponding to the vanishing energy-momentum of the electron-positron system is obtained.Comment: 35 pages, minor correction

Positronium collapse and the maximum magnetic field in pure QED

A maximum value for the magnetic field is determined, which provides the full compensation of the positronium rest mass by the binding energy in the maximum symmetry state and disappearance of the energy gap separating the electron-positron system from the vacuum. The compensation becomes possible owing to the falling to the center phenomenon. The maximum magnetic field may be related to the vacuum and describe its structure.Comment: 4 pages, accepted for publication in Phys. Rev. Letter

Collective modes for an array of magnetic dots in the vortex state

The dispersion relations for collective magnon modes for square-planar arrays of vortex-state magnetic dots, having closure magnetic flux are calculated. The array dots have no direct contact between each other, and the sole source of their interaction is the magnetic dipolar interaction. The magnon formalism using Bose operators along with translational symmetry of the lattice, with the knowledge of mode structure for the isolated dot, allows the diagonalization of the system Hamiltonian giving the dispersion relation. Arrays of vortex-state dots show a large variety of collective mode properties, such as positive or negative dispersion for different modes. For their description, not only dipolar interaction of effective magnetic dipoles, but non-dipolar terms common to higher multipole interaction in classical electrodynamics can be important. The dispersion relation is shown to be non-analytic as the value of the wavevector approaches zero for all dipolar active modes of the single dot. For vortex-state dots the interdot interaction is not weak, because, the dynamical part (in contrast to the static magnetization of the vortex state) dot does not contain the small parameter, the ratio of vortex core size to the dot radius. This interaction can lead to qualitative effects like the formation of modes of angular standing waves instead of modes with definite azimuthal number known for the insolated vortex state dot

Межпрофессиональное сотрудничество как основное направление взаимодействия зарубежного судебно-экспертного сообщества

The paper reflects on the outcomes of the most recent conference of the International Association of Forensic Sciences (IAFS) held in Toronto, Canada. The meeting of delegates from all continents was organized around the theme «Inter-Professional Collaboration in Forensic Science», with the aim of exploring forensic scientists' responses to the challenges of the modern world. The meeting outcomes are analyzed in terms of valuable insights for the development of forensic practicesin Russia through the strengthening of multidisciplinary methodological approachesПредставлены результаты конференции Международной ассоциации судебной экспертизы (IAFS), которая состоялась в Торонто (Канада). Встреча экспертов со всех континентов проходила под девизом «Межпрофессиональное сотрудничество в судебной экспертизе» и была посвящена поиску адекватных ответов судебных экспертов на вызовы современного мира. Итоги международной встречи анализируются в плане дальнейшего развития российской судебно-экспертной практики на основе укрепления междисциплинарных методических подходо

Компетенция и компетентность в судебно-экспертной деятельности (итоги шестого Петербургского международного юридического форума)

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