Radiative transitions of high energy neutrino in dense matter

The quantum theory of the ``spin light'' (electromagnetic radiation emitted by a massive neutrino propagating in dense matter due to the weak interaction of a neutrino with background fermions) is developed. In contrast to the Cherenkov radiation, this effect does not disappear even if the medium refractive index is assumed to be equal to unity. The formulas for the transition rate and the total radiation power are obtained. It is found out that radiation of photons is possible only when the sign of the particle helicity is opposite to that of the effective potential describing the interaction of a neutrino (antineutrino) with the background medium. Due to the radiative self-polarization the radiating particle can change its helicity. As a result, the active left-handed polarized neutrino (right-handed polarized antineutrino) converting to the state with inverse helicity can become practically ``sterile''. Since the sign of the effective potential depends on the neutrino flavor and the matter structure, the ``spin light'' can change a ratio of active neutrinos of different flavors. In the ultra relativistic approach, the radiated photons averaged energy is equal to one third of the initial neutrino energy, and two thirds of the energy are carried out by the final ``sterile'' neutrinos. This fact can be important for the understanding of the ``dark matter'' formation mechanism on the early stages of evolution of the Universe.Comment: 7 pages, latex, one misprint in eq. 12 correcte

Differential contribution of electrically evoked dorsal root reflexes to peripheral vasodilatation and plasma extravasation

<p>Abstract</p> <p>Background</p> <p>Dorsal root reflexes (DRRs) are antidromic activities traveling along the primary afferent fibers, which can be generated by peripheral stimulation or central stimulation. DRRs are thought to be involved in the generation of neurogenic inflammation, as indicated by plasma extravasation and vasodilatation. The hypothesis of this study was that electrical stimulation of the central stump of a cut dorsal root would lead to generation of DRRs, resulting in plasma extravasation and vasodilatation.</p> <p>Methods</p> <p>Sprague-Dawley rats were prepared to expose spinal cord and L4-L6 dorsal roots under pentobarbital general anesthesia. Electrical stimulation of either intact, proximal or distal, cut dorsal roots was applied while plasma extravasation or blood perfusion of the hindpaw was recorded.</p> <p>Results</p> <p>While stimulation of the peripheral stump of a dorsal root elicited plasma extravasation, electrical stimulation of the central stump of a cut dorsal root generated significant DRRs, but failed to induce plasma extravasation. However, stimulation of the central stump induced a significant increase in blood perfusion.</p> <p>Conclusions</p> <p>It is suggested that DRRs are involved in vasodilatation but not plasma extravasation in neurogenic inflammation in normal animals.</p

Neutrino spin rotation in dense matter and electromagnetic field

Exact solutions of the Dirac--Pauli equation for massive neutrino with anomalous magnetic moment interacting with dense matter and strong electromagnetic field are found. The complete system of neutrino wavefunctions, which show spin rotation properties are obtained and their possible applications are discussed.Comment: 11 pages, latex, misprints are correcte

Modern Trends in Analysis of Cholera Vibrios Metabolism and Nutrient Requirements

Modern insights into cholera vibrios physiology in different life conditions are considered in the review. Described are metabolic peculiarities of V. cholerae growing on nutrient media and in vivo, as well as in cholera patient organism, with special emphasis on alterations of pathogenicity factors synthesis at different stages of the disease. Considered is biofilm role in V. cholerae preservation in inter-epidemic period. Regulation of cholera vibrios growth is shown to depend upon environmental signals which shift metabolism and alter nutrient requirements

Plasma induced fermion spin-flip conversion fL→fR+γf_L \to f_R + \gamma

The fermion spin-flip conversion $f_L \to f_R + \gamma$ is considered, caused by the difference of the additional energies of the electroweak origin, acquired by left- and right-handed fermions (neutrino, electron) in medium. An accurate taking account of the fermion and photon dispersion in medium is shown to be important.Comment: 5 pages, LaTeX, 1 PS figure, based on the talk presented by A.V. Kuznetsov at the XV International Seminar Quarks'2008, Sergiev Posad, Moscow Region, May 23-29, 2008, to appear in the Proceeding

A VLBA survey of the core shift effect in AGN jets I. Evidence for dominating synchrotron opacity

The effect of a frequency dependent shift of the VLBI core position (known as the "core shift") was predicted more than three decades ago and has since been observed in a few sources, but often within a narrow frequency range. This effect has important astrophysical and astrometric applications. To achieve a broader understanding of the core shift effect and the physics behind it, we conducted a dedicated survey with NRAO's Very Long Baseline Array (VLBA). We used the VLBA to image 20 pre-selected sources simultaneously at nine frequencies in the 1.4-15.4 GHz range. The core position at each frequency was measured by referencing it to a bright, optically thin feature in the jet. A significant core shift has been successfully measured in each of the twenty sources observed. The median value of the core shift is found to be 1.21 mas if measured between 1.4 and 15.4 GHz, and 0.24 mas between 5.0 and 15.4 GHz. The core position, r, as a function of frequency, n, is found to be consistent with an r n^-1 law. This behavior is predicted by the Blandford & Koenigl model of a purely synchrotron self-absorbed conical jet in equipartition. No systematic deviation from unity of the power law index in the r(n) relation has been convincingly detected. We conclude that neither free-free absorption nor gradients in pressure and/or density in the jet itself and in the ambient medium surrounding the jet play a significant role in the sources observed within the 1.4-15.4 GHz frequency range. These results support the interpretation of the parsec-scale core as a continuous Blandford-Koenigl type jet with smooth gradients of physical properties along it.Comment: 31 pages, 6 figures, 5 tables; accepted to Astronomy & Astrophysic