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

A Multi-Frequency Study of 3C309.1

Here we summarize our results from a detailed multi-frequency study of the QSO 3C309.1 based on the Very Long Baseline Array (VLBA) observations made in mid 1998. From our images, we find a curved jet extending up to 100 milliarcseconds (mas) to the east at low frequencies with two main components, A and B. A preliminary astrometric analysis (Ros and Lobanov 2001) provides a determination of the core position at different frequencies by phase-referencing to a nearby radio source, QSO S5 1448+76. The changes of the core position with frequency suggest high opacity close to the core caused by synchrotron self-absorption. Due to the large astrometric uncertainties we cannot draw any conclusions about the values of the opacity gradients at high frequencies. We believe that a detailed analysis of the frequency depedence of the core position will reveal the profile of the matter distribution in the broad line region, as was initially suggested by Lobanov (1998).Comment: To be published in the volume "Highlights of Spanish Astrophysics (III), Proceedings of the 5th Scientific Meeting of the Spanish Astronomical Society" of the Astrophysics and Space Science Library (Kluwer), J. Gallego, J. Zamorano, N. Cardiel (eds.), 1 page, 1 figure, no abstract, needs kapproc.st

Resonance enhancement of neutrino oscillations due to transition magnetic moments

Studying neutrino propagation in static background of dense matter and electromagnetic field [1] we obtained that the resonance enhancement of neutrino oscillations due to transition magnetic moments is possible. In this work we calculate the probabilities of spin-flavor transitions using solutions of the neutrino evolution equation in slowly varying magnetic field within the adiabatic approximation. We find that the resonance behavior of the transition probabilities is strictly connected to the neutrino polarization.Comment: 8 pages, 2 figures, LaTe