8,016 research outputs found
High energy neutrino spin light
The quantum theory of spin light (electromagnetic radiation emitted by a
Dirac 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.Comment: 12 pages, Latex. To appear in Phys. Lett.
Neutrino-antineutrino pair production by a photon in a dense matter
The possibility of radiative effects that are due to interaction of fermions
with a dense matter is investigated. Neutrino-antineutrino photo-production is
studied. The rate of this process is calculated in the Furry picture. It is
demonstrated that this effect does not disappear even if the medium refractive
index is assumed to be equal to unity. The rate obtained strongly depends on
the polarization states of the particles involved. This leads to evident
spatial asymmetries, which may have certain consequences observable in
astrophysical and cosmological studies.Comment: 10 pages, Late
Physical properties of the jet in 0836+710 revealed by its transversal structure
Studying the internal structure of extragalactic jets is crucial for
understanding their physics. The Japanese-led space VLBI project VSOP has
presented an opportunity for such studies, by reaching baseline lengths of up
to 36,000 km and resolving structures down to an angular size of
mas at 5 GHz. VSOP observations of the jet in 0836+710 at 1.6 and 5 GHz have
enabled tracing of the radial structure of the flow on scales from 2 mas to 200
mas along the jet and determination of the wavelengths of individual
oscillatory modes responsible for the formation of the structure observed. We
apply linear stability analysis to identify the oscillatory modes with modes of
Kelvin-Helmholtz instability that match the wavelengths of the structures
observed. We find that the jet structure in 0836+710 can be reproduced by the
helical surface mode and a combination of the helical and elliptic body modes
of Kelvin-Helmholtz instability. Our results indicate that the jet is
substantially stratified and different modes of the instability grow inside the
jet at different distances to the jet axis. The helical surface mode can be
driven externally, and we discuss the implications of the driving frequency on
the physics of the active nucleus in 0836+710.Comment: Accepted for publication in Astronomy & Astrophysics Letter
Brightness temperature constraints from interferometric visibilities
The brightness temperature is an effective parameter that describes the
physical properties of emitting material in astrophysical objects. It is
commonly determined by imaging and modeling the structure of the emitting
region and estimating its flux density and angular size. Reliable approaches
for visibility-based estimates of brightness temperature are needed for
interferometric experiments in which poor coverage of spatial frequencies
prevents successful imaging of the source structure, for example, in
interferometric measurements made at millimeter wavelengths or with orbiting
antennas. Such approaches can be developed by analyzing the relations between
brightness temperature and visibility amplitude and its r.m.s. error. A method
is introduced for directly calculating the lower and upper limits of the
brightness temperature from visibility measurements. The visibility-based
brightness temperature estimates are shown to agree well with the image-based
estimates obtained in the 2\,cm MOJAVE survey and the 3\,mm CMVA survey, with
good agreement achieved for interferometric measurements at spatial frequencies
exceeding . The method provides an essential tool for
constraining brightness temperature in all interferometric experiments with
poor imaging capability.Comment: Accepted for publication in Astronomy and Astrophysics; 10 pages; 9
figure
Neutrino self-polarization effect in matter
The quasi-classical theory of the spin light of neutrino () in
background matter, accounting for the neutrino polarization, is developed. The
neutrino transitions and rates in
matter are calculated. It is shown that the in matter leads to the
neutrino conversion from active to sterile states (neutrino
self-polarization effect in matter).Comment: LaTex 9 pages, no figure
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
- …