4,976 research outputs found
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
Does the Borexino experiment have enough resolution to detect the neutrino flavor day-night asymmetry?
The Earth's density distribution can be approximately considered piecewise
continuous at the scale of two-flavor oscillations of neutrinos with energies
about 1 MeV. This quite general assumption appears to be enough to analytically
calculate the day-night asymmetry factor. Using the explicit time averaging
procedure, we show that, within the leading-order approximation, this factor is
determined by the electron density immediately before the detector, i.e. in the
Earth's crust. Within the approximation chosen, the resulting asymmetry factor
does not depend either on the properties of the inner Earth's layers or on the
substance and the dimensions of the detector. For beryllium neutrinos, we
arrive at the asymmetry factor estimation of about , which
is at least one order of magnitude beyond the present experimental resolution,
including that of the Borexino experiment.Comment: 16 pages, 3 figures; Talk given at the 17th International Seminar on
High Energy Physics "QUARKS'2012" (Yaroslavl, Russia, June 4-10, 2012); to
appear in the Proceedings volum
Theory of condensation of indirect excitons in a trap
We present theoretical studies of condensation of indirect excitons in a
trap. Our model quantifies the effect of screening of the trap potential by
indirect excitons on exciton condensation. The theoretical studies are applied
to a system of indirect excitons in a GaAs/AlGaAs coupled quantum well
structure in a diamond-shaped electrostatic trap where exciton condensation was
studied in earlier experiments. The estimated condensation temperature of the
indirect excitons in the trap reaches hundreds of milliKelvin
Extragalactic Relativistic Jets and Nuclear Regions in Galaxies
Past years have brought an increasingly wider recognition of the ubiquity of
relativistic outflows (jets) in galactic nuclei, which has turned jets into an
effective tool for investigating the physics of nuclear regions in galaxies. A
brief summary is given here of recent results from studies of jets and nuclear
regions in several active galaxies with prominent outflows.Comment: 5 pages; contribution to ESO Astrophysical Symposia, "Relativistic
Astrophysics and Cosmology", eds. B. Aschenbach, V. Burwitz, G. Hasinger, B.
Leibundgut (Springer: Heidelberg 2006
Multi-frequency investigation of the parsec- and kilo-parsec-scale radio structures in high-redshift quasar PKS 1402+044
We investigate the frequency-dependent radio properties of the jet of the
luminous high-redshift (z = 3.2) radio quasar PKS 1402+044 (J1405+0415) by
means of radio interferometric observations. The observational data were
obtained with the VLBI Space Observatory Programme (VSOP) at 1.6 and 5 GHz,
supplemented by other multi-frequency observations with the Very Long Baseline
Array (VLBA; 2.3, 8.4, and 15 GHz) and the Very Large Array (VLA; 1.4, 5, 15,
and 43 GHz). The observations span a period of 7 years. We find that the
luminous high-redshift quasar PKS 1402+044 has a pronounced "core-jet"
morphology from the parsec to the kilo-parsec scales. The jet shows a steeper
spectral index and lower brightness temperature with increasing distance from
the jet core. The variation of brightness temperature agrees well with the
shock-in-jet model. Assuming that the jet is collimated by the ambient magnetic
field, we estimate the mass of the central object as ~10^9 M_sun. The upper
limit of the jet proper motion of PKS 1402+044 is 0.03 mas/yr (~3c) in the
east-west direction.Comment: 9 pages, 6 figures
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