5,363 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
Stationary and non-stationary solutions of the evolution equation for neutrino in matter
We study solutions of the equation which describes the evolution of a
neutrino propagating in dense homogeneous medium in the framework of the
quantum field theory. In the two-flavor model the explicit form of Green
function is obtained, and as a consequence the dispersion law for a neutrino in
matter is derived. It is shown that there exist both the solutions describing
the stationary states and the solutions describing the spin-flavor coherent
states of the neutrino. The stationary states may be different from the mass
eigenstates, and the wave function of a state with a definite flavor should be
constructed as a linear combination of the wave functions of the stationary
states with coefficients, which depend on the mixing angle in matter. In the
ultra-relativistic limit the wave functions of the spin-flavor coherent states
coincide with the solutions of the quasi-classical evolution equation.
Quasi-classical approximation of the wave functions of spin-flavor coherent
states is used to calculate the probabilities of transitions between neutrino
states with definite flavor and helicity.Comment: 11 pages, 6 figures, revised versio
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
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
Inhibition of light tunneling for multichannel excitations in longitudinally modulated waveguide arrays
We consider evolution of multichannel excitations in longitudinally modulated
waveguide arrays where refractive index either oscillates out-of-phase in all
neighboring waveguides or when it is modulated in phase in several central
waveguides surrounded by out-of-phase oscillating neighbors. Both types of
modulations allow resonant inhibition of light tunneling, but only the
modulation of latter type conserves the internal structure of multichannel
excitations. We show that parameter regions where light tunneling inhibition is
possible depend on the symmetry and structure of multichannel excitations.
Antisymmetric multichannel excitations are more robust than their symmetric
counterparts and experience nonlinearity-induced delocalization at higher
amplitudes.Comment: 17 pages, 6 figures, to appear in Physical Review
Starbursts and black hole masses in X-shaped radio galaxies: Signatures of a merger event?
We present new spectroscopic identifications of 12 X-shaped radio galaxies
and use the spectral data to derive starburst histories and masses of the
nuclear supermassive black holes in these galaxies. The observations were done
with the 2.1-m telescope of the Observatorio Astron\'omico Nacional at San
Pedro M\'artir, M\'exico. The new spectroscopic results extend the sample of
X-shaped radio galaxies studied with optical spectroscopy. We show that the
combined sample of the X-shaped radio galaxies has statistically higher
black-hole masses and older episodes of star formation than a control sample of
canonical double-lobed radio sources with similar redshifts and luminosities.
The data reveal enhanced star-formation activity in the X-shaped sample on the
timescales expected in galactic mergers. We discuss the results obtained in the
framework of the merger scenario.Comment: 9 pages, 10 figures, accepted for publication in Astronomy &
Astrophysic
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