900 research outputs found
Neutrino spin oscillations in gravitational fields
We study neutrino spin oscillations in gravitational fields. The
quasi-classical approach is used to describe the neutrino spin evolution. First
we examine the case of a weak gravitational field. We obtain the effective
Hamiltonian for the description of neutrino spin oscillations. We also receive
the neutrino transition probability when a particle propagates in the
gravitational field of a rotating massive object. Then we apply the general
technique to the description of neutrino spin oscillations in the Schwarzschild
metric. The neutrino spin evolution equation for the case of the neutrino
motion in the vicinity of a black hole is obtained. The effective Hamiltonian
and the transition probability are also derived. We examine the neutrino
oscillations process on different circular orbits and analyze the frequencies
of spin transitions. The validity of the quasi-classical approach is also
considered.Comment: RevTeX4, 9 pages, 1 esp figure; article was revised, some misprints
were corrected, 6 references added; accepted for publication in
Int.J.Mod.Phys.
Neutrino spin relaxation in medium with stochastic characteristics
The helicity evolution of a neutrino interacting with randomly moving and
polarized matter is studied. We derive the equation for the averaged neutrino
helicity. The type of the neutrino interaction with background fermions is not
fixed. In the particular case of a tau-neutrino interacting with
ultrarelativistic electron-positron plasma we obtain the expression for the
neutrino helicity relaxation rate in the explicit form. We study the neutrino
spin relaxation in the relativistic primordial plasma. Supposing that the
conversion of left-handed neutrinos into right-handed ones is suppressed at the
early stages of the Universe evolution we get the upper limit on the
tau-neutrino mass.Comment: 6 pages, RevTeX4; 2 references added; more detailed discussion of
correlation functions and cosmological neutrinos is presented; version to be
published in Int. J. Mod. Phys.
Parametric Resonance of Neutrino Oscillations in Electromagnetic Wave
Within the Lorentz invariant formalizm for description of neutrino evolution
in electromagnetic fields and matter we consider neutrino spin oscillations in
the circular polarized electromagnetic wave, the amplitude of which is a
modulated function of time. It is shown for the first time that the parametric
resonance of neutrino oscillations can occur in such a system.Comment: The enlarged version of contribution to the Proceedings of the Third
International Workshop on New Worlds in Astroparticle Physics (Faro, 2000
Evolution of coupled fermions under the influence of an external axial-vector field
The evolution of coupled fermions interacting with external axial-vector
fields is described with help of the classical field theory. We formulate the
initial conditions problem for the system of two coupled fermions in
(3+1)-dimensional space-time. This problem is solved using the perturbation
theory. We obtain in the explicit form the expressions for the leading and next
to the leading order terms in the expansion over the strength of external
fields. It is shown that in the relativistic limit the intensity of the fermion
field coincides with the transition probability in the two neutrinos system
interacting with moving and polarized matter.Comment: RevTeX4, 8 pages, 1 eps figure; revised variant, neutral currents
interactions of flavor neutrinos are included, some typos corrected, 1
reference added; accepted for publication in Eur.Phys.J.
Formation of bound states of electrons in spherically symmetric oscillations of plasma
We study spherically symmetric oscillations of electrons in plasma in the
frame of classical electrodynamics. Firstly, we analyze the electromagnetic
potentials for the system of radially oscillating charged particles. Secondly,
we consider both free and forced spherically symmetric oscillations of
electrons. Finally, we discuss the interaction between radially oscillating
electrons through the exchange of ion acoustic waves. It is obtained that the
effective potential of this interaction can be attractive and can transcend the
Debye-Huckel potential. We suggest that oscillating electrons can form bound
states at the initial stages of the spherical plasma structure evolution. The
possible applications of the obtained results for the theory of natural
plasmoids are examined.Comment: 9 pages in LaTeX2e, no figures; paper was significantly modified, 2
new references added, some inessential mathematics was removed, many typos
were corrected; final variant to be published in Physica Script
Creation of Dirac neutrinos in a dense medium with time-dependent effective potential
We consider Dirac neutrinos interacting with background fermions in the frame
of the standard model. We demonstrate that a time-dependent effective potential
is quite possible in a protoneutron star (PNS) at certain stages of its
evolution. For the first time, we formulate a nonperturbative treatment of
neutrino processes in a matter with arbitrary time-dependent effective
potential. Using linearly growing effective potential, we study the typical
case of a slowly varying matter interaction potential. We calculate
differential mean numbers of pairs created from the vacuum by
this potential and find that they crucially depend on the magnitude of masses
of the lightest neutrino eigenstate. These distributions uniformly span up to
eV energies for muon and tau neutrinos created in PNS core due to the
compression just before the hydrodynamic bounce and up to eV
energies for all three active neutrino flavors created in the neutronization.
Considering different stages of the PNS evolution, we derive constraints on
neutrino masses, eV corresponding to the
nonvanishing pairs flux produced by this mechanism. We show
that one can distinguish such coherent flux from chaotic fluxes of any other
origin. Part of these neutrinos, depending on the flavor and helicity, are
bounded in the PNS, while antineutrinos of any flavor escape the PNS. If the
created pairs are , then a part of the corresponding
neutrinos also escape the PNS. The detection of and with
such low energies is beyond current experimental techniques.Comment: 18 pages, Revtex4.1, 1 eps figure, 2 columns; minimal changes,
version to be published in Phys. Rev.
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