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.

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 $\nu \bar{\nu}$ 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 $\sim 10$ eV energies for muon and tau neutrinos created in PNS core due to the compression just before the hydrodynamic bounce and up to $\sim 0.1$ 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, $m_{\nu}\lesssim (10^{-8}-10^{-7})$ eV corresponding to the nonvanishing $\nu \bar{\nu}$ 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 $\nu_{e}\bar{\nu}_{e}$, then a part of the corresponding neutrinos also escape the PNS. The detection of $\nu$ and $\bar{\nu}$ 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.

Spin light of neutrino in gravitational fields

We predict a new mechanism for the spin light of neutrino ($SL\nu$) that can be emitted by a neutrino moving in gravitational fields. This effect is studied on the basis of the quasiclassical equation for the neutrino spin evolution in a gravitational field. It is shown that the gravitational field of a rotating object, in the weak-field limit, can be considered as an axial vector external field which induces the neutrino spin procession. The corresponding probability of the neutrino spin oscillations in the gravitational field has been derived for the first time. The considered in this paper $SL\nu$ can be produced in the neutrino spin-flip transitions in gravitational fields. It is shown that the total power of this radiation is proportional to the neutrino gamma factor to the fourth power, and the emitted photon energy, for the case of an ultra relativistic neutrino, could span up to gamma-rays. We investigate the $SL\nu$ caused by both gravitational and electromagnetic fields, also accounting for effects of arbitrary moving and polarized matter, in various astrophysical environments. In particular, we discuss the $SL\nu$ emitted by a neutrino moving in the vicinity of a rotating neutron star, black hole surrounded by dense matter, as well as by a neutrino propagating in the relativistic jet from a quasar.Comment: 14 pages in LaTex with 1 eps figure; derivation of the neutrino spin oscillations probability in gravitational fields and several clarifying notes are added, typos correcte

Oscillations of Dirac and Majorana neutrinos in matter and a magnetic field

We study the evolution of massive mixed Dirac and Majorana neutrinos in matter under the influence of a transversal magnetic field. The analysis is based on relativistic quantum mechanics. We solve exactly the evolution equation for relativistic neutrinos, find the neutrino wave functions, and calculate the transition probability for spin-flavor oscillations. We analyze the dependence of the transition probability on the external fields and compare the cases of Dirac and Majorana neutrinos. The evolution of Majorana particles in vacuum is also studied and correction terms to the standard oscillation formula are derived and discussed. As a possible application of our results we discuss the spin-flavor transitions in supernovae.Comment: RevTeX4, 15 pages, 4 eps figures. The paper was significantly revised; 17 references were added, many misprints throughout the text were corrected. The variant to be published in Phys. Rev.

Pairing of charged particles in a quantum plasmoid

We study a quantum spherically symmetric object which is based on radial plasma oscillations. Such a plasmoid is supposed to exist in a dense plasma containing electrons, ions, and neutral particles. The method of creation and annihilation operators is applied to quantize the motion of charged particles in a self-consistent potential. We also study the effective interaction between oscillating particles owing to the exchange of a virtual acoustic wave, which is excited in the neutral component of plasma. It is shown that this interaction can be attractive and result in the formation of ion pairs. We discuss possible applications of this phenomenon in astrophysical and terrestrial plasmas.Comment: 17 pages, no figures, two columns, LaTeX2e; paper was significantly revised; title was changed; 16 new references were included; the discussion on ion-acoustic waves was added to Sec. 2; Secs. 3 and 4 were shortened; a more detailed discussion was added to Sec. 7; accepted for publication to J.Phys.

Effective attraction between oscillating electrons in a plasmoid via acoustic waves exchange

We consider the effective interaction between electrons due to the exchange of virtual acoustic waves in a low temperature plasma. Electrons are supposed to participate in rapid radial oscillations forming a spherically symmetric plasma structure. We show that under certain conditions this effective interaction can result in the attraction between oscillating electrons and can be important for the dynamics of a plasmoid. Some possible applications of the obtained results to the theory of natural long-lived plasma structures are also discussed.Comment: 14 pages in LaTeX2e, two columns, 3 eps figures; minimal changes, some typos are corrected; version published on-line in Proc. R. Soc.