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We consider the matter effects on neutrinos moving in background on the basis of the corresponding quantum wave equations. Both Dirac and Majorana neutrino cases are discussed. The effects for Dirac neutrino reflection and trapping as well as neutrino-antineutrino annihilation and νν pair creation in matter at the interface between two media with different densities are considered. The spin light of neutrino in matter is also discussed.

Abstract. We reconsider the standard scheme for description of neutrino spin-flavor oscillations aiming at a rigorous derivation of evolution equation for the mixed flavor neutrino states in magnetic field. For this purpose we obtain the evolution equation in the physical basis of massive neutrinos and then trace its transformation into the flavor basis. The effective Hamiltonian of the resulting equation relevant to interaction with the magnetic field differs from the standard one by several entries. The approach leads to interesting relations of the neutrino magnetic moments defined in the two neutrino bases and to some additional subtle properties of the formalism.

We predict a new mechanism for the spin light of neutrino (SLν) 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 SLν 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 SLν 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 SLν 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.

The modified Dirac equation for the neutrino in a material medium and its solution for a nonuniform motion of the medium with a velocity gradient along a certain direction are examined in the present paper. This formulation of the problem is analogous to the problem of electron motion in a constant uniform magnetic field. This is manifested through a similar character of particle wave functions that in both cases describe the states with circular orbits. A new mechanism of confinement of low-energy neutrinos in fast-rotating dense astrophysical objects is predicted based on this property of the wave functions. As an example of their application, a process of spin light ( SL ν ) of neutrino is examined in this configuration of matter.

The spin light of neutrino (SLν) is a new possible mechanism of electromagnetic radiation by a massive neutrino (with a nonzero magnetic moment) moving in media. Since the prediction of this mechanism, the question has been debated in a number of publications as whether the effect can be of any significance for realistic astrophysical conditions. Although this effect is strongly suppressed due to smallness of neutrino magnetic moment, for ultrahigh energy neutrinos (PeV neutrinos recently observed by the IceCube collaboration, for instance) the SLν might be of interest in the case of neutrinos propagating in dense matter. An advanced view on the SLν in matter is given, and several astrophysical settings (a neutron star, supernova, Gamma-Ray Burst (GRB), and relic neutrino background) for which the effect can be realized are considered. Taking into account the threshold condition and also several competing processes, we determine conditions for which the SLν mechanism is possible. We conclude that the most favorable case of the effect manifestation is provided by ultra dense matter of neutron stars and ultrahigh energy of the radiating neutrino, and note that these conditions can be met within galaxy clusters. It is also shown that due to the SLν specific polarization properties this electromagnetic mechanism is of interest in the connection with the observed polarization of GRB emission.

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We develop the theory of spin light of neutrino in matter ($SL\nu$) and include the effect of plasma influence on the emitted photon. We use the special technique based on exact solutions of particles wave equations in matter to perform all the relevant calculations, and track how the plasmon mass enters the process characteristics including the neutrino energy spectrum, $SL\nu$ rate and power. The new feature it induces is the existence of the process threshold for which we have found the exact expression and the dependence of the rate and power on this threshold condition. The $SL\nu$ spatial distribution accounting for the above effects has been also obtained. These results might be of interest in connection with the recently reported hints of ultra-high energy neutrinos $E = 1 \div 10$ PeV observed by IceCube.Comment: 8 pages, 2 figures, v2: typos corrected, discussions adde