Field-induced axion decay a→e+e−a \to e^+ e^- in plasma

The axion decay $a \to e^+ e^-$ is investigated in the presence of a plasma and an external magnetic field. The results demonstrate a strong catalyzing influence of medium. The axion lifetime in the magnetic field of order $10^{15}$ G and at the temperature of order 10 MeV is reduced to $10^4$ s.Comment: 9 pages, latex, 2 PS figures, corrected some typo

The radiative decay of a high energy neutrino in the Coulomb field of a nucleus

In the framework of the Standard Model with lepton mixing the radiative decay $\nu_i \rightarrow \nu_j \gamma$ of a neutrino of high ($E_\nu \sim 100 \, GeV$) and super-high ($E_\nu \ge 1 \, TeV$) energy is investigated in the Coulomb field of a nucleus. Estimates of the decay probability and ``decay cross-section'' for neutrinos of these energies in the electric field of a nucleus permit one to discuss the general possibility of carrying out a neutrino experiment, subject to the condition of availability in the future of a beam of neutrinos of these high energies. Such an experiment could give unique information on mixing angles in the lepton sector of the Standard Model which would be independent of the specific neutrino masses if only the threshold factor ($1 - m_j^4 / m_i^4$) was not close to zero. (Published in Phys.Lett.B 323 (1994) 179).Comment: 5 pages, LaTeX, Yaroslavl, Yaroslavl State University preprint YARU-HE-93/0

Photon decay gamma->nu anti-nu in an external magnetic field

The process of the photon decay into the neutrino - antineutrino pair in a magnetic field is investigated. The amplitude and the probability are analysed in the limits of relatively small and strong fields. The probability is suppressed by a factor (G_F m^2_e)^2 as compared with the probability of the pure electromagnetic process gamma -> e- e+. However, the process with neutrinos could play a role of an additional channel of stellar energy-loss.Comment: 8 pages, LaTeX, typos fixed, minor modifications, version accepted to Physics Letters

Axion decay a→ff~a \to f \tilde f in a strong magnetic field

The axion decay into charged fermion-antifermion pair $a ~\to f ~\tilde f$ is studied in external crossed and magnetic fields. The result we have obtained can be of use to re-examine the lower limit on the axion mass in case of possible existence of strong magnetic fields at the early Universe stage.Comment: 6 pages, latex. Amended version, references added, to be published in Phys.Lett.

High energy neutrino absorption by W production in a strong magnetic field

An influence of a strong external magnetic field on the neutrino self-energy operator is investigated. The width of the neutrino decay into the electron and W boson, and the mean free path of an ultra-high energy neutrino in a strong magnetic field are calculated. A kind of energy cutoff for neutrinos propagating in a strong field is defined.Comment: 13 pages, LaTeX, 1 EPS figure, submitted to Physics Letters

Electromagnetic Catalysis of the Radiative Decay of the Axion

The radiative decay of the axion $a \to \gamma \gamma$ is investigated in an external electromagnetic field in DFSZ model in which axion couples to both quarks and leptons at tree level. The decay probability is strongly catalyzed by the external field, namely, the field removes the main suppression caused by the smallness of the axion mass.Comment: Minor revision, references added, to be published in Phys.Lett.

Photon splitting above the pair creation threshold in a strong magnetic field

The process of photon splitting $\gamma \to \gamma \gamma$ in a strong magnetic field is investigated both below and above the pair creation threshold. Contrary to the statement by Baier et al., the ``allowed'' channel \alw is shown not to be a comprehensive description of splitting in the strong field because the ``forbidden'' channel \frb is also essential. The partial amplitudes and the splitting probabilities are calculated taking account of the photon dispersion and large radiative corrections near the resonance.Comment: 13 pages, 3 figures, LaTeX, uses epsf.sty, numerical error in eq.(11) corrected, typos fixed, presentation improved, accepted to Physics Letters

Vector Leptoquarks Could Be Rather Light?

Some low-energy manifestations of a minimal extension of the Standard Model based on the quark-lepton $SU(4)_V \otimes SU(2)_L \otimes G_R$ symmetry of the Pati-Salam type are analysed. Given this symmetry a new type of mixing in the quark-lepton interactions is shown to be required. An additional arbitrariness of the mixing parameters could allow to decrease noticeably the lower bound on the leptoquark mass $M_X$ originated from the $\pi$ and $K$ decays and the $\mu e$ conversion. The only mixing independent bound emerging from the cosmological limit on the $\pi^0 \rightarrow \nu \bar{\nu}$ decay width is $M_X > 18~TeV$.Comment: 10 pages, LaTeX, Yaroslavl, Yaroslavl State University preprint YARU-HE-94/0

Plasma influence on the neutrino - electron processes in a strong magnetic field

An influence of the magnetized electron - positron plasma on the absorption and loss of the energy and momentum in a process of neutrino propagation is investigated. A total contribution of all crossed processes, $\nu \to \nu e^- e^+$, $\nu e^- \to \nu e^-$, $\nu e^+ \to \nu e^+$, $\nu e^- e^+ \to \nu$, is found for the first time, which appears not to depend on the chemical potential of electron-positron gas. Relatively simple expressions for the probability and mean losses of the neutrino energy and momentum are obtained, which are suitable for a quantitative analysis.Comment: 8 pages, 1 ps figure, LaTeX, uses espcrc2.sty,epsf.sty, based on the talks presented at the Xth International Baksan School "Particles and Cosmology", Baksan Valley, Kabardino Balkaria, Russia, April 19-25, 1999 and the International Workshop "Particles in Astrophysics and Cosmology: From Theory to Observation", Valencia, Spain, May 3-8, 199

Neutrino-electron processes in a dense magnetized plasma

The neutrino-electron scattering in a dense degenerate magnetized plasma under the conditions $\mu^2 > 2eB \gg \mu E$ is investigated. The volume density of the neutrino energy and momentum losses due to this process are calculated. The results we have obtained demonstrate that plasma in the presence of an external magnetic field is more transparent for neutrino than non-magnetized plasma. It is shown that neutrino scattering under conditions considered does not lead to the neutrino force acting on plasma.Comment: 11 pages, LATEX, to be published in Central European Science Journa