Weak neutral currents and neutrino electromagnetic properties

The phenomenological Hamiltonian for weak lepton interaction that contains, along with a charged current V-A interaction, a neutral current V-A interation and the dispersion method are used to study the effect of lepton and nucleon currents on the electromagnetic properties of the neutrino. Expressions are obtained for the neutrino formfactor F(q²) when it satisfies the dispersion relations without subtraction and with one subtraction.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 43–48, May, 1977.     

Fast neutrino decay and solar neutrino detectors

The neutrino decay solution of the solar neutrino problem is revisited in the context of majoron models. It is shown that for a definite range of parameters this scenario reconciles both the Homestake and the Kamiokande data. The prediction for Gallium detectors is also given. Attention is devoted to the analysis of the signal, which is the crucial prediction of this scenario. It is shown that the sensitivity of Borexino is sufficient to observe this signal and to distinguish it from the alternative signal provided by hybrid models of neutrino oscillation and magnetic moment transitions. Other sources of solar production are also reviewed (matter induced decay, MSW catalized decay or the decay of solar 17 keV neutrinos).     

Double-beta decay and neutrino mass

Recent achievements in the study of double-beta (ββ) decay are presented. We discuss the potential of this process to search, beyond Standard Model physics, for the QRPA-based methods used for the calculation of the relevant nuclear matrix elements and the derivation of the neutrino mass from both ββ-decay calculations and neutrino oscillation and cosmological data. The key position of the ββ-decay experiments in resolving the neutrino absolute mass is highlighted.     

Beta decay in the field of an electromagnetic wave and experiments on measuring the neutrino mass

Investigations of the effect of an electromagnetic wave field on the beta-decay process are used to analyze the tritium-decay experimental data on the neutrino mass. It is shown that the electromagnetic wave can distort the beta spectrum, shifting the end point to the higher energy region. This phenomenon is purely classical and it is associated with the electron acceleration in the radiation field. Since strong magnetic fields exist in setups for precise measurement of the neutrino mass, the indicated field can appear owing to the synchrotron radiation mechanism. The phenomenon under consideration can explain the experimentally observed anomalies in the spectrum of the decay electrons; in particular, the effect of the “negative square of the neutrino mass.”     

Alpha decay within Feshbach theory of nuclear reactions

In the framework of Feshbach theory of nuclear reactions the α-decay widths are determined by the α— daughter-nucleus optical potential and by the preformation factors. It is shown that the calculated absolute values of the α-widths for the light Po isotopes are in good agreement with the experimental data if the real part of the optical potential using parameters obtained by fitting low-energy α-scattering is used.     

Radiative neutrino decay in superstring models

The rate for the radiative decay of neutrinos is calculated in E₆ superstring models with light colour triplet isosinglets h and h. In contrast to the standard model, the rate is not suppressed either by the GIM mechanism or by helicity matching. Comparison with astrophysical data allows one to set an upper limit on the Yukawa couplings QL and λd^cv^ch. Taking it is found that , compatible with m_vc, m_vμ in the range 10–100 eV. From the cosmological requirement of not photo-ionizing light elements after nucleosynthesis, it follows that the v_τ must lie in the same mass range and consequently .     

Weak neutral currents and neutrino transport

Transport coefficients are evaluated for a mixture of neutrinos and complex nuclei with neutral current weak interaction as proposed by Freedman. The transport properties of this system are particularly relevant to the neutrino transport supernova model.     

The electromagnetic mechanism of plasmon decay to a neutrino pair in a strongly magnetized electron gas

An expression for the neutrino luminosity of a degenerate electron gas in a strong magnetic field via plasmon decay to a neutrino pair due to electromagnetic neutrino moments is derived. The neutrino luminosity of the medium in an electromagnetic reaction channel is shown to be comparable with the luminosity in a weak channel. The relative upper bounds for the effective magnetic neutrino moment are obtained.     

Matter induced neutrino decay and solar antineutrinos

The properties of matter-induced neutrino decay with majoron emission are analysed in some details for the cases of Majorana, ZKM and Dirac neutrinos. The result of such a decay of solarv _e 's in the sun interior could be the appearance of \(\bar \nu _e \) flux. Assuming that the neutrinos have only standard weak interactions, the solar \(\bar \nu _e \) flux can be at the border of detectability for the future large volume detectors like Borex or Super-Kamiokande. However, the \(\bar \nu _e \) signal can be considerably larger, provided the neutrinos have new non-standard interactions with matter.     

Radiative decay of neutrino and primordial nucleosynthesis

Radiative decay of massive unstable neutrinos is examined in detail. Constraints on their mass and lifetime are established by solving the networks of nucleosynthesis and calculating the spectra of high-energy photons produced by massive neutrino decay. It is found that primordial nucleosynthesis sets stringent constraints on the mass and the lifetime of massive unstable neutrinos. According to these constraints together with constraints derived from other cosmological consideration and laboratory experiments, radiative decay of massive τ neutrinos is not allowed except for the case that the mass and the lifetime of the τ neutrino satisfy rather strict constraints; 30 MeV ≲ m_ντ ≲ 70 MeV, 10² s ≲ τ_ντ ≲ 10⁴ s. Constraints on neutrinos in the 4th generation are also derived.     

Possible neutrino capture in an electromagnetic field

The stationary states of a neutrino, considered a neutron with a vanishingly small mass, in the combined fields of a longitudinal and of a linearly polarized plane wave, and in the field of a circularly polarized wave, are obtained and analyzed. The effective mass of the neutrino is calculated.Tomsk Polytechnic University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 16–20, September, 1993.     

Spin-dependent sum rule for high-energy neutrino reactions

We present a sum rule which related the inclusive cross section for high-energy neutrino scattering on polarized proton targets to the axial-vector coupling constant. The derivation of the sum rule rests on the equal-time algebra of the time-components of the weak currents. The sum rule also provides a discriminatory test of unified models of weak and electromagnetic interactions based on spontaneously-broken gauge symmetry.     

Radiative neutrino decay in a strong magnetic field

The radiative decay of neutrinos in a strong magnetic field that have relatively high energies, E ? m _e , is studied with allowance for positronium contribution to the photon polarization operator in the vicinity of the cyclotron resonance. It is shown that the probability for the process ν → νγ increases substantially upon taking into account the positronium contribution.     

Majorana neutrino masses and the neutrinoless double-beta decay

Neutrinoless double-beta decay is forbidden in the Standard Model of electroweak and strong interaction but allowed in most Grand Unified Theories (GUTs). Only if the neutrino is a Majorana particle (identical with its antiparticle) and if it has a mass is neutrinoless double-beta decay allowed. Apart from one claim that the neutrinoless double-beta decay in ⁷⁶Ge is measured, one has only upper limits for this transition probability. But even the upper limits allow one to give upper limits for the electron Majorana neutrino mass and upper limits for parameters of GUTs and the minimal R-parity-violating supersymmetric model. One further can give lower limits for the vector boson mediating mainly the right-handed weak interaction and the heavy mainly right-handed Majorana neutrino in left-right symmetric GUTs. For that, one has to assume that the specific mechanism is the leading one for neutrinoless double-beta decay and one has to be able to calculate reliably the corresponding nuclear matrix elements. In the present work, one discusses the accuracy of the present status of calculating of the nuclear matrix elements and the corresponding limits of GUTs and supersymmetric parameters. The text was submitted by the author in English.