Self-energy operator of a massive neutrino in an external magnetic field

The effect of the magnetic field on the properties of a massive neutrino is analyzed. A general expression is derived in terms of the self-energy operator of the neutrino in an external magnetic field of arbitrary strength. This expression is valid for any relationship between the masses of the neutrino, a charged lepton, and a W-boson. An anomalous magnetic moment of a standard neutrino is investigated. The probability of massive neutrino decay into a W-boson and a charged lepton is calculated for various values of the magnetic field strength.     

Neutrino self-energy operator and neutrino magnetic moment

A simple method for calculating the magnetic moment of a massive neutrino on the basis of its self-energy operator is presented. An expression for the magnetic moment of a massive neutrino in an external electromagnetic field is obtained in the R _ξ gauge for the case of an arbitrary ratio of the lepton and W-boson masses.     

Charge and magnetic moment of the neutrino in the background field method and in the linear R_{\xi}^L gauge

We present a computation of the charge and the magnetic moment of the neutrino in the recently developed electro-weak Background Field Method and in the linear gauge. First, we deduce a formal Ward-Takahashi identity which implies the immediate cancellation of the neutrino electric charge. This Ward-Takahashi identity is as simple as that for QED. The computation of the (proper and improper) one loop vertex diagrams contributing to the neutrino electric charge is also presented in an arbitrary gauge, checking in this way the Ward-Takahashi identity previously obtained. Finally, the calculation of the magnetic moment of the neutrino, in the minimal extension of the Standard Model with massive Dirac neutrinos, is presented, showing its gauge parameter and gauge structure independence explicitly. Received: 6 July 1999 / Revised version: 27 October 1999 / Published online: 27 January 2000     

Electromagnetic form factors of a massive neutrino

Electromagnetic form factors of a massive neutrino are studied in a minimally extended standard model in an arbitrary R_ξ gauge and taking into account the dependence on the masses of all interacting particles. The contribution from all Feynman diagrams to the electric, magnetic, and anapole form factors, in which the dependence of the masses of all particles as well as on gauge parameters is accounted for exactly, are obtained for the first time in explicit form. The asymptotic behavior of the magnetic form factor for large negative squares of the momentum of an external photon is analyzed and the expression for the anapole moment of a massive neutrino is derived. The results are generalized to the case of mixing between various flavors of the neutrino. Explicit expressions are obtained for the electric, magnetic, and electric dipole and anapole transitional form factors as well as for the transitional electric dipole moment.     

Spin and dispersion of a massive Dirac neutrino in a magnetized plasma

The total energy shift of a polarized massive Dirac neutrino in an electron–positron plasma in a constant magnetic field is investigated. The calculation in the Feynman gauge is performed for the first time by using the Matsubara temperature Green functions. The dependence of the dispersion relation and the anomalous magnetic moment of the neutrino on the magnetic field strength, spin, energy, direction of motion, neutrino mass, and the plasma parameters is analyzed. The results of investigations for the massive neutrino in the limiting case are compared with those obtained earlier by other authors for the massless left neutrino.     

Neutrino electromagnetic properties

The main goal of the paper is to give a short review on neutrino electromagnetic properties. In the introductory part of the paper a summary on what we really know about neutrinos is given: we discuss the basics of neutrino mass and mixing as well as the phenomenology of neutrino oscillations. This is important for the following discussion on neutrino electromagnetic properties that starts with a derivation of the neutrino electromagnetic vertex function in the most general form, that follows from the requirement of Lorentz invariance, for both the Dirac and Majorana cases. Then, the problem of the neutrino form factor definition and calculation within gauge models is considered. In particular, we discuss the neutrino electric charge form factor and charge radius, dipole magnetic and electric and anapole form factors. Available experimental constraints on neutrino electromagnetic properties are also discussed, and the recently obtained experimental limits on neutrino magnetic moments are reviewed. The most important neutrino electromagnetic processes involving a direct neutrino coupling with photons (such as neutrino radiative decay, neutrino Cherenkov radiation, spin light of neutrino and plasmon decay into neutrino-antineutrino pair in media) and neutrino resonant spin-flavor precession in a magnetic field are discussed at the end of the paper.     

Electromagnetic properties of massive neutrinos in a polarized electromagnetic wave

Radiative corrections are studied to the mass of a Dirac neutrino moving in an electromagnetic field of the flat-wave type (crossed fields + wave). In the framework of the Weinberg-Salam-Glashow standard model, the dependence of the neutrino anomalous magnetic moment on the external field parameters is studied. The possibility of the induction of an anomalous electric moment by the electromagnetic wave is noted.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 76–80, April, 1989.     

Interference phase of mass neutrino in CM space--time

In the gravitational field of central mass with electric and magnetic charges and magnetic moment (CM space-time), this paper calculates the interference phase of mass neutrino along geodesic in the radial direction, and discusses the contribution of the electric and magnetic charges and magnetic moment of the central mass to the phase.     

Neutrino mass effect on the nuclear muon capture

Multipole expansion of the partial transition amplitude in the nuclear muon capture with massive lefthanded Dirac neutrino has been derived. The multipole amplitudes for the partial nuclear transitions are given as the explicit functions of the neutrino mass parameter. As an example, the capture rate, the recoil asymmetry and the neutrino polarization are investigated in terms of these multipole amplitudes. The transversal neutrino polarization provides a connection between theT-violation and the neutrino mass: ifT-odd component in the neutrino polarization is observed, then neutrino must be a massive particle. It turns out that in the capture rate and recoil polarization, the effects due to very small neutrino mass can be proportional to the square ratio of the neutrino mass to its momentum, while the neutrino transversal polarization is proportional to this ratio only. Under the recent limits on the muon neutrino mass, the observable effects inthe partial transition may be below the order of ?10^?3.     

Neutrino dispersion properties in an external magnetic field

The neutrino self-energy operator Σ(p) in a magnetic field is calculated for the case of high-energy neutrinos, this corresponding to the crossed field approximation. The probability of the neutrino decay ν → e ^? W ⁺ is found by using the imaginary part of the operator Σ(p). A simple analytic result is obtained in the parameter region that is the most interesting from the physical point of view and which was not considered earlier. The contribution of an external magnetic field to the neutrino magnetic moment is calculated. The result obtained here for this contribution corrects formulas available previously.     

Superstring induced mass and magnetic moment of the neutrino and the time modulation of the solar neutrino flux

The new Yukawa couplings involving heavy matter E₆ fields predicted in the framework of superstring theories are considered as a source of mass and magnetic moment for the neutrino. Given the experimental bound m_ve < 46 eV bounds are derived on the neutrino magnetic moment thus generated. Finally, a scenario is produced where the induced magnetic moment has the correct magnitude (∼10⁻¹¹ μ_B) to explain an alleged depletion or solar neutrino flux during periods of maximum solar activity.     

Massive neutrinos

There have been recent discussions, associated with the solar neutrino problem, that consider the neutrino to have rest mass. Here we give a discussion of massive neutrinos in general relativity. There are no solutions to the Einstein-zero mass neutrino equations for spherically-symmetric spacetimes. A sphrically-symmetric solution to the Einstein - massive neutrino equations is presented.     

Neutrino mass and magnetic moment in supersymmetry without R-parity in the light of recent data

We consider the generation of neutrino Majorana mass and transition magnetic moment by the lepton-number violating λ and/or λ′ couplings in R-parity-violating supersymmetric models. We update (and improve) the existing upper limits on the relevant couplings using the most recent data on neutrino masses and mixings, indicating also the possible improvement by the GENIUS project. We study the implication of this update on the induced neutrino magnetic moment.     

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.     

On the massive Dirac neutrino radiative decay

The presence of right-handed currents and left-right mixing contributes to the neutrino radiative decay amplitude a term that is directly proportional to the charged lepton mass. This has led to the suggestion that observable decays of relic neutrinos might occur in the left-right model or the mirror model. Explicit calculations in these models are carried out including a careful analysis of the origin of neutrino mass, here assumed to be a Dirac mass. It is found that the amplitude is proportional to the neutrino mass and thus too small to be of interest. A brief comment on the neutrino magnetic moment in anSU(2) _L ×U(1) _Y model, which contains an iso-singlet charged scalar η⁺, is also presented.     

News from ASTRID

A new superferric magnetic storage ring with highly homogeneous field at 1.45 T and weak electrostatic focussing is described which has been set up at the Brookhaven National Laboratory (BNL), USA, for a precision measurement of the magnetic anomaly of the muon. The toroidal storage volume has a radius of 7 m and a diameter of 9 cm. Precision magnetic field determination based on pulsed NMR on protons in H₂O yields the field to better than 0.1 ppm everywhere within the storage region. Follow on experiments using the setup have been already suggested to search for a finite mass of the muon neutrino and to search for an electric dipole moment of the muon with significantly increased accuracy. The high homogeneity of the field suggests the usage of such devices as a mass spectrometer for heavier particles as well. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the Neutrino Millicharge

The neutrino luminosity of a degenerate electron gas in a strong magnetic field under conditions of the neutron-star crust owing to plasmon decay to a neutrino pair via a nonstandard mechanism associated with the hypothesized neutrino electric millicharge is calculated. Relative upper bounds on the magnitude of the millicharge are obtained from a comparison of the results of this calculation with the neutrino luminosity caused by the respective standard process and with the luminosity induced by the neutrino magnetic moment.     

A fourth generation neutrino with a standard Higgs scalar solves both the solar neutrino and dark matter problems

Weakly interacting massive particles (WIMPs) can solve both the solar neutrino and dark matter problems. In this paper we show that a fourth generation Dirac neutrino with mass between 4–10 GeV, in conjunction with the standard, albeit light, Higgs with mass of order 400 MeV, is a candidate WIMP. We describe both the astrophysical and particle physics consequences of this new WIMP.     

Neutrino induced magnetic moment and spin precession

When propagating through a dispersing medium, a massive neutrino acquires an induced magnetic moment that may give rise to a helicity flip in an external magnetic field with a larger probability than that caused by the anomalous magnetic moment. This phenomenon is investigated in the framework of relativistic quantum mechanics and of the generalized Bargmann–Michel–Telegdi equation.     

Mass properties of active and sterile neutrinos in a phenomenological (3 + 1 + 2) model

A generalized model involving three active neutrinos and three sterile neutrinos of different mass, one being relatively heavy [(3 + 1 + 2) model], is considered on the basis of experimental data, which admit the existence of anomalies beyond the minimally extended standard model featuring three active neutrinos of different mass. Basic properties used to describe massive active and sterile neutrinos are studied along with methods for determining the absolute scale of neutrino masses and for estimating neutrino masses on the basis of available experimental data. In the approximation of CP conservation, admissible values of the elements of the neutrino mass matrix are found from numerical calculations versus the possible values of the mass of one of the sterile neutrinos. The dependences of the mass properties of the neutrinos on the sterile-neutrino mass are constructed with allowance for possible sterile-neutrino contributions. The respective results can be used to interpret and predict results of various neutrino experiments.