Majorana neutrino transition magnetic moment in a variant of Zee model with horizontal symmetry

A SU(2) _H symmetric variant of Zee model of lepton flavor violation is presented and is shown to lead to neutrino transition magnetic moment of the order required to explain the solar neutrino deficit and the possible anticorrelation of solar neutrino flux with sunspot activity via VVO mechanism. The use of horizontal symmetry leads to totally degenerate neutrino states which may be combined to form a ZKM Dirac neutrino with naturally small mass.     

Effect of the neutrino magnetic moment on the properties of the muon

The effect of the neutrino dipole magnetic moment on the properties of the muon is investigated within the standard model of electroweak interactions and a model based on the SU(2) _L × SU(2) _R × U(1) _B-L gauge group (left-right model). In the case of the Dirac neutrino, muon decay through the channel µ^? → e ^?γ is studied with allowance for the neutrino dipole magnetic moment. It is shown that, both in the standard model supplemented with an SU(2) _L right-handed neutrino singlet and in the standard model featuring two doublets of Higgs fields, radiative muon decay is unobservable. In the left-right model, the contributions of diagrams associated with the neutrino dipole magnetic moment become significant only in the case of a mutual compensation of the contributions of diagrams involving the electromagnetic vertices of charged gauge bosons and singly charged Higgs bosons. At specific values of the parameters of the left-right model, one can then obtain an experimental upper limit on the branching fraction of this reaction. The contributions of the neutrino dipole magnetic moment to the muon anomalous magnetic moment are found for the Dirac and the Majorana neutrino. It is established that, both in the standard model and in the left-right model, values of the neutrino anomalous magnetic moment that are required for explaining the (g ? 2)_µ anomaly are in excess of the theoretical predictions for this moment.     

One model for magnetic solar neutrino interactions,cosmological neutrino decays,and new particle resonant production by interactions of neutrinos from Cygnus X-3

Standard model extensions which include a charged, weak-singlet scalar particle can induce an electron-neutrino magnetic moment large enough to implement the Voloshin-Vysotski-Okun solution to the solar neutrino problem and observed anticorrelation of sunspots and neutrino flux. The resonant production and decay of such a charged scalar particle by neutrinos from ultra-high energy point sources of cosmic rays such as Cygnus X-3 has been discussed in the literature as a possible source of an anomalous muon signal in deep underground detectors. We argue here that there are versions of the charged scalar model which simultaneously can accommodate the above phenomena and in addition predict a radiative neutrino decay whose lifetime is about 10²⁴ s. This value is consistent with that needed for a dark-matter neutrino of about 30 eV mass to yield a flux of UV photons which could explain several puzzling observations of H_α emission from the galactic disk and from the intergalactic HI cloud in Leo.     

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.     

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.     

About the Earth density and the neutrino interaction

We visit again the problem to extract information about the mass distribution of the Earth using neutrino collisions with the Earth matter. The topic was addressed in several opportunities using different observable related with the neutrino flux arriving to a neutrino telescope like IceCube. In the present work we have used an observable that is weakly dependent of the initial flux. We check the homogeneity hypothesis and fit a simplified Earth model consistent with the observational value of the Earth mass and the inertia moment.     

Spin flip of neutrinos with magnetic moment in core-collapse supernova

Neutrinos with magnetic moment experience chirality flips while scattering off charged particles. It is known that if neutrino is a Dirac fermion, then such chirality flips lead to the production of sterile right-handed neutrinos inside the core of a star during the stellar collapse, which may facilitate the supernova explosion and modify the supernova neutrino signal. In the present paper we reexamine the production of right-handed neutrinos during the collapse using a dynamical model of the collapse. We refine the estimates of the values of the Dirac magnetic moment which are necessary to substantially alter the supernova dynamics and neutrno signal. It is argued in particular that Super-Kamiokande will be sensitive at least to μ _{ν Dirac} = 10⁻¹³μ_B in case of a galactic supernova explosion. Also we briefly discuss the case of Majorana neutrino magnetic moment. It is pointed out that in the inner supernova core spin flips may quickly equilibrate electron neutrinos with nonelectron antineutrinos if μ _{ν Majorana} ≳ 10⁻¹²μ_B. This may lead to various consequences for supernova physics.     

Lepton flavour symmetry and the neutrino magnetic moment

With the standard model gauge group and the three standard left-handed Weyl neutrinos, two minimal scenarios are investigated where an arbitrary non-Abelian lepton flavour symmetry groupG _H is responsible for a light neutrino with a large magnetic moment. In the first case, with scalar fields carrying lepton flavour, some finetuning is necessary to get a small enough neutrino mass for _v =O(10)^–11 _B. In the second scenario, the introduction of heavy charged gauge singlet fermions with lepton flavour allows for a strictly massless neutrino to one-loop order. In both cases, the interference mechanism for smallm and large _v is unique, independently ofG _H . In explicit realizations of the two scenarios, the horizontal groups are found to be non-Abelian extensions of a Zeldovich-Konopinski-Mahmoud lepton number symmetry. Only a discrete part ofG _H is spontaneously broken leading to a light Dirac neutrino with a large magnetic moment.     

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.     

The Voloshin-Vysotski-Okun solution to the solar-neutrino problem in a left-right model

The apparent anticorrelation between the solarneutrino flux and the sun-spot number can be explained if electron neutrino has a large magnetic moment. A model with SU(2) _L ×SU(2) _R ×U(1) _B?l gauge interaction is presented in which the electron neutrino has a large magnetic moment. The ingredients of the model are (i) the absence of the usual discrete left-right symmetry, (ii) new fermions that are singlets under SU(2) _L and SU(2) _R and (iii) two doublets and a charged singlet of higgs. The model utilises the see-saw mechanism of Gell-Mann, Ramond and Slansky give masses to all quarks and leptons. The large magnetic moment of the electron neutrino is achieved through charged singlet higgs fields.     

Electromagnetic properties of massive neutrinos

The vertex function for a virtual massive neutrino is calculated in the limit of soft real photons. A method based on employing the neutrino self-energy operator in a weak external electromagnetic field in the approximation linear in the field is developed in order to render this calculation of the vertex function convenient. It is shown that the electric charge and the electric dipole moment of the real neutrino are zero; only the magnetic moment is nonzero for massive neutrinos. A fourth-generation heavy neutrino of mass not less than half of the Z-boson mass is considered as a massive neutrino.     

Possible manifestations of the existence of a fourth-generation neutrino

A fourth generation of fermions predicted by the phenomenological heterotic string models can possess a new, strictly conserved charge. Among other things, this leads to the hypothesis of the existence of a fourth massive stable neutrino. A comparison of this hypothesis with the data obtained in the DAMA underground experiment to search for massive weakly-interacting cosmic particles with hidden mass and with the EGRET measurements of the >1 GeV galactic gamma-ray background gives a value m≈50 GeV for the possible mass of the fourth neutrino. It is shown that the hypothesis can be checked in accelerator experiments. The positron signal from annihilation of massive relic neutrinos in the galaxy is calculated. A search for this signal is is within the reach of planned cosmic-ray investigations. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 6, 402–406 (25 March 1999)     

Classical Electromagnetic Interaction of a Point Charge and a Magnetic Moment: Considerations Related to the Aharonov–Bohm Phase Shift

A fundamentally new understanding of the classical electromagnetic interaction of a point charge and a magnetic dipole moment through order v ² /c ² is suggested. This relativistic analysis connects together hidden momentum in magnets, Solem's strange polarization of the classical hydrogen atom, and the Aharonov–Bohm phase shift. First we review the predictions following from the traditional particle-on-a-frictionless-rigid-ring model for a magnetic moment. This model, which is not relativistic to order v ² /c ² , does reveal a connection between the electric field of the point charge and hidden momentum in the magnetic moment; however, the electric field back at the point charge due to the Faraday-induced changing magnetic moment is of order 1/c ⁴ and hence is negligible in a 1/c ² analysis. Next we use a relativistic magnetic moment model consisting of many superimposed classical hydrogen atoms (and anti-atoms) interacting through the Darwin Lagrangian with an external charge but not with each other. The analysis of Solem regarding the strange polarization of the classical hydrogen atom is seen to give a fundamentally different mechanism for the electric field of the passing charge to change the magnetic moment. The changing magnetic moment leads to an electric force back at the point charge which (i) is of order 1/c ² , (ii) depends upon the magnetic dipole moment, changing sign with the dipole moment, (iii) is odd in the charge q of the passing charge, and (iv) reverses sign for charges passing on opposite sides of the magnetic moment. Using the insight gained from this relativistic model and the analogy of a point charge outside a conductor, we suggest that a realistic multi-particle magnetic moment involves a changing magnetic moment which keeps the electromagnetic field momentum constant. This means also that the magnetic moment does not allow a significant shift in its internal center of energy. This criterion also implies that the Lorentz forces on the charged particle and on the point charge are equal and opposite and that the center of energy of each moves according to Newton's second law F=Ma where F is exactly the Lorentz force. Finally, we note that the results and suggestion given here are precisely what are needed to explain both the Aharonov–Bohm phase shift and the Aharonov–Casher phase shift as arising from classical electromagnetic forces. Such an explanation reinstates the traditional semiclassical connection between classical and quantum phenomena for magnetic moment systems.     

Neutrino masses,mixings, and FCNC’s in an <Emphasis Type="Italic">S</Emphasis><Subscript>3</Subscript> flavor symmetric extension of the standard model

By introducing threeHiggs fields that are SU(2) doublets and a flavor permutational symmetry, S ₃, in the theory, we extend the concepts of flavor and generations to the Higgs sector and formulate a Minimal S ₃-Invariant Extension of the Standard Model. The mass matrices of the neutrinos and charged leptons are re-parameterized in terms of their eigenvalues, then the neutrino mixing matrix, V _PMNS, is computed and exact, explicit analytical expressions for the neutrino mixing angles as functions of the masses of neutrinos and charged leptons are obtained in excellent agreement with the latest experimental data. We also compute the branching ratios of some selected flavor-changing neutral current (FCNC) processes, as well as the contribution of the exchange of neutral flavor-changing scalars to the anomaly of the magnetic moment of the muon, as functions of the masses of charged leptons and the neutral Higgs bosons. We find that the S ₃ × Z ₂ flavor symmetry and the strong mass hierarchy of the charged leptons strongly suppress the FCNC processes in the leptonic sector, well below the present experimental bounds by many orders of magnitude. The contribution of FCNC’s to the anomaly of the muon’s magnetic moment is small, but not negligible.     

A<Subscript>4</Subscript> symmetry and lepton masses and mixing

Stimulated by Ma’s idea, which explains the tribimaximal neutrino mixing by assuming an A₄ flavor symmetry, a lepton mass matrix model is investigated. A Frogatt–Nielsen-type model is assumed, and the flavor structures of the masses and mixing are caused by the VEVs of SU(2)_L singlet scalars φ_i ^u and φ_i ^d (i=1,2,3), which are assigned to 3 and (1 ,1 ’,1 ”) of A₄, respectively. Possible charged lepton and neutrino mass spectra and mixing are investigated.     

Limits on the neutrino magnetic moment from solar neutrino experiments

If neutrinos have non-vanishing mass and non-vanishing magnetic moments, then electron neutrinos emitted in nuclear reactions in the solar interior may undergo flavour oscillations, spin precession or resonant spin-flavour precession. Assuming equal values for the magnetic moments of all neutrino flavours and using the data from Homestake and SuperKamiokande we obtain an upper limit on the neutrino magnetic moment and find μ_νe ≤ (2.2 − 2.3) × 10⁻¹⁰μ_B, within four standard solar models. We also point out that this limit may be further reduced if the detector threshold energy for the ν_e,χe⁻ scattering is decreased.     

Search for new phenomena using single photon events at LEP1

Data are presented on the reaction e⁺e^? → γ + no other detected particle at centre-of-mass energies of 89.48, 91.26 and 93.08 GeV. The cross-section for this reaction is related directly to the number of light neutrino generations which couple to the Z° boson, and to several other possible phenomena such as the production of excited neutrinos, the production of any invisible ‘X’ particle, and the magnetic moment of the tau neutrino. Based on the observed number of single photon events, the number of light neutrinos that couple to the Z° is measured to be N_v = 2.89 ± 0.38. No evidence is found for anomalous production of energetic single photons, and upper limits at 95% confidence level are determined for excited neutrino production (BR < 4 ? 8 × 10^?6 depending on its mass), production of an invisible ‘X’ particle (σ, < 0.1 pb for masses below 60 GeV), and the magnetic moment of the tau neutrino (< 5.1 × 10^-6 μB).     

Elastic ν<Subscript>μ</Subscript><Emphasis Type="Italic">e</Emphasis> scattering as a source for determining the muonic neutrino mass and investigation of its electromagnetic properties

Electroweak (EW) and electromagnetic (EM) contributions to the cross sections of elastic scattering of muonic neutrinos by electron are analyzed. The effect of the neutrino mass and root-mean-square charge radius on the angular and energy distributions of product electrons and the total scattering cross sections is considered. The possibility of measuring the muon neutrino magnetic moment μ_ν by selecting its contribution to the ν_μ e-scattering cross sections is analyzed.     

Gemma experiment: Three years of the search for the neutrino magnetic moment

The result of the 3-year neutrino magnetic moment measurement at the Kalinin Nuclear Power Plant (KNPP) with the GEMMA spectrometer is presented. Antineutrino-electron scattering is investigated. A high-purity germanium detector of 1.5 kg placed at a distance of 13.9 m from the 3 GW_th reactor core is exposed to the antineutrino flux of 2.7 × 10¹³ cm⁻² s⁻¹. The scattered electron spectra taken in (5184 + 6798) and (1853 + 1021) h for the reactor ON and OFF periods are compared. The upper limit for the neutrino magnetic moment μ_v < 3.2 × 10⁻¹¹μ _B at 90% CL is derived from the data processing.