Lifetimes and branching ratios of heavy leptons

The decay properties of charged heavy leptons are discussed under the assumption that the conjectured leptons (and their associated neutrinos) participate in the weak interactions like the known leptons.     

Leptonic CP-violation and mirror leptons

We study leptonic CP-violation within a single fermion generation in an extended electro-weak model where new right-handed leptons, so-called mirror leptons, exist and mix with standard left-handed leptons. Essential differences are pointed out between the mixing of a left-handed neutrino with a mirror neutrino in such a model and the ordinary mixing of two left-handed neutrinos in the standard model. E.g. in the mirror case CP-violation may occur even if neutrinos are Dirac particles. The number of physical CP-violation phases is determined for different mixing schemes and parameterizations of the leptonic weak currents in terms of these phases are presented.     

Neutrino masses and flavor mixing

We study a model for the mass matrices of the leptons, based on texture zero elements. We are able to relate the mass eigenvalues of the charged leptons and of the neutrinos to the mixing angles, and can predict the masses of the neutrinos. We find a normal hierarchy—the masses are 0.005 eV, 0.01 eV and 0.05 eV. Predictions for the double beta decay and the reactor neutrino experiments are made.     

Neutrino Production via e-e+ Collision at Z-Boson Peak

The production of the three normal neutrinos via e^-e⁺ collision at Z-boson peak (neutrino production in a Z-factory) is investigated thoroughly. The differences of v_e-pair production from v_μ-pair and v_τ-pair production are presented in various aspects. Namely the total cross sections, relevant differential cross sections and the forward-backward asymmetry etc. for these neutrinos are presented in terms of figures as well as numerical tables. The restriction on the room for the mixing of the three species of light neutrinos with possible externals (heavy neutral leptons and/or sterile neutrinos) from refined measurements of the invisible width of Z-boson is discussed.     

Heavy majorana neutrinos atep colliders

Heavy Majorana neutrinos (N), predicted in various extensions of the standard model, are examined with respect to the present limits on their masses and mixings with ordinary leptons resulting in explicit examples of allowed values of interest for present and planned accelerator energies. The decayN→Zv is added to the previously available formalism and all dominating branching ratios are calculated. The production of Majorana neutrinos through charged current interactions in theep colliders HERA and LEP ⊕ LHC is investigated using Monte Carlo event simulation. Signals in terms of isolated leptons and jets are found and shown to be effective in suppressing the dominating standard model backgrounds. The discovery limits of such Majorana neutrinos are, for a mixing of 1%, about 160 GeV at HERA and 700 GeV at LEP ⊕ LHC.     

Different varieties of massive Dirac neutrinos

The concept of Majorana and Dirac massive neutrinos is discussed for the case in which there are several types, or flavors, of leptons. Different varieties of Dirac neutrinos are possible, distinguised by their magnetic moments and anomalous interactions with probabilities proportional to (m/E)².     

Structure quantum numbers and unstable leptons

Wave equations make it possible to ascribe the quantum numbers to leptons theoretically. Minimal extension of the groups describing stable leptons led to three new types of groups. Each of them has an appropriate structure invariant ±1.0 and its own set of substructures having a physical interpretation in terms of stable leptons. The properties of the above-mentioned groups allow one to generate new types of equations and to relate them with two doublets (particle-antiparticle) of massive, charged unstable leptons and a doublet of massive unstable neutrinos.     

Can scalar neutrinos or massive Dirac neutrinos be the missing mass?

Scalar neutrinos and massive Dirac neutrinos in the mass range 2–20 GeV have been proposed as candidates to provide the dark matter in the halo of our galaxy. If so, the particles are captured inthe Earth with an efficiency of 10⁻¹⁰ − 10⁻⁷. For Dirac neutrinos more massive than about 9 GeV and scalar neutrinos more massive than abour 12 GeV, enough are captured to produce an observable neutrino flux at the surface of the Earth (∼ 10⁻² cm⁻² s⁻¹ for sneutrinos and ∼ 1.4 × 10⁻³ cm⁻² s⁻¹ for Dirac neutrinos), several orders of magnitude above atmospheric background and above what is observed. Hence stable scalar neutrinos of mass 12–20 GeV or Dirac neutrinos of mass 9–20 GeV cannot be the dominant component of the halo.     

Universality and the weak neutral current

We consider the possibility that the weak neutral current displays both muon-electron and quark-lepton universality. Such a model contains three parameters which we determine, within limits, from existing data on deep inelastic scattering of neutrinos off nucleons and elastic scattering of neutrinos off leptons. We show that such a model is consistent with other results on elastic neutrino-nucleon scattering and neutrino-induced production of single pions.     

Exact consequences of universality in SU(2) × U(1) gauge models

Exact consequences of universality within SU(2) × U(1) gauge models, with leptons in doublets and singlets, and for arbitrary vacuum expectation values of the Higgs fields, imply an extended Weinberg-Salam structure for leptons, with all neutrinos massless (the inverse statement is obvious). We also discuss approximate universality.     

Contributed report: Flavor anarchy for Majorana neutrinos

We argue that neutrino flavor parameters may exhibit features that are very different from those of quarks and charged leptons. Specifically, within the Proggatt-Nielsen (FN) framework, charged fermion parameters depend on the ratio between two scales, while for neutrinos a third scale — that of lepton number breaking — is involved. Consequently, the selection rules for neutrinos may be different. In particular, if the scale of lepton number breaking is similar to the scale of horizontal symmetry breaking, neutrinos may become flavor-blind even if they carry different horizontal charges. This provides an attractive mechanism for neutrino flavor anarchy.     

Some new symmetric relations and prediction of left-and right-handed neutrino masses using Koide's relation

The masses of the three generations of charged leptons are known to completely satisfy Koide's mass relation,but the question remains of whether such a relation exists for neutrinos.In this paper,by considering the seesaw mechanism as the mechanism generating tiny neutrino masses,we show how neutrinos satisfy Koide's mass relation,on the basis of which we systematically give exact values of both left-and right-handed neutrino masses.     

Electroweak jet cascading in the decay of superheavy particles

We study decays of superheavy particles X into leptons. We show that they initiate cascades similar to QCD parton jets, if m(X) greater or similar 10(6) GeV. Electroweak cascading is studied and the energy spectra of the produced leptons are calculated in the framework of a broken SU(2) model of weak interactions. As application, important for the Z-burst model for ultrahigh energy cosmic rays, we consider decays of superheavy particles coupled on tree level only to neutrinos and derive a stringent limit for these decays from the observed diffuse extragalactic gamma-ray flux.     

Isosinglet neutral heavy lepton production in high energy e-γ collisions

We evaluate the potential for searching for isosinglet neutral heavy leptons (N), such as right-handed neutrinos, in the next generation of e⁺e⁻ linear colliders, paying special attention to contributions from the various γe→WN initiated by photons from beamstrahlung and laser back-scattering. We find that these mechanisms are both competitive and complementary to the standard e⁺e⁻→νN annihilation processe for producing neutral heavy leptons in these machines and greatly extends the search range over HERA and LEP200.     

Lepton number violation in softly broken supersymmetry (II)

We study the implications of explicit lepton-number violating soft operators in a general low-energy effective theory with softly broken supersymmetry. Nonzero but relatively small VEVs of scalar neutrinos could exist. In the case where the VEVs of scalar neutrinos vanish, appreciable coefficients of the lepton-number violating soft operators are allowed. We also emphasize the role played by the mixing between the superpartners of the left- and right-handed leptons in the lepton family number violating process μ→eγ.     

On the interaction of high-energy cosmic leptons with neutralino dark matter

The interaction of neutralino cold dark matter with cosmic-ray electrons is considered in terms of the supersymmetric Standard Model. The production of heavy supersymmetric particles in collisions and their decay are shown to give rise to leptons and neutrinos with certain energies and to relativistic neutralinos. The possibility of detecting dark matter through its interaction with cosmic rays is discussed.     

Detection of supernova neutrinos at spallation neutron sources

After considering supernova shock effects, Mikheyev-Smirnov-Wolfenstein effects, neutrino collective effects, and Earth matter effects, the detection of supernova neutrinos at the China Spallation Neutron Source is studied and the expected numbers of different flavor supernova neutrinos observed through various reaction channels are calculated with the neutrino energy spectra described by the Fermi-Dirac distribution and the "beta fit"distribution respectively. Furthermore, the numerical calculation method of supernova neutrino detection on Earth is applied to some other spallation neutron sources, and the total expected numbers of supernova neutrinos observed through different reactions channels are given.     

Signatures for Majorana neutrinos at hadron colliders

The Majorana nature of neutrinos may only be experimentally verified via lepton-number violating processes involving charged leptons. We explore the Delta L = 2 like-sign dilepton production at hadron colliders to search for signals of Majorana neutrinos. We find significant sensitivity for resonant production of a Majorana neutrino in the mass range of 10-80 GeV at the current run of the Tevatron with 2 fb(-1) integrated luminosity and in the range of 10-400 GeV at the CERN LHC with 100 fb(-1).     

Glashow-Weinberg-Salam theory of electroweak interactions and the neutral currents

In the first part of the review we expound in detail the unified theory of weak and electromagnetic interactions of Glashow, Weinberg and Salam. In the second part, on the basis of this theory a number of the neutral current induced processes are discussed. We consider in detail the deep inelastic scattering of neutrinos on nucleons, the P-odd asymmetry in the deep inelastic scattering of longitudinally polarized electrons by nucleons, the scattering of neutrinos on electrons, the elastic scattering of neutrinos on nucleons, and the electron-positron annihilation into leptons.     

A scenario for generating the fermionic mass spectrum and its predictions

All observed regularities and irregularities of the fermionic mass spectrum follow naturally from a universal two-level GUT scenario. Calculability requires relative orthogonality of the inter-family tree-level contributions and the radiative inner-family ones. This predicts the yet unobserved masses and mixings of the quarks and leptons. In particular, the masses and large mixings of the neutrinos can account for the missing solar neutrinos in terms of vacuum oscillations. A CP violation at GUT energies, induces the observed weak CP violation inK-decay, via radiative corrections.