Lepton assignment in E7 model and multilepton production by neutrinos

We propose a lepton assignment within the frame work of E7 gauge model and show that observed multilepton events by neutrinos can be explained, within this assignment, by the production of a heavy lepton.     

Coherent active-sterile neutrino flavor transformation in the early universe

We solve the problem of coherent Mikheyev-Smirnov-Wolfenstein resonant active-to-sterile neutrino flavor conversion driven by an initial lepton number in the early Universe. We find incomplete destruction of the lepton number in this process and a sterile neutrino energy distribution with a distinctive cusp and high energy tail. These features imply alteration of the nonzero lepton number primordial nucleosynthesis paradigm when there exist sterile neutrinos with rest masses m(s) approximately 1 eV. This could result in better light element probes of (constraints on) these particles.     

τ lepton decays

We discuss recent results on τ lepton physics obtained at the BABAR,Belle and KEDR detectors.They include tests of lepton universality using new measurements of τ lepton mass and some branching fractious.Also described are selected results on τ lepton hadronic decays coming from BABAR and Belle.     

THE EMC EFFECT AND THE LIGHT-CONE QUANTUM FIELD THEORY

We indicate that final state interactions can be neglected if one calculate deep inelastic lepton nucleus scattering in the time-ordered perturbation theory in the infinite momentum frame,or its equivalent,the light-cone perturbation theory in an ordinary frame.We thus extend the light-cone quantum field theory to baryon-meson field to establish a relativistic composite model of nuclei,and then apply the impulse approximation to deep inelastic lepton nucleus scattering in this model.     

Leptogenesis bound on spontaneous symmetry breaking of global lepton number

We propose a new class of leptogenesis bounds on the spontaneous symmetry breaking of global lepton number. These models have a generic feature of inducing new lepton number violating interactions, due to the presence of the Majorons. We analyzed the singlet Majoron model with right-handed neutrinos to find that the lepton number should be broken above 10⁵ GeV to realize a successful leptogenesis because the annihilations of the right-handed neutrinos into the massless Majorons and into the standard model Higgs should go out of equilibrium before the sphaleron process is over. We then argue that this type of leptogenesis constraint should exist in the singlet–triplet Majoron models as well as in a class of R-parity violating supersymmetric Majoron models.     

Allowed excitation of unnatural-parity states in the 208Pb(4He, 6He) reaction

We consider, in the context of simple gauge models, the possibility that lepton number is a spontaneously broken global symmetry, leading to massive Majorana neutrinos. We find that the usual objections associated with global symmetry breakdown may be moot in this case since the Goldstone boson associated with lepton number breakdown - the majoron - is so weakly coupled to matter that it may have well escaped detection.     

Neutrino masses from SUSY: Different contributions and their implications

We discuss the various sources of neutrino masses in supersymmetric standard models with explicit lepton number violation. We show that the bilinear lepton number violating soft terms in models with either bilinear or trilinear lepton number violating couplings in the superpotential, play an important role in determining the neutrino mass spectrum. A comparative study of the neutrino mass spectrum and its implications for the present neutrino anomalies in these models is presented.     

A study of B meson oscillations using hadronic Z0 decays containing leptons

An event sample enriched in semileptonic decays of b hadrons is selected using an inclusive lepton selection from approximately 3.0 million hadronic Z⁰ decays collected with the OPAL detector. This sample is used to investigate B meson oscillations by reconstructing a proper decay time for the parent of each lepton, using a jet charge method to estimate the production flavour of this parent, and using the lepton charge to tag the decay flavour. We measure the mass difference between the two B⁰ _d mass eigenstates     

Leptogenesis via a varying Weinberg operator:a semi-classical approach

In this paper, we introduce leptogenesis via a varying Weinberg operator from a semi-classical perspective.This mechanism is motivated by the breaking of an underlying symmetry which triggers a phase transition that causes the coupling of the Weinberg operator to become dynamical. Consequently, a lepton anti-lepton asymmetry arises from the interference of the Weinberg operator at two different spacetime points. Using the semi-classical approach,we treat the Higgs as a background field and show that a reflection asymmetry between leptons and anti-leptons is generated in the vicinity of the bubble wall. We solve the equations of motion of the lepton and anti-lepton quasiparticles to obtain the final lepton asymmetry.     

Large transverse momentum lepton pair production at the Large Hadron Collider

We study the large transverse momentum distribution of lepton pairs produced in heavy-ion collisions, making use of the perturbative QCD. Referring to the calculation of the parton-parton production process into lepton pairs at the Relativistic Heavy Ion Collider (RHIC), the production of lepton pairs at large transverse momentum is extended to the Large Hadron Collider (LHC). The contribution of the parton-parton production process into lepton pairs in Pb-Pb collisions at the LHC is calculated, including the complete processes at large transverse momentum. Lepton pair production with the direct single photon process and the resolved single photon process are considered and confirmed to be significant at the LHC.     

Search for new physics using high-mass tau pairs from 1.96 TeV pp collisions

We present the results of a search for anomalous resonant production of tau lepton pairs with large invariant mass, the first such search using the CDF II Detector in Run II of the Tevatron pp collider. Such anomalous production could arise from various new physics processes. In a data sample corresponding to 195 pb(-1) of integrated luminosity we predict 2.8+/-0.5 events from standard model background processes and observe 4. We use this result to set limits on the production of heavy scalar and vector particles decaying to tau lepton pairs.     

Effect of neutrino trapping on the three flavor FFLO phase of QCD

We compute the effect of a non-zero lepton chemical potential on the structure of the three flavor Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase of QCD at finite temperature. We show that, as in the BCS case, the lepton chemical potential favors two-species color superconductivity and disfavors the three species pairing. We stress that this study could be relevant for the cooling of a proto-neutron star with a FFLO core, if the temperatures are higher than the un-trapping temperature.     

Semi-inclusive deep inelastic lepton scattering in a pion cloud model

In this note we explore the consequences of the pion cloud model for semi-inclusive deep inelastic lepton scattering. We argue that by scattering on a few-nucleon target, the detection of the recoiling target would provide a valuable test of the meson cloud model. We estimate the semi-inclusive cross section for deep inelastic lepton scattering on a³He target, as function of Bjorkenx and target recoil momentum.     

Probing lepton structure at the SSC

If quarks and leptons are composite objects with common constituents, then there exist two-quark-two-lepton contact interactions which could affect lepton pair production at the SSC. We show that for a range of compositeness scales and lepton pair invariant masses, the contact interaction contributions dominate the standard model contributions to the cross section. In this regime, we show that there should be a measurable and statistically significant front-back asymmetry.     

Low mass lepton pair production and pion dynamics in ultrarelativistic heavy ion collisions

The production of lepton pairs with low invariant mass as probes for the pion dynamics in relativistic nuclear collisions is discussed in some detail. We emphasize the implications of a possible large positive pion chemical potential for the production rate of lepton pairs. We find a strong enhancement in the low invariant mass region, \(2m_\pi \leqslant M_{\mu ^ + \mu ^ - } \leqslant 600\,MeV\) , for lepton pairs which are produced via the annihilation of pions in the hot and dense collision zone. Various sources of background which could mask this enhancement are discussed in some detail. We present and compare calculations for dilepton mass spectra based on different nuclear collision scenarios. It is found that the di-muon mass spectrum can serve as a useful probe to distinguish between these different scenarios.     

Photon-neutrino interactions

We discuss the interaction of photons with neutrinos including two lepton loops. The parity violation in the γ ν → γν channel due to two lepton loops is substantially enhanced relative to the one lepton loop contribution. However, there is no corresponding enhancement in the parity conserving amplitude in either the direct or the cross channel \(\gamma \gamma \to v\bar v\).     

Baryogenesis from mixing of lepton doublets

It is shown that the mixing of lepton doublets of the Standard Model can yield sizable contributions to the lepton asymmetry, that is generated through the decays of right-handed neutrinos at finite temperature in the early Universe. When calculating the flavour-mixing correlations, we account for the effects of Yukawa as well as of gauge interactions. We compare the freeze-out asymmetry from lepton-doublet mixing to the standard contributions from the mixing and direct decays of right-handed neutrinos. The asymmetry from lepton mixing is considerably large when the mass ratio between the right-handed neutrinos is of order of a few, while it becomes Maxwell-suppressed for larger hierarchies. For an intermediate range between the case of degenerate right-handed neutrinos (resonant leptogenesis) and the hierarchical case, lepton mixing can yield the main contribution to the lepton asymmetry.     

Space Anisotropy Search at Colliders

In the framework of model with Lorentz violation (LV) we discuss a physical observables for q\(\bar q\) pair production at lepton–lepton colliders and describe the experimental signal to be detected. We obtain a conservative limits on Lorentz-violating dimensionless coupling for quark sector from LEP data. We also make a phenomenological prediction for LV model at the future lepton collider.     

Equation of State of Protoneutron Star Matter

We have calculated the equation of state of protoneutron star matter by using the lowest order constrained variational method. In our calculations, the modern Argonne potential (AV₁₈) together with its older model potential (AV₁₄) are used. It is found that the equation of state for high lepton fraction is stiffer than for low lepton fraction. It is seen that the increasing effect of pressure due to high lepton fraction and due to entropy are comparable. It is shown that the temperature and adiabatic index depend on the values of both entropy and lepton fraction.     

Processes with Higgs Scalar Bosons in External Electromagnetic Fields

In this paper we consider the processes with real and virtual Higgs scalar H-boson in the presence of an external constant electromagnetic field. We get formulae for the probability of the H-boson emission by a charged lepton and the field radiative H-boson effects (i.e. the contribution to the mass and the anomalous magnetic moment of the lepton.