Showing papers on "Lepton published in 1992"
TL;DR: It is found that the lepton-number-violating out-of-equilibrium decays of right-handed neutrinos combined with anomalous electroweak processes can generate the baryon number of the Universe, and that the scenario works for a wide range of parameters in the neutrino sector.
Abstract: If right-handed Majorana neutrinos are added to the standard model, then lepton-number-violating out-of-equilibrium decays of right-handed neutrinos combined with anomalous electroweak processes can generate the baryon number of the Universe. We analyze this mechanism in detail, and determine the ranges of parameters for which the correct baryon number is generated. We find that the scenario works for a wide range of parameters in the neutrino sector, including right-handed neutrino masses ranging from \ensuremath{\sim}1 TeV to \ensuremath{\sim}${10}^{19}$ GeV, depending on the assumptions made about the structure of the neutrino mass matrices.
503 citations
TL;DR: In this paper, the total τ hadronic width can be accurately calculated using analyticity and the operator product expansion, and the theoretical analysis of this observable is updated to include all available perturbative and nonperturbative corrections.
497 citations
CERN1
TL;DR: In this paper, the perturbative QCD prediction to the total hadronic width of the tau lepton is re-examined, and a more convergent perturbation expansion is proposed, which is associated with a smaller renormalization-scheme dependence and better-defined higher-order uncertainties.
290 citations
26 Jun 1992
TL;DR: In this article, the authors focus on what we know and may hope to know about the mass of the neutrino and its particle-antiparticle symmetry, and discuss both theoretical and experimental techniques.
Abstract: Neutrinos play a decisive part in nuclear and elementary particle physics, as well as in astrophysics and cosmology. Some of their most basic properties, such as their mass and charge conjugation symmetry, are largely unknown. This book focuses on what we know and may hope to know about the mass of the neutrino and its particle-antiparticle symmetry. Topics include neutrino mixing, neutrino decay, neutrino oscillations, double beta decay, solar neutrinos, supernova neutrinos and related issues. The authors stress the physical concepts, and discuss both theoretical and experimental techniques. This updated second edition differs from the first in that it contains an expanded coverage of experimental results and theoretical advances. Since publication of the first edition, many issues that were at that time unresolved, such as tritium beta decay and reactor neutrino oscillations, have been clarified and are discussed here. Also included is an expanded coverage of solar and supernova neutrinos. This book deals with one of the most intriguing issues in modern physics, and will be of value to researchers, graduate students and advanced undergraduates specializing in experimental and theoretical particle physics and nuclear physics.
267 citations
TL;DR: In this paper, a comprehensive set of mass and coupling limits are presented for a number of rare hadronic and leptonic decays at the e+e− collider at the LEP, and the searches performed by ALEPH for Higgs bosons, supersymmetric particles, and for evidence of compositeness are reviewed.
192 citations
TL;DR: In this paper, it was shown that the Lagrangian describing parity conserving models can be reformulated in terms of a basis in which each term of Lagrangians is parity invariant, although gauge invariance is not manifest.
Abstract: It has been shown that parity may be an exact unbroken symmetry of nature. This requires a doubling of the number of physical particles, although only two parameters beyond those in the Standard Model are introduced. In this paper, the authors show that the Lagrangian describing parity conserving models can be reformulated in terms of a basis in which each term of the Lagrangian is parity invariant, although gauge invariance is not manifest. The authors then examine some further experimental signatures of parity conservation. The authors point out that, in the simplest case, there is one parity-even and one parity-odd physical neutral Higgs mass eigenstate, whose Yukawa coupling constants are 1/ sq. root 2 that of the Standard Model Higgs boson. Furthermore, half of their widths are generated by almost invisible decay modes. Also, if neutrinos are massive then the ordinary and mirror neutrinos will, in the minimal case, be maximally mixed due to parity conservation. This means that vacuum oscillations can be large, thus providing a possible solution to the solar neutrino problem.
157 citations
TL;DR: In this article, gravitationally induced masses and mass splittings of Majorana, Zeldovich-Konopinski-Mahmoud, and Dirac neutrinos are discussed.
Abstract: We discuss gravitationally induced masses and mass splittings of Majorana, Zeldovich-Konopinski-Mahmoud, and Dirac neutrinos. Among other implications, these effects can provide a solution of the solar neutrino puzzle. In particular, we show how this may work in the 17 keV neutrino picture.
142 citations
TL;DR: In this article, a mechanism in a class of superstring standard-like models was proposed to explain the mass hierarchy between the top and bottom quarks, and the bottom quark and tau lepton Yukawa couplings were obtained from quartic order terms.
139 citations
TL;DR: In this article, a technique to sum up the regular corrections appearing under the analytical continuation from the space like momentum region to the time like one is proposed, and a perturbative part of the inclusive semileptonic decay width of the τ-lepton is analyzed in detail.
Abstract: A technique to sum up the regular corrections appearing under the analytical continuation from the space like momentum region to the time like one is proposed. A perturbative part of the inclusive semileptonic decay width of the τ-lepton in analyzed in detail.
136 citations
TL;DR: In this paper, the cosmological consequences of neutrino degeneracy are explored with particular attention to the effects on primordial nucleosynthesis, and a combination of bounds from DBBN and the density and expansion rate of the Universe constraints the e-neutrino deformation (−0.06 ⪅ξe⪅1.1), the μ, τ-NE, τ−6.9) and, the nucleon-to-photon rati0 (2.8⫅η10−19).
131 citations
TL;DR: In this paper, the authors studied the QCD production mechanisms for lepton and quark pairs of high mass M that carry a large fraction x of the projectile momentum, and showed that the dominant contribution comes from peripheral processes in which low-x spectator quarks interact with the target, with the hardness scale of the collision being given by Q 2 = M 2 (1−x).
TL;DR: In this paper, a new algorithm for the generation of the complete O(α) QED corrections for τ decays into leptons is presented, which can be easily combined with this library and any other big packages like KORALB or KorALZ which contain TAUOLA.
TL;DR: Several results follow if the interactions of new scalars possess approximate flavor symmetries, and present experimental bounds allow these exotic scalars to have a weak-scale mass.
Abstract: The quark and lepton mass matrices possess approximate flavor symmetries. Several results follow if the interactions of new scalars possess these approximate symmetries. Present experimental bounds allow these exotic scalars to have a weak-scale mass. The Glashow-Weinberg criterion is rendered unnecessary. Finally, rare leptonic {ital B} meson decays provide powerful probes of these scalars, expecially if they are leptoquarks.
TL;DR: In this paper, the off-diagonal lepton-lepton-Higgs boson vertex induced by one-loop electroweak corrections was calculated in the context of the standard model in which one right-handed neutrino for each family has been introduced.
TL;DR: In this paper, the Drell-Yan process is used to measure the transverse spin polarization distribution of quarks in a proton, which contributes at leading twist to the angular distribution of lepton pair production in doubly polarized proton-proton collisions.
Abstract: The transverse spin polarization distribution of quarks in a proton contributes at leading twist to the angular distribution of lepton pair production in doubly polarized proton-proton collisions. Although this distribution is straightforward to define in the QCD-improved parton model and represents a fundamental quark degree of freedom, it has never been measured. Moreover, deeply inelastic electroproduction experiments are only sensitive to this distribution at the higher twist level, and then mix this contribution with others, including the one coming from multiparton initial states. Reviewing this, we conclude that the Drell-Yan process is the best way to measure the quark transverse spin polarization distribution.
TL;DR: In this paper, neutral heavy leptons that are isosinglets under the standard SU (2)L gauge group were searched for and no evidence for a signal has been found and the limit Br(NSu0 → vlNl) < 3 x 10−5 at the 95% CL for mass range from 3 GeV up to Mz.
TL;DR: In this article, the leading two-loop electroweak contributions to the muon anomalous magnetic moment were calculated in the standard model and diagrams with logarithmically enhanced contributions were selected.
TL;DR: In this paper, the authors demonstrate that the ability to polarize the photons produced by backscattering laser beams at a TeV scale linear e + e − collider could make it possible to determine whether or not a neutral Higgs boson produced in photon-photon collisions is a CP eigenstate.
TL;DR: Searches for the top quark in pp collisions at the Fermilab Tevatron Collider and the previous search for eμ final states for tt→ecbμvb decays has been extended to include the ee and μμ channels.
Abstract: We present results from searches for the top quark pp¯ collisions at the Fermilab Tevatron Collider. The data sample was collected during 1988–89 with the Collider Detector at Fermilab and has an integrated luminosity of 4.1 pb−1. Our previous search for eμ final states for tt¯→eνb μνb¯ decays has been extended to include the ee and μμ channels. In addition, we have searched in each event with a high-transverse-momentum lepton accompanied by hadron jets for a low-transverse-momentum muon as a tag of a bottom quark in tt¯→lνbqq¯b¯ decays. A lower limit on the top-quark mass of 91 GeV/c2 is obtained at the 95% confidence level, assuming standard model decays.
TL;DR: In this paper, the angular decay distribution of leptons from W-production at high-qT in p p collisions was measured and it was shown that large deviations from the well-known (1+cos θ2) distribution valid at low-qTs are expected already at moderate transverse W-momentum (qT≈20GeV).
TL;DR: The recently resurrected 17-keV neutrino is incorporated into this model, which proposes a model in which Dirac neutrinos can have such short lifetimes as to explain the solar-neutrino problem.
Abstract: Constraints on Dirac-neutrino decay into invisible particles are surveyed. Neutrino lifetimes short enough to explain the solar-neutrino problem are allowed by present terrestrial and cosmological measurements. A model in which Dirac neutrinos can have such short lifetimes is proposed. The recently resurrected 17-keV neutrino is incorporated into this model.
TL;DR: In this paper, shadowing in lepton-deuteron scattering is analyzed using double interaction formalism where they relate shadowing to inclusive diffractive processes and find that the shadowing effects are very small, less than 2% or so.
TL;DR: In this article, the attainable rates for anomalous leptonic lepton muon and tau number violating decays such as μ→eγ, μ→3e, τ→μγ, τβγ, γββ, τ βγ, ββββδ, τγ, αββα, βα, τα, αα, εβα βα ββα αβαβαα αααβγ βαααγαγβαγγαββγα
Abstract: Lepton flavor violating rates can be experimentally measurable even if the observed neutrinos are strictly massless. We make a study of the attainable rates for anomalous leptonic muon and tau number violating decays such as μ→eγ, μ→3e, τ→μγ, τ→eγ, τ→μμ+ μ−, τ→ ee+e−, τ→eμ+μ−, etc. as well as semileptonic lepton flavor violating tau decays such as τ→μπ0, τ→eπ0, τ→eη, etc. All muonic violating decays can be as large as the present limits from LAMPF, TRIUMF and PSI. The corresponding tau violating processes can all be at the limit of sensitivity of the upcoming τ factories.
TL;DR: In this paper, polarization effects in semi-leptonic decays of polarized and unpolarized heavy Λ-type baryons into heavy and into light Λ type Baryons are discussed.
TL;DR: A simple but quantitatively accurate formalism for tracking the approach of the sterile state to thermal equilibrium is introduced and it is found that {mu}{ital m} must be less than 3{times}10{sup {minus}5} eV{sup 2}, which is too small to explain atmospheric neutrino observations.
Abstract: If a neutrino has both Dirac and Majorana masses ({ital m},{mu}), as some recent models predict, {nu}{leftrightarrow}{bar {nu}} oscillations within a single generation may cause a violation of the nucleosynthesis bound on the number of light neutrino species. Taking into account the effects of finite temperature and density, we find that {mu}{ital m} must be less than 3{times}10{sup {minus}5} eV{sup 2}, which is too small to explain atmospheric neutrino observations. The bound can be softened to 0.05 eV{sup 2} if the right-handed components couple to massless bosons (Majorons). We introduce a simple but quantitatively accurate formalism for tracking the approach of the sterile state to thermal equilibrium.
TL;DR: In this paper, the properties of the Z resonance were measured on the basis of 190 000Z decays into fermion pairs collected with the ALEPH detector at LEP, and the forward-backward asymmetry in leptonic decays was used to determine the ratio of vector to axial-vector coupling constants of leptons.
Abstract: The properties of theZ resonance are measured on the basis of 190 000Z decays into fermion pairs collected with the ALEPH detector at LEP. Assuming lepton universality,Mz=(91.182±0.009exp±0.020L∶P) GeV,ГZ=(2484±17) MeV, σhad0=(41.44±0.36) nb, andГjad/Гll=21.00±0.20. The corresponding number of light neutrino species is 2.97±0.07. The forward-back-ward asymmetry in leptonic decays is used to determine the ratio of vector to axial-vector coupling constants of leptons:gv2(MZ2)/gA2(MZ2)=0.0072±0.0027. Combining these results with ALEPH results on quark charge and\(b\bar b\) asymmetries, and τ polarization, sin2θW(MZ2). In the contex of the Minimal Standard Model, limits are placed on the top-quark mass.
TL;DR: In this article, the number of tau neutrinos produced from the decays of D s mesons in the dump was estimated, and the data limit the possible magnetic moment of the neutrino to be below 5.4×10 −7 ω B.
TL;DR: It is argued that the neutrino effective potential must be defined from the dispersion relation and not directly from the self-energy.
Abstract: We consider a neutrino of any flavor propagating through a thermal background of charged leptons, nucleons, and neutrinos. The neutrino self-energy is calculated in a general gauge up to terms of order ${\mathit{g}}^{2}$/${\mathit{m}}_{\mathit{W}}^{4}$, and it is shown that, although the self-energy depends on the gauge parameter, the dispersion relation is independent of it. On the basis of this result it is argued that the neutrino effective potential must be defined from the dispersion relation and not directly from the self-energy. Explicit formulas for the effective potential are given.
TL;DR: In this article, the energy distribution of the decay leptons was investigated in semileptonic Λb decays, where the lepton energy distribution is sensitive to the standard model parameters via the nontrivial Θb polarization.