5,687 research outputs found

    Compositeness Effects in the Anomalous Weak-Magnetic Moment of Leptons

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    We investigate the effects induced by excited leptons, at the one-loop level, in the anomalous magnetic and weak-magnetic form factors of the leptons. Using a general effective Lagrangian approach to describe the couplings of the excited leptons, we compute their contributions to the weak-magnetic moment of the τ\tau lepton, which can be measured on the ZZ peak, and we compare it with the contributions to gμ−2g_\mu - 2, measured at low energies.Comment: Latex File using Rev Tex. 16 pages 5 .eps figure

    Standard Model: An Introduction

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    We present a primer on the Standard Model of the electroweak interaction. Emphasis is given to the historical aspects of the theory's formulation. The radiative corrections to the Standard Model are presented and its predictions for the electroweak parameters are compared with the precise experimental data obtained at the Z pole. Finally, we make some remarks on the perspectives for the discovery of the Higgs boson, the most important challenge of the Standard Model.Comment: 101 pages, 14 figures, To be published in "Particle and Fields", Proceedings of the X J. A. Swieca Summer School (World Scientific, Singapore, 2000

    Fermion Helicity Flip in Weak Gravitational Fields

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    The helicity flip of a spin-12{\textstyle \frac{1}{2}} Dirac particle interacting gravitationally with a scalar field is analyzed in the context of linearized quantum gravity. It is shown that massive fermions may have their helicity flipped by gravity, in opposition to massless fermions which preserve their helicity.Comment: RevTeX 3.0, 8 pages, 3 figures (available upon request), Preprint IFT-P.013/9

    New Higgs Interactions in ZZ\gamma and Z\gamma\gamma Production

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    The effect of new operators that only modify the bosonic couplings of the Higgs boson, without altering the WW\gamma or WWZ three-point functions, are examined in the e+e- -> ZZ\gamma and Z\gamma\gamma processes. We analyse the constraints on these interactions that can be imposed by the LEP II collider at CERN and at the Next Linear Collider.Comment: 7 pages, RevTeX, 3 postscript figure

    A new correlator in quantum spin chains

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    We propose a new correlator in one-dimensional quantum spin chains, the s−s-Emptiness Formation Probability (s−s-EFP). This is a natural generalization of the Emptiness Formation Probability (EFP), which is the probability that the first nn spins of the chain are all aligned downwards. In the s−s-EFP we let the spins in question be separated by ss sites. The usual EFP corresponds to the special case when s=1s=1, and taking s>1s>1 allows us to quantify non-local correlations. We express the s−s-EFP for the anisotropic XY model in a transverse magnetic field, a system with both critical and non-critical regimes, in terms of a Toeplitz determinant. For the isotropic XY model we find that the magnetic field induces an interesting length scale.Comment: 6 pages, 1 figur

    Bounds on Contact Interactions from LEP1 Data and the High-Q2Q^2 HERA Events

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    A contact four-fermion interaction between light quarks and electrons has been evoked as a possible explanation for the excess of events observed by HERA at high-Q2Q^2. We explore the 1-loop effects of such interaction in limit of the effective scale. Our results are able to discard some of the contact interactions as possible explanation for the HERA events

    Detecting Large Concept Extensions for Conceptual Analysis

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    When performing a conceptual analysis of a concept, philosophers are interested in all forms of expression of a concept in a text---be it direct or indirect, explicit or implicit. In this paper, we experiment with topic-based methods of automating the detection of concept expressions in order to facilitate philosophical conceptual analysis. We propose six methods based on LDA, and evaluate them on a new corpus of court decision that we had annotated by experts and non-experts. Our results indicate that these methods can yield important improvements over the keyword heuristic, which is often used as a concept detection heuristic in many contexts. While more work remains to be done, this indicates that detecting concepts through topics can serve as a general-purpose method for at least some forms of concept expression that are not captured using naive keyword approaches

    Supersymmetric Higgs pair discovery prospects at hadron colliders

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    We study the potential of hadron colliders in the search for the pair production of neutral Higgs bosons in the framework of the Minimal Supersymmetric Standard Model. Using analytical expressions for the relevant amplitudes, we perform a detailed signal and background analysis, working out efficient kinematical cuts for the extraction of the signal. The important role of squark loop contributions to the signal is emphasised. If the signal is sufficiently enhanced by these contributions, it could even be observable at the next run of the upgraded Tevatron collider in the near future. At the LHC the pair production of light and heavy Higgs bosons might be detectable simultaneously.Comment: 5 pages, hep99, 6 figures; Presented at the International Europhysics Conference on High Energy Physics, Tampere, Finland, 15-21 July 199
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