72 research outputs found

    Improved analysis of the bounds from the electroweak precision tests on the 4-site model

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    We present a new complete analysis of the electroweak precision observables within the recently proposed 4-site Higgsless model, which is based on the SU(2)_L x SU(2)_1 x SU(2)_2 x U(1)_Y gauge symmetry and predicts six extra gauge bosons, W_{1,2} and Z_{1,2}. Within the epsilon_i (i=1,2,3,b) parametrization, we compute for the first time the EWPT bounds via a complete numerical algorithm going beyond commonly used approximations. Both epsilon_{1,3} impose strong constraints. Hence, it is mandatory to consider them jointly when extracting EWPT bounds and to fully take in to account the correlations among the electroweak precison measurements. The phenomenological consequence is that the extra gauge bosons must be heavier than 250 GeV. Their couplings to SM fermions, even if bounded, might be of the same order of magnitude than the SM ones. In contrast to other Higgsless models, the 4-site model is not fermiophobic. The new gauge bosons could thus be discovered in the favoured Drell-Yan channel already during the present run of the LHC experiment.Comment: Latex file, 35 pages, 10 figures, corrected typos, published versio

    Isolating Vector Boson Scattering at the LHC: gauge cancellations and the Equivalent Vector Boson Approximation vs complete calculations

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    We have studied the possibility of extracting the W+W−→W+W−W^+W^-\to W^+W^- signal using the process us→cdW+W−us\to cd W^+W^- as a test case. We have investigated numerically the strong gauge cancellations between signal and irreducible background, analysing critically the reliability of the Equivalent Vector Boson Approximation which is commonly used to define the signal. Complete matrix elements are necessary to study Electro--Weak Symmetry Breaking effects at high WWWW invariant mass.Comment: Final version published in PR

    Higgs Production in Charged Current Six Fermion Processes at Future e+e−e^+e^- Colliders

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    We study higgs physics at future e+e−e^+e^- colliders taking into account the full set of Feynman diagrams for six fermion final states, which are produced for higgs masses near or above the two WW's threshold. In particular we examine events where one isolated lepton or two isolated leptons of different flavours signal the presence of two W∗\rm W^*'s. For these charged current processes, a detailed analysis of the relevance of irreducible and QCD background shows that appropriate cuts are generally sufficient to deal with it in the case of reconstructed or missing higgs mass distributions. These latter are however affected by a non negligible distortion and shift of the maximum.Comment: Latex, 16 pages, 8 Ps figures included. Revised version. One fig. added, qcd curve in fig.5 corrected, various changes in the tex

    Non-conserved currents and gauge-restoring schemes in single W production

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    We generalize the inclusion of the imaginary parts of the fermionic one-loop corrections for processes with unstable vector bosons to the case of massive external fermions and non conservation of weak currents. We study the effect of initial and final state fermion masses in single W production in connection with the gauge-invariant treatment of the finite-width effects of W and Z bosons, giving numerical comparisons of different gauge-invariance-preserving schemes in the energy range of LEP2 and LC for e+e- -> e- v u d. We do not find significant differences between the results obtained in the imaginary part fermion loop scheme and in other exactly gauge preserving methods.Comment: 12 pages, 3 fig
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