72 research outputs found
Improved analysis of the bounds from the electroweak precision tests on the 4-site model
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
We have studied the possibility of extracting the signal
using the process 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
invariant mass.Comment: Final version published in PR
Higgs Production in Charged Current Six Fermion Processes at Future Colliders
We study higgs physics at future 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 's threshold. In particular we
examine events where one isolated lepton or two isolated leptons of different
flavours signal the presence of two '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
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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