Interference Effects in Higgs production through Vector Boson Fusion in the Standard Model and its Singlet Extension

Interference effects play an important role in Electroweak Physics. They are responsible for the restoration of unitarity al large energies. When, as is often the case, higher order corrections are only available for some particular subamplitude, interferences need to be carefully computed in order to obtain the best theoretical prediction. In the new proposal to estimate the total Higgs width from the off shell cross section, the interference between the Higgs signal and the background is essential. It has been recently pointed out in gluon fusion that whenever more than one neutral, CP even, scalars are present in the spectrum large cancellations can occur. We extend these studies to Vector Boson Scattering, examining interference effects in the Higgs sector in the Standard Model and its one Higgs Singlet extension

Boson Fusion and Higgs production at the LHC in six fermion final states with one charged lepton pair

Boson boson scattering and Higgs production in boson boson fusion will be actively investigated at the LHC. We have performed a parton level study of all processes of the type $q_1 q_2 \to q_3 q_4 q_5 q_6 l^+l^-$ using for the first time a full fledged six fermion Monte Carlo event generator which employs exact matrix elements at \O(\alpha_{em}^6). We have examined Higgs production in vector boson fusion followed by the decay chain $H\to ZZ\to l^+l^-jj$, including exactly all electroweak irreducible backgrounds. In the high mass region we have compared the case of a relatively light Higgs with the no-Higgs case. The integrated cross section for the latter case is more than twice that in the former for a minimum invariant mass of the $ZV$ pair of about 800 \GeV. We find, in a preliminary anlysis at parton level that, summing up the muon and the electron channels, about 30 events are expected in the light Higgs case for L=100 $fb^{-1}$.Comment: Final version published in Phys.Rev.

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

We study higgs physics at future $e^+e^-$ 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 $W$'s threshold. In particular we examine events where one isolated lepton or two isolated leptons of different flavours signal the presence of two $\rm W^*$'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

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 $W^+W^-\to W^+W^-$ signal using the process $us\to cd W^+W^-$ 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 $WW$ invariant mass.Comment: Final version published in PR