Unitarization models for vector boson scattering at the LHC

Effective Field Theories (EFT) can be used to quantify deviations from the Standard Model in a model independent way: keeping the symmetries and local gauge invariance. It is possible then to write new physics as an extension of the Standard Model in an Effective Lagrangian including higher dimensional operators composed of the already known fields. In general, it is of interest to study the EFT for electroweak precision tests, as they are among the most sensitive searches to constrain new physics. Therefore, precise knowledge of the Triple Gauge Couplings and Quartic Gauge Couplings is desirable, as new physics effects could manifest in their final states. Once the higher dimensional operators are included in the Effective Lagrangian, the amplitudes have terms that grow proportional to the energy, hence the cross section falls off more slowly than expected and it points to a unitarity violation of the S matrix: this implies that the Effective Field Theory is used beyond its validity region and it leads to a non-physical cross section, an idea that has been used previously to indicate the scale of new physics. This unitarity problem needs to be solved, as nature guarantees unitarity conservation. The unitarity bounds are calculated from the partial wave analysis of the on-shell 2→2 scattering amplitudes and a unitarization scheme needs to be used to reconstruct the off-shell amplitudes. In this work, a T-matrix unitarization scheme is described for Vector Boson Scattering at the LHC and implemented in VBFNLO, a parton level Monte Carlo for processes with electroweak bosons.