Unitarization effects in EFT predictions of WZ scattering at the LHC

Effective field theories are an incredibly powerful tool in order to study and understand the true nature of the symmetry breaking sector dynamics of the Standard Model. However, they can suffer from some theoretical problems such as that of unitarity violation. Nevertheless, to interpret experimental data correctly, a fully unitary prescription is needed. To this purpose, unitarization methods are addressed, but each of them leads to a different (unitary) prediction. Because of this, there is an inherent theoretical uncertainty in the determination of the effective field theory parameters due to the choice of one unitarization scheme. In this work, we quantify this uncertainty, assuming a strongly interacting electroweak symmetry breaking sector, described by the effective electroweak chiral Lagrangian. We focus on the bosonic part of this effective Lagrangian and choose in particular the WZ scattering as our main vector boson scattering channel to study the sensitivity to new physics at the LHC. We study the different predictions of various well-known unitarization methods, considering the full coupled system of helicity amplitudes, and construct the 95% confidence level exclusion regions for the most relevant electroweak chiral Lagrangian parameters, given by the two anomalous quartic gauge couplings a4 and a5. This provides a consistent analysis of the different constraints on electroweak chiral Lagrangian parameters that can be achieved by using different unitarization methods in a combined way.