Abstract
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, in order 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 VBS 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 $a_4$ and $a_5$. This provides a consistent analysis of the different constraints on EChL parameters that can be achieved by using different unitarization methods in a combined way.
Highlights
The discovery of the Higgs boson by the ATLAS and CMS experiments supposed great success of the Standard Model (SM), it posed a lot of new questions about the symmetry breaking sector of the electroweak (EW) theory, questions such as why the Higgs boson is so light, since its mass is so similar to that of the EW gauge bosons; whether the Higgs boson is an elementary or a composite particle; what mechanism generates its potential; and others
We assume a strongly interacting electroweak symmetry breaking (EWSB) sector, properly described by the effective electroweak chiral Lagrangian (EChL) [nowadays called the Higgs effective field theory (HEFT)], and we focus on the bosonic sector of this Lagrangian, choosing to study the particular vector boson scattering (VBS) process given by the WZ channel, as an example that is interesting from the experimental detection perspective
To check that the effective W approximation (EWA) works for our purpose here, we compare the EWA predictions for the cases of the SM and the EChL with the corresponding full results from the Monte Carlo MADGRAPH version 5 (MG5) [45,46], and we find very good agreement in both cases
Summary
The discovery of the Higgs boson by the ATLAS and CMS experiments supposed great success of the Standard Model (SM), it posed a lot of new questions about the symmetry breaking sector of the electroweak (EW) theory, questions such as why the Higgs boson is so light, since its mass is so similar to that of the EW gauge bosons; whether the Higgs boson is an elementary or a composite particle; what mechanism generates its potential; and others. We quantify the uncertainty due to the choice of unitarization scheme present in the determination of some of the most relevant low-energy constants for VBS processes To this aim, we assume a strongly interacting EWSB sector, properly described by the effective electroweak chiral Lagrangian (EChL) [nowadays called the Higgs effective field theory (HEFT)] [8,9,10,11,12,13,14,15,34,35,36,37,38,39,40,41,42], after this discovery), and we focus on the bosonic sector of this Lagrangian, choosing to study the particular VBS process given by the WZ channel, as an example that is interesting from the experimental detection perspective Within this framework, we characterize the unitarity violation that arises in the predictions of the WZ → WZ cross sections, and we analyze the impact that a variety of well-established unitarization methods have on them.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
