  In this work we explore in detail the presence of scalar resonances in $WW$
fusion process in the context of the LHC experiments working in the theoretical
framework provided by Higgs Effective Field Theories (HEFT). While the
phenomenology of vector resonances is reasonably understood in the framework of
Weinberg sum-rules and unitarization studies, scalar resonances are a lot less
constrained and, more importantly do depend on HEFT low-energy effective
couplings different from the ones of vector resoances that are difficult to
constrain experimentally. More specifically, unitarization techniques combined
with the requirement of causality allows us to set non-trivial bounds on Higgs
self-interactions. This is due to the need of considering coupled channels in
the scalar case along the unitarization process. As a byproduct, we can gain
some relevant information on the Higgs sector from $WW\to WW$ elastic processes
without needing to consider two Higgs production.
