  In this contribution to the Snowmass process 2013 (which is a preliminary
version of [1]) we give a brief review of how new physics could enter in the
electroweak (EW) sector of the Standard Model (SM). This new physics, if it is
directly accessible at low energies, can be parameterized by explicit
resonances having certain quantum numbers. The extreme case is the decoupling
limit where those resonances are very heavy and leave only traces in the form
of deviations in the SM couplings. Translations are given into
higher-dimensional operators leading to such deviations. As long as such
resonances are introduced without a UV-complete theory behind it, these models
suffer from unitarity violation of perturbative scattering amplitudes. We show
explicitly how theoretically sane descriptions could be achieved by using a
unitarization prescription that allows a correct description of such a
resonance without specifying a UV-complete model.
