  In order to explore a possible dynamical nature for the Higgs field (such as
its being a pseudo-Goldstone boson) we develop a renormalizable Lagrangian
based on the minimal $SO(5)$ linear $\sigma$-model with the symmetry softly
broken to $SO(4)$, including gauge bosons and fermions. We then present the
phenomenological implications and constraints from precision observables and
the impact on present and future LHC data.
