Light 'Higgs', yet strong interactions

The claimed finding of a light Higgs boson makes the minimal Standard Model unitary. Yet, we recall that the general low-energy dynamics for the minimal electroweak symmetry breaking sector with three Goldstone bosons and one light scalar is not so. We construct the effective Lagrangian for these four particles and their scattering amplitudes, that can be extracted from LHC experiments when longitudinal W, Z modes be properly isolated for E ≫ MW (equivalence theorem). We then observe the known increase in interaction strength with energy and explore various unitarization methods in the literature in the absence of other new physics (as LHC experiments fail to report anything up to 600 GeV). Our generic conclusion is that for most of parameter space the high-energy scattering of the longitudinal W's is strongly interacting (with the Minimal Standard Model a remarkable exception). We find and study a second σ-like scalar pole of the WLWL amplitude. (paper)