The 690 GeV scalar resonance

Spontaneous symmetry breaking through the Higgs field has been experimentally confirmed as a basic ingredient of the Standard Model. However, the origin of the phenomenon may not be entirely clear, because, in perturbation theory, the vacuum turns out to be a metastable state. An alternative scenario was proposed that implies a second resonance of the Higgs field ${\cal H}$ with a well delimited mass $(M_H)^{\rm Theor} = 690\,(30)$ GeV. This stabilises the potential, but, owing to an $H$ coupling to longitudinal $W$s with the same typical strength as that of the low-mass state with $m_h= 125$ GeV, it would still remain a relatively narrow resonance. Our scope here is twofold. First, leaving out many details, we outline a simple logical path where the, apparently surprising, idea of such a second resonance follows from basic properties of $\Phi^4$ theories. Secondly, we spell out a definite experimental signature of this resonance that is clearly visible in various LHC data. As a by-product, the ${\cal H} ^3$ term gives $\kappa_\lambda = (M_H/m_h) \sim$ 5.5 consistently with the ATLAS and CMS data.