Speaker
Description
The nature of electroweak symmetry breaking remains one of the last theoretical unknowns of the Standard Model. New physics which significantly alters EWSB from the SM prediction must be non-decoupling and does not admit a SMEFT expansion. In arXiv:2409.18177, we extend the SM with a spanning set of scalar electroweak multiplets that gain the majority of their mass via the Higgs mechanism. These particles by definition are non-decoupling, many of them are not excluded by current data and they generate a pattern of deviations in low energy observables distinct from SMEFT (although they may be accommodated in HEFT). We show that any such scalar is discoverable at a future precision lepton collider and may leave imprints of a first order phase transition which are detectable by future gravitational-wave experiments such as LISA. This is a test of the assumption of decoupling NP that is built into the SMEFT.
