Although the 125 GeV Higgs boson discovered at the LHC is often heralded as the origin of mass, it may not in fact be the origin of Yukawa couplings. In alternative models, Yukawa couplings may instead arise from a seesaw type mechanism involving the mixing of Standard Model (SM) chiral fermions with new vector-like fermions, controlled by the vacuum expectation value (VEV) of a new complex Higgs singlet field, within a two Higgs doublet model, which breaks a gauged or global U(1)' symmetry. For example, such a model could arise from a 5d version of the Standard Model based on SO(3) symmetry with the vector-like fermions being Kaluza-Klein excitations. We discuss the experimental signals of such models in B-physics experiments, LHC collider searches, and the (g-2) electron and muon experiments. Neutrino masses could originate from vector-like neutrinos in a Type Ib seesaw mechanism, leading to signatures in lepton flavour violation and the neutrino experiments and SHiP, with dark matter originating from the right-handed neutrino portal.
With support from FCT through project UIDB/00777/2020