A scale invariant extension of the Georgi Machacek model

Abstract

We present a classically scale-invariant extension of the Georgi--Machacek model, wherein the electroweak scale is generated radiatively via the Coleman--Weinberg mechanism within the Gildener--Weinberg framework. A real gauge-singlet scalar is introduced alongside the usual Higgs doublet and scalar triplets, and all mass scales emerge from dimensional transmutation. The model predicts a pseudo-Goldstone boson of scale symmetry (the scalon), the observed 125 GeV Higgs boson, and an additional heavy neutral scalar, alongside the charged and doubly-charged states of the original Georgi--Machacek structure. We derive the full set of theoretical constraints from perturbative unitarity, vacuum stability, and high-scale perturbativity, and confront the model with experimental bounds from electroweak precision observables, LHC Higgs signal strengths, and direct LHC searches for $H_5^{\pm\pm}$ production via vector-boson fusion with subsequent decay to $W^\pm W^\pm$. A comprehensive numerical scan identifies viable parameter regions consistent with all of these constraints, with every viable point developing a Landau pole at or below $\sim 10^9$ GeV, establishing the model as a predictive effective theory valid up to intermediate scales.