A scale invariant extension of the Georgi Machacek model

Hamza Taibi

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arXiv · 2504.19187

A scale invariant extension of the Georgi Machacek model

Hamza Taibi

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Abstract

We propose a classically scale-invariant extension of the Georgi--Machacek model by augmenting its custodial $SU(2)_L \times SU(2)_R$-symmetric Higgs sector -- originally composed of a doublet and two triplets -- with a gauge-singlet scalar. Employing the Gildener--Weinberg formalism, we demonstrate that radiative symmetry breaking via the Coleman--Weinberg mechanism dynamically generates the electroweak scale along a flat direction. The scalar spectrum retains the quintet ($H_5$) and triplet ($H_3$) states of the original model while introducing three CP-even singlets: a pseudo-Goldstone boson (the \emph{scalon}), which acquires mass at one loop, and two additional massive scalars. One of these massive states corresponds to the observed $125\,\mathrm{GeV}$ Higgs boson. We rigorously derive theoretical constraints from vacuum stability and perturbative unitarity, and we incorporate experimental bounds from electroweak precision tests (notably the $S$ parameter) and Higgs signal strength measurements. Our parameter space analysis identifies viable regions where the scalon mass is below approximately $200\,\mathrm{GeV}$ and the heavier scalar remains under $600\,\mathrm{GeV}$. This framework addresses the hierarchy problem without fine-tuning, preserves custodial symmetry (with $\rho \approx 1$ at tree level), and predicts testable deviations in Higgs couplings. Together with the extended scalar sector, these signatures provide promising avenues for direct investigation at collider experiments.

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Hamza Taibi. 2025-04-27. A scale invariant extension of the Georgi Machacek model. https://arxiv.org/abs/2504.19187

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