All the generalized Georgi-Machacek models

Abstract

The Georgi-Machacek model adds two SU(2)_L-triplet scalars to the Standard Model in such a way as to preserve custodial SU(2) symmetry. We study the generalizations of the Georgi-Machacek model to SU(2)_L representations larger than triplets. Perturbative unitarity considerations limit the possibilities to models containing only SU(2)_L quartets, quintets, or sextets. These models are phenomenologically interesting because they allow the couplings of the 125 GeV Higgs boson to WW and ZZ to be larger than their values in the Standard Model. We write down the most general custodial SU(2)-preserving scalar potentials for these models and outline their phenomenology. We find that experimental and theoretical constraints on the fermiophobic custodial-fiveplet states present in each of the models lead to absolute upper bounds on the 125 GeV Higgs boson coupling strength to WW and ZZ.