Particle Seminar

Monday, July 13, 2020

Speaker: Carlos de Lima

Affiliation: Carleton

Time: 2:30PM -- 3:30PM

Location: Virtual seminar on zoom

Title: Lower bound on the triplet vev for the Z2 symmetric Georgi-Machacek Model

The Z2 symmetric version of the Georgi-Machacek (GM2) has a non-decoupling behavior. Such a feature makes it impossible to hide any new physics from electroweak observables by making the particles arbitrarily heavy. We explore this model, especially the singlet sector where we do not assume the mass hierarchy between the Higgs and the CP-even singlet. Such an assumption is widely made in the study of the GM model but can hide an important phase of the theory. The better understanding of the singlet sector of this model opens the possibility of contributions for the Higgs total width. Since the total width is of order MeV, and any contribution from this model naturally is GeV, the parameter space is heavily constrained. Together with Higgs to diphoton bounds, we can exclude all the parameter space where the decay can happen at 95%CL. This exclusion generates a lower bound on the expectation value of the triplets of 8.84GeV. The lower bound makes it impossible to not have deviations from the Standard Model in all observables. For instance, the Higgs couplings to fermions and gauge bosons cannot be Standard Model at the same time, having at least 1.5% deviation.