Some new observations for the Georgi-Machacek scenario with triplet Higgs

TL;DR

This paper updates constraints on the Georgi-Machacek model with triplet Higgs fields, exploring how collider data, scalar decays, and theoretical limits shape its phenomenology and potential for new physics signals.

Contribution

It provides an updated analysis of the Georgi-Machacek scenario, including the effects of custodial symmetry breaking and diverse decay channels, expanding the phenomenological understanding of triplet Higgs models.

Findings

Relaxed bounds on triplet contributions due to new decay modes.

Enhanced $ ext{γγ}$ and $Z ext{γ}$ decay rates of custodial singlet scalar.

Significant trilinear interactions involving charged scalars, $W$, and $Z$ bosons.

Abstract

The Georgi-Machacek model, introducing a complex and a real scalar triplet as additional components of the electroweak symmetry breaking sector, enables substantial triplet contributions to the weak gauge boson masses, subject to the equality of the complex and the real triplet vacuum expectation values (vev) via a custodial SU(2) symmetry. We present an updated set of constraints on this scenario, from collider data (including those from 137/139~fb$^{-1}$ of luminosity at the Large Hadron Collider), available data on the 125-GeV scalar, indirect limits and also theoretical restrictions from vacuum stability and unitarity. It is found that some bounds get relaxed, and the phenomenological potential of the scenario is more diverse, if the doubly charged scalar in the spectrum can decay not only into two like-sign $W$'s but also into one or two singly charged scalars. Other interesting features are noticed in a general approach, such as substantial $\gamma\gamma$ and $Z\gamma$ branching ratios of the additional custodial singlet scalar, and appreciable strength of the trilinear interaction of a charged scalar, the $W$ and the $Z$. Finally,, we take into account the possibility of custodial SU(2) breaking, resulting in inequality of the real and the complex scalar vevs which too in principle may allow large triplet contribution to weak boson masses. Illustrative numerical results on the modified limits and predictions are presented, once more taking into account all the constraints mentioned above.