Light Scalars in the Extended Georgi-Machacek Model

TL;DR

This paper performs comprehensive global fits of the extended Georgi-Machacek models, analyzing light scalar signals around 95 GeV and deriving constraints on model parameters based on collider, B-physics, and theoretical data.

Contribution

It provides the first detailed global fit analysis of the extended Georgi-Machacek model including light scalars and experimental excesses, constraining VEVs and scalar masses.

Findings

The 95 GeV excesses are compatible with the 125 GeV Higgs data.

The triplet VEVs are constrained to below 12-15 GeV.

Scalar masses are limited to below 600 GeV.

Abstract

We perform global fits of the CP-conserving Georgi-Machacek (GM) and extended Georgi-Machacek (eGM) models, incorporating a light CP-even beyond the Standard Model (BSM) scalar within the mass range of $90$ GeV to $100$ GeV. These fits combine the Higgs signal strengths and direct search limits from ATLAS and CMS at $\sqrt{s} = 8$ and $13$ TeV, $B$-physics observables, and theoretical constraints arising from next-to-leading order (NLO) unitarity and BFB constraints. From the global fit, we show that the LHC diphoton and LEP $b\bar{b}$ excesses around $95$ GeV are well compatible with the $125$ GeV Higgs data. Whereas the CMS ditau excess is incompatible with the $125$ GeV Higgs signal strength data in both the CP-conserving GM and eGM models. We present the results from the combined fit, including the $95$ GeV Higgs signal strength data. In the eGM model, the triplet VEV cannot exceed $12$ GeV for additional BSM scalar masses below $160$ GeV and approximately $20$ GeV for additional BSM scalar masses above $160$ GeV. The masses of additional BSM scalars cannot exceed $600$ GeV. The maximum mass splitting is of around $120$ GeV within the members of each custodial multiplet, and up to $250$ GeV between the members of different multiplets. In the GM model, these constraints become more stringent: the triplet VEV is limited to below $15$ GeV, which tightens to $4$ GeV once the BSM scalar masses are below $160$ GeV. Masses of the quintet $m_5$ and the triplet $m_3$ are restricted to be below $530$ GeV and $320$ GeV, respectively. A mass hierarchy, $m_5 > m_3$, is favoured in the high-mass region, with the mass splitting constrained to be less than $210$ GeV.