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LHC signatures of a generalized Georgi-Machacek model

Saiyad Ashanujjaman ^1,2,*, Andreas Crivellin ^3,†, Siddharth P. Maharathy ^4,5,6,‡, and Anil Thapa ^7,§

¹Institut für Theoretische Teilchenphysik, Karlsruhe Institute of Technology, Engesserstraße 7, D-76128 Karlsruhe, Germany
²Institut für Astroteilchenphysik, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany
³Physik-Institut, Universität Zürich, Winterthurerstrasse 190, CH–8057 Zürich, Switzerland
⁴School of Physics and Institute for Collider Particle Physics, University of the Witwatersrand, Johannesburg, Wits 2050, South Africa
⁵iThemba LABS, National Research Foundation, PO Box 722, Somerset West 7129, South Africa
⁶Indian Institute of Science Education and Research Pune, Dr. Homi Bhabha Road, Pune 411008, India
⁷Physics Department, Colorado State University, Fort Collins, Colorado 80523, USA

^*Contact author: saiyad.ashanujjaman@kit.edu
^†Contact author: andreas.crivellin@cern.ch
^‡Contact author: siddharth.prasad.maharathy@cern.ch
^§Contact author: a.thapa@colostate.edu

Phys. Rev. D 112, 035040 – Published 28 August, 2025

DOI: https://doi.org/10.1103/wzjg-3fqg

Abstract

Vector-boson fusion productions of new Higgs bosons decaying into pairs of electroweak gauge bosons ( $W^{\pm} W^{\pm}$ , $W Z$ , and $Z Z$ ) are smoking-gun signature of new Higgs bosons in general, and of the Georgi-Machacek (GM) model in particular. Notably, ATLAS has observed a $3.3 σ$ excess in $W^{\pm} W^{\pm}$ at $\approx 450 GeV$ and a $2.8 σ$ excess in the $W Z$ channel at $\approx 375 GeV$ , while compact muon solenoid reported weaker-than-expected limits at these masses. In this article, we consider a generalized version of the GM model without the custodial $S U (2)_{C}$ symmetry in the scalar potential as a minimal model to explain these excesses. In the limit of small mixing among the Higgs bosons, the $W^{\pm} W^{\pm}$ and $W Z$ signals can be explained by the doubly and singly charged Higgs bosons originating primarily from the $Y = 1$ triplet, while respecting the bounds from $Z Z$ searches. Furthermore, the neutral Higgs boson mostly contained in the $Y = 0$ triplet can account for the ( $\approx 4 σ$ ) excess at $\approx 152 GeV$ in associated diphoton production. Furthermore, the model is consistent with the constraints from vacuum stability and the Standard Model Higgs signal strength measurements, such that it can provide a valid combined explanation for some of the most significant LHC excesses.

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Phys. Rev. D 112, 035040– Published 28 August, 2025

Vol. 112, Iss. 3 — 1 August 2025

Received 6 March 2025
Accepted 1 August 2025

DOI: https://doi.org/10.1103/wzjg-3fqg

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

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LHC signatures of a generalized Georgi-Machacek model

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