LHC Signatures of the Generic Georgi-Machacek Model

Abstract

Vector-boson fusion production of new Higgs bosons decaying into pairs of electroweak gauge bosons ($W^\pm W^\pm$, $WZ$ and $ZZ$) is a smoking-gun signature of the Georgi-Machacek (GM) Model. Notably, ATLAS has observed a $3.3\sigma$ excess in $W^\pm W^\pm$ at $\approx 450\,$GeV and a $2.8\sigma$ excess in the $WZ$ channel at $\approx 375\,$GeV, while CMS reported weaker-than-expected limits at these masses. However, the canonical custodial-symmetric GM Model cannot accommodate these signals, as it predicts mass degeneracy among the new gauge-philic Higgs bosons. To overcome this obstacle, we consider a generalized version of the GM Model without the custodial $SU(2)_C$ symmetry in the scalar potential. In the limit of small mixing among the Higgs bosons, the $W^\pm W^\pm$ and $WZ$ excesses can be explained by the doubly and singly-charged Higgs bosons originating primarily from the $Y=1$ triplet, while respecting the bounds from $ZZ$ searches. Furthermore, the neutral Higgs boson mostly contained in the $Y=0$ triplet can account for the excess at $\approx 152\,$GeV in associated di-photon production, while being consistent with constraints from vacuum stability and the Standard Model Higgs signal strength measurements.