Higgs couplings in a model with triplets

TL;DR

The paper addresses whether an extended Higgs sector with scalar triplets can modify Higgs couplings to vector bosons beyond the Standard Model expectations while keeping the electroweak rho parameter near unity. It analyzes the Georgi–Machacek model with a doublet and two triplets, derives the $hWW$, $hZZ$, and $hff$ couplings for a CP-even Higgs $h$, and computes gg-initiated production and decay rates by scaling SM widths with the corresponding couplings. The results show that $\bar{g}_{hWW}$ and $\bar{g}_{hZZ}$ can lie on an ellipse and exceed SM values, and that $\bar{g}_{hWW}$ and $\bar{g}_{hZZ}$ can differ if $h$ mixes with the custodial fiveplet $H_5^0$, enabling dramatic enhancements in $gg\to h\to ZZ$ while suppressing $h\to WW$ in some regions. These findings have important implications for Higgs coupling extraction at the LHC and motivate searches for additional triplet states, with absolute coupling measurements ultimately benefiting from future $e^+e^-$ colliders.)

Abstract

We study the couplings of a CP-even neutral Higgs boson h in a model containing one scalar SU(2)_L doublet, one real triplet, and one complex triplet with hypercharge 1. Because the two triplets contribute to the rho parameter with opposite signs, the triplet vacuum expectation values can be sizable. We show that (i) the hWW and hZZ couplings can be larger than the corresponding values in the Standard Model, and (ii) the ratio of the WW and ZZ couplings of h can be different than the corresponding ratio in the Standard Model. Neither of these results can occur in models containing only Higgs doublets. We also compute the rates for gg --> h --> WW and gg --> h --> ZZ and find that, for reasonable parameter values and M_h ~ 140-180 GeV, the hadron collider rate for gg --> h --> WW (ZZ) can be up to 20% (5 times) larger than in the Standard Model. We discuss implications for Higgs coupling extraction at the LHC.

Figures (9)

• Figure 1: Normalized Higgs couplings $\bar{g}_{hZZ}$ versus $\bar{g}_{hWW}$ for a mixed state $h$ in the Georgi-Machacek model, for $c_H = 0.6$, 0.9, and 0.95 (left to right). We sampled both signs for $a$, $b$, and $c$ in Eq. (\ref{['eq:coupsdrzero']}). Points corresponding to a mixture of $H_1^0$ and $H_1^{0\prime}$ lie along the diagonal $\bar{g}_{hWW} = \bar{g}_{hZZ}$. $H_5^0$ is indicated by the crossed circle on the lower right boundary of the ellipse.
• Figure 2: The rate for $gg \to h \to WW$ normalized to its SM value plotted as a function of $\bar{g}_{hWW}^2$, for $M_h = 140$, 160 and 180 GeV (left to right), with $c_H = 0.9$. The solid line shows points for which $h = \cos\theta H_1^0 + \sin\theta H_1^{0 \prime}$ and the crossed circle near the origin indicates the point corresponding to $H_5^0$. The dashed horizontal line shows the Tevatron upper limit on the rate for $gg \to h \to WW$ for the corresponding Higgs mass from Ref. Aaltonen:2010sv.
• Figure 3: As in Fig. \ref{['fig:W9W']} but for $c_H = 0.95$.
• Figure 4: The rate for $gg \to h \to WW$ normalized to its SM value plotted as a function of $\bar{g}_{hZZ}^2$, for $M_h = 140$, 160 and 180 GeV (left to right), with $c_H = 0.9$. The solid line shows points for which $h = \cos\theta H_1^0 + \sin\theta H_1^{0 \prime}$ and the crossed circle at the lower edge of the allowed region indicates the point corresponding to $H_5^0$. The dashed horizontal line shows the Tevatron upper limit on the rate for $gg \to h \to WW$ for the corresponding Higgs mass from Ref. Aaltonen:2010sv.
• Figure 5: As in Fig. \ref{['fig:W9Z']} but for $c_H = 0.95$.