Correlating Resonant Di-Higgs and Tri-Higgs Production to $H\to VV$ in the 2HDM

Abstract

The observation of resonant di-Higgs production, which would strongly suggest the existence of a new heavy neutral scalar $H$, has been searched for extensively at the LHC. In the two-Higgs doublet model (2HDM) with $m_H\gg m_h$, where $h$ is the Higgs boson of mass 125 GeV observed at the LHC, we show that a direct correlation emerges between $\mathrm{Br}(H\to hh)$ and $\mathrm{Br}(H\to VV)$, with $V=Z,W$, which depends only on $m_H$ (and $m_V$). In particular, for heavy scalar masses between 500 GeV and 1 TeV, we find that $\mathrm{Br}(H\to hh)/\mathrm{Br}(H\to ZZ)\approx 9.4\pm 0.25$. Moreover, $H\to hh$ is a dominant decay mode over a significant region of the parameter space and serves as the primary probe for a heavy scalar resonance at current and future hadron colliders. The origin of these predictions is most transparent in the Higgs basis, where the term in the scalar potential proportional to ${\mathcal{H}}_1^{†}{\mathcal{H}}_1{\mathcal{H}}_1^{†}{\mathcal{H}}_2$ (and its hermitian conjugate) generates the leading contributions to the $Hhh$ and $Hhhh$ couplings in the decoupling limit of the 2HDM. Additionally, the latter coupling governs the resonant prompt tri-Higgs production via $H\to hhh$, which is also directly correlated to $H\to hh$ (and $H\to VV$), and can yield rates large enough to be measured at the High-Luminosity LHC.

Comments: 11 pages, 3 figures, v2: minor corrections and references added; v3: a few minor additions and clarifications, including a new figure and a few new references; v4: final version matches the published version