Highly Enhanced Contributions of Heavy Higgs Bosons and New Leptons to Muon $g-2$ and Prospects at Future Colliders

We show that, in a two Higgs doublet model type II extended by vectorlike leptons, the contributions from heavy neutral and charged Higgs bosons to the anomalous magnetic moment of the muon simultaneously feature chiral enhancement from masses of new leptons and ${\tan }^2\beta$ enhancement from couplings of Higgs bosons. Assuming moderate values of new Yukawa couplings, not exceeding one, that can remain perturbative to very high energy scales, the measured value of muon $g-2$ can be explained within one standard deviation even with 6.5 TeV leptons or 20 TeV Higgs bosons. Allowing new couplings near the perturbativity limit, these mass ranges extend to 45 TeV for leptons and 185 TeV for Higgs bosons. In spite of the high scale of new physics, this scenario can be completely probed at planned future colliders.

Figure 1

$W$, $Z$, $h$ $H$, $A$, $H^{\pm }$ diagrams contributing to $(g-2{)}_{\mu }$.

Figure 2

Scenarios satisfying $\mathrm{\Delta }{a}_{\mu }^{\exp }$ within $1\sigma$ in the $m_H-\tan \beta$ plane for Yukawa couplings not exceeding 1 (top), 0.5 (inset in top), and $\sqrt{4\pi }$ (bottom). Colors indicate masses of the lightest new lepton. Lightly shaded crosses without filled circles correspond to scenarios with heavy Higgs bosons contributing less than 50% to $\mathrm{\Delta }{a}_{\mu }$.

Figure 3

The same scenarios as in Fig. 2 in the $m_H-\min (M_L,M_E)$ plane with colors indicating $-\delta {\lambda }_{\mu \mu }^h/({\lambda }_{\mu \mu }^h{)}_{\mathrm{SM}}$.

Figure 4

The same scenarios as in Fig. 2 in the $m_H-\min (M_L,M_E)$ plane with colors indicating the largest relative modification of muon couplings to $Z$.