Suppression of the Higgs Dimuon Decay

It is often stated that elimination of tree-level flavor-changing neutral currents in multi-Higgs models requires that all fermions of a given charge to couple to the same Higgs boson. A counterexample was provided by Abe, Sato and Yagyu in a muon-specific two-Higgs doublet model with a softly-broken $Z_4$ symmetry. In this model, all fermions except the muon couple to one Higgs and the muon couples to the other. We study the phenomenology of the model and show that there is a wide range of parameter-space in which the branching ratios of the 125 GeV Higgs are very close to their Standard Model values, with the exception of the branching ratio into muons, which can be substantially suppressed -- this is an interesting possibility, since the current value of this branching ratio is $0.5 \pm 0.7$ times the Standard Model value. We also study the charged Higgs boson and show that, if it is lighter than $200$ GeV, it could have a large branching ratio into $μν$ - even substantially larger than the usual decay into $τν$. The decays of the heavy neutral scalars are also studied. The model does have a relationship between the branching ratios of the 125 GeV Higgs into $Z$'s, $τ$'s and $μ$'s, which can be tested in future accelerators.

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