Decay of Z into Two Light Higgs Bosons

If the standard electroweak gauge model is extended to include two or more Higgs doublets, there may be a neutral Higgs boson $h$ which is light (with a mass of say 10 GeV) but the $hZZ$ coupling is suppressed so that it has so far escaped experimental detection. However, the effective $hhZZ$ coupling is generally unsuppressed, hence the decay of Z into two light Higgs bosons plus a fermion-antifermion pair may have an observable branching fraction, especially if $h$ decays invisibly as for example in the recently proposed doublet Majoron model.