Singlet-Higgs-boson signals at electron-positron colliders

The possibility of production of singlet Higgs particles coupling to exotic fermions at the CERN $e^{+}{e}^{-}$ Collider LEP or the SLAC Linear Collider through the loop-induced decay $Z^0\to h^0\gamma$ is discussed and decay signatures for the singlet Higgs boson are suggested. It appears that singlet Higgs bosons may be detectable with ${10}^7$ $Z^0\text{'}\mathrm{s}$, if the unknown masses and couplings are in the right range.