Higgs-boson-exchange contributions to neutrinoless double-βdecay

We have calculated the contributions to the neutrinoless $\beta \beta$ decay ${}_{}{}^{48}{}_{}{}^{}\mathrm{Ca}$(g.s.)${\to }^{48}$Ti(g.s.) arising from the exchange of both Higgs scalars and Majorana neutrinos. We find, contrary to previous claims, that the Higgs-boson-exchange mechanism has no effect on the limits that can be placed on the masses and right-handed couplings of Majorana neutrinos. We also find that these limits are less stringent than those imposed by $\beta \beta$ decay experiments in several other nuclei.