Lepton-number-violating decays of heavy flavors induced by doubly-charged Higgs boson

We study lepton-number-violating (LNV) decays of heavy flavors ($\tau$ lepton and top quark) induced by doubly-charged Higgs boson in the Higgs triplet model. It is found that the branching fractions of LNV $\tau^- \to \ell^{+}M_1^-M_2^-$ decays are highly suppressed compared with the current experimental limits. On the other hand, for LNV top quark decays, the most optimistic branching ratios for $t\to b{\mathrm{\ell }}^{+}{\mathrm{\ell }}^{+}{W}^{-}$ turn out to be at the level of $\sim {10}^{-7}-{10}^{-8}$. The observation of these rare top quark decays would be a clear signal of LNV processes, and their non-observation would allow us to constraint the parameters of the Higgs triplet model.