  If the observed light neutrino masses are induced by their Yukawa couplings
to singlet right-handed neutrinos, natural smallness of those renders direct
collider tests of the electroweak scale neutrino mass mechanisms almost
impossible both in the case of Dirac and Majorana (seesaw of type I) neutrinos.
However, in the triplet Higgs seesaw scenario the smallness of light neutrino
masses may come from the smallness of B-L breaking parameters, allowing sizable
Yukawa couplings even for a TeV scale triplet. We show that, in this scenario,
measuring the branching fractions of doubly charged Higgs to different
same-charged lepton flavours at LHC and/or ILC experiments will allow one to
measure the neutrino mass parameters which neutrino oscillation experiments are
insensitive to, including the neutrino mass hierarchy, lightest neutrino mass
and Majorana phases.
