  Cascade seesaw mechanism generates neutrino mass at higher dimension (5+4n)
operators through tree level diagram which bring the seesaw scale down to TeV
and provide collider signatures within LHC reach. In particular, both Type-II
scalar and Type-III heavy fermion seesaw signatures exist in such a scenario.
Doubly charged scalar decays into diboson is dominant. We perform a thorough
study on the LHC signals and the Standard Model background. We draw the
conclusion that multilepton final state from interplay of doubly charged scalar
and heavy fermion can provide distinguishable signatures from conventional
seesaw mechanisms.
