Heavy Majorana neutrinos in the effective Lagrangian description: Application to hadron colliders

We consider the effects of heavy Majorana neutrinos N with sub-TeV masses and argue that the mere observation of these particles would be a signal of physics beyond the minimal seesaw mechanism. We describe the N interactions using an effective Lagrangian and exhibit the complete set of effective operators of dimension ⩽6 involving the N and Standard Model fields. We argue that these interactions can be relatively easy to track at high-energy colliders. For example, we find that new physics (beyond the N  ) at the TeV-scale can yield thousands of characteristic same-sign lepton number violating ℓ+ℓ+jjℓ+ℓ+jj events (j   = light jet) at the LHC if mN≲600 GeVmN≲600 GeV, which can also have a distinctive forward-backward asymmetry signal; even the Tevatron has good prospects for this signature if mN≲300 GeVmN≲300 GeV.