Three-body decays of heavy Dirac and Majorana fermions

André de Gouvêa, Patrick J. Fox, Boris J. Kayser, Kevin J. Kelly

Research output: Contribution to journalArticlepeer-review

16 Scopus citations


Nonzero neutrino masses imply the existence of degrees of freedom and interactions beyond those in the Standard Model. A powerful indicator of what these might be is the nature of the massive neutrinos: Dirac fermions versus Majorana fermions. While addressing the nature of neutrinos is often associated with searches for lepton-number violation, there are several other features that distinguish Majorana from Dirac fermions. Here, we compute in great detail the kinematics of the daughters of the decays into charged-leptons and neutrinos of hypothetical heavy neutral leptons at rest. We allow for the decay to be mediated by the most general four-fermion interaction Lagrangian. We demonstrate, for example, that when the daughter charged-leptons have the same flavor or the detector is insensitive to their charges, polarized Majorana-fermion decays have zero forward-backward asymmetry in the direction of the outgoing neutrino (relative to the parent spin), whereas Dirac-fermion decays can have large asymmetries. Going beyond studying forward-backward asymmetries, we also explore the fully differential width of the three-body decays. It contains a wealth of information not only about the nature of the new fermions but also the nature of the interactions behind their decays.

Original languageEnglish (US)
Article number015038
JournalPhysical Review D
Issue number1
StatePublished - Jul 1 2021

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


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