Effective Field Theory for a Heavy Majorana Fermion

We formulate an effective theory for systems containing a heavy Majorana fermion, such as bound states of a long-lived gluino. This "Majorana HQET" has the same degrees of freedom as the well-studied Dirac HQET. It respects an emergent U(1) symmetry despite the fundamental absence of a U(1) for Majorana fermions. Reparameterization invariance works identically in the two HQETs. Remarkably, while a Dirac HQET may or may not be charge conjugation symmetric, a charge conjugation symmetry emerges in all Majorana HQETs, potentially offering low energy probes to distinguish the two theories.